Cerebral Cortex Advance Access originally published online on February 1, 2006
Cerebral Cortex 2007 17(1):108-115; doi:10.1093/cercor/bhj128
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Published by Oxford University Press 2006.
Impairment and Facilitation of Transverse Patterning after Lesions of the Perirhinal Cortex and Hippocampus, Respectively
1 Department of Experimental Psychology, University of Cambridge, Cambridge, UK, 2 Laboratory of Neuropsychology, National Institute of Mental Health, Bethesda, MD, USA
Address correspondence to Dr L. M. Saksida, Department of Experimental Psychology, University of Cambridge, Downing Street, Cambridge CB2 3EB, UK. Email: lms42{at}cam.ac.uk.
We have recently suggested that certain effects of perirhinal cortex removals in monkeys can be attributed to the lesion compromising complex configural representations of visual stimuli. On this view, monkeys with perirhinal cortex lesions will be impaired on acquisition of discrimination problems that possess high "feature ambiguity," that is, those in which many of the same features belong to both rewarded and unrewarded stimuli. A subclass of feature-ambiguous problems includes "configural" discrimination problems in which all features are ambiguous. In the present study, we tested control monkeys and monkeys with bilateral lesions of perirhinal cortex on a configural discrimination problem, the transverse-patterning task (i.e., A+ vs. B-, B+ vs. C-, C+ vs. A-), using complex 2-dimensional visual stimuli. In addition, we investigated the effects of lesions to another structure that has been implicated in configural learning, the hippocampus. Monkeys with perirhinal cortex lesions were impaired, whereas monkeys with selective hippocampal lesions were facilitated, on acquisition of the transverse-patterning task. These data do not provide support for mass action theories of medial temporal lobe function, which cannot account for the opposing effects of the 2 lesions. These results are, however, compatible with a view that perirhinal cortex, and not the hippocampus, contains complex configural representations of visual stimuli critical to the solution of the transverse-patterning task.
Key Words: configural learning • discrimination learning • inferotemporal cortex • object recognition • rhesus monkey • ventral visual stream
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