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Is short term memory ability inherited?

Is short term memory ability inherited?



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Have any studies been done on the inheritability of different mental abilities such as short-term-memory, long term memory and so on.

Many studies, if at all, seem to rely on an over-all IQ. This seems extremely wide-ranging when mental abilities can be made of so many different parts. Someone with a good memory may not have good reasoning skills etc.

For example if a man has a short term memory able to memorise 10 numbers at a time and a woman has a short-term-memory able to memorise 5 numbers at a time. How many numbers could their children memorise?

I seem to remember a documentary about the extraordinary memories of 'native' Australians compared to their European descended compatriots. So this seems one piece of evidence that memory ability can be inherited.


Have any studies been done on the inheritability of different mental abilities such as short-term-memory, long term memory and so on.

One of the most replicated findings of behavioral genetics is that all psychological traits show significant and substantial genetic influence, however not 100% genetic influence (Plomin et al, 2016). So yes, short term memory has a heritability of larger than zero, but smaller than one.

Many studies, if at all, seem to rely on an over-all IQ. This seems extremely wide-ranging when mental abilities can be made of so many different parts. Someone with a good memory may not have good reasoning skills etc.

It is certainly true that it is possible to have good memory and low reasoning ability (The most extreme being some savants, e.g. Kim Peek). However, abilities are positively correlated. Therefore, high ability X makes it statistically more likely that the individual is higher in ability Y as well, for practically any cognitive abilities X and Y (Certainly for memory and reasoning). This was discovered more than a century ago (Spearman, 1904). Although the increased likelihood may only be modest.

For example if a man has a short term memory able to memorise 10 numbers at a time and a woman has a short-term-memory able to memorise 5 numbers at a time. How many numbers could their children memorise?

There are multiple reasons why you couldn't predict in any exact manner the short term memory abilities of the child.

First, while heritability is larger than zero, it is also smaller than one. In other words, not only genetic differences are responsible for differences in short term memory.

Second, the genetics are not even determined in a unique way from the parents. Said in another way, you cannot predict the exact genetic makeup of a child from its parents' DNA. It depends on how the recombination of the mother's and father's genes. The most obvious demonstration of this is that biological siblings do not have identical DNA. Therefore, even if short term memory was 100% heritable (It isn't), you still wouldn't be able to exactly predict the short term memory of the child just from knowing the parents.

The most you could say is statistical. Parents with better short term memory will, on average, have children with better short term memory.

I seem to remember a documentary about the extraordinary memories of 'native' Australians compared to their European descended compatriots. So this seems one piece of evidence that memory ability can be inherited.

Now you're getting into a socially sensitive topic of population differences in cognitive abilities. I don't know what documentary you've watched. Personally, I haven't seen the evidence that native Australians have extraordinary memory abilities. Of course, I would be open to see such evidence. However, one thing to note is that even if native Australians showed high ability in memory, that fact in itself does not prove that the difference is due to genetic differences. Memory is only partially heritable. It could simply be that due to whatever environmental or social cause that they showed enhanced memory. Of course, I'm not saying that it is impossible either.


Classification by temporal direction [ edit | edit source ]

Prospective Memory: Tying ribbon or string around a finger is the iconic mnemonic device for remembering a particular thought, which one consciously trains oneself to associate with the string.

A further major way to distinguish different memory functions is whether the content to be remembered is in the past, retrospective memory, or whether the content is to be remembered in the future, prospective memory. Thus, retrospective memory as a category includes semantic memory and episodic/ autobiographical memory. In contrast, prospective memory is memory for future intentions, or remembering to remember (Winograd, 1988). Prospective memory can be further broken down into event- and time-based prospective remembering. Time-based prospective memories are triggered by a time-cue, such as going to the doctor (action) at 4pm (cue). Event-based prospective memories are intentions triggered by cues, such as remembering to post a letter (action) after seeing a mailbox (cue). Cues do not need to be related to the action (as the mailbox example is), and lists, sticky-notes, knotted hankerchiefs, or string around the finger (see box) are all examples of cues that are produced by people as a strategy to enhance prospective memory.


Developmental cognitive genetics: how psychology can inform genetics and vice versa

Developmental neuropsychology is concerned with uncovering the underlying basis of developmental disorders such as specific language impairment (SLI), developmental dyslexia, and autistic disorder. Twin and family studies indicate that genetic influences play an important part in the aetiology of all of these disorders, yet progress in identifying genes has been slow. One way forward is to cut loose from conventional clinical criteria for diagnosing disorders and to focus instead on measures of underlying cognitive mechanisms. Psychology can inform genetics by clarifying what the key dimensions are for heritable phenotypes. However, it is not a one-way street. By using genetically informative designs, one can gain insights about causal relationships between different cognitive deficits. For instance, it has been suggested that low-level auditory deficits cause phonological problems in SLI. However, a twin study showed that, although both types of deficit occur in SLI, they have quite different origins, with environmental factors more important for auditory deficit, and genes more important for deficient phonological short-term memory. Another study found that morphosyntactic deficits in SLI are also highly heritable, but have different genetic origins from impairments of phonological short-term memory. A genetic perspective shows that a search for the underlying cause of developmental disorders may be misguided, because they are complex and heterogeneous and are associated with multiple risk factors that only cause serious disability when they occur in combination.

Figures

Schematic showing inheritance pattern for…

Schematic showing inheritance pattern for a small stretch of DNA. The grey region…

Illustration of DeFries–Fulker analysis. Data…

Illustration of DeFries–Fulker analysis. Data are transformed so that the population mean =…

Causal route from auditory temporal…

Causal route from auditory temporal processing deficit to language impairment, based on Tallal…

Mean scaled scores on two…

Mean scaled scores on two receptive language tests (TROG and WISC-R Comprehension) and…

Risk factor model, in which…

Risk factor model, in which environmental risk for language impairment is indexed by…

Illustration of frequency of underlying…

Illustration of frequency of underlying deficits in children with unimpaired hearing and those…


Neuroscientists identify brain circuit motifs that support short-term memory

Figure 1 All-optical method. A laser beam was precisely positioned (magenta lines) onto neurons of interest, causing those neurons to be activated (yellow shading). By observing changes in the surrounding circuit, the researchers could infer the presence of effective connections. Credit: Daie, Svoboda & Druckmann.

Humans have the innate ability to store important information in their mind for short periods of time, a capability known as short-term memory. Over the past few decades, numerous neuroscientists have tried to understand how neural circuits store short-term memories, as this could lead to approaches to assist individuals whose memory is failing and help to devise memory enhancing interventions.

Researchers at Stanford and the Janelia Research Campus, Howard Hughes Medical Institute have recently identified neural circuit motifs involved in how humans store short-term memories. Their findings, published in Nature Neuroscience, suggest that memory-related neural circuits contain recurrently connected modules that independently maintain selective and continuous activity.

"Short-term memories are of approximately 10 seconds or so, for example, if you needed to remember a phone number while you looked for a pen to write the number," Kayvon Daie, one of the researchers who carried out the study, told Medical Xpress. "Individual neurons, however, are very forgetful, as they can only remember their inputs for about 10 milliseconds. It has been hypothesized that if two forgetful neurons were connected to each other, they could continuously remind each other of what they were supposed to remember so that the circuit can now hold information for many seconds."

The primary objective of the study carried out by Daie and his colleagues Karel Svoboda and Shaul Druckmann was to understand how neurons encode short-term memories. For instance, they wanted to determine whether two neurons connected with each other exchange information that humans are trying to remember, allowing a neural circuit to store this information for several seconds. The researchers tested this idea by measuring the interactions between different neurons.

While the idea that neurons storing memories are connected has been around for some time now, testing it experimentally has proved fairly challenging. To test it, researchers would first need to identify neurons that store memories and then measure their connectivity. To do this, Daie and his colleagues employed recently developed methods that allow scientists to record and manipulate neuronal activity with high levels of precision using light.

