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Temporal lobe activity during complex discriminations of familiar and novel objects and faces
BARENSE, M.D., HENSON, R.N.A. & Graham, K.S.
Fifteenth Annual Meeting of the Cognitive Neuroscience Society, F93
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Recent studies indicate that structures in the medial temporal lobe (MTL) support processes beyond long-term declarative memory, including complex visual discrimination. For example, amnesic patients with circumscribed hippocampal lesions had selective difficulties making oddity judgements for scenes shown simultaneously from multiple viewpoints, but not those presented from the same viewpoint. Patients with larger MTL lesions, including damage to the perirhinal cortex, showed additional problems with oddity judgement for faces presented from different, but not the same, viewpoints (Lee et al, 2005). To extend these findings, healthy young participants were scanned using fMRI while they carried out a version of the oddity judgement task used previously in patients. Three different types of stimuli were used (scenes, novel objects, novel faces), presented from either different or same viewpoints. A baseline task of size oddity judgements was employed. In a second experiment, participants were scanned using a dual echo EPI sequence (spin and gradient echo) which minimized MTL susceptibility-artefacts while they completed oddity judgements for both familiar and novel faces and objects. Across the different conditions, different patterns of MTL activation were observed. Oddity judgements of scenes presented from different views elicited significant activity in the posterior hippocampus and parahippocampal cortex bilaterally when compared to size, face or object judgements. By contrast, the face and object different views oddity tasks produced greater activity in more anterior MTL regions, including the perirhinal cortex, when compared to scene and size judgements. These observations support previous patient and imaging findings and provide further evidence that the MTL is recruited during complex visual discriminations which place minimal demand on mnemonic processes. The findings also provide further evidence for specialization of function within the MTL, as oddity judgements for scenes, faces and objects activated different MTL regions. Funded by the Medical Research Council.