Title: To be or not to be afraid: Neural representation of fear and coping
Speaker: Prof. K. C. Liang
Department of Psychology,
National Taiwan University
Time: 2014/4/22 Tue 14:00 ~ 16:00
Venue: R101 Science Building 5 (中央大學科五館 101 教室).
Abstract:
The prevailing theory on neural representation of fear suggests that the amygdala is the sole site for acquisition and storage of such memory. This view is supported by findings from Pavlovian fear conditioning, as acquisition and/or retention of this task were associated with synaptic plasticity in the amygdala and compromised by lesions of it. However, Pavlovian conditioning allows little or no opportunity of coping, an act that an organism would normally adopt when being frightened in natural habitat. We investigated neural basis of fear memory in an inhibitory avoidance task that involves both classical and operant conditioning, thus active coping is allowed. We found that operation of memory in this task involves brain regions in addition to the amygdala, such as the dorsal hippocampus, nucleus accumbens, medial prefrontal cortex, etc. The amygdala is conceived to play a key role in connecting neutral cues to aversive events by simple association of Pavlovian conditioning. Yet our data suggest that the dorsal hippocampus can also accomplish the same work by combinatorial integration, in which any cue embedded in the configuration, not necessarily CS, can evoked the memory. Further, in the inhibitory avoidance task but not Pavlovian fear conditioning, information processing in the amygdala, hippocampus and medial prefrontal cortex would converge in the nucleus accumbens, which is construed as a neural interface between emotion and motivated action. The difference may be related to possibility of active coping in the former task but not in the latter. Finally, fear memory forged by Pavlovian conditioning is believed to be stored permanently in the amygdala by most (but not all) published studies. In contrast, the critical site for retrieving a fear memory forged by the inhibitory avoidance task shifts from the hippocampus and amygdala to medial prefrontal cortex during an extended retention time. The results suggest that fear memory involving operant conditioning and active coping may form not only a primary representation in the limbic area but also a secondary one in the cortex. Given that evolutionarily the lateral prefrontal cortex in primates corresponds to the medial prefrontal cortex in rats, translocation of fear memory from the limbic system to the cerebral cortex may be the root of a neural mechanism foretelling the emotion labeling effect in reducing negative emotion, a phenomenon involving the lateral prefrontal cortex in humans and much heeded in nowadays literature.