Short-latency afferent inhibition and modulation of contralateral and ipsilateral motor output: A neurophysiological study

Objective: Sensorimotor integration involves processing sensory input to modulate motor output through cortical-subcortical interactions. Short-latency afferent inhibition (SAI), a transcranial magnetic stimulation (TMS) protocol, is widely used to investigate this phenomenon. In this study, we investigated sensorimotor integration by assessing SAI using both contralateral (conventional protocol) and ipsilateral (experimental protocol) peripheral electrical stimulation, including interstimulus intervals (ISIs) preceding the cortical response of somatosensory evoked potentials (N20). Methods: Twenty-four healthy participants underwent TMS over the primary motor cortex (M1), paired with either ipsilateral or contralateral median nerve stimulation at various ISIs relative to individual N20 latencies (-2 ms, -1 ms, +2 ms, +3 ms, +4 ms). Both hemispheres and stimulation conditions (ipsilateral, contralateral) were tested. Results: Significant MEP amplitude reduction occurred with contralateral stimulation at ISIs preceding (only dominant hemisphere) and following the N20 response (both hemispheres). Ipsilateral stimulation did not modulate motor output at any ISI. Conclusion: Our results confirm that SAI is a strictly lateralized phenomenon, occurring exclusively with contralateral peripheral stimulation and elicitable at intervals preceding the N20 response, but limited to the dominant hemisphere. Significance: These findings emphasize the pivotal role of contralateral thalamo-cortical circuits in sensorimotor integration and provide deeper insights into the mechanisms underlying the short-latency afferent inhibition (SAI) phenomenon.