Neural basis of Transcranial Magnetic Stimulation at the single-cell Level

Abstract Transcranial Magnetic Stimulation (TMS) can non-invasively modulate neural activity in humans. Despite three decades of research, the spatial extent of the cortical area activated by TMS is still controversial. Moreover, how TMS interacts with task-related activity during motor behavior is unknown. We applied single-pulse TMS over the macaque parietal cortex while recording single-unit activity at various distances from the center of stimulation during grasping. The spatial extent of the TMS-induced activation was remarkably restricted, affecting single neurons in a volume of cortex measuring less than 2 mm. In task-related neurons, TMS evoked a transient excitation followed by reduced activity, which was paralleled by a significantly longer grasping time. Furthermore, TMS- induced activity and task-related activity did not summate in single neurons. These results furnish crucial experimental evidence for the neural basis of the TMS effect at the single-cell level and uncover, the neural underpinnings of behavioral effects of TMS.