Effects of repetitive cortical stimulation on the silent period evoked by magnetic stimulation

Abstract

The effects of repetitive transcranial stimulation (rTMS) on brain activity remain unknown. In healthy subjects, we studied the effects of rTMS on the duration of the cortical silent period (SP). Repetitive stimuli were delivered with a Cadwell High Speed Magnetic Stimulator and a figure-of-eight coil placed over the hand motor area. rTMS was delivered in trains of 11 or 20 stimuli at frequencies of 3 and 5 Hz and at stimulation intensities of 110 and 120% of motor threshold. The SP was recorded from the forearm muscles during a voluntary contraction (20% of maximum effort). rTMS delivered at a frequency of 3 and 5 Hz and intensities of 110 and 120% motor threshold prolonged the duration of the SP, without modifying either the size or the latency of the muscle-evoked potentials (MEP). A conditioning train of 11 stimuli at 3 Hz had no effect on the duration of the SP evoked by a single magnetic shock delivered 600 ms after the train. These findings show that rTMS increases the duration of the cortical SP, but does so only during the train of stimuli. rTMS probably changes the duration of the SP by facilitating cortical inhibitory interneurons.

Repetitive magnetic stimulation of cortical motor areas in Parkinson's disease: Implications for the pathophysiology of cortical function

“…In an earlier study, we observed that in normal subjects rTMS delivered at frequencies of 3 and 5 Hz prolongs the duration of the SP and probably does so by altering the activity of the cortical inhibitory interneurons. 10,11 Here we now show that rTMS prolongs the cortical SP to a similar extent, also in patients with PD. The normal pattern of cortical SPs during rTMS in PD suggests that the cortical inhibitory interneurons mediating the SP as tested by rTMS function normally.…”

“…9 Besides altering the MEPs, trains of rTMS prolong the duration of the cortical SP evoked by magnetic stimuli. 10,11 Repetitive stimu-lation of the motor cortex therefore influences the activity of excitatory as well as inhibitory neural elements of cortical motor areas. We investigated the effects of rTMS on MEPs and cortical SPs in patients with PD.…”

Informing Dose-Finding Studies of Repetitive Transcranial Magnetic Stimulation to Enhance Motor Function: A Qualitative Systematic Review

“…The primary purposes of included studies with healthy adult participants were to investigate the mechanisms underlying the effect of rTMS stimuli on transmission in corticospinal pathways 27,28,41,46 ; the effects of a specific dose of rTMS on transmission in corticospinal pathways 15,16,[32][33][34]36,42,45,47 ; the effects of different doses of rTMS on transmission in corticospinal pathways 21,30,38,39,40,43,44,50 ; the effects of 2 waveforms of rTMS 22,26,51 ; whether rTMSinduced changes in transmission in corticospinal pathways last beyond application of stimuli 31 ; the effects on movement control of using rTMS 35,42,48,52,53 ; the differences in response to rTMS between healthy adults and people with actual or potential movement disorder. [17][18][19][20] The primary purpose of the included study with participants after stroke was to investigate the effects of rTMS on recovery of movement after stroke.…”

Repetitive transcranial magnetic stimulation to improve mood and motor function in Parkinson's disease

“…In contrast to single-pulse or paired-pulse TMS, rTMS involves the application of trains of pulses at a constant rate to a cortical target. Depending on the stimulation protocol, rTMS can change regional excitability and neuronal activity from minutes to hours beyond the time of stimulation [4,10,11]. Because of a transsynaptic spread of excitation through cortico -cortical or cortico -subcortical connections, rTMS can produce conditioning effects in distant cortical [11,12] or subcortical areas such as the basal ganglia [13 -15].…”