Changing cortical excitability with low-frequency magnetic stimulation

Transcranial magnetic stimulation (TMS) is now the preferred method for noninvasive brain stimulation in human subjects. Single and paired-pulse TMS can test different excitatory and inhibitory cortical circuits and have been used to study the pathophysiology of many neurologic and psychiatric disorders.1 A different way of applying TMS is repetitive TMS (rTMS), which refers to regularly repeated stimuli to a single scalp site. rTMS can modulate cortical excitability, and the effect depends on the frequency of stimulation. High-frequency (>5 Hz) stimulation increases cortical excitability and is a promising treatment for depression. Recently, Boroojerdi et al.2 showed that high-frequency rTMS of the dorsolateral prefrontal cortex can improve cognitive processing in normal subjects. This raises the possibility of using such intervention in the rehabilitation of brain injuries.3 In contrast, low-frequency rTMS at a stimulation rate of approximately one per second decreases cortical excitability beyond the period of stimulation.4 Although this effect was initially observed in the …