Lasting cortical activation after repetitive TMS of the motor cortex - A glucose metabolic study

Objective: Cerebral [F-18]fluorodeoxy-D-glucose PET ([F-18]FDG-PET) was use d to visualize the lasting neuronal activation after repetitive transcrania l magnetic stimulation (rTMS) over the left hand area of the primary motor cortex (M1(HAND)). Background: Applied over M1(HAND), rTMS has been shown t o produce a modulation of corticomotor excitability beyond the time of stim ulation itself. Methods: Eight right-handed subjects underwent nonquantitat ive [F-18]FDG-PET measurements during two experimental conditions: at rest and after focal subthreshold 5-Hz rTMS over the left M1(HAND). In the post- rTMS condition, [F-18]FDG was injected immediately after the administration of 1,800 magnetic pulses over the left M1(HAND). Relative differences in n ormalized regional cerebral metabolic rate of glucose (normalized rCMRglc) between conditions were determined using a voxel-by-voxel Student's t-test and volume-of-interest (VOI) analysis. Analysis was a priori restricted to the M1(HAND), the supplementary motor area (SMA), and the primary auditory cortex of both hemispheres. Results: A 5-Hz rTMS of the left M1(HAND), caus ed a lasting relative increase in normalized rCMRglc within the M1(HAND) bi laterally and the SMA. The magnitude and the topographic pattern of persist ing relative rCMRglc increases within these motor cortical areas demonstrat ed considerable interindividual variations. Conclusions: Subthreshold 5-Hz repetitive transcranial magnetic stimulation (rTMS) over the hand area of t he primary motor cortex is associated with a persisting neuronal activation in a distinct set of motor cortical areas beyond the time of stimulation. The current findings demonstrate that [F-18]FDG-PET can localize and quanti fy regional net changes in synaptic cortical activity after rTMS and thus m ight elucidate the mechanisms underlying rTMS-associated therapeutic effect s.