Structural And Functional Feedback From The Basal Nucleus Of Amygdala To Area 17 In Cats

The amygdala, the center of emotion control, receives information from all sensory system, especial from visual system. Visual information is mainly transmitted to the amygdala by two pathways, cortical pathway (primary visual cortex--ventral high-order visual cortex---amygdala) and sub-cortical pathway (retina---thalamus---amygdala). Amaral et al find that in primates, amygdala is reciprocally connected with ventral visual cortex and can also send direct projections to primary visual cortex. Some functional investigations demonstrate that when electrical stimulating the basal nucleus of amygdala in rabbits (rat), evoked potential could be recorded throughout the whole primary visual cortex and the firing of single cell was significantly inhibited. But it is unclear whether amygdala directly projects to primary visual cortex (area 17) in the cat and how amygdala modulates the subtle visual response such orientation, direction, ocular dominance selectivity.Combing retrograde tracers (FluoroGold,2%) and visual field potential (VEPs) recording, we investigate the feedback projections from basal nucleus to area 17. Our results show that there are the feedback projections from the basal nucleus to area 17;--- about 30% P cells in basal nucleus are labeled by retrograde injected FluoroGold in area 17, and these cells were widely distributed in an irregular manner. These results prove that direct feedback projections exist from the basal nucleus to primary visual cortex in cats. When electrically stimulating basal nucleus by electrode, VEPs could be recorded throughout the whole area 17 and the fast latency of VEPs was only 4.3-4.5ms, which indicates basal nucleus may be interconnected with area 17 by mon-synapse.Combining intrinsic optical imaging in vivo, single unit recordings and microinjection in basal nucleus ofthe cat, we investigated the functional feedback from the basal nucleus. When the basal nucleus of amygdala was excited or inhibited by micro injection of glutamate or GABA, responses of the visual cortex to gratings were significantly modulated accordingly. The response amplitude increases after glutamate injection, and decreases after GABA injection; the difference between preferred and non-preferred orientation enhances or reduces accordingly, this suggests that the basal nucleus facilitate the response of primary visual cortex. On the other hand, the patterns of preferred orientation map, half height bandwidth of orientation tuning curve and orientation or direction selectivity remains invariant, demonstrating that when the basal nucleus is inhibited or excited, the response ofprimary visual cortex evoked by the gratings of different orientation vary in proportion.These findings suggest that the basal nucleus of amygdala sends direct projections to the primary visual cortex and play a key role in the visual perception by modulating the visual response, and thus provide anatomical and physiological evidence of certain psychological paradigms.