Functional decortication by cortical spreading depression does not prevent forced extinction of conditioned saccharin aversion in rats.

Conditioned taste aversion established in rats by association of saccharin drinking with subsequent lithium chloride intoxication decreased saccharin intake to 22% of normal consumption. Force-feeding saccharin to intact and functionally decorticate trained rats returned saccharin consumption on the next day to 62% (n equals 18) and 77% (n equals 19), respectively. Over-trained conditioned saccharin aversion was affected by forced extinction in a similar way (saccharin intake increased from 28% to 50% and 63%, respectively). Intact brain rats refused to swallow saccharin during forced feeding. while functionally decorticate animals showed no signs of aversion; but extinction was almost equal in both cases. Application of lithium chloride after forced feeding of saccharin in functionally decorticate rats neither prevented extinction of conditioned taste aversion nor reestablished the aversion habit extinguished earlier with intact brain. It is concluded that acquisition of the conditioned taste aversion requires cortical input to a short-term memory file, whereas decorticate extinction can be induced by subcortical gustatory processing analogous to the mechanism controlling feeding behavior during the preweaning period.