Memory Formation in the Motor Cortex Ipsilateral to a Training Hand

Human Cortical Physiology Section and Stroke Neurorehabilitation Clinic, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20817, USA.
Cerebral Cortex (Impact Factor: 8.67). 07/2008; 18(6):1395-406. DOI: 10.1093/cercor/bhm173
Source: PubMed


Cortical reorganization within the primary motor cortex (M1) contralateral to a practicing hand has been extensively investigated. The extent to which the ipsilateral M1 participates in these plastic changes is not known. Here, we evaluated the influence of unilateral hand practice on the organization of the M1 ipsilateral and contralateral to the practicing hand in healthy human subjects. Index finger movements elicited by single-pulse transcranial magnetic stimulation (TMS) delivered to each M1 were evaluated before and after practice of unilateral voluntary index finger abduction motions. Practice increased the proportion and acceleration of TMS-evoked movements in the trained direction and the amplitude of motor-evoked potentials (MEPs) in the abduction agonist first dorsal interosseous (FDI) muscle in the practicing hand and decreased the proportion and acceleration of TMS-evoked abduction movements and MEP amplitudes in the abduction agonist FDI in the opposite resting hand. Our findings indicate that unilateral hand practice specifically weakened the representation of the practiced movement in the ipsilateral M1 to an extent proportional to the strengthening effect in the contralateral M1, a result that varied with the practicing hand's position. These results suggest a more prominent involvement of interacting bilateral motor networks in motor memory formation and probably acquisition of unimanual motor skills than previously thought.

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    • "However, this time, the performance gains were negatively correlated with the size of the MEP. This observation is in line with previous studies reporting reduced corticospinal excitability after exercising with low contraction strengths [30]–[32]. Therefore, it seems as if both training adaptations are accompanied by task specific (short-term) adaptations of electrophysiological variables, i.e. the MEP. Alternatively one may speculate that the sequence of tasks determined the direction of adaptation, i.e. the first task increased the MEPs while the second task decreased the MEP size. "
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    PLoS ONE 12/2013; 8(12):e81038. DOI:10.1371/journal.pone.0081038 · 3.23 Impact Factor
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    • "Upper limb movements involve a fine balance between proximal stability and distal dexterity, presenting a unique motor control challenge to the central nervous system. There is a growing body of evidence that skilled upper limb function is under the control of both contralateral (cM1) and ipsilateral (iM1) motor cortices (Chen et al., 1997; Gerloff et al., 1998; Muellbacher et al., 2000; Hummel et al., 2003; Sohn et al., 2003; Verstynen et al., 2005; Davare et al., 2007; Duque et al., 2008; Perez and Cohen, 2008, 2009; Lee et al., 2010). Exactly how iM1 contributes to ipsilateral upper limb control is unclear, and is likely to involve both interhemispheric and descending projections. "
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    • "Then, following the imperative signal, the amplitude of MEPs progressively increased . This increase was more pronounced when the imperative signal had indicated a left-hand response, compared to when it had indicated a right-hand response (left-hand nonselected), reflecting a selective buildup of activity in the motor cortex controlling the forthcoming response (Duque et al., 2008; Michelet et al., 2010). Based on bounded-accumulation models, two predictions exist on how reward could regulate the buildup of motor activity during response selection (Fig. 1A). "
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