Fig. 3. Multiple sites of peripheral co-stimulation. The figure summarizes peripheral sensory receptors and axons that can be excited by transcranial magnetic stimulation (TMS).

Blue box. Auditory stimulation by the loud, high frequency click sound produced in the coil and cable during discharge, causing auditory evoked potentials (AEP) in the EEG. Yellow box. Somatosensory stimulation of peripheral sensory and motor axons (i.e., peripheral branches of the facial, trigeminal or occipital nerve) give rise to cortical somatosensory potentials (SEPs). Excitation of peripheral motor nerves lead to sensory input caused by the evoked muscle twitches. Twitch-induced sensory input also occurs, when TMS of motor cortex produces motor evoked potentials (MEP). In addition, the proximal segments of the facial and trigeminal nerves can be effectively excited by TMS at many scalp sites, even within the commonly used range of stimulus intensities. Green box. Somatosensory stimulation may arise from magneto-electric stimulation of afferent myelinated nerve fibers or mechanical stimulation of unencapsulated Ruffini-like receptors in the dura mater. Red box. The skin contains various receptors responding to coil-induced tonic pressure or TMS-induced coil vibration (Meissner’s corpuscles, Merkel’s disks and Pacinian corpuscles) and stretch due to coil movement (Ruffini corpuscles).