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The influence mechanism of categories and concepts on fear generalization
2017, 40(5):
1266-1273.
The acquisition of fear is of vital importance to the survival of humans and animals, which can help individuals realize danger and then defend rapidly. Since acquired fear stimuli can take many forms, it is necessary to generalize conditioned reflexes to other potentially dangerous stimuli. For instance, after being bitten by a snake, the individual will avoid other snakes or situations where snakes may appear. Although the appropriate generalization of fear is conducive to adapting to the changing environment, excessive generalization, such as "once bitten, twice shy", will seriously affect our daily life. And it even lead to post-traumatic stress disorder (PTSD), phobia (Phobia), obsessive-compulsive disorder (obsessive-compulsive disorder, OCD),or other anxiety disorders. Thus, fear acquisition and generalization is crucial in the field of psychology.
Pavlovian conditioning is a classical paradigm to study the topic of fear generalization. In classical fear conditioning, a neutral stimulus that pairs with the aversive event acquires aversive properties. Furthermore, other similar stimulus can also elicit fear response. For the past century, Pavlovian conditioning, as an experimental model for understanding the animal’s fear acquisition, plays a major role in understanding the behavioral and neurophysiological mechanisms of fear acquisition, expression, inhibition, and generalization. It’s worth noting that human beings, unlike animals, have the ability to integrate the previous knowledge and experience, and use the concepts of classification to learn fear.
The generalization fear of human, divided into several parts (perception, classification, and concept), is introduced in this paper. Different parts have different experimental procedures. Variants that closely resemble the CS+ (neutral stimulus that pairs with the aversive event) evoke more fear than variants that have less in common with the CS+. What’s more, discrimination thresholds can be changed by aversive learning. On the other hand, the similarity of concepts and the typicality of classified members can promote the gradient and intensity of fear generalization. However, perceptual generalization research scarcely speaks to the role of conceptual meaning while conceptual generalization research rarely addresses the importance of physical form. In real life, these two factors are often at the same time work together to promote the generalization of fear. It is helpful for us to understand the essence of anxiety disorders by integrating the two kinds of research. It is a remarkable fact that， if high-order of learning, reasoning, and conceptual system are involved in fear generalization, then we need to expand the neural circuit of fear learning. Conditional reflex system, cognitive system (categorizing process、 conceptual representation and inductive reasoning system) can be linked together to generalize the fear we have learned to the unknown stimuli.
Lissek (2012) proposed a perceptual generalization model of fear. That is, if a generalization stimulus is sufficient similar to the CS+, the hippocampus initiates a pattern completion process to trigger a conditioned response. Insufficient similar, on the other hand, initiates pattern separation processes in the hippocampus, which leads to activation of the vmPFC that inhibits the expression of fear. Hence, fear generalization is determined by pattern completion versus pattern separation processes. With respect to generalization of higher order fear learning, the hippocampus and surrounding regions are important for SPC. Hippocampal-amygdala coupling may play a critical role in generalization based category to make the individual generalizes preferentially toward typical category members. It’s worth noting that amygdale-lateral FFG connectivity was selectively enhanced when conditioned to animals. Intrinsic cortical connectivity with the amygdala may be better for survive which makes evolutionary sense.
These theoretical and empirical studies can provide the following three aspects of the clinical implication. (1) Category-based inductive reasoning suggests that typical things are more representative than atypical things. Therefore, using the typical stimuli in extinction may be a better choice. (2) In clinical treatment, combining the similar and the opposite of concept may be critical to the treatment of clinical anxiety disorders. (3) Exposure to a series of stimuli associated with the original aversive stimulus (classification related) may also be an ideal treatment during exposure therapy.
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