Citation

Strigaro G, Ruge D, Chen JC, Marshall L, Desikan M, Cantello R, Rothwell JC. J. Physiol. 2015; 593(10): 2365-2377.

Affiliation

Sobell Department of Motor Neuroscience and Movement Disorders, University College London Institute of Neurology, London, United Kingdom; Department of Translational Medicine, Section of Neurology, University of Piemonte Orientale ''A. Avogadro'', Novara, Italy.

Copyright

(Copyright © 2015, The Physiological Society, Publisher John Wiley and Sons)

DOI

10.1113/JP270135

PMID

25762215

Abstract

The major link between the visual and motor systems is via the dorsal stream pathways from visual to parietal and frontal areas of cortex. Although the pathway appears indirect, there is evidence that visual input can reach the motor cortex at relatively short latency. To shed some light on its neural bases, we studied the visuo-motor interaction using paired transcranial magnetic stimulation (paired-TMS). Motor evoked potentials (MEPs) were recorded from the right FDI in sixteen healthy volunteers. A conditioning stimulus (CS) was applied over the phosphene hotspot of visual cortex, followed by a test stimulus (TS) over left M1 at random interstimulus intervals (ISIs, 12-40 ms). The effects of paired stimulation were re-tested during visual and auditory reaction-time tasks (RT). Finally, we measured the effects of a CS on short-interval intracortical inhibition (SICI). At rest, a CS over the occiput significantly (p<0.001) suppressed test MEPs at ISIs 18-40 ms. In the visual RT, inhibition at ISI = 40 ms (but not 18 ms) was replaced by a time-specific facilitation (p<0.001) whereas in the auditory RT the CS no longer had any effect on MEPs. Finally, an occipital CS facilitated SICI with an ISI = 40 ms (p<0.01). We conclude that it is possible to study separate functional connections from visual to motor cortices using paired-TMS at ISI = 18-40 ms. The connections are inhibitory at rest and possibly mediated by inhibitory interneurones in motor cortex. The effect at ISI = 40 ms reverses into facilitation during a visuomotor, but not audiomotor RT. This suggests that it plays a role in visuomotor integration. This article is protected by copyright. All rights reserved.

Language: en