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Conditional fear and its relationship with the amygdala and the hippocampus

Conditional fear and its relationship with the amygdala and the hippocampus

Fear is a basic emotion that helps us protect ourselves from certain dangers. It is an emotion closely related to survival. Nevertheless, there are situations where this fear can be conditioned to completely neutral situations or stimuli, what is known as conditioned fear. Imagine that a small child every time he enters a room gives him a fright. Soon, it is very possible that this child is afraid of the room itself.

For this conditioning to take place, There are two fundamental brain structures: the amygdala and the hippocampus. The amygdala represents a key element in emotions and the hippocampus in spatial memory. In this way, we can condition the fear of a specific place. Throughout the article we will review what is conditioned fear as well as the key role of these two brain structures.

Content

  • 1 Conditional fear, what is it?
  • 2 Conditional fear and tonsil
  • 3 Contextual and hippocampal conditioned fear

Conditional fear, what does it consist of?

Before entering fully into the role of the amygdala and hippocampus in conditioned fear, we will review what this process consists of. As defined by the team of Carlos Ibérico (2007), in the conditioning of fear "A neutral stimulus, which does not in itself produce an emotional response, is followed by an unconditional aversive stimulus (IS). After certain matings, the neutral stimulus will indicate the onset of IS and will cause a fear response associated with the expectation of the Aversive EI".

Through this process, a stimulus that was originally neutral, becomes a conditioned stimulus (EC). To understand it better, let's imagine that we conducted an experiment with rats. We have a rodent in a cage with a floor that gives small electric shocks (EI). For a few trials, a sound (neutral stimulus) is activated, which is followed by a discharge (unconditional aversive stimulus). When sufficient tests are performed, the sound ends up causing a fear reaction on its own. That is, sound has become a conditioned stimulus.

Conditional fear and tonsil

The role of the tonsil in conditioned fear has been extensively investigated. LeDoux and his team (2000), conducted an experiment with rats to see what role the amygdala played in the conditioning of auditory fear. Initially, they caused lesions in the auditory pathways in rats, specifically bilateral lesions of the lateral geniculate nucleus. In this case, they observed that the fear conditioned to a tone was blocked, however, the bilateral lesions produced in the auditory cortex did not prevent it.

What do these findings indicate? That in order for fear conditioning to occur, the signals that cause the tone must reach the medial geniculate nucleus, but not the auditory cortex. They also found the existence of another pathway from the medial geniculate nucleus to another structure: the amygdala. They found out that the lesions of the tonsil as well as those of the medial geniculate nucleus prevented conditioned fear.

The amygdala receives the input of all sensory systems. This structure is related to learning and maintaining the emotional meaning of sensory signals. So that, the amygdala is fundamental in this process since through it the aversion to a fear-conditioned stimulus is learned and maintained.. In the amygdala, the evaluation process on the emotional importance of a specific sound is produced based on previous experiences with it. From here, the circuits responsible for sympathetic response and behavior in the hypothalamus and the gray periaqueductal substance are activated.

Contextual and hippocampal conditioned fear

Conditional fear can also be associated with a specific context. Imagine that we return home every day from work on a quiet street in the city. One day, someone with a covered head tells us to give him all the money: they are robbing us. From this experience, there is a high probability that we will stop passing through that street and take alternative routes. In this way, the street of robbery will have been conditioned to fear, that is, the street itself will elicit the emotion of fear.

The process through which a harmless context can produce fear by associating it with stimuli that induce fear is known as contextual conditioned fear. In this type of conditioning not only the amygdala comes into play, but also the hippocampus. The hippocampus is a key structure in spatial location memory processesThus, it is an important structure in this type of conditioning.

Antoniadis and McDonald (2000), demonstrated that the bilateral lesion of the hippocampus before conditioning blocks the appearance of the fear response to the context without blocking the development of fear of explicit conditional stimulation. If we move this finding to the example of the thief, it could be said that we do not lose our fear of the thief but we do not go to the street, that is, we would not develop fear of going back there.

On the other hand, when the injury occurs after conditioning blocks the memory of the fear response without changing the memory of the fear response to the explicit conditional stimulus. If we return to the example of the thief, in this case, we would be afraid of the thief but the memory of fear response in the street would be blocked, that is, the street would stop being scary.

Bibliography

  • Antoniadis, E. and McDonald, R. (2000). Amygdala, hippocampus and discrimibative fear conditioning to context. Behavioural Brain Research, 108, (1), 1-19.
  • Ibérico, C., Vansteenwegen, D, Vervliet, B. and Hermans, D. (2007). The effect of (im) predictability on contextual fear: a replica of basic findings. Journal of Psychology, 25, (1), 81-101.
  • LeDoux, J. (2000). Emotion circuits in the brain. Annual Reviews Neuroscience, 23, 155-184.
  • Pinel, J. (2006). Biopsychology. Madrid: Addison-Wesley.