Cerebral Cortex Advance Access published online on October 26, 2007
Cerebral Cortex, doi:10.1093/cercor/bhm159
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Dorsal Premotor Cortex Exerts State-Dependent Causal Influences on Activity in Contralateral Primary Motor and Dorsal Premotor Cortex
1 Wellcome Trust Centre for Neuroimaging at UCL, Institute of Neurology, University College London, London, UK, 2 Sobell Department of Motor Neuroscience and Movement Disorders, Institute of Neurology, University College London, London, UK, 3 UCL Institute of Cognitive Neuroscience and Department of Psychology, University College London, London, UK, 4 Department of Brain Repair and Rehabilitation, Institute of Neurology, University College London, UK
Address correspondence to Sven Bestmann. Wellcome Trust Centre for Neuroimaging at UCL, Institute of Neurology, University College London, Queen Square, WC1N 3BG, London, UK.Email: s.bestmann{at}fil.ion.ucl.ac.uk
During voluntary action, dorsal premotor cortex (PMd) may exert influences on motor regions in both hemispheres, but such interregional interactions are not well understood. We used transcranial magnetic stimulation (TMS) concurrently with event-related functional magnetic resonance imaging to study such interactions directly. We tested whether causal influences from left PMd upon contralateral (right) motor areas depend on the current state of the motor system, involving regions engaged in a current task. We applied short bursts (360 ms) of high- or low-intensity TMS to left PMd during single isometric left-hand grips or during rest. TMS to left PMd affected activity in contralateral right PMd and primary motor cortex (M1) in a state-dependent manner. During active left-hand grip, high (vs. low)-intensity TMS led to activity increases in contralateral right PMd and M1, whereas activity decreases there due to TMS were observed during no-grip rest. Analyses of condition-dependent functional coupling confirmed topographically specific stronger coupling between left PMd and right PMd (and right M1), when high-intensity TMS was applied to left PMd during left-hand grip. We conclude that left PMd can exert state-dependent interhemispheric influences on contralateral cortical motor areas relevant for a current motor task.
Key Words: concurrent TMS-fMRI • effective connectivity • grip force • motor preparation • transcallosal inhibition