Interhemispheric sensorimotor integration; an upper limb phenomenon?

Publication date: 1 October 2016 Source:Neuroscience, Volume 333 Author(s): Kathy L. Ruddy, Ellen Jaspers, Martin Keller, Nicole Wenderoth Somatosensory information from the limbs reaches the contralateral Primary Sensory Cortex (S1) with a delay of 23ms for finger, and 40ms for leg (somatosensory N20/N40). Upon arrival of this input in the cortex, motor evoked potentials (MEPs) elicited by Transcranial Magnetic Stimulation (TMS) are momentarily inhibited. This phenomenon is called ‘short latency afferent inhibition (SAI)’ and can be used as a tool for investigating sensorimotor interactions in the brain. We used SAI to investigate the process of sensorimotor integration in the hemisphere ipsilateral to the stimulated limb. We hypothesized that ipsilateral SAI would occur with a delay following the onset of contralateral SAI, to allow for transcallosal conduction of the signal. We electrically stimulated the limb either contralateral or ipsilateral to the hemisphere receiving TMS, using a range of different interstimulus intervals (ISI). We tested the First Dorsal Interosseous (FDI) muscle in the hand, and Tibialis Anterior (TA) in the lower leg, in three separate experiments. Ipsilateral SAI was elicited in the upper limb (FDI) at all ISIs that were greater than N20+18ms (all p <.05) but never at any earlier timepoint. No ipsilateral SAI was detected in the lower limb (TA) at any of the tested ISIs. The delayed onset timing of ipsilateral SAI suggests ...
Source: Neuroscience - Category: Neuroscience Source Type: research