"Using a series of recently developed techniques, we could activate specific neurons and then observe how those neurons influence the rest of the circuit," Daie said. "Our prediction was: if we stimulate a memory neuron, we should see increased activity in neighboring memory neurons."

Figure 2: Example photostimulation experiment. (Left) Map of network activity during memory period. Neurons are color-coded to reflect their activity during the memory period. After characterizing network activity, the researchers selected a group of neurons that were selective for memory type 1 (black circles). (Right) Change in activity following photostimulation. The targeted neurons show large amplitude increases in their activity (yellow pixels), but we also observe many changes in the surrounding network reflecting interactions between the stimulated and non-stimulated population. Credit: Daie, Svoboda & Druckmann.

The experimental observations gathered by Daie and his colleagues were aligned with their predictions. In addition to confirming that memory neurons are connected to each other, their findings suggest that they are organized in clusters.

"We found that neurons tended to be connected in clusters," Druckmann said. "This means that the circuit was composed of many independent clusters, or modules, that were each able to store short-term memories independently. We hypothesize that such a circuit architecture could be useful to making memory storage more reliable."

In their experiments, Daie and his colleagues only activated groups of 8 neurons within a circuit composed of 100,000 neurons. Nonetheless, the researchers found that activating these groups of neurons still caused changes in the animals' behavior.

"Essentially, we were able to modify the mouse's short-term memory by activating a tiny fraction of the mouse's neurons," Daie said. "We also found that there was a counterintuitive relationship between the activity of the stimulated neurons and the animals' behavior."

The recent study carried out by this team of researchers offers new valuable insight about the role of neural circuit motifs in short-term memory processes. In their future studies, Daie and his colleagues would like to identify ways to predict what memories will be altered when specific neurons are activated. In addition, they plan to explore ways of modifying more complex and elaborate memories.

"We were surprised that activating neurons that seemed to be related to one memory actually ended up driving the opposite action," Daie said. "While we were able to predict when this might happen by observing the changes that we implemented to the network at large, the real brain proved more complex than our initial thought that driving neurons related to a memory will always push behavior to that memory."


2 thoughts on &ldquo Coding in Short-term Memory &rdquo

I found your post interesting because you explained how certain things can become a memory based on the stimulus that is perceived. I have found myself in many situations where this has been proved to be correct. For instance, recently I heard a song playing on the radio and I did not know the name of it nor did I hear the song playing before. So, I caught a line of it and I sung it in my head over and over, until I reached my computer to google that line. Then, I wrote down the name and artist of that song so that I would always have it if I wanted to hear it again. I listened to the song again, and over the next couple of hours the song was stuck in my head, and I found myself constantly singing it. As you stated “ auditory information can be coded into short term memory without the individual’s awareness.” This is interesting, because I didn’t realize that I was singing a part of the song repeatedly, until my friend yelled at me to stop.

The things that we perceive can become a part of our short term memory, and that memory can be influenced by suggestions. For instance, I remember being on a bus when the driver hit a car that was turning. Everything happened so quickly and unexpectedly that I couldn’t tell if the car that was turning was in the wrong, or if it was the bus driver. However, I do remember the bus driver saying “You all saw that, he wasn’t supposed to turn.” This influenced my memory of this event, because then when I recalled this event I remember the car turning as being in the wrong, even though I honestly did not know who was in the wrong.

I like how you made three different example to explain three different types of information that can be coded into a person’s short term memory without the individual’s awareness. These examples helped me to review the coding in short-term memory. I found that your first example is interesting. That always happen to me as well. Sometimes I heard songs on the street or on the radio but i couldn’t catch the title of the song or the singer, I would quickly get on the radio’s website to look for the song or type as much as the lyrics that i heard and search on google. I have never thought about that the reason why I always rush in looking for the song is because our short-term memory won’t last long unless we rehearse it and turn it into long-term memory, I need to find the song when the auditory remnant in our short term memory is still on.


In conclusion

A deficit in expressive language learning and syntax in children with Down syndrome emerges gradually with chronological age and includes much individual variation. The linear component of individual growth is predicted, in our sample, by chronological age at start of study and two measures of short-term memory: one auditory, the other visual. Rate of change in the visual component also predicts rate of change in comprehension. Implications for language intervention and research arise from these findings.

Acknowledgement

This research was supported by NIH Grant R01 HD-23353 and funds from the National Down Syndrome Society. The help of the participants is gratefully acknowledged. Collaborators on this work reported here include Dr. Linda Hesketh, Dr. Donna Boudreau, Dr. Hye-Kyeung Seung, Dr. Elizabeth Kay-Raining Bird, Dr. Scott E. Schwartz, Dr. Giuliana Miolo, Sally Miles, and Heidi Sindberg. We thank Dr. Doris Kistler for statistical assistance.


Examining the Relationship Between Gender and Short-Term Memory

The aim of this experiment is to test whether or not gender will have an effect on a person’s ability to recall information from his or her short-term memory.

We know that there are three stages of memory: sensory-where our brain takes in sensations received through our senses and keeps it long enough to be able to process the information and decide what needs attention, short-term- which has limited amounts of information for a limited amount of time, and long-term memory where we process and keep the information for a long time or permanently.

In this experiment, the experimenters are testing the different genders short-term memory by taking 20 male and female participants aging between 18 and 30 years old. The experimenters arrange 25 miscellaneous objects, such as an apple, banana, ball, radio, cup, etc. in front of the classroom behind fixed curtains. The participants were brought into the classroom and could be tested together or be separated into smaller groups, then instructed to observe the objects for two minutes. After the two minutes the curtains were shut, hiding the objects, then the participants were asked to recall and list down the objects on a piece of paper for five minutes. After the five minutes, the experimenters collected the papers and tally the results.

IV: Gender of the participants

DV: ability of male and females to recall the objects

The female participants proved the hypothesis of having a higher score of their ability to recall information from the short-term memory. Females average ability to recall the objects was 64.2 and the average for males was 63. However, this shows only a 1.2% difference between the genders test scores.

I think this experiment is valid, it had a strong number of participants, allowing the same number of participants for both genders. It’s easy to replicate so this experiment can be redone to further prove, or even disprove, the results. It followed ethical guidelines, the participants weren’t exposed to danger. The experimenter also put in a note how some people can be more gifted than other by nature, noting something that could be a limiting factor. However, I think the design could have been better- rather than giving them an option to test all together or in a big group they should have had a set way to carry out the experiment, this could have interfered with the results.


Short-Term Memory☆

Abstract

Short-term memory (STM) refers to systems which provide retention of limited amounts of material for a limited time period (seconds). Most investigated systems include Phonological, Spatial, and Visual STM, while STM storage exists also in other domains, as the somatosensory system. STM includes storage and rehearsal components, with the latter providing maintenance of events in memory against short-term forgetting. Discrete brain regions support STM, with left hemisphere posterior parietal and premotor frontal networks being more involved in Phonological STM, and right hemisphere regions in spatial STM. STM contributes to learning of new information and aspects of speech comprehension and production.


Contents

Sensory memory holds information, derived from the senses, less than one second after an item is perceived. The ability to look at an item and remember what it looked like with just a split second of observation, or memorization, is the example of sensory memory. It is out of cognitive control and is an automatic response. With very short presentations, participants often report that they seem to "see" more than they can actually report. The first precise experiments exploring this form of sensory memory were conducted by George Sperling (1963) [24] using the "partial report paradigm." Subjects were presented with a grid of 12 letters, arranged into three rows of four. After a brief presentation, subjects were then played either a high, medium or low tone, cuing them which of the rows to report. Based on these partial report experiments, Sperling was able to show that the capacity of sensory memory was approximately 12 items, but that it degraded very quickly (within a few hundred milliseconds). Because this form of memory degrades so quickly, participants would see the display but be unable to report all of the items (12 in the "whole report" procedure) before they decayed. This type of memory cannot be prolonged via rehearsal.

