Neurobiology of fear
Kluver and Bucy (1939) found out that monkeys with lesions of the amygdala showed several changes based on their behavior, such as lack of fear and extreme tameness. Similarly, Kaada et al. (1960) found out that certain nuclei within the amygdala contribute differently to defensive and fearful behavior. However, new studies about the amygdala in recent years have brought new understanding about the neurobiology of fear. For instance, Davis (1992) suggested that neurobehavioral system approaches have enabled a clear understanding of the role of particular nuclei within the amygdala through the use of Pavlovian fear conditioning paradigms. This approach does not just aim to transfer power from one stimulus to another, but it involves cognitive aspects; that is, animals make representations, predictions, and relations between circumstances, situations, and events.
Neurobehavioral system approach
Neurobehavioral system approach can be used to analyze fear at different levels: cellular biology, neuroanatomy, and behavior. The integrated neurobehavioral approach has brought a significant understanding of fear as well as helping in comprehending neurobiology of depressive disorders and anxiety. Fear results in depressive disorders and anxiety.
Fear Circuitry: Amygdala
Amygdala is central to the neural circuitry and is responsible for modulating and mediating numerous fear behaviors such as freezing. There are 13 nuclei within the amygdala, with each one of them having sub-nuclei, but only some of these affect fear, that is, central nucleus and basolateral complex. The main role of basolateral complex in fear is sensory information evaluation in dimensions of emotional vigilance and valence, which consequently influence other brain regions as well as amygdala nuclei to respond appropriately to fearful stimuli.
Lateral nucleus
Lateral nucleus lesions are responsible for blocking fear-conditioned responses and fear conditioning. Therefore, the lateral nucleus is a storage and plasticity site for fear conditioning as well as mediating responses for behavioral fear, including freezing. It is also responsible for learning and memory of fear
Central nucleus
The central nucleus is critical for conditioned fear expression. It consists of post-training and pretraining lesions that block various fear measures such as changes in blood pressure and heart rate, fear-potentiated startle, and fear-conditioned freezing. Although the central nucleus is not responsible for learning and memory of fear, it brings arousal and attention during fear.
Therefore, I learned that the amygdala is an important part in the understanding of human anxiety and fear, as well as depressive behaviors. However, there are questions if the distinction between the unconditioned and conditioned fear in animals has been relevant in enhancing our understanding of anxiety and fear in humans. According to the study above, the amygdala, specifically the central nucleus and basolateral complex, is unnecessary for unconditioned fear to predator’s odor. This implies that unconditioned paradigms may be used successfully for particular phobias or species fear ecologically relevant stimuli.