The effects of subthreshold 1 Hz repetitive TMS on cortico-cortical and interhemispheric coherence.
OBJECTIVE
Repetitive transcranial magnetic stimulation (rTMS) shows promise as a treatment for various movement and psychiatric disorders. Just how rTMS may have persistent effects on cortical function remains unclear. We hypothesised that it may act by modulating cortico-cortical and interhemispheric connectivity. To this end we assessed cortico-cortical and interhemispheric coherence before and after low frequency, subthreshold rTMS of the left motor cortex.


METHODS
Fifteen healthy subjects received one train (1Hz, 90% of active motor threshold, 1500 stimuli) of rTMS to the left motor hand area. Spectral power and coherence estimates were calculated between different electroencephalogram (EEG) signals at rest and while muscles of the distal upper limb were tonically contracted.


RESULTS
rTMS over the left motor hand area caused a significant increase in ipsilateral EEG-EEG coherence and in the interhemispheric coherence between motor areas in the alpha band. The effects of rTMS lasted up to 25 min post-stimulation. There was no significant change in EEG-EEG coherence over the hemisphere contralateral to stimulation.


CONCLUSIONS
Low frequency, subthreshold rTMS of the motor cortex increases ipsilateral cortico-cortical and interhemispheric coherence in the alpha band. This may, in part, mediate the inhibitory effects of low frequency rTMS.
Strens
Lucy H A
LH
Sobell Department of Neurophysiology, Institute of Neurology, Queen Square, London, UK.
Oliviero
Antonio
A
Bloem
Bastiaan R
BR
Gerschlager
Willibald
W
Rothwell
John C
JC
Brown
Peter
P
D000328:Adult; D001921:Brain / Q000502:physiology*; D004558:Electric Stimulation; D004569:Electroencephalography; D004574:Electromagnetic Fields; D004576:Electromyography; D005260:Female; D007839:Functional Laterality; D006225:Hand; D006801:Humans; D008280:Magnetics; D008297:Male; D008875:Middle Aged; D009044:Motor Cortex / Q000502:physiology*