Three types of sensory memories exist. Iconic memory is a fast decaying store of visual information, a type of sensory memory that briefly stores an image that has been perceived for a small duration. Echoic memory is a fast decaying store of auditory information, also a sensory memory that briefly stores sounds that have been perceived for short durations. [25] Haptic memory is a type of sensory memory that represents a database for touch stimuli.

Short-term memory is also known as working memory. Short-term memory allows recall for a period of several seconds to a minute without rehearsal. Its capacity, however, is very limited. In 1956, George A. Miller (1920-2012), when working at Bell Laboratories, conducted experiments showing that the store of short-term memory was 7±2 items. (Hence, the title of his famous paper, "The Magical Number 7±2.") Modern estimates of the capacity of short-term memory are lower, typically of the order of 4–5 items [26] however, memory capacity can be increased through a process called chunking. [27] For example, in recalling a ten-digit telephone number, a person could chunk the digits into three groups: first, the area code (such as 123), then a three-digit chunk (456), and, last, a four-digit chunk (7890). This method of remembering telephone numbers is far more effective than attempting to remember a string of 10 digits this is because we are able to chunk the information into meaningful groups of numbers. This is reflected in some countries' tendencies to display telephone numbers as several chunks of two to four numbers.

Short-term memory is believed to rely mostly on an acoustic code for storing information, and to a lesser extent on a visual code. Conrad (1964) [28] found that test subjects had more difficulty recalling collections of letters that were acoustically similar, e.g., E, P, D. Confusion with recalling acoustically similar letters rather than visually similar letters implies that the letters were encoded acoustically. Conrad's (1964) study, however, deals with the encoding of written text thus, while memory of written language may rely on acoustic components, generalizations to all forms of memory cannot be made.

The storage in sensory memory and short-term memory generally has a strictly limited capacity and duration, which means that information is not retained indefinitely. By contrast, long-term memory can store much larger quantities of information for potentially unlimited duration (sometimes a whole life span). Its capacity is immeasurable. For example, given a random seven-digit number, one may remember it for only a few seconds before forgetting, suggesting it was stored in short-term memory. On the other hand, one can remember telephone numbers for many years through repetition this information is said to be stored in long-term memory.

While short-term memory encodes information acoustically, long-term memory encodes it semantically: Baddeley (1966) [29] discovered that, after 20 minutes, test subjects had the most difficulty recalling a collection of words that had similar meanings (e.g. big, large, great, huge) long-term. Another part of long-term memory is episodic memory, "which attempts to capture information such as 'what', 'when' and 'where ' ". [30] With episodic memory, individuals are able to recall specific events such as birthday parties and weddings.

Short-term memory is supported by transient patterns of neuronal communication, dependent on regions of the frontal lobe (especially dorsolateral prefrontal cortex) and the parietal lobe. Long-term memory, on the other hand, is maintained by more stable and permanent changes in neural connections widely spread throughout the brain. The hippocampus is essential (for learning new information) to the consolidation of information from short-term to long-term memory, although it does not seem to store information itself. It was thought that without the hippocampus new memories were unable to be stored into long-term memory and that there would be a very short attention span, as first gleaned from patient Henry Molaison [31] after what was thought to be the full removal of both his hippocampi. More recent examination of his brain, post-mortem, shows that the hippocampus was more intact than first thought, throwing theories drawn from the initial data into question. The hippocampus may be involved in changing neural connections for a period of three months or more after the initial learning.

Research has suggested that long-term memory storage in humans may be maintained by DNA methylation, [32] and the 'prion' gene. [33] [34]

Multi-store model Edit

The multi-store model (also known as Atkinson–Shiffrin memory model) was first described in 1968 by Atkinson and Shiffrin.

The multi-store model has been criticised for being too simplistic. For instance, long-term memory is believed to be actually made up of multiple subcomponents, such as episodic and procedural memory. It also proposes that rehearsal is the only mechanism by which information eventually reaches long-term storage, but evidence shows us capable of remembering things without rehearsal.

The model also shows all the memory stores as being a single unit whereas research into this shows differently. For example, short-term memory can be broken up into different units such as visual information and acoustic information. In a study by Zlonoga and Gerber (1986), patient 'KF' demonstrated certain deviations from the Atkinson–Shiffrin model. Patient KF was brain damaged, displaying difficulties regarding short-term memory. Recognition of sounds such as spoken numbers, letters, words and easily identifiable noises (such as doorbells and cats meowing) were all impacted. Visual short-term memory was unaffected, suggesting a dichotomy between visual and audial memory. [35]

Working memory Edit

In 1974 Baddeley and Hitch proposed a "working memory model" that replaced the general concept of short-term memory with an active maintenance of information in the short-term storage. In this model, working memory consists of three basic stores: the central executive, the phonological loop and the visuo-spatial sketchpad. In 2000 this model was expanded with the multimodal episodic buffer (Baddeley's model of working memory). [36]

The central executive essentially acts as an attention sensory store. It channels information to the three component processes: the phonological loop, the visuo-spatial sketchpad, and the episodic buffer.

The phonological loop stores auditory information by silently rehearsing sounds or words in a continuous loop: the articulatory process (for example the repetition of a telephone number over and over again). A short list of data is easier to remember.

The visuospatial sketchpad stores visual and spatial information. It is engaged when performing spatial tasks (such as judging distances) or visual ones (such as counting the windows on a house or imagining images).

The episodic buffer is dedicated to linking information across domains to form integrated units of visual, spatial, and verbal information and chronological ordering (e.g., the memory of a story or a movie scene). The episodic buffer is also assumed to have links to long-term memory and semantical meaning.

The working memory model explains many practical observations, such as why it is easier to do two different tasks (one verbal and one visual) than two similar tasks (e.g., two visual), and the aforementioned word-length effect. Working memory is also the premise for what allows us to do everyday activities involving thought. It is the section of memory where we carry out thought processes and use them to learn and reason about topics. [36]

Researchers distinguish between recognition and recall memory. Recognition memory tasks require individuals to indicate whether they have encountered a stimulus (such as a picture or a word) before. Recall memory tasks require participants to retrieve previously learned information. For example, individuals might be asked to produce a series of actions they have seen before or to say a list of words they have heard before.

By information type Edit

Topographical memory involves the ability to orient oneself in space, to recognize and follow an itinerary, or to recognize familiar places. [37] Getting lost when traveling alone is an example of the failure of topographic memory. [38]

Flashbulb memories are clear episodic memories of unique and highly emotional events. [39] People remembering where they were or what they were doing when they first heard the news of President Kennedy's assassination, [40] the Sydney Siege or of 9/11 are examples of flashbulb memories.

Anderson (1976) [41] divides long-term memory into declarative (explicit) and procedural (implicit) memories.

Declarative Edit

Declarative memory requires conscious recall, in that some conscious process must call back the information. It is sometimes called explicit memory, since it consists of information that is explicitly stored and retrieved. Declarative memory can be further sub-divided into semantic memory, concerning principles and facts taken independent of context and episodic memory, concerning information specific to a particular context, such as a time and place. Semantic memory allows the encoding of abstract knowledge about the world, such as "Paris is the capital of France". Episodic memory, on the other hand, is used for more personal memories, such as the sensations, emotions, and personal associations of a particular place or time. Episodic memories often reflect the "firsts" in life such as a first kiss, first day of school or first time winning a championship. These are key events in one's life that can be remembered clearly.

