title: Exploring the specific time course of interhemispheric inhibition between the human primary sensory cortices.
abstract: The neurophysiological mechanism of interhemispheric inhibition (IHI) between the human primary sensory cortices (S1s) is poorly understood. Here we used a paired median nerve somatosensory evoked potential protocol to observe S1-S1 IHI from the dominant to the nondominant hemisphere with electroencephalography. In 10 healthy, right-handed individuals, we compared mean peak-to-peak amplitudes of five somatosensory evoked potential components (P14/N20, N20/P25, P25/N30, N30/P40, and P40/N60) recorded over the right S1 after synchronous versus asynchronous stimulation of the right and left median nerves. Asynchronous conditioning + test stimuli (CS+TS) were delivered at interstimulus intervals of 15, 20, 25, 30, and 35 ms. We found that, in relation to synchronous stimulation, when a CS to the left S1 preceded a TS to the right S1 at the short intervals (15 and 20 ms) the amplitude of the cortical N20/P25 complex was significantly depressed, whereas at the longer intervals (25, 30, and 35 ms) significant inhibition was observed for the thalamocortical P14/N20 as well as the cortical N20/P25 components. We conclude that the magnitude of S1 IHI appears to depend on the temporal asynchrony of bilateral inputs and the specific timing is likely reflective of a direct transcallosal mechanism. Employing a method that enables direct S1 IHI to be reliably quantified may provide a novel tool to assess potential IHI imbalances in individuals with neurological damage, such as stroke.
authors.affiliation: Department of Physical Therapy, Faculty of Medicine, University of British Columbia, Vancouver, British Columbia, Canada; and.
authors.forename: Sonia M
authors.initials: SM
authors.lastname: Brodie
authors.affiliation: Department of Physical Therapy, Faculty of Medicine, University of British Columbia, Vancouver, British Columbia, Canada; and.
authors.forename: Anica
authors.initials: A
authors.lastname: Villamayor
authors.affiliation: Department of Physical Therapy, Faculty of Medicine, University of British Columbia, Vancouver, British Columbia, Canada; and.
authors.forename: Michael R
authors.initials: MR
authors.lastname: Borich
authors.affiliation: Department of Physical Therapy, Faculty of Medicine, University of British Columbia, Vancouver, British Columbia, Canada; and Centre for Brain Health, University of British Columbia, Vancouver, British Columbia, Canada lara.boyd@ubc.ca.
authors.forename: Lara A
authors.initials: LA
authors.lastname: Boyd
mesh_terms: D000328:Adult; D005073:Evoked Potentials, Somatosensory; D005260:Female; D007839:Functional Laterality; D006801:Humans; D008297:Male; D008475:Median Nerve / Q000502:physiology; D009433:Neural Inhibition; D011930:Reaction Time; D013003:Somatosensory Cortex / Q000502:physiology*
keywords: electroencephalography; interhemispheric inhibition; primary sensory cortex; sensory evoked potentials; transcallosal inhibition