30 Hz theta-burst stimulation over primary somatosensory cortex modulates corticospinal output to the hand.
BACKGROUND
The primary somatosensory cortex (SI) is important for hand function and has direct connectivity with the primary motor cortex (M1). Much of our present knowledge of this connectivity and its relevance to hand function is based on animal research. In humans, less is known about the neural mechanisms by which SI influences motor circuitry that outputs to the muscles controlling the hand.


OBJECTIVE
The present study investigated the influence of SI on corticospinal excitability, and inhibitory and excitatory intracortical neural circuitry within M1 before and after continuous theta-burst stimulation (cTBS). Motor-evoked potentials (MEPs), short-latency intracortical inhibition (SICI) and intracortical facilitation (ICF) were recorded from the first dorsal interosseous (RFDI) muscle of the right hand following 30 Hz cTBS over left-hemisphere SI and M1 delivered in separate sessions.


RESULTS
cTBS over SI facilitated MEPs and did not alter ICF or SICI. cTBS delivered over M1 suppressed MEPs and ICF and did not alter SICI.


CONCLUSIONS
These findings indicate that SI influences corticospinal output to the hand, possibly via corticocortical projections, and may be one mechanism by which somatosensory information influences hand control.
Department of Kinesiology, McMaster University, 1280 Main Street West, Hamilton, ON L8S 4L8, Canada.
Mark F
MF
Jacobs
Department of Kinesiology, McMaster University, 1280 Main Street West, Hamilton, ON L8S 4L8, Canada.
Philemon
P
Tsang
Department of Kinesiology, McMaster University, 1280 Main Street West, Hamilton, ON L8S 4L8, Canada.
Kevin G H
KG
Lee
Department of Kinesiology, McMaster University, 1280 Main Street West, Hamilton, ON L8S 4L8, Canada.
Michael J
MJ
Asmussen
Department of Kinesiology, McMaster University, 1280 Main Street West, Hamilton, ON L8S 4L8, Canada.
Christopher M
CM
Zapallow
Department of Kinesiology, McMaster University, 1280 Main Street West, Hamilton, ON L8S 4L8, Canada. Electronic address: nelsonaj@mcmaster.ca.
Aimee J
AJ
Nelson
D000293:Adolescent; D019054:Evoked Potentials, Motor / Q000502:physiology; D005260:Female; D006225:Hand / Q000502:physiology*; D006801:Humans; D008297:Male; D009044:Motor Cortex / Q000502:physiology*; D011712:Pyramidal Tracts / Q000502:physiology*; D013003:Somatosensory Cortex / Q000502:physiology*; D050781:Transcranial Magnetic Stimulation / Q000379:methods*; D055815:Young Adult
Continuous theta-burst stimulation; Hand motor control; Primary somatosensory cortex; TMS