28. Visuomotor functional connectivity: A TMS study

Abstract

The interaction between visual inputs and motor system is of crucial importance in movement control. We studied the functional connectivity between visual and motor cortex by means of transcranial magnetic stimulation. Sixteen volunteers (21–51 yrs) participated in this study. We measured resting motor threshold (RMT) of the hand motor area and phosphene threshold (PT). A conditioning stimulus (CS) delivered over visual cortex at different intensities (80 and 90% PT) was followed at random interstimulus intervals (ISIs) (12, 15, 18, 21, 24, 27, 30, 35 and 40 ms) by a test stimulus (TS) over left motor cortex to evoke a motor evoked potential (MEP) of ∼1 mV from right FDI. The conditioned-MEP was expressed as a percentage of the unconditioned-MEP amplitude. One-way ANOVAs analyzed the effects of the CS with “ISIs” as main factor. ANOVA showed a main effect of ISI when the CS intensity was 80% PT ( F (9, 90) = 3.410, p = 0.001) and 90% PT ( F (9, 99) = 3.081, p = 0.003). Post hoc analysis confirmed that the size of the conditioned-MEP was significantly reduced at 18, 21, 24, 40 ms ( p < 0.05) with 80% PT, and significantly reduced at 18, 21, 27, 30, 35, 40 ms ( p < 0.02) with 90% PT. In subjects at rest, conditioning stimuli over the visual cortex produce inhibitory changes on corticospinal excitability with a time course between 18 and 40 ms.