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

ABSTRACT 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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Available from: Riccardo Mazzocchio, Jul 31, 2015
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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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    • "An alternative explanation for the conflicting results might be differences in the characteristics of the tasks employed (Bonato et al. 1996, Carroll et al. 2008, Duque et al. 2008, Lee et al. 2010). Participants in the study by Duque et al. (2008) performed repetitive finger movements at 1 Hz for 30 min, and Bonato et al. (1996) required subjects to produce repetitive maximal-speed finger movements for 1 min. The performance of such cyclic tasks has the potential to induce central fatigue and cause substantial reduction in MEP response in the trained limb (Brasil-Neto et al. 1994, Zanette et al. 1995). "
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