Dissociation of core and shell single-unit activity in the nucleus accumbens in free-choice novelty.

Core and shell regions of the nucleus accumbens (NAcc) have been implicated in different aspects of goal-directed behavior. To assess these differences at the neuronal level, we evaluated core and shell single-unit activity in eight rats during one-trial, free-choice entry into a novel compartment. Changes in firing rate during approach of (orientation toward) and entry into (nose cross) novelty were assessed relative to a pre-novelty baseline when the animals were behaviorally active. Increases and decreases in neuronal activity were recorded in both regions during both phases of the novelty response. The regional distribution of these responses, however, was significantly different during the approach phase with roughly equal proportions of neuronal excitations (8/29) and inhibitions (6/29) in core but a shift away from excitation (2/40) toward inhibition (12/40) in shell. No regional differences emerged during subsequent approach of the familiar compartment from the novel chamber or during entry to either the novel or familiar compartment. Taken together, our results during approach to free-choice novelty indicate a regional dissociation in NAcc firing rate may play a role in appetitive behavior.