Lasting cortical activation after repetitive TMS of the motor cortex

Abstract

Objective: Cerebral [¹⁸F]fluorodeoxy-d-glucose PET ([¹⁸F]FDG-PET) was used to visualize the lasting neuronal activation after repetitive transcranial magnetic stimulation (rTMS) over the left hand area of the primary motor cortex (M1_HAND).

Background: Applied over M1_HAND, rTMS has been shown to produce a modulation of corticomotor excitability beyond the time of stimulation itself.

Methods: Eight right-handed subjects underwent nonquantitative [¹⁸F]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, [¹⁸F]FDG was injected immediately after the administration of 1,800 magnetic pulses over the left M1_HAND. Relative differences in normalized 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 caused a lasting relative increase in normalized rCMRglc within the M1_HAND bilaterally and the SMA. The magnitude and the topographic pattern of persisting relative rCMRglc increases within these motor cortical areas demonstrated considerable interindividual variations.

Conclusions: Subthreshold 5-Hz repetitive transcranial magnetic stimulation (rTMS) over the hand area of the 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 [¹⁸F]FDG-PET can localize and quantify regional net changes in synaptic cortical activity after rTMS and thus might elucidate the mechanisms underlying rTMS-associated therapeutic effects.