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Updated: Jun 6, 2026
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Intracortical Inhibition Within the Primary Motor Cortex Can Be Modulated by Changing the Focus of Attention
Published on: September 11, 2017
Dissecting the mechanisms underlying short-interval intracortical inhibition using exercise
Steve Vucic1, Benjamin C Cheah, Matthew C Kiernan
1Department of Neurology, Sydney Medical School Westmead, University of Sydney, Sydney, NSW 2145, Australia.
Cerebral Cortex (New York, N.Y. : 1991)
|November 13, 2010
Summary
Fatiguing hand exercise reduces both early and late phases of short-interval intracortical inhibition (SICI). These findings suggest synaptic processes predominantly explain the distinct mechanisms of SICI phases.
Area of Science:
- Neuroscience
- Motor Control
- Human Physiology
Background:
- Two distinct phases of short-interval intracortical inhibition (SICI) have been identified at different interstimulus intervals (ISIs).
- The mechanisms of the early SICI phase (ISI 1 ms) are debated, while the later phase (ISI 3 ms) is known to be synaptically mediated.
- Fatiguing exercise is known to reduce SICI, impacting cortical excitability.
Purpose of the Study:
- To investigate the effects of fatiguing hand exercise on the two distinct phases of SICI.
- To elucidate the underlying neural mechanisms of the different SICI phases by examining their response to exercise-induced fatigue.
Main Methods:
- Threshold tracking transcranial magnetic stimulation (TMS) was employed to assess SICI in 22 healthy subjects.
- SICI was measured at baseline, during, and at various recovery intervals following fatiguing hand exercise (120s voluntary contraction periods).
- Responses were recorded over the abductor pollicis brevis muscle.
Main Results:
- Fatiguing exercise significantly reduced both SICI phases: the early phase (ISI 1 ms) from 9.5% to 2.5% and the later phase (ISI 3 ms) from 16.8% to 11.6%.
- The time course of SICI reduction differed between the two phases, indicating distinct recovery patterns.
- Both phases showed significant reductions (P < 0.05).
Conclusions:
- Synaptic processes appear to be the primary mechanism underlying both the early and later phases of SICI.
- The differential time course of reduction suggests distinct, though potentially overlapping, neural pathways contribute to each SICI phase.
- These findings advance our understanding of cortical inhibition mechanisms and their modulation by exercise.
