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The Journal of Neuroscience, March 1, 2006, 26(9):2449-2457; doi:10.1523/JNEUROSCI.4431-05.2006
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Behavioral/Systems/Cognitive
Dissociable Roles for the Nucleus Accumbens Core and Shell in Regulating Set Shifting
Stan B. Floresco, Sarvin Ghods-Sharifi, Claudia Vexelman, andOrsolya Magyar Department of Psychology and Brain Research Center, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z4
Correspondence should be addressed to Dr. Stan B. Floresco, Department of Psychology and Brain Research Center, University of British Columbia, 2136 West Mall, Vancouver, British Columbia, Canada V6T 1Z4. Email: floresco{at}psych.ubc.ca
The ability to behave in a flexible manner is an executive function mediated in part by different regions of the prefrontal cortex. The present study investigated the role of two major efferents of the prefrontal cortex, the nucleus accumbens (NAc) core and shell, in behavioral flexibility using a maze-based strategy set-shifting task. During initial discrimination training, rats learned to use either an egocentric response or a visual-cue discrimination strategy to obtain food reward. During the set shift, animals had to shift from the previously acquired response or visual-cue-based strategy and learn the alternate discrimination. Inactivation of the NAc core, induced by infusion of the GABA agonists baclofen and muscimol, did not impair initial acquisition of either a response or visual-cue discrimination but severely disrupted shifting from one strategy to another. Analysis of the type of errors revealed that impairments in set shifting were not attributable to increased perseveration but to a disruption of the acquisition and maintenance of a new strategy. In contrast, inactivation of the NAc shell did not impair acquisition of either a response or a visual-cue discrimination, or shifting from one strategy to another. However, inactivation of the NAc shell before initial discrimination training improved performance during the set shift relative to control animals. These data indicate that the NAc core and shell make dissociable contributions to behavioral flexibility during set shifting. The NAc core facilitates the acquisition and maintenance of novel behavioral strategies and elimination of inappropriate response options, whereas the shell may mediate learning about irrelevant stimuli.
Key words: cognitive flexibility; ventral striatum; prefrontal cortex; associative learning; schizophrenia; GABA; rat
Received Oct. 17, 2005; revised Jan. 23, 2006; accepted Jan. 23, 2006.
Correspondence should be addressed to Dr. Stan B. Floresco, Department of Psychology and Brain Research Center, University of British Columbia, 2136 West Mall, Vancouver, British Columbia, Canada V6T 1Z4. Email: floresco{at}psych.ubc.ca
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