Activation of frontal premotor areas during suprathreshold transcranial magnetic stimulation of the left primary sensorimotor cortex: A glucose metabolic PET study

We employed cerebral (18)Fluoro-deoxyglucose positron emission tomography ( [F-18]FDG-PET) to visualize neuronal activation of the frontal motor and pr emotor cortex during suprathreshold repetitive transcranial magnetic stimul ation (rTMS) applied to the left primary sensorimotor hand area (SM1(HAND)) . Twelve right-handed normal subjects underwent two [F-18]FDG-PET measureme nts at baseline without rTMS and during suprathreshold 2 Hz rTMS of the lef t SM1(HAND). In the rTMS condition, 1,800 magnetic stimuli at an intensity of 140% of motor-resting threshold were delivered immediately after intrave nous injection of [F-18]FDG. Relative differences in the normalized regiona l cerebral metabolic rate for glucose (rCMRglc) between the rTMS condition and baseline were determined using a voxel-by-voxel Student's t-test and a volume-of-interest analysis. Data analysis was a priori restricted to prima ry motor and premotor areas in the frontal cortex, namely the SM1, the supp lementary motor area (SMA), the lateral premotor cortex (PMC), and the caud al anterior cingulate cortex (ACC) of either hemisphere. In addition to a r elative increase in normalized rCMRglc in the stimulated SM1(HAND), suprath reshold rTMS was associated with well-localized increases in normalized rCM Rglc in the caudal SMA and ACC on the medial wall of the frontal cortex and in the right precentral gyrus in the lateral PMC rostrally to the SM1. The se data demonstrate that a selective activation of the SM1(HAND) is paralle led by an activation of a distinct set of remote premotor areas, suggesting a functional interaction between the primary motor and premotor cortex in humans. Hum. Brain Mapping 12:157-167, 2001. (C) 2001 Wiley-Liss, Inc.