Research suggests that declarative memory is supported by several functions of the medial temporal lobe system which includes the hippocampus. [42] Autobiographical memory – memory for particular events within one's own life – is generally viewed as either equivalent to, or a subset of, episodic memory. Visual memory is part of memory preserving some characteristics of our senses pertaining to visual experience. One is able to place in memory information that resembles objects, places, animals or people in sort of a mental image. Visual memory can result in priming and it is assumed some kind of perceptual representational system underlies this phenomenon. [42]

Procedural Edit

In contrast, procedural memory (or implicit memory) is not based on the conscious recall of information, but on implicit learning. It can best be summarized as remembering how to do something. Procedural memory is primarily used in learning motor skills and can be considered a subset of implicit memory. It is revealed when one does better in a given task due only to repetition – no new explicit memories have been formed, but one is unconsciously accessing aspects of those previous experiences. Procedural memory involved in motor learning depends on the cerebellum and basal ganglia. [43]

A characteristic of procedural memory is that the things remembered are automatically translated into actions, and thus sometimes difficult to describe. Some examples of procedural memory include the ability to ride a bike or tie shoelaces. [44]

By temporal direction Edit

Another major way to distinguish different memory functions is whether the content to be remembered is in the past, retrospective memory, or in the future, prospective memory. John Meacham introduced this distinction in a paper presented at the 1975 American Psychological Association annual meeting and subsequently included by Ulric Neisser in his 1982 edited volume, Memory Observed: Remembering in Natural Contexts. [45] [46] [47] Thus, retrospective memory as a category includes semantic, episodic and autobiographical memory. In contrast, prospective memory is memory for future intentions, or remembering to remember (Winograd, 1988). Prospective memory can be further broken down into event- and time-based prospective remembering. Time-based prospective memories are triggered by a time-cue, such as going to the doctor (action) at 4pm (cue). Event-based prospective memories are intentions triggered by cues, such as remembering to post a letter (action) after seeing a mailbox (cue). Cues do not need to be related to the action (as the mailbox/letter example), and lists, sticky-notes, knotted handkerchiefs, or string around the finger all exemplify cues that people use as strategies to enhance prospective memory.

To assess infants Edit

Infants do not have the language ability to report on their memories and so verbal reports cannot be used to assess very young children's memory. Throughout the years, however, researchers have adapted and developed a number of measures for assessing both infants' recognition memory and their recall memory. Habituation and operant conditioning techniques have been used to assess infants' recognition memory and the deferred and elicited imitation techniques have been used to assess infants' recall memory.

Techniques used to assess infants' recognition memory include the following:

  • Visual paired comparison procedure (relies on habituation): infants are first presented with pairs of visual stimuli, such as two black-and-white photos of human faces, for a fixed amount of time then, after being familiarized with the two photos, they are presented with the "familiar" photo and a new photo. The time spent looking at each photo is recorded. Looking longer at the new photo indicates that they remember the "familiar" one. Studies using this procedure have found that 5- to 6-month-olds can retain information for as long as fourteen days. [48]
  • Operant conditioning technique: infants are placed in a crib and a ribbon that is connected to a mobile overhead is tied to one of their feet. Infants notice that when they kick their foot the mobile moves – the rate of kicking increases dramatically within minutes. Studies using this technique have revealed that infants' memory substantially improves over the first 18-months. Whereas 2- to 3-month-olds can retain an operant response (such as activating the mobile by kicking their foot) for a week, 6-month-olds can retain it for two weeks, and 18-month-olds can retain a similar operant response for as long as 13 weeks. [49][50][51]

Techniques used to assess infants' recall memory include the following:

  • Deferred imitation technique: an experimenter shows infants a unique sequence of actions (such as using a stick to push a button on a box) and then, after a delay, asks the infants to imitate the actions. Studies using deferred imitation have shown that 14-month-olds' memories for the sequence of actions can last for as long as four months. [52]
  • Elicited imitation technique: is very similar to the deferred imitation technique the difference is that infants are allowed to imitate the actions before the delay. Studies using the elicited imitation technique have shown that 20-month-olds can recall the action sequences twelve months later. [53][54]

To assess children and older adults Edit

Researchers use a variety of tasks to assess older children and adults' memory. Some examples are:

  • Paired associate learning – when one learns to associate one specific word with another. For example, when given a word such as "safe" one must learn to say another specific word, such as "green". This is stimulus and response. [55][56]
  • Free recall – during this task a subject would be asked to study a list of words and then later they will be asked to recall or write down as many words that they can remember, similar to free response questions. [57] Earlier items are affected by retroactive interference (RI), which means the longer the list, the greater the interference, and the less likelihood that they are recalled. On the other hand, items that have been presented lastly suffer little RI, but suffer a great deal from proactive interference (PI), which means the longer the delay in recall, the more likely that the items will be lost. [58]
  • Cued recall – one is given a significant hints to help retrieve information that has been previously encoded into the person's memory typically this can involve a word relating to the information being asked to remember. [59] This is similar to fill in the blank assessments used in classrooms.
  • Recognition – subjects are asked to remember a list of words or pictures, after which point they are asked to identify the previously presented words or pictures from among a list of alternatives that were not presented in the original list. [60] This is similar to multiple choice assessments.
  • Detection paradigm – individuals are shown a number of objects and color samples during a certain period of time. They are then tested on their visual ability to remember as much as they can by looking at testers and pointing out whether the testers are similar to the sample, or if any change is present.
  • Savings method – compares the speed of originally learning to the speed of relearning it. The amount of time saved measures memory. [61]
  • Implicit-memory tasks – information is drawn from memory without conscious realization.
  • Transience – memories degrade with the passing of time. This occurs in the storage stage of memory, after the information has been stored and before it is retrieved. This can happen in sensory, short-term, and long-term storage. It follows a general pattern where the information is rapidly forgotten during the first couple of days or years, followed by small losses in later days or years.
  • Absent-mindedness – Memory failure due to the lack of attention. Attention plays a key role in storing information into long-term memory without proper attention, the information might not be stored, making it impossible to be retrieved later.

Brain areas involved in the neuroanatomy of memory such as the hippocampus, the amygdala, the striatum, or the mammillary bodies are thought to be involved in specific types of memory. For example, the hippocampus is believed to be involved in spatial learning and declarative learning, while the amygdala is thought to be involved in emotional memory. [62]

Damage to certain areas in patients and animal models and subsequent memory deficits is a primary source of information. However, rather than implicating a specific area, it could be that damage to adjacent areas, or to a pathway traveling through the area is actually responsible for the observed deficit. Further, it is not sufficient to describe memory, and its counterpart, learning, as solely dependent on specific brain regions. Learning and memory are usually attributed to changes in neuronal synapses, thought to be mediated by long-term potentiation and long-term depression.

In general, the more emotionally charged an event or experience is, the better it is remembered this phenomenon is known as the memory enhancement effect. Patients with amygdala damage, however, do not show a memory enhancement effect. [63] [64]

Hebb distinguished between short-term and long-term memory. He postulated that any memory that stayed in short-term storage for a long enough time would be consolidated into a long-term memory. Later research showed this to be false. Research has shown that direct injections of cortisol or epinephrine help the storage of recent experiences. This is also true for stimulation of the amygdala. This proves that excitement enhances memory by the stimulation of hormones that affect the amygdala. Excessive or prolonged stress (with prolonged cortisol) may hurt memory storage. Patients with amygdalar damage are no more likely to remember emotionally charged words than nonemotionally charged ones. The hippocampus is important for explicit memory. The hippocampus is also important for memory consolidation. The hippocampus receives input from different parts of the cortex and sends its output out to different parts of the brain also. The input comes from secondary and tertiary sensory areas that have processed the information a lot already. Hippocampal damage may also cause memory loss and problems with memory storage. [65] This memory loss includes retrograde amnesia which is the loss of memory for events that occurred shortly before the time of brain damage. [61]

Cognitive neuroscientists consider memory as the retention, reactivation, and reconstruction of the experience-independent internal representation. The term of internal representation implies that such a definition of memory contains two components: the expression of memory at the behavioral or conscious level, and the underpinning physical neural changes (Dudai 2007). The latter component is also called engram or memory traces (Semon 1904). Some neuroscientists and psychologists mistakenly equate the concept of engram and memory, broadly conceiving all persisting after-effects of experiences as memory others argue against this notion that memory does not exist until it is revealed in behavior or thought (Moscovitch 2007).

