Blood oxygenation changes resulting from suprathreshold transcranial magnetic stimulation

The hemodynamic response to low-intensity transcranial magnetic stimulation (TMS) has previously been demonstrated at motor cortex using near infrared spectroscopy (NIRS). To investigate the effect of TMS on oxy-hemoglobin (HbO) at prefrontal cortex, both subthreshold and suprathreshold TMS relative to resting motor threshold (rMT) were applied at typical intensities used in experimental settings. Although there was no significant change after 90% and 110% rMT TMS, there was a significant drop in HbO after 130% rMT TMS. This drop was maximal at approximately 8 seconds post-TMS. This study may have implications for determining appropriate TMS intensities when stimulating nonmotor areas.