Cerebral Cortex Advance Access published online on February 4, 2009
Cerebral Cortex, doi:10.1093/cercor/bhp005
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Detection of Fixed and Variable Targets in the Monkey Prefrontal Cortex
1 MRC Cognition and Brain Sciences Unit, Cambridge CB2 7EF, UK, 2 Department of Experimental Psychology, University of Oxford, Oxford OX1 3UD, UK
Address correspondence to Makoto Kusunoki, PhD, Department of Experimental Psychology, University of Oxford, South Parks Road, Oxford OX1 3UD, UK. Fax: +44-(0)-1865-310447. Email: makoto.kusunoki{at}psy.ox.ac.uk.
Behavioral significance is commonly coded by prefrontal neurons. The significance of a stimulus can be fixed through experience; in complex behavior, however, significance commonly changes with short-term context. To compare these cases, we trained monkeys in 2 versions of visual target detection. In both tasks, animals monitored a series of pictures, making a go response (saccade) at the offset of a specified target picture. In one version, based on "consistent mapping" in human visual search, target and nontarget pictures were fixed throughout training. In the other, based on "varied mapping," a cue at trial onset defined a new target. Building up over the first 1 s following this cue, many cells coded short-term context (cue/target identity) for the current trial. Thereafter, the cell population showed similar coding of behavioral significance in the 2 tasks, with selective early response to targets, and later, sustained activity coding target or nontarget until response. This population similarity was seen despite quite different activity in the 2 tasks for many single cells. At the population level, the results suggest similar prefrontal coding of fixed and short-term behavioral significance.
Key Words: association memory • behavioral category • target detection • unit activity