One question that is crucial in cognitive neuroscience is how information and mental experiences are coded and represented in the brain. Scientists have gained much knowledge about the neuronal codes from the studies of plasticity, but most of such research has been focused on simple learning in simple neuronal circuits it is considerably less clear about the neuronal changes involved in more complex examples of memory, particularly declarative memory that requires the storage of facts and events (Byrne 2007). Convergence-divergence zones might be the neural networks where memories are stored and retrieved. Considering that there are several kinds of memory, depending on types of represented knowledge, underlying mechanisms, processes functions and modes of acquisition, it is likely that different brain areas support different memory systems and that they are in mutual relationships in neuronal networks: "components of memory representation are distributed widely across different parts of the brain as mediated by multiple neocortical circuits". [66]

    . Encoding of working memory involves the spiking of individual neurons induced by sensory input, which persists even after the sensory input disappears (Jensen and Lisman 2005 Fransen et al. 2002). Encoding of episodic memory involves persistent changes in molecular structures that alter synaptic transmission between neurons. Examples of such structural changes include long-term potentiation (LTP) or spike-timing-dependent plasticity (STDP). The persistent spiking in working memory can enhance the synaptic and cellular changes in the encoding of episodic memory (Jensen and Lisman 2005).
  • Working memory. Recent functional imaging studies detected working memory signals in both medial temporal lobe (MTL), a brain area strongly associated with long-term memory, and prefrontal cortex (Ranganath et al. 2005), suggesting a strong relationship between working memory and long-term memory. However, the substantially more working memory signals seen in the prefrontal lobe suggest that this area play a more important role in working memory than MTL (Suzuki 2007). and reconsolidation. Short-term memory (STM) is temporary and subject to disruption, while long-term memory (LTM), once consolidated, is persistent and stable. Consolidation of STM into LTM at the molecular level presumably involves two processes: synaptic consolidation and system consolidation. The former involves a protein synthesis process in the medial temporal lobe (MTL), whereas the latter transforms the MTL-dependent memory into an MTL-independent memory over months to years (Ledoux 2007). In recent years, such traditional consolidation dogma has been re-evaluated as a result of the studies on reconsolidation. These studies showed that prevention after retrieval affects subsequent retrieval of the memory (Sara 2000). New studies have shown that post-retrieval treatment with protein synthesis inhibitors and many other compounds can lead to an amnestic state (Nadel et al. 2000b Alberini 2005 Dudai 2006). These findings on reconsolidation fit with the behavioral evidence that retrieved memory is not a carbon copy of the initial experiences, and memories are updated during retrieval.

Study of the genetics of human memory is in its infancy though many genes have been investigated for their association to memory in humans and non-human animals. A notable initial success was the association of APOE with memory dysfunction in Alzheimer's disease. The search for genes associated with normally varying memory continues. One of the first candidates for normal variation in memory is the protein KIBRA, [67] which appears to be associated with the rate at which material is forgotten over a delay period. There has been some evidence that memories are stored in the nucleus of neurons. [68] [ non-primary source needed ]

Genetic underpinnings Edit

Several genes, proteins and enzymes have been extensively researched for their association with memory. Long-term memory, unlike short-term memory, is dependent upon the synthesis of new proteins. [69] This occurs within the cellular body, and concerns the particular transmitters, receptors, and new synapse pathways that reinforce the communicative strength between neurons. The production of new proteins devoted to synapse reinforcement is triggered after the release of certain signaling substances (such as calcium within hippocampal neurons) in the cell. In the case of hippocampal cells, this release is dependent upon the expulsion of magnesium (a binding molecule) that is expelled after significant and repetitive synaptic signaling. The temporary expulsion of magnesium frees NMDA receptors to release calcium in the cell, a signal that leads to gene transcription and the construction of reinforcing proteins. [70] For more information, see long-term potentiation (LTP).

One of the newly synthesized proteins in LTP is also critical for maintaining long-term memory. This protein is an autonomously active form of the enzyme protein kinase C (PKC), known as PKMζ. PKMζ maintains the activity-dependent enhancement of synaptic strength and inhibiting PKMζ erases established long-term memories, without affecting short-term memory or, once the inhibitor is eliminated, the ability to encode and store new long-term memories is restored. Also, BDNF is important for the persistence of long-term memories. [71]

The long-term stabilization of synaptic changes is also determined by a parallel increase of pre- and postsynaptic structures such as axonal bouton, dendritic spine and postsynaptic density. [72] On the molecular level, an increase of the postsynaptic scaffolding proteins PSD-95 and HOMER1c has been shown to correlate with the stabilization of synaptic enlargement. [72] The cAMP response element-binding protein (CREB) is a transcription factor which is believed to be important in consolidating short-term to long-term memories, and which is believed to be downregulated in Alzheimer's disease. [73]

DNA methylation and demethylation Edit

Rats exposed to an intense learning event may retain a life-long memory of the event, even after a single training session. The long-term memory of such an event appears to be initially stored in the hippocampus, but this storage is transient. Much of the long-term storage of the memory seems to take place in the anterior cingulate cortex. [74] When such an exposure was experimentally applied, more than 5,000 differently methylated DNA regions appeared in the hippocampus neuronal genome of the rats at one and at 24 hours after training. [75] These alterations in methylation pattern occurred at many genes that were down-regulated, often due to the formation of new 5-methylcytosine sites in CpG rich regions of the genome. Furthermore, many other genes were upregulated, likely often due to hypomethylation. Hypomethylation often results from the removal of methyl groups from previously existing 5-methylcytosines in DNA. Demethylation is carried out by several proteins acting in concert, including the TET enzymes as well as enzymes of the DNA base excision repair pathway (see Epigenetics in learning and memory). The pattern of induced and repressed genes in brain neurons subsequent to an intense learning event likely provides the molecular basis for a long-term memory of the event.

Epigenetics Edit

Studies of the molecular basis for memory formation indicate that epigenetic mechanisms operating in brain neurons play a central role in determining this capability. Key epigenetic mechanisms involved in memory include the methylation and demethylation of neuronal DNA, as well as modifications of histone proteins including methylations, acetylations and deacetylations.

Stimulation of brain activity in memory formation is often accompanied by the generation of damage in neuronal DNA that is followed by repair associated with persistent epigenetic alterations. In particular the DNA repair processes of non-homologous end joining and base excision repair are employed in memory formation. [ citation needed ]

Up until the mid-1980s it was assumed that infants could not encode, retain, and retrieve information. [76] A growing body of research now indicates that infants as young as 6-months can recall information after a 24-hour delay. [77] Furthermore, research has revealed that as infants grow older they can store information for longer periods of time 6-month-olds can recall information after a 24-hour period, 9-month-olds after up to five weeks, and 20-month-olds after as long as twelve months. [78] In addition, studies have shown that with age, infants can store information faster. Whereas 14-month-olds can recall a three-step sequence after being exposed to it once, 6-month-olds need approximately six exposures in order to be able to remember it. [52] [77]

Although 6-month-olds can recall information over the short-term, they have difficulty recalling the temporal order of information. It is only by 9 months of age that infants can recall the actions of a two-step sequence in the correct temporal order – that is, recalling step 1 and then step 2. [79] [80] In other words, when asked to imitate a two-step action sequence (such as putting a toy car in the base and pushing in the plunger to make the toy roll to the other end), 9-month-olds tend to imitate the actions of the sequence in the correct order (step 1 and then step 2). Younger infants (6-month-olds) can only recall one step of a two-step sequence. [77] Researchers have suggested that these age differences are probably due to the fact that the dentate gyrus of the hippocampus and the frontal components of the neural network are not fully developed at the age of 6-months. [53] [81] [82]

In fact, the term 'infantile amnesia' refers to the phenomenon of accelerated forgetting during infancy. Importantly, infantile amnesia is not unique to humans, and preclinical research (using rodent models) provides insight into the precise neurobiology of this phenomenon. A review of the literature from behavioral neuroscientist Dr Jee Hyun Kim suggests that accelerated forgetting during early life is at least partly due to rapid growth of the brain during this period. [83]

One of the key concerns of older adults is the experience of memory loss, especially as it is one of the hallmark symptoms of Alzheimer's disease. However, memory loss is qualitatively different in normal aging from the kind of memory loss associated with a diagnosis of Alzheimer's (Budson & Price, 2005). Research has revealed that individuals' performance on memory tasks that rely on frontal regions declines with age. Older adults tend to exhibit deficits on tasks that involve knowing the temporal order in which they learned information [84] source memory tasks that require them to remember the specific circumstances or context in which they learned information [85] and prospective memory tasks that involve remembering to perform an act at a future time. Older adults can manage their problems with prospective memory by using appointment books, for example.

