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Cerebral Cortex Advance Access published online on May 8, 2009
Cerebral Cortex, doi:10.1093/cercor/bhp094
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© 2009 The Authors
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Neural Signatures of Stimulus Features in Visual Working Memory—A Spatiotemporal Approach

Helen M. Morgan1, Margaret C. Jackson1, Christoph Klein1, Harald Mohr2, Kimron L. Shapiro1 and David E. J. Linden1,3

1 Wolfson Centre for Clinical and Cognitive Neuroscience and Wales Institute of Cognitive Neuroscience, School of Psychology, Bangor University, Gwynedd LL57 2AS, UK, 2 Institute of Psychology, Johann Wolfgang Goethe University, 60054 Frankfurt, Germany, 3 North Wales Clinical School, Wrexham LL13 7YP, UK

Address correspondence to Dr Helen M. Morgan, School of Psychology, Bangor University, Penrallt Road, Bangor, Gwynedd LL57 2AS, UK. Email: h.morgan{at}bangor.ac.uk.

We examined the neural signatures of stimulus features in visual working memory (WM) by integrating functional magnetic resonance imaging (fMRI) and event-related potential data recorded during mental manipulation of colors, rotation angles, and color–angle conjunctions. The N200, negative slow wave, and P3b were modulated by the information content of WM, and an fMRI-constrained source model revealed a progression in neural activity from posterior visual areas to higher order areas in the ventral and dorsal processing streams. Color processing was associated with activity in inferior frontal gyrus during encoding and retrieval, whereas angle processing involved right parietal regions during the delay interval. WM for color–angle conjunctions did not involve any additional neural processes. The finding that different patterns of brain activity underlie WM for color and spatial information is consistent with ideas that the ventral/dorsal "what/where" segregation of perceptual processing influences WM organization. The absence of characteristic signatures of conjunction-related brain activity, which was generally intermediate between the 2 single conditions, suggests that conjunction judgments are based on the coordinated activity of these 2 streams.

Key Words: EEG • fMRI • source analysis • visual • working memory


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