A model of amygdala–hippocampal–prefrontal interaction in fear conditioning and extinction in animals

Empirical research has shown that the amygdala, hippocampus, and ventromedial prefrontal cortex (vmPFC) are involved in fear conditioning. However, the functional contribution of each brain area and the nature of their interactions are not clearly understood. Here, we extend existing neural network models of the functional roles of the hippocampus in classical conditioning to include interactions with the amygdala and prefrontal cortex. We apply the model to fear conditioning, in which animals learn physiological (e.g. heart rate) and behavioral (e.g. freezing) responses to stimuli that have been paired with a highly aversive event (e.g. electrical shock). The key feature of our model is that learning of these conditioned responses in the central nucleus of the amygdala is modulated by two separate processes, one from basolateral amygdala and signaling a positive prediction error, and one from the vmPFC, via the intercalated cells of the amygdala, and signaling a negative prediction error. In addition, we propose that hippocampal input to both vmPFC and basolateral amygdala is essential for contextual modulation of fear acquisition and extinction. The model is sufficient to account for a body of data from various animal fear conditioning paradigms, including acquisition, extinction, reacquisition, and context specificity effects. Consistent with studies on lesioned animals, our model shows that damage to the vmPFC impairs extinction, while damage to the hippocampus impairs extinction in a different context (e.g., a different conditioning chamber from that used in initial training in animal experiments). We also discuss model limitations and predictions, including the effects of number of training trials on fear conditioning.     

Internet and Advertisement

The Internet has revolutionized the way knowledge is currently produced, stored and disseminated. A few finger clicks on a keyboard can save time and many hours of search in libraries or shopping in stores. Online trademarks with an (e-) prefix such as e-library, e-business, e-health etc., are increasingly part of our daily professional vocabularies. However, the Internet has also produced multiple negative side effects, ranging from an unhealthy dependency to a dehumanization of human relationships. Fraudulent, unethical and scam practices are also flourishing through for example misleading online advertising methods. Some social and professional networks gather users’ profiles for selling and advertising purposes, sometimes by making it technically difficult to unsubscribe. Here, I discuss some of these unethical aspects and propose some potential solutions to reduce them.