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Part IV. Revealing the Orbitofrontal Cortex through the Amygdala and Striatum |
A Comparison of Reward-Contingent Neuronal Activity in Monkey Orbitofrontal Cortex and Ventral StriatumGuiding Actions toward Rewards
JANINE M. SIMMONSa,
SABRINA RAVELa,
MUNETAKA SHIDARAb AND
BARRY J. RICHMONDa
a Laboratory of Neuropsychology, National Institute of Mental Health, Bethesda, Maryland, USA b Graduate School of Comprehensive Human Sciences, University of Tsukuba, Tsukuba, Japan
Key Words: motivation • limbic system • basal ganglia • electrophysiology
Address for correspondence: Janine M. Simmons, M.D., Ph.D., Room 1B80, Building 49, Laboratory of Neuropsychology, National Institute of Mental Health, Bethesda, MD 20892. Voice: 301-402-4599; fax: 301-402-0046. simmonsj{at}mail.nih.gov
We have investigated how neuronal activity in the orbitofrontal-ventral striatal circuit is related to reward-directed behavior by comparing activity in these two regions during a visually guided reward schedule task. When a set of visual cues provides information about reward contingency, that is, about whether or not a trial will be rewarded, significant subpopulations of neurons in both orbitofrontal cortex and ventral striatum encode this information. Orbitofrontal and ventral striatal neurons also differentiate between rewarding and non-rewarding trial outcomes, whether or not those outcomes were predicted. The size of the neuronal subpopulation encoding reward contingency is twice as large in orbitofrontal cortex (50% of neurons) as in ventral striatum (26%). Reward-contingency-dependent activity also appears earlier during a trial in orbitofrontal cortex than in ventral striatum. The peak reward-contingency representation in orbitofrontal cortex (31% of neurons), occurs during the wait period, a period of high anticipation prior to any action. The peak ventral striatal representation of reward contingency (18%) occurs during the go period, a time of action. We speculate that signals from orbitofrontal cortex bias ventral striatal activity, and that a flow of reward-contingency information from orbitofrontal cortex to ventral striatum serves to guide actions toward rewards.
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