IMAGING HUMAN INTRACEREBRAL CONNECTIVITY BY PET DURING TMS

NON-INVASIVE imaging of human inter-regional neural connectivity by po sitron emission tomography (PET) during transcranial magnetic stimulat ion (TMS) was performed. The hand area of primary motor cortex (M1) in the left cerebral hemisphere was stimulated with TMS while local and remote effects were recorded with PET. At the stimulated site, TMS inc reased blood flow (12-20%) in a highly focal manner, without an inhibi tory surround. Remote covariances, an index of connectivity with M1, w ere also focal. Connectivity patterns established in non-human species were generally confirmed. Excitatory connectivity (positive covarianc e) was observed in ipsilateral primary and secondary somatosensory are as (S1 and S2), in ipsilateral ventral, lateral premotor cortex (M2) a nd in contralateral supplementary motor area (SMA). Inhibitory connect ivity (negative covariance) was observed in contralateral M1.