Somatosensory-motor cortex interactions measured using dual-site transcranial magnetic stimulation.
BACKGROUND
Dual-site transcranial magnetic stimulation (ds-TMS) is a neurophysiological technique to measure functional connectivity between cortical areas.


OBJECTIVE/HYPOTHESIS
To date, no study has used ds-TMS to investigate short intra-hemispheric interactions between the somatosensory areas and primary motor cortex (M1).


METHODS
We examined somatosensory-M1 interactions in the left hemisphere in six experiments using ds-TMS. In Experiment 1 (n = 16), the effects of different conditioning stimulus (CS) intensities on somatosensory-M1 interactions were measured with 1 and 2.5 ms inter-stimulus intervals (ISIs). In Experiment 2 (n = 16), the time-course of somatosensoy-M1 interactions was studied using supra-threshold CS intensity at 6 different ISIs. In Experiment 3 (n = 16), the time-course of short-interval cortical inhibition (SICI) and effects of different CS intensities on SICI were measured similar to Experiments 1 and 2. Experiment 4 (n = 13) examined the effects of active contraction on SICI and somatosensory-M1 inhibition. Experiments 5 and 6 (n = 10) examined the interactions between SAI with either 1 ms SICI or somatosensory-M1 inhibition.


RESULTS
Experiments 1 and 2 revealed reduced MEP amplitudes when applying somatosensory CS 1 ms prior to M1 TS with 140 and 160% CS intensities. Experiment 3 demonstrated that SICI at 1 and 2.5 ms did not correlate with somatosensory-M1 inhibition. Experiment 4 found that SICI but not somatosensory-M1 inhibition was abolished with active contraction. The results of Experiments 5-6 showed SAI was disinhibited in presence of somatosensory-M1 while SAI was increased in presence of SICI.


CONCLUSION
Collectively, the results support the notion that the somatosensory areas inhibit the ipsilateral M1 at very short latencies.
['Brown|Matt J N|MJN|', 'Weissbach|Anne|A|', 'Pauly|Martje G|MG|', 'Vesia|Michael|M|', 'Gunraj|Carolyn|C|', 'Baarbé|Julianne|J|', 'Münchau|Alexander|A|', 'Bäumer|Tobias|T|', 'Chen|Robert|R|']
D000328:Adult D004576:Electromyography D019054:Evoked Potentials, Motor D005260:Female D007839:Functional Laterality D006801:Humans D008297:Male D009044:Motor Cortex D009433:Neural Inhibition D013003:Somatosensory Cortex D050781:Transcranial Magnetic Stimulation D055815:Young Adult
Somatosensory Motor Dual-site TMS Paired-pulse TMS Sensorimotor control TMS