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dc.contributor.authorErmer, Elsa
dc.contributor.authorHarcum, Stacey
dc.contributor.authorLush, Jaime
dc.contributor.authorMagder, Laurence S.
dc.contributor.authorWhitall, Jill
dc.contributor.authorWittenberg, George F.
dc.contributor.authorDimyan, Michael A.
dc.date.accessioned2020-10-29T17:37:11Z
dc.date.available2020-10-29T17:37:11Z
dc.date.issued2020-10-06
dc.identifier.urihttp://hdl.handle.net/10713/13968
dc.description.abstractInterhemispheric interactions are important for arm coordination and hemispheric specialization. Unilateral voluntary static contraction is known to increase bilateral corticospinal motor evoked potential (MEP) amplitude. It is unknown how increasing and decreasing contraction affect the opposite limb. Since dynamic muscle contraction is more ecologically relevant to daily activities, we studied MEP recruitment using a novel method and short interval interhemispheric inhibition (IHI) from active to resting hemisphere at 4 phases of contralateral ECR contraction: Rest, Ramp Up [increasing at 25% of maximum voluntary contraction (MVC)], Execution (tonic at 50% MVC), and Ramp Down (relaxation at 25% MVC) in 42 healthy adults. We analyzed the linear portion of resting extensor carpi radialis (ECR) MEP recruitment by stimulating at multiple intensities and comparing slopes, expressed as mV per TMS stimulation level, via linear mixed modeling. In younger participants (age ≤ 30), resting ECR MEP recruitment slopes were significantly and equally larger both at Ramp Up (slope increase = 0.047, p < 0.001) and Ramp Down (slope increase = 0.031, p < 0.001) compared to rest, despite opposite directions of force change. In contrast, Active ECR MEP recruitment slopes were larger in Ramp Down than all other phases (Rest:0.184, p < 0.001; Ramp Up:0.128, p = 0.001; Execution: p = 0.003). Older (age ≥ 60) participants’ resting MEP recruitment slope was higher than younger participants across all phases. IHI did not reduce MEP recruitment slope equally in old compared to young. In conclusion, our data indicate that MEP recruitment slope in the resting limb is affected by the homologous active limb contraction force, irrespective of the direction of force change. The active arm MEP recruitment slope, in contrast, remains relatively unaffected. Older participants had steeper MEP recruitment slopes and less interhemispheric inhibition compared to younger participants.en_US
dc.description.sponsorshipRehabilitation Research and Development Serviceen_US
dc.description.urihttps://doi.org/10.3389/fnhum.2020.581008en_US
dc.language.isoenen_US
dc.publisherFrontiers Media S.A.en_US
dc.relation.ispartofFrontiers in Human Neuroscienceen_US
dc.subjectagingen_US
dc.subjectcortical dynamicsen_US
dc.subjectdisinhibitionen_US
dc.subjectinterhemispheric inhibition (IHI)en_US
dc.subjectmotor evoked potential (MEP) recruitment slopeen_US
dc.titleContraction Phase and Force Differentially Change Motor Evoked Potential Recruitment Slope and Interhemispheric Inhibition in Young Versus Olden_US
dc.typeArticleen_US
dc.identifier.doi10.3389/fnhum.2020.581008
dc.source.volume14


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