Feedback of the amygdala globally modulates visual response of primary visual cortex in the cat

The amygdala is an important center for emotional behavior, and it influences other cortical regions. Long feedback projections from the amygdala to the primary visual cortex were recently reported in the cat and monkey, two animal models for vision research. However, the detailed functional roles of these extensive projections still remain largely unknown. In this study, intrinsic signal optical imaging was used to investigate the visually driven responses of the primary visual cortex of cats as focal drugs were injected into the basal nucleus of the amygdala. Both the visually evoked global signals and differential signals in the functional maps of the primary visual cortex were enhanced or reduced by glutamate-induced activation or GABA-induced deactivation of neurons in the amygdala, respectively. This modulation was found to be non-selective, consistent with the gain control mechanism-both the preferred orientation and its mapped orientation tuning width remained unchanged. The single unit recordings showed similar results supporting the above observations. These results suggest that the distal feedback signals of the amygdala enhance the primary sensory information processing in a non-selective, gain-control fashion. This provides direct neurophysiological evidence and insight for previous studies on emotional-cue related psychological studies.