Authors:

BARENSE, M.D., Bussey, T.J., LEE, A.C.H., ROGERS, T.T., Saksida, L.M., Murray, E.A., HODGE, J.R. & GRAHAM, K.S.

Reference:

Year of publication:

2004

CBU number:

6081

Abstract:

Studies in nonhuman primates challenge the view that structures in the medial temporal lobe (MTL) constitute a unitary system involved in memory, suggesting instead that MTL regions make independent contributions to both memory and perception. Specifically, the perirhinal cortex may be involved in the perceptual discrimination of complex objects with a large number of overlapping features. To test this view, the performance of two groups of patients, one with selective bilateral hippocampal damage and another with damage to regions in the MTL, including perirhinal cortex, was assessed on concurrent object discriminations similar to those used in monkeys (Bussey et al, 2002). Subjects were presented with four types of stimuli (barcodes, blobs, bugs and animals) within which were three levels of perceptual discrimination: (a) maximum feature ambiguity, in which all features were ambiguous (i.e., both rewarded and not rewarded); (b) intermediate feature ambiguity, in which half of the features were ambiguous; and (c) minimum feature ambiguity, in which no object features were ambiguous. Whereas patients with damage limited to the hippocampus bilaterally performed similarly to controls, cases with more extensive damage to the MTL showed impairments on all conditions with explicitly ambiguous features (i.e., intermediate and maximum conditions), but normal performance on the minimum barcode and animal conditions. Thus, performance in these patients was modulated by a perceptual factor. These results are consistent with findings from similar experiments in nonhuman primates (Bussey et al, 2002), and together these studies support a view in which MTL structures are involved in both perceptual and mnemonic processing. Funded by the Medical Research Council and Alzheimerís Research Trust. (not in HPR 50)