Subthreshold transcranial magnetic stimulation (TMS) over the motor cortex can shorten the simple reaction time in contralateral arm muscles if the cortical shock is given at about the same time as the reaction stimulus. The present experiments were designed to investigate whether this phenomenon is due to a specific facilitatory effect on cortical circuitry. The simple visual reaction time was shortened by 20-50 ms when subthreshold TMS was given over the contralateral motor cortex. Reaction time was reduced to the same level whether the magnetic stimulus was given over the bilateral motor cortices or over other points on the scalp (Cz, Pz). Indeed, similar effects could be seen with conventional electrical stimulation over the neck, or even when the coil was discharged (giving a click sound) near the head. We conclude that much of the effect of TMS on simple reaction time is due to intersensory facilitation, although part of it may be ascribed to a specific effect on the excitability of motor cortex.
The central motor pathways were studied with the technique of percutaneous electrical stimulation of the central nervous system in 40 normal volunteers. There were no significant differences between the right and left sides, or between males and females. A linear correlation between the cortical latency (Lcor) or the spinal latency (Lsp) and body height was observed, however, there was no correlation between the central conduction time (CCT) (Lcor-Lsp) and body height. Consequently, the CCT appears to provide a reliable estimate of the function of central motor pathways. We have established normal values for eight muscles at rest that would be required for localizing a very small intraspinal lesion.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.