title: Demand on skillfulness modulates interhemispheric inhibition of motor cortices.
abstract: The role of primary motor cortex (M1) in the control of hand movements is still unclear. Functional magnetic resonance imaging (fMRI) studies of unimanual performance reported a relationship between level of precision of a motor task and additional ipsilateral M1 (iM1) activation. In the present study, we determined whether the demand on accuracy of a movement influences the magnitude of the inhibitory effect between primary motor cortices (IHI). We used transcranial magnetic stimulation (TMS) to measure active IHI (aIHI) of the iM1 on the contralateral M1 (cM1) in the premovement period of a left-hand motor task. Ten healthy participants manipulated a joystick to point to targets of two different sizes. For aIHI, the conditioning stimulus (CS) was applied to iM1, and the test stimulus (TS) to cM1, with an interstimulus interval of 10 ms. The amount of the inhibitory effect of the CS on the motor-evoked potential (MEP) of the subsequent TS was expressed as percentage of the mean MEP amplitude evoked by the single TS. Across different time points of aIHI measurements in the premovement period, there was a significant effect for target size on aIHI. Preparing to point to small targets was associated with weaker aIHI compared with pointing to large targets. The present findings suggest that, during the premovement period, aIHI from iM1 on cM1 is modulated by the demand on accuracy of the motor task. This is consistent with task fMRI findings showing bilateral M1 activation during high-precision movements but only unilateral M1 activity during low-precision movements.
authors.affiliation: Department of Neurology and.
authors.forename: Miles
authors.initials: M
authors.lastname: Wischnewski
authors.affiliation: Department of Neurology and.
authors.forename: Greg M
authors.initials: GM
authors.lastname: Kowalski
authors.affiliation: Department of Neurology and.
authors.forename: Farrah
authors.initials: F
authors.lastname: Rink
authors.affiliation: Department of Neurology and Department of Rehabilitation Medicine, Emory University, Atlanta, Georgia;
authors.forename: Samir R
authors.initials: SR
authors.lastname: Belagaje
authors.affiliation: Department of Neurology and Radiology;
authors.forename: Marc W
authors.initials: MW
authors.lastname: Haut
authors.affiliation: Department of Biostatistics, West Virginia University, Morgantown, West Virginia.
authors.forename: Gerald
authors.initials: G
authors.lastname: Hobbs
authors.affiliation: Department of Neurology and Department of Rehabilitation Medicine, Emory University, Atlanta, Georgia; cathrin.buetefisch@emory.edu.
authors.forename: Cathrin M
authors.initials: CM
authors.lastname: Buetefisch
mesh_terms: D000368:Aged; D004576:Electromyography; D019054:Evoked Potentials, Motor / Q000502:physiology; D005260:Female; D007839:Functional Laterality / Q000502:physiology*; D006225:Hand / Q000502:physiology; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D009044:Motor Cortex / Q000000981:diagnostic imaging / Q000502:physiology*; D009048:Motor Skills / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology; D009433:Neural Inhibition / Q000502:physiology*; D009483:Neuropsychological Tests; D011930:Reaction Time; D050781:Transcranial Magnetic Stimulation
keywords: interhemispheric inhibition; motor control; primary motor cortex; transcranial magnetic stimulation