Suppression of somatosensory stimuli during motor planning may explain levels of balance and mobility after stroke
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The ability to actively suppress, or gate, irrelevant sensory information is required for safe and efficient walking in sensory-rich environments. Both motor attention and motor planning alter somatosensory evoked potentials (SEPs) in healthy adults. This study's aim was to examine the effect of motor attention on processing of irrelevant somatosensory information during plantar flexion motor planning after stroke. Thirteen healthy older adults and 11 individuals with stroke participated. Irrelevant tibial nerve stimulation was delivered while SEPs were recorded over Cz, overlaying the leg portion of the sensorimotor cortex at the vertex of the head. Three conditions were tested in both legs: (1) Rest, (2) Attend To, and (3) Attend Away from the stimulated limb. In conditions 2 and 3, relevant vibration cued voluntary plantar flexion movements of the stimulated (Attend To) or non-stimulated (Attend Away) leg. SEP amplitudes were averaged during motor planning per condition. Individuals with stroke did not show attention-mediated gating of the N40 component associated with irrelevant somatosensory information during motor planning. It may be that dysfunction in pathways connecting to area 3b explains the lack of attention-mediated gating of the N40. Also, attention-mediated gating during motor planning explained significant and unique variance in a measure of community balance and mobility combined with response time. Thus, the ability to gate irrelevant somatosensory information appears important for stepping in both older adults and after stroke. Our data suggest that therapies that direct motor attention could positively impact walking after stroke.
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