Impact of repetitive transcranial magnetic stimulation of the parietal cortex on metabolic brain activity: a 14C-2DG tracing study in the cat.

Transcranial magnetic stimulation (TMS) is increasingly utilized in clinical neurology and neuroscience. However, detailed knowledge of the impact and specificity of the effects of TMS on brain activity remains unresolved. We have used 14C-labeled deoxyglucose (14C-2DG) mapping during repetitive TMS (rTMS) of the posterior and inferior parietal cortex in anesthetized cats to study, with exquisite spatial resolution, the local and distant effects of rTMS on brain activity. High-frequency rTMS decreases metabolic activity at the primary site of stimulation with respect to homologue areas in the unstimulated hemisphere. In addition, rTMS induces specific distant effects on cortical and subcortical regions known to receive substantial efferent projections from the stimulated cortex. The magnitude of this distal impact is correlated with the strength of the anatomical projections. Thus, in the anesthetized animal, the impact of rTMS is upon a distributed network of structures connected to the primary site of application.