EFFECTS OF LESIONS OF THE MEDIAL PARABRACHIAL NUCLEUS (PBNM) - TASTE DISCRIMINATION AND LITHIUM-CHLORIDE-INDUCED AVERSION LEARNING AFTER DELAYED AND CONTIGUOUS INTERSTIMULUS INTERVALS

This article analyzes the effects of lesions to the medial parabrachia l nucleus (PBNm) in taste aversion learning (TAL) and taste discrimina tion tasks (TDT). In the first experiment, control and lesioned rats w ere presented with a delayed TAL task in which presentation of the gus tatory stimulus was followed 15 min later by the intragastric administ ration of LiCl. In the second experiment, ingestion of the gustatory s timulus was followed immediately by LiCl administration. Control anima ls successfully learned both tasks, whereas PBNm-lesioned animals lear ned only the second task. In the third experiment, the animals were su bjected to TDT with water, saccharine, and quinine. The lesioned anima ls ingested significantly different amounts of stimuli from that inges ted by control rats, showing a clear preference for high concentration s of saccharine; the lesioned animals rejected high concentrations of quinine to a lesser degree than did control animals. In a fourth exper iment, PBNm-lesioned animals were able to solve a delayed TAL task whe n discriminated gustatory stimuli were used. These results are interpr eted as evidence that the PBNm lesion interferes with gustatory proces sing and that the temporal demands imposed by Experiment 1 obviate the use of exteroceptive cues.