Multimodal integration and modulation of visual and somatosensory inputs on the corticospinal excitability

Objective

Corticospinal excitability may be affected by various sensory inputs under physiological conditions. In this study, we aimed to investigate the corticospinal excitability by using multimodal conditioning paradigms of combined somatosensory electrical and visual stimulation to understand the sensory-motor integration.

Methods

We examined motor evoked potentials (MEP) obtained by using transcranial magnetic stimulation (TMS) that were conditioned by using a single goggle–light-emitting diode (LED) stimulation, peripheral nerve electrical stimulation (short latency afferent inhibition protocol), or a combination of both (goggle-LED+electrical stimulation) at different interstimulus intervals (ISIs) in 14 healthy volunteers.

Results

We found MEP inhibition at ISIs of 50–60 ms using the conditioned goggle-LED stimulation. The combined goggle-LED stimulation at a 60 ms ISI resulted in an additional inhibition to the electrical stimulation.

Conclusions

Visual inputs cause significant modulatory effects on the corticospinal excitability. Combined visual and somatosensory stimuli integrate probably via different neural circuits and/or interneuron populations. To our knowledge, multimodal integration of visual and somatosensory inputs by using TMS-short latency inhibition protocol have been evaluated via electrophysiological methods for the first time in this study.