title: Interaction between visual and motor cortex: a transcranial magnetic stimulation study.
abstract: The major link between the visual and motor systems is via the dorsal stream pathways from visual to parietal and frontal areas of the cortex. Although the pathway appears to be indirect, there is evidence that visual input can reach the motor cortex at relatively short latency. To shed some light on its neural basis, we studied the visuomotor interaction using paired transcranial magnetic stimulation (TMS). Motor-evoked potentials (MEPs) were recorded from the right first dorsal interosseous in sixteen healthy volunteers. A conditioning stimulus (CS) was applied over the phosphene hotspot of the visual cortex, followed by a test stimulus over the left primary motor cortex (M1) with a random interstimulus interval (ISI) in range 12-40 ms. The effects of paired stimulation were retested 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 with an ISI in the range 18-40 ms. In the visual RT, inhibition with an ISI of 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 of 40 ms (P < 0.01). We conclude that it is possible to study separate functional connections from visual to motor cortices using paired-TMS with an ISI in the range 18-40 ms. The connections are inhibitory at rest and possibly mediated by inhibitory interneurones in the motor cortex. The effect with an ISI of 40 ms reverses into facilitation during a visuomotor RT but not an audiomotor RT. This suggests that it plays a role in visuomotor integration.
authors.affiliation: Sobell Department of Motor Neuroscience and Movement Disorders, University College London Institute of Neurology, London, UK.|Department of Translational Medicine, Section of Neurology, University of Piemonte Orientale 'A. Avogadro', Novara, Italy.
authors.forename: Gionata
authors.initials: G
authors.lastname: Strigaro
authors.affiliation: Sobell Department of Motor Neuroscience and Movement Disorders, University College London Institute of Neurology, London, UK.
authors.forename: Diane
authors.initials: D
authors.lastname: Ruge
authors.affiliation: Sobell Department of Motor Neuroscience and Movement Disorders, University College London Institute of Neurology, London, UK.|Neuroscience Laboratory, Department of Neurology, China Medical University Hospital, Taichung, Taiwan.|School of Medicine, China Medical University, Taichung, Taiwan.
authors.forename: Jui-Cheng
authors.initials: JC
authors.lastname: Chen
authors.affiliation: Sobell Department of Motor Neuroscience and Movement Disorders, University College London Institute of Neurology, London, UK.
authors.forename: Louise
authors.initials: L
authors.lastname: Marshall
authors.affiliation: Sobell Department of Motor Neuroscience and Movement Disorders, University College London Institute of Neurology, London, UK.
authors.forename: Mahalekshmi
authors.initials: M
authors.lastname: Desikan
authors.affiliation: Department of Translational Medicine, Section of Neurology, University of Piemonte Orientale 'A. Avogadro', Novara, Italy.
authors.forename: Roberto
authors.initials: R
authors.lastname: Cantello
authors.affiliation: Sobell Department of Motor Neuroscience and Movement Disorders, University College London Institute of Neurology, London, UK.
authors.forename: John C
authors.initials: JC
authors.lastname: Rothwell
mesh_terms: D000328:Adult; D004569:Electroencephalography; D005072:Evoked Potentials, Auditory / Q000502:physiology; D019054:Evoked Potentials, Motor / Q000502:physiology; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009044:Motor Cortex / Q000502:physiology*; D011930:Reaction Time / Q000502:physiology; D050781:Transcranial Magnetic Stimulation; D014793:Visual Cortex / Q000502:physiology*