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The Journal of Neuroscience, July 19, 2006, 26(29):7547-7554; doi:10.1523/JNEUROSCI.1535-06.2006

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Behavioral/Systems/Cognitive
Abnormal Categorization and Perceptual Learning in Patients with Hippocampal Damage

Kim S. Graham,¹ Victoria L. Scahill,¹ Michael Hornberger,¹ Morgan D. Barense,¹ Andy C. H. Lee,¹ Timothy J. Bussey,² and Lisa M. Saksida²

¹Medical Research Council Cognition and Brain Sciences Unit, Cambridge CB2 2EF, United Kingdom, and ²Department of Experimental Psychology, University of Cambridge, Cambridge CB2 3EB, United Kingdom

Correspondence should be addressed to Dr. Kim S. Graham, Medical Research Council Cognition and Brain Sciences Unit, 15 Chaucer Road, Cambridge CB2 2EF, UK. Email: kim.graham{at}mrc-cbu.cam.ac.uk

Prevailing theory holds that the medial temporal lobe (MTL) subserves declarative memory exclusively, whereas nondeclarative memory is independent of this brain region. Recent studies in patients with amnesia, however, have shown that performance on declarative memory tasks may not always be dependent on a single MTL memory system, instead highlighting the critical role of anatomically distinct structures in processing different stimulus types. In particular, the hippocampus has been implicated in spatial memory, whereas perirhinal cortex seems critical for object memory. To assess whether stimulus type would also be a key dimension in nondeclarative memory, patients with selective hippocampal lesions were tested on simple categorization and perceptual learning of faces and virtual reality scenes. The patients demonstrated preserved categorization and perceptual learning of faces but abnormal performance when the stimuli to be discriminated were virtual reality scenes. These findings imply that stimulus type may be a more critical predictor of performance on memory tasks (declarative and nondeclarative) than previously thought. They also suggest that reports of good nondeclarative memory after MTL damage may, in some cases, simply reflect the use of stimuli that fail to tap the processes dependent on structures in this region, such as spatial processing in the case of the hippocampus.

Key words: nondeclarative memory; scene discrimination; object discrimination; hippocampus; amnesia; medial temporal lobe

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Received Aug. 23, 2005; revised May 8, 2006; accepted May 16, 2006.

Correspondence should be addressed to Dr. Kim S. Graham, Medical Research Council Cognition and Brain Sciences Unit, 15 Chaucer Road, Cambridge CB2 2EF, UK. Email: kim.graham{at}mrc-cbu.cam.ac.uk

This article has been cited by other articles:

				A. C. H. Lee, V. L. Scahill, and K. S. Graham Activating the Medial Temporal Lobe during Oddity Judgment for Faces and Scenes Cereb Cortex, March 1, 2008; 18(3): 683 - 696. [Abstract] [Full Text] [PDF]

				S. J. Bartko, B. D. Winters, R. A. Cowell, L. M. Saksida, and T. J. Bussey Perceptual Functions of Perirhinal Cortex in Rats: Zero-Delay Object Recognition and Simultaneous Oddity Discriminations J. Neurosci., March 7, 2007; 27(10): 2548 - 2559. [Abstract] [Full Text] [PDF]

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