Excitation threshold of the motor cortex estimated with transcranial magnetic stimulation electroencephalography

Abstract

The excitation threshold of the human motor cortex was estimated on the basis of electroencephalographic responses evoked by transcranial magnetic stimulation. The hand area of the primary motor cortex was stimulated at 10 intensities, for seven healthy individuals. The four dominant peaks of the overall brain response could be reliably determined when stimulation was intense enough to induce a cortical electric field of approximately 33-44 mV/mm. This may be estimated as the threshold for evoking measurable brain activity by motor-cortex transcranial magnetic stimulation. The remarkably low threshold reflects the excellent sensitivity of the combination of transcranial magnetic stimulation and electroencephalography for the study of neuronal function of the cortex.

The Cerebellum in Emotion Regulation: A Repetitive Transcranial Magnetic Stimulation Study

“…Even though recent findings show that physiological responses can be obtained at stimulation intensities well below the motor threshold [17,49], higher intensities than the currently applied stimulation of 45% machine output which corresponds to~80% MT in the present sample, may have had more pronounced effects on mood and EEG ratios. However, findings from a recent study show that intensities as low as 60% MT are sufficient enough to evoke EEG responses in superficial nerve tissue of the primary motor cortex, suggesting that intensities well below the neural excitation threshold can have significant physiological effects [49].…”

“…However, findings from a recent study show that intensities as low as 60% MT are sufficient enough to evoke EEG responses in superficial nerve tissue of the primary motor cortex, suggesting that intensities well below the neural excitation threshold can have significant physiological effects [49].…”

Shared reduction of oscillatory natural frequencies in bipolar disorder, major depressive disorder and schizophrenia

“…) TMS was delivered on the convexity of the middle caudal portion of the superior frontal gyrus close to the midline (Broadmann's areas 6), with the current perpendicular to its main axis. To ensure significant EEG responses (Casali et al, 2010;Komssi et al, 2007;Rosanova et al, 2009) intensity of TMS induced electric field was always 490 V/m as estimated by the NBS system, for each study participant. We delivered about 200-300 stimuli for each session at a frequency randomly jittered between 1.5 and 1.8 s (equivalent to about 0.5-0.6 Hz).…”

Effects of alcohol on TMS-evoked N100 responses

“…The largest EEG activity after TMS pulse occurs at about 100 ms (Bender et al, 2005;Bonato et al, 2006;Komssi et al, 2004Komssi et al, , 2007Paus et al, 2001). Several time-locked EEG responses have been found in association with single-pulse TMS of M1, viz., N15 (vertex-negative EEG deflection approximately 15 ms poststimulus), P30, N45, P55, N100, P180, and N280 (Bender et al, 2005;Komssi and Kähkönen, 2006;Komssi et al, 2002;Paus et al, 2001).…”

“…The origin of the TMS-evoked EEG deflections is unknown, except for the N45 response, which has been localized into the ipsilateral central sulcus (Paus et al, 2001). When motor cortex was stimulated by different stimulus intensities (20-120% of MT), the slopes of intensity-dependency varied depending on time after stimulation indicating that different neural processes are involved (Komssi et al, 2004(Komssi et al, , 2007. The negative peak about 100 ms after singlepulse TMS is one of the most prominent components in the EEG being visible even in single trials (Nikouline et al, 1999;Paus et al, 2001;Tiitinen et al, 1999).…”