Cortical pattern separation and item-specific memory encoding

Pidgeon, L. M. and Morcom, A. M. (2016) Cortical pattern separation and item-specific memory encoding. Neuropsychologia, 85, pp. 256-271. (doi: 10.1016/j.neuropsychologia.2016.03.026) (PMID:27018483)

Abstract

Pattern separation and pattern completion are fundamental brain processes thought to be critical for episodic memory encoding and retrieval, and for discrimination between similar memories. These processes are best understood in the hippocampus, but are proposed to occur throughout the brain, in particular in sensory regions. Cortical, as well as hippocampal, pattern separation may therefore support formation of event-unique memory traces. Using fMRI, we investigated cortical pattern separation and pattern completion and their relationship to encoding activity predicting subsequent item-specific compared to gist memory. During scanning, participants viewed images of novel objects, repeated objects, and objects which were both perceptually and conceptually similar to previously presented images, while performing a size judgement task. In a later surprise recognition test, they judged whether test items were ‘same’ ‘similar’ or ‘new’ relative to studied items. Activity consistent with pattern separation – responses to similar items as if novel – was observed in bilateral occipito-temporal cortex. Activity consistent with pattern completion – responses to similar items as if repeated – was observed in left prefrontal cortex and hippocampus. Curve fitting analysis further revealed that graded responses to change in image conceptual and perceptual similarity in bilateral prefrontal and right parietal regions met specific computational predictions for pattern separation for one or both of these similarity dimensions. Functional overlap between encoding activity predicting subsequent item-specific recognition and pattern separation activity was also observed in left occipital cortex and bilateral inferior frontal cortex. The findings suggest that extrahippocampal regions including sensory and prefrontal cortex contribute to pattern separation and pattern completion of visual input, consistent with the proposal that cortical pattern separation contributes to formation of item-specific memory traces, facilitating accurate recognition memory.

• Item Type: Articles
• Additional Information: Laura M. Pidgeon was supported by a PhD studentship from the University of Edinburgh Centre for Cognitive Ageing and Cognitive Epidemiology (CCACE), part of the cross-council Lifelong Health and Wellbeing Initiative, Grant number G0700704/84698. Alexa M. Morcom is a member of CCACE and was supported by an RCUK Academic Fellowship at the University of Edinburgh. The study was supported by pilot funding from the Centre for Cognitive Ageing and Cognitive Epidemiology.
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Morcom, Dr Alexa and Lyall, Dr Laura
• Authors: Pidgeon, L. M., and Morcom, A. M.
• College/School: College of Medical Veterinary and Life Sciences > School of Health & Wellbeing > Mental Health and Wellbeing; College of Medical Veterinary and Life Sciences > School of Psychology & Neuroscience
• Journal Name: Neuropsychologia
• Publisher: Elsevier
• ISSN: 0028-3932
• ISSN (Online): 1873-3514
• Published Online: 24 March 2016
• Copyright Holders: Copyright © 2016 Elsevier Ltd.
• First Published: First published in Neuropsychologia 85: 256-271
• Publisher Policy: Reproduced in accordance with the publisher copyright policy