Gene transcription profiles were determined for the human frontal cortex of individuals from age 26 to 106 years. Numerous genes were identified with reduced expression after age 40, and especially after age 70. [86] Genes that play central roles in memory and learning were among those showing the most significant reduction with age. There was also a marked increase in DNA damage, likely oxidative damage, in the promoters of those genes with reduced expression. It was suggested that DNA damage may reduce the expression of selectively vulnerable genes involved in memory and learning. [86]

Much of the current knowledge of memory has come from studying memory disorders, particularly amnesia. Loss of memory is known as amnesia. Amnesia can result from extensive damage to: (a) the regions of the medial temporal lobe, such as the hippocampus, dentate gyrus, subiculum, amygdala, the parahippocampal, entorhinal, and perirhinal cortices [87] or the (b) midline diencephalic region, specifically the dorsomedial nucleus of the thalamus and the mammillary bodies of the hypothalamus. [88] There are many sorts of amnesia, and by studying their different forms, it has become possible to observe apparent defects in individual sub-systems of the brain's memory systems, and thus hypothesize their function in the normally working brain. Other neurological disorders such as Alzheimer's disease and Parkinson's disease [89] can also affect memory and cognition. Hyperthymesia, or hyperthymesic syndrome, is a disorder that affects an individual's autobiographical memory, essentially meaning that they cannot forget small details that otherwise would not be stored. [90] Korsakoff's syndrome, also known as Korsakoff's psychosis, amnesic-confabulatory syndrome, is an organic brain disease that adversely affects memory by widespread loss or shrinkage of neurons within the prefrontal cortex. [61]

While not a disorder, a common temporary failure of word retrieval from memory is the tip-of-the-tongue phenomenon. Sufferers of Anomic aphasia (also called Nominal aphasia or Anomia), however, do experience the tip-of-the-tongue phenomenon on an ongoing basis due to damage to the frontal and parietal lobes of the brain.

Memory dysfunction can also occur after viral infections. [91] Many patients recovering from COVID-19 experience memory lapses. Other viruses can also elicit memory dysfunction, including SARS-CoV-1, MERS-CoV, Ebola virus and even influenza virus. [91] [92]

Interference can hamper memorization and retrieval. There is retroactive interference, when learning new information makes it harder to recall old information [93] and proactive interference, where prior learning disrupts recall of new information. Although interference can lead to forgetting, it is important to keep in mind that there are situations when old information can facilitate learning of new information. Knowing Latin, for instance, can help an individual learn a related language such as French – this phenomenon is known as positive transfer. [94]

Stress has a significant effect on memory formation and learning. In response to stressful situations, the brain releases hormones and neurotransmitters (ex. glucocorticoids and catecholamines) which affect memory encoding processes in the hippocampus. Behavioural research on animals shows that chronic stress produces adrenal hormones which impact the hippocampal structure in the brains of rats. [95] An experimental study by German cognitive psychologists L. Schwabe and O. Wolf demonstrates how learning under stress also decreases memory recall in humans. [96] In this study, 48 healthy female and male university students participated in either a stress test or a control group. Those randomly assigned to the stress test group had a hand immersed in ice cold water (the reputable SECPT or 'Socially Evaluated Cold Pressor Test') for up to three minutes, while being monitored and videotaped. Both the stress and control groups were then presented with 32 words to memorize. Twenty-four hours later, both groups were tested to see how many words they could remember (free recall) as well as how many they could recognize from a larger list of words (recognition performance). The results showed a clear impairment of memory performance in the stress test group, who recalled 30% fewer words than the control group. The researchers suggest that stress experienced during learning distracts people by diverting their attention during the memory encoding process.

However, memory performance can be enhanced when material is linked to the learning context, even when learning occurs under stress. A separate study by cognitive psychologists Schwabe and Wolf shows that when retention testing is done in a context similar to or congruent with the original learning task (i.e., in the same room), memory impairment and the detrimental effects of stress on learning can be attenuated. [97] Seventy-two healthy female and male university students, randomly assigned to the SECPT stress test or to a control group, were asked to remember the locations of 15 pairs of picture cards – a computerized version of the card game "Concentration" or "Memory". The room in which the experiment took place was infused with the scent of vanilla, as odour is a strong cue for memory. Retention testing took place the following day, either in the same room with the vanilla scent again present, or in a different room without the fragrance. The memory performance of subjects who experienced stress during the object-location task decreased significantly when they were tested in an unfamiliar room without the vanilla scent (an incongruent context) however, the memory performance of stressed subjects showed no impairment when they were tested in the original room with the vanilla scent (a congruent context). All participants in the experiment, both stressed and unstressed, performed faster when the learning and retrieval contexts were similar. [98]

This research on the effects of stress on memory may have practical implications for education, for eyewitness testimony and for psychotherapy: students may perform better when tested in their regular classroom rather than an exam room, eyewitnesses may recall details better at the scene of an event than in a courtroom, and persons suffering from post-traumatic stress may improve when helped to situate their memories of a traumatic event in an appropriate context.

Stressful life experiences may be a cause of memory loss as a person ages. Glucocorticoids that are released during stress, damage neurons that are located in the hippocampal region of the brain. Therefore, the more stressful situations that someone encounters, the more susceptible they are to memory loss later on. The CA1 neurons found in the hippocampus are destroyed due to glucocorticoids decreasing the release of glucose and the reuptake of glutamate. This high level of extracellular glutamate allows calcium to enter NMDA receptors which in return kills neurons. Stressful life experiences can also cause repression of memories where a person moves an unbearable memory to the unconscious mind. [61] This directly relates to traumatic events in one's past such as kidnappings, being prisoners of war or sexual abuse as a child.

