Lateralized contributions of the cerebral cortex, parabrachial nucleus, and amygdala to acquisition and retrieval of passive avoidance reaction in rats: a functional ablation study.

Reversible blockade of the neocortex by spreading depression and of the parabrachial nucleus (PBN) and amygdala (AMG) by tetrodotoxin (TTX) injection was used to study lateralization of passive avoidance reaction (PAR) engrams in rats. In Experiment 1, PAR acquisition was not disrupted by posttrial TTX applied into the PBN or AMG or into both of these structures in the same hemisphere but was impaired when the AMG and PBN were blocked in opposite hemispheres. In Experiment 2, retrieval of PAR acquired with intact brain was not impaired by unilateral TTX blockade of the AMG. In Experiment 3, PAR was acquired with posttrial TTX blockade of the AMG and PBN in one hemisphere. Full or partial block of PAR retrieval was induced by functional decortication of the contra- or ipsilateral hemisphere, respectively, whereas blockade of either AMG was ineffective. It is concluded that PAR acquisition requires ipsilateral interaction of the AMG and PBN and that the two hemicortices contribute differentially to the retrieval of engrams formed under such conditions.