Effects of environmental experience on behavior and neuronal activity in nucleus accumbens core and shell in an appetitive learning task
Anatomical, pharmacological, and electrophysiological investigations have established the involvement of the nucleus accumbens (NAcc) in appetitive behavior and reinforcement learning. Based upon anatomical and functional differences, NAcc has been divided into core and shell regions; however, assessment of neuronal responding in these brain areas during the acquisition of a learned appetitive behavioral response has remained largely unexplored. Other contemporary research shows that exposure to environmental enrichment alters appetitive behavior, learning, and NAcc function. To investigate the impact of differential environmental experience on these phenomena, behavior and neuronal activity in both NAcc core and shell was recorded from environmentally enriched (EE), socially isolated th, and socially housed (SH) rats during acquisition of a three-phase, operant-shaping procedure for sucrose reinforcement. Behavioral assessment revealed that SI rats exhibited less discriminative appetitive behavior than EE rats during the third phase of training. Neuronal recordings were collected during the first training session, the third training session, and post-acquisition (PTA) sessions of the phase-three training protocol. Changes in the firing rate of core and shell neurons were evaluated during nose-poke cue (trial onset), good poke (operant response), feeder cue (indicating sucrose availability), and sucrose delivery (consummatory response). During the first training session, EE rats exhibited a greater proportion of neuronal responses during good poke in core and during sucrose delivery in core and shell. During the third training session, when learning differences were apparent in EE and SI rats, a greater proportion of core neurons in EE relative to SI rats increased their firing rate during both nose-poke cue and feeder cue. Also, cumulative responses in core neurons were more numerous in EE rats during the four assessed events in this session. In addition, overall responding in shell neurons decreased during all three appetitive task events (nose-poke cue, good poke, and feeder cue) in PTA recordings relative to the first training session. Likewise, the response magnitudes of shell excitations overall were significantly reduced during nose-poke cue and feeder cue in the PTA recordings relative to the first training session. Collectively, these recordings reveal neuronal correlates of the dispositional and learning differences in EE and SI rats while further implicating the NAcc core in reinforcement learning and NAcc shell in appetitive flexible, approach behavior prior to contextual familiarity.
0989: Physiological psychology