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Cerebral Cortex Advance Access originally published online on April 24, 2009
Cerebral Cortex 2009 19(12):2946-2958; doi:10.1093/cercor/bhp064
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© The Author 2009. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permissions@oxfordjournals.org

The Brain Network Underlying Serial Visual Search: Comparing Overt and Covert Spatial Orienting, for Activations and for Effective Connectivity

S.L. Fairhall1, I. Indovina1,2, J. Driver3 and E. Macaluso1

1 Neuroimaging Laboratory, Santa Lucia Foundation, 00179 Rome, Italy, 2 Behavioral and Clinical Neuroscience Institute, University of Cambridge, Cambridge CB2 3EB, UK, 3 UCL Institute of Cognitive Neuroscience, University College London, London WC1N 3AR, UK

Address correspondence to email: s.fairhall{at}hsantalucia.it.

We used functional magnetic resonance imaging (fMRI) to investigate the brain basis of overt and covert forms of attention during search, while employing stringent control of both eye movements and attentional shifts. A factorial design compared overt and covert forms of goal-directed serial search versus stimulus-driven tracking. To match ocular changes and the number and magnitude of attention shifts across cells in the design, stimulus-driven tracking involved trial-specific "replay" of previous goal-directed eye movements. We found that, in terms of cortical activations, engagement of the dorsal fronto-parietal network by goal-directed attention did not depend on oculomotor requirements, being found similarly for covert attention, in accord with other work. However, analyses of effective connectivity (or "functional coupling") revealed that information flow within this network changed significantly as a function of both the task (goal-directed or stimulus-driven) and the overt versus covert form of attention. Additionally, we observed a distinct set of subcortical regions (pulvinar and caudate nucleus) engaged primarily during the covert form of goal-directed search. We conclude that dynamics within the dorsal fronto-parietal attentional system flexibly reorganize to integrate task demands and oculomotor requirements.

Key Words: attention • conjunction search • dynamic causal modeling • fMRI • oculomotor


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