Electrolytic lesions to nucleus accumbens core and shell have dissociable effects on conditioning to discrete and contextual cues in aversive and appetitive procedures respectively

Abstract

The nucleus accumbens (n. acc.) has been implicated in conditioning to both discrete and contextual cues but its precise role is as yet controversial because conflicting patterns of effect have been reported. These inconsistencies may relate to the extent to which the lesions used encroach on different subfields of n. acc. and the use of different task variants. The present study compared the effects of selective lesions of shell and core subfields of nucleus accumbens (n. acc.) across aversive and appetitive trace conditioning variants. In both experiments, an auditory stimulus was contiguous with footshock or food, or presented at a trace interval. A continuous flashing light in each case provided an experimental background stimulus. Conditioning to the cues provided by the experimental chambers was also assessed. Rats with electrolytic lesions to the n. acc. shell and core showed different patterns of effect in aversive (Experiment 1) and appetitive (Experiment 2) variants of this procedure. In Experiment 1, the core lesion reduced the difference between trace and contiguously conditioned groups, in responding to the discrete noise stimulus. However, neither lesion had any detectable effect on contextual conditioning. In Experiment 2, the shell lesion clearly increased contextual conditioning, selectively in the trace conditioned group, but neither lesion had any detectable effect on discrete cue conditioning. Thus, whilst the shell and core lesions produced dissociable effects on discrete cue and contextual conditioning, the conclusions to be drawn depend on the procedural variant in use.