Interactions between two different inhibitory systems in the human motor cortex
Article first published online: 5 AUG 2004
The Journal of Physiology
Volume 530, Issue 2, pages 307–317, January 2001
How to Cite
Sanger, T. D., Garg, R. R. and Chen, R. (2001), Interactions between two different inhibitory systems in the human motor cortex. The Journal of Physiology, 530: 307–317. doi: 10.1111/j.1469-7793.2001.0307l.x
- Issue published online: 5 AUG 2004
- Article first published online: 5 AUG 2004
- (Received 26 May 2000; accepted after revision 13 October 2000)
- 1Intracortical inhibition in the human motor cortex has been previously demonstrated using paired-pulse transcranial magnetic stimulation (TMS) protocols at short intervals (1-6 ms; short interval intracortical inhibition, SICI) with a subthreshold conditioning pulse preceding a suprathreshold test pulse, and at long intervals (50-200 ms; long interval intracortical inhibition, LICI) with suprathreshold conditioning and test pulses.
- 2We investigated whether different circuits mediate these inhibitory phenomena and how they interact. In nine healthy volunteers, we applied TMS to the motor cortex and recorded motor evoked potentials from the first dorsal interosseous muscle.
- 3With increasing test pulse strength, LICI decreases but SICI tends to increase. There was no correlation between the degree of SICI and LICI.
- 4We tested the interactions between SICI and LICI. SICI was reduced or eliminated in the presence of LICI. Loss of SICI was seen even with a conditioning stimulus too weak to induce significant LICI.
- 5Our findings demonstrate that different cell populations mediate SICI and LICI. The results are consistent with the hypothesis that LICI inhibits SICI through presynaptic GABAB receptors. Testing of SICI in the presence of LICI may be a non-invasive way of evaluating inhibitory interactions in the human motor cortex.