The more long term the exposure to stress is, the more impact it may have. However, short term exposure to stress also causes impairment in memory by interfering with the function of the hippocampus. Research shows that subjects placed in a stressful situation for a short amount of time still have blood glucocorticoid levels that have increased drastically when measured after the exposure is completed. When subjects are asked to complete a learning task after short term exposure they often have difficulties. Prenatal stress also hinders the ability to learn and memorize by disrupting the development of the hippocampus and can lead to unestablished long term potentiation in the offspring of severely stressed parents. Although the stress is applied prenatally, the offspring show increased levels of glucocorticoids when they are subjected to stress later on in life. [99] One explanation for why children from lower socioeconomic backgrounds tend to display poorer memory performance than their higher-income peers is the effects of stress accumulated over the course of the lifetime. [100] The effects of low income on the developing hippocampus is also thought be mediated by chronic stress responses which may explain why children from lower and higher-income backgrounds differ in terms of memory performance. [101]

Making memories occurs through a three-step process, which can be enhanced by sleep. The three steps are as follows:

Sleep affects memory consolidation. During sleep, the neural connections in the brain are strengthened. This enhances the brain's abilities to stabilize and retain memories. There have been several studies which show that sleep improves the retention of memory, as memories are enhanced through active consolidation. System consolidation takes place during slow-wave sleep (SWS). [102] This process implicates that memories are reactivated during sleep, but that the process doesn't enhance every memory. It also implicates that qualitative changes are made to the memories when they are transferred to long-term store during sleep. During sleep, the hippocampus replays the events of the day for the neocortex. The neocortex then reviews and processes memories, which moves them into long-term memory. When one does not get enough sleep it makes it more difficult to learn as these neural connections are not as strong, resulting in a lower retention rate of memories. Sleep deprivation makes it harder to focus, resulting in inefficient learning. [102] Furthermore, some studies have shown that sleep deprivation can lead to false memories as the memories are not properly transferred to long-term memory. One of the primary functions of sleep is thought to be the improvement of the consolidation of information, as several studies have demonstrated that memory depends on getting sufficient sleep between training and test. [103] Additionally, data obtained from neuroimaging studies have shown activation patterns in the sleeping brain that mirror those recorded during the learning of tasks from the previous day, [103] suggesting that new memories may be solidified through such rehearsal. [104]

Although people often think that memory operates like recording equipment, this is not the case. The molecular mechanisms underlying the induction and maintenance of memory are very dynamic and comprise distinct phases covering a time window from seconds to even a lifetime. [105] In fact, research has revealed that our memories are constructed: "current hypotheses suggest that constructive processes allow individuals to simulate and imagine future episodes, [106] happenings, and scenarios. Since the future is not an exact repetition of the past, simulation of future episodes requires a complex system that can draw on the past in a manner that flexibly extracts and recombines elements of previous experiences – a constructive rather than a reproductive system." [66] People can construct their memories when they encode them and/or when they recall them. To illustrate, consider a classic study conducted by Elizabeth Loftus and John Palmer (1974) [107] in which people were instructed to watch a film of a traffic accident and then asked about what they saw. The researchers found that the people who were asked, "How fast were the cars going when they smashed into each other?" gave higher estimates than those who were asked, "How fast were the cars going when they hit each other?" Furthermore, when asked a week later whether they had seen broken glass in the film, those who had been asked the question with smashed were twice more likely to report that they had seen broken glass than those who had been asked the question with hit. There was no broken glass depicted in the film. Thus, the wording of the questions distorted viewers' memories of the event. Importantly, the wording of the question led people to construct different memories of the event – those who were asked the question with smashed recalled a more serious car accident than they had actually seen. The findings of this experiment were replicated around the world, and researchers consistently demonstrated that when people were provided with misleading information they tended to misremember, a phenomenon known as the misinformation effect. [108]

Research has revealed that asking individuals to repeatedly imagine actions that they have never performed or events that they have never experienced could result in false memories. For instance, Goff and Roediger [109] (1998) asked participants to imagine that they performed an act (e.g., break a toothpick) and then later asked them whether they had done such a thing. Findings revealed that those participants who repeatedly imagined performing such an act were more likely to think that they had actually performed that act during the first session of the experiment. Similarly, Garry and her colleagues (1996) [110] asked college students to report how certain they were that they experienced a number of events as children (e.g., broke a window with their hand) and then two weeks later asked them to imagine four of those events. The researchers found that one-fourth of the students asked to imagine the four events reported that they had actually experienced such events as children. That is, when asked to imagine the events they were more confident that they experienced the events.

Research reported in 2013 revealed that it is possible to artificially stimulate prior memories and artificially implant false memories in mice. Using optogenetics, a team of RIKEN-MIT scientists caused the mice to incorrectly associate a benign environment with a prior unpleasant experience from different surroundings. Some scientists believe that the study may have implications in studying false memory formation in humans, and in treating PTSD and schizophrenia. [111] [112]

Memory reconsolidation is when previously consolidated memories are recalled or retrieved from long-term memory to your active consciousness. During this process, memories can be further strengthened and added to but there is also risk of manipulation involved. We like to think of our memories as something stable and constant when they are stored in long-term memory but this isn't the case. There are a large number of studies that found that consolidation of memories is not a singular event but are put through the process again, known as reconsolidation. [113] This is when a memory is recalled or retrieved and placed back into your working memory. The memory is now open to manipulation from outside sources and the misinformation effect which could be due to misattributing the source of the inconsistent information, with or without an intact original memory trace (Lindsay and Johnson, 1989). [114] One thing that can be sure is that memory is malleable.

This new research into the concept of reconsolidation has opened the door to methods to help those with unpleasant memories or those that struggle with memories. An example of this is if you had a truly frightening experience and recall that memory in a less arousing environment, the memory will be weaken the next time it is retrieved. [113] "Some studies suggest that over-trained or strongly reinforced memories do not undergo reconsolidation if reactivated the first few days after training, but do become sensitive to reconsolidation interference with time." [113] This, however does not mean that all memory is susceptible to reconsolidation. There is evidence to suggest that memory that has undergone strong training and whether or not is it intentional is less likely to undergo reconsolidation. [115] There was further testing done with rats and mazes that showed that reactivated memories were more susceptible to manipulation, in both good and bad ways, than newly formed memories. [116] It is still not known whether or not these are new memories formed and it's an inability to retrieve the proper one for the situation or if it's a reconsolidated memory. Because the study of reconsolidation is still a newer concept, there is still debate on whether it should be considered scientifically sound.

A UCLA research study published in the June 2008 issue of the American Journal of Geriatric Psychiatry found that people can improve cognitive function and brain efficiency through simple lifestyle changes such as incorporating memory exercises, healthy eating, physical fitness and stress reduction into their daily lives. This study examined 17 subjects, (average age 53) with normal memory performance. Eight subjects were asked to follow a "brain healthy" diet, relaxation, physical, and mental exercise (brain teasers and verbal memory training techniques). After 14 days, they showed greater word fluency (not memory) compared to their baseline performance. No long-term follow-up was conducted it is therefore unclear if this intervention has lasting effects on memory. [117]

There are a loosely associated group of mnemonic principles and techniques that can be used to vastly improve memory known as the art of memory.

The International Longevity Center released in 2001 a report [118] which includes in pages 14–16 recommendations for keeping the mind in good functionality until advanced age. Some of the recommendations are to stay intellectually active through learning, training or reading, to keep physically active so to promote blood circulation to the brain, to socialize, to reduce stress, to keep sleep time regular, to avoid depression or emotional instability and to observe good nutrition.

Memorization is a method of learning that allows an individual to recall information verbatim. Rote learning is the method most often used. Methods of memorizing things have been the subject of much discussion over the years with some writers, such as Cosmos Rossellius using visual alphabets. The spacing effect shows that an individual is more likely to remember a list of items when rehearsal is spaced over an extended period of time. In contrast to this is cramming: an intensive memorization in a short period of time. the spacing effect is exploited to improve memory in spaced repetition flashcard training. Also relevant is the Zeigarnik effect which states that people remember uncompleted or interrupted tasks better than completed ones. The so-called Method of loci uses spatial memory to memorize non-spatial information. [119]

Plants lack a specialized organ devoted to memory retention, so plant memory has been a controversial topic in recent years. New advances in the field have identified the presence of neurotransmitters in plants, adding to the hypothesis that plants are capable of remembering. [120] Action potentials, a physiological response characteristic of neurons, have been shown to have an influence on plants as well, including in wound responses and photosynthesis. [120] In addition to these homologous features of memory systems in both plants and animals, plants have also been observed to encode, store and retrieve basic short-term memories.

One of the most well-studied plants to show rudimentary memory is the Venus flytrap. Native to the subtropical wetlands of the eastern United States, Venus Fly Traps have evolved the ability to obtain meat for sustenance, likely due to the lack of nitrogen in the soil. [121] This is done by two trap-forming leaf tips that snap shut once triggered by a potential prey. On each lobe, three triggers hairs await stimulation. In order to maximize the benefit to cost ratio, the plant enables a rudimentary form of memory in which two trigger hairs must be stimulated within 30 seconds in order to result in trap closure. [121] This system ensures that the trap only closes when potential prey is within grasp.

The time lapse between trigger hair stimulations suggests that the plant can remember an initial stimulus long enough for a second stimulus to initiate trap closure. This memory isn't encoded in a brain, as plants lack this specialized organ. Rather, information is stored in the form of cytoplasmic calcium levels. The first trigger causes a subthreshold cytoplasmic calcium influx. [121] This initial trigger isn't enough to activate trap closure, so a subsequent stimulus allows for a secondary influx of calcium. The latter calcium rise superimposes on the initial one, creating an action potential that passes threshold, resulting in trap closure. [121] Researchers, to prove that an electrical threshold must be met to stimulate trap closure, excited a single trigger hair with a constant mechanical stimulus using Ag/AgCl electrodes. [122] The trap closed after only a few seconds. This experiment gave evidence to demonstrate that the electrical threshold, not necessarily the number of trigger hair stimulations, was the contributing factor in Venus Fly Trap memory. It has been shown that trap closure can be blocked using uncouplers and inhibitors of voltage-gated channels. [122] After trap closure, these electrical signals stimulate glandular production of jasmonic acid and hydrolases, allowing for digestion of the prey. [123]

The field of plant neurobiology has gained a large amount of interest over the past decade, leading to an influx of research regarding plant memory. Although the Venus flytrap is one of the more highly studied, many other plants exhibit the capacity to remember, including the Mimosa pudica through an experiment conducted by Monica Gagliano and colleagues in 2013. [124] To study the Mimosa pudica, Gagliano designed an appartus with which potted mimosa plants could be repeatedly dropped the same distance and at the same speed. It was observed that the plants defensive response of curling up its leaves decreased over the 60 times the experiment was repeated per plant. To confirm that this was a mechanism of memory rather than exhaustion, some of the plants were shaken post experiment and displayed normal defensive responses of leaf curling. This experiment also demonstrated long term memory in the plants, as it was repeated a month later and the plants were observed to remain unfazed by the dropping. As the field expands, it is likely that we will learn more about the capacity of a plant to remember.


Short-Term Memory and the Human Hippocampus

Every undergraduate psychology student is taught that short-term memory, the ability to temporarily hold in mind information from the immediate past (e.g., a telephone number) involves different psychological processes and neural substrates from long-term memory (e.g., remembering what happened yesterday). This dichotomous account of memory is grounded on evidence of neuropsychological dissociations such as those shown by patients with damage to medial temporal lobe (MTL), who until now have been thought to exhibit impaired long-term memory but normal short-term memory (Squire, 1992). In recent years, however, this viewpoint has faced considerable challenges, given accumulating evidence suggesting that short-term memory and long-term memory, rather than being qualitatively distinct, may in fact share similar underlying neural mechanisms (for review, see Jonides et al., 2008).

A key recent observation is that patients with MTL damage perform poorly not only on long-term memory tasks, but also on short-term memory tasks that involve remembering novel information across brief intervals. Whereas the perirhinal cortex appears to support short-term memory for novel object information (Brown and Aggleton, 2001), neuropsychological evidence suggests that the hippocampus is critical when associative information is involved (for review, see Jonides et al., 2008), in line with its proposed function as a relational binder in long-term memory (Cohen and Eichenbaum, 1993). For instance, in one recent study, patients with hippocampal amnesia were impaired at remembering the locations of novel objects, even across a delay of a few seconds (Jonides et al., 2008).

We know from neuropsychological evidence, therefore, that the hippocampus is critical to short-term memory for associative information. What is not clear from the neuropsychological data, however, is how the hippocampus supports this function. Hannula and Ranganath (2008) use functional magnetic resonance imaging (fMRI) to address this important issue by characterizing brain activity during each phase of a short-term associative memory task and by linking such neural activity to behavioral performance. Whereas a subsequent memory approach has been widely used to study long-term recognition memory, this has not been possible in previous short-term memory experiments because of the near-ceiling performance typically achieved by subjects. To circumvent this problem, the authors chose a relatively difficult task to ensure that sufficient numbers of correct and incorrect trials would be generated.

The paradigm used shares similarities with a task known to be hippocampal-dependent based on previous neuropsychological data (Hartley et al., 2007). During the sample phase of each trial, subjects viewed a novel scene consisting of four objects (out of a set of nine objects), each in one of nine possible locations in a 3 × 3 grid [Hannula and Ranganath (2008), their Fig. 1 (http://www.jneurosci.org/cgi/content/full/28/1/116/F1)]. To encourage use of a hippocampally mediated allocentric (or world-centered) strategy, rather than an egocentric (or viewer-centered) strategy thought to rely on parietal and prefrontal cortices, subjects were asked to form a mental image of the scene rotated 90° to the right of the original viewpoint. They were then required to maintain the rotated representation during the ensuing 11 s delay phase in anticipation of the test stimulus. During the test phase, subjects' memory for the positions of the objects was assessed. This was done by asking them to classify, by button press, the test stimulus according to whether it constituted (1) a “match” (i.e., the original scene rotated 90°) (2) “mismatch-position” (i.e., one object occupied a new location) (3) “mismatch-swap” (i.e., two objects had swapped locations“). Performance in all conditions was significantly greater than a chance level of 33% correct responses: 78, 65, and 60% on match, mismatch-position and, mismatch-swap displays, respectively.

The authors first performed a subsequent memory analysis by contrasting correct trials with incorrect trials. This revealed that hippocampal activity during the sample phase predicted successful recognition judgments in the test phase [Hannula and Ranganath (2008), their Fig. 2 (http://www.jneurosci.org/cgi/content/full/28/1/116/F2)[. Critically, a subsequent memory correlation was also observed in the hippocampus during the test phase [Hannula and Ranganath (2008), their Fig. 3 (http://www.jneurosci.org/cgi/content/full/28/1/116/F3)]. This finding rules out an otherwise problematic explanation that greater neural activity during the sample phase predicts subsequent success not through the encoding of object-location associative information, but rather the objects (e.g., drums, birdbath) themselves. Indeed, a subsequent memory correlation was observed in the perirhinal cortex selectively during the sample phase, in line with proposals that this neural region is critical for the encoding of item-specific information.

Interestingly, there were no significant differences in hippocampal activity as a function of accuracy during the delay period. Although caution is advised in interpreting such a null finding, this result does suggest that persistent neural firing in the hippocampus does not occur during the delay period of short-term memory tasks, as is thought to occur in the entorhinal cortex. One possibility is that the hippocampus supports short-term memory for associative information through transient changes in synaptic efficacy, rather than active maintenance (Jonides et al., 2008). Alternatively, active maintenance may occur, but by a different mechanism not detectable by fMRI (e.g., involving theta/gamma oscillations).

These results suggest that the hippocampus plays an important role in the encoding and retrieval, but perhaps not the active maintenance, of novel associative information in short-term memory. But how does the hippocampus compute the novelty, or conversely familiarity, of the test stimulus such that a correct recognition judgment can be made? An influential theoretical proposal is that the hippocampus acts as a comparator (or match-mismatch detector), identifying discrepancies between previous predictions based on past experience and current sensory inputs (Norman and O'Reilly, 2003) (for review, see Kumaran and Maguire, 2007). One strategy for assessing the validity of this hypothesis is to characterize how hippocampal activity varies as a function of the novelty or familiarity of the test stimulus. Empirical evidence consistent with predictions arising from a comparator model was provided by a recent study using this approach (Kumaran and Maguire, 2006), with hippocampal activity observed specifically under conditions of match-mismatch, and not in response to the mere presence of novelty per se.