Monaural Auditory Cue Affects the Process of Choosing the Initial Swing Leg in Gait Initiation.

The authors investigated the effect of an auditory cue on the choice of the initial swing leg in gait initiation. Healthy humans initiated a gait in response to a monaural or binaural auditory cue. When the auditory cue was given in the ear ipsilateral to the preferred leg side, the participants consistently initiated their gait with the preferred leg. In the session in which the side of the monaural auditory cue was altered trial by trial randomly, the probability of initiating the gait with the nonpreferred leg increased when the auditory cue was given in the ear contralateral to the preferred leg side. The probability of choosing the nonpreferred leg did not increase significantly when the auditory cue was given in the ear contralateral to the preferred leg side in the session in which the auditory cue was constantly given in the ear contralateral to the preferred leg side. The reaction time of anticipatory postural adjustment was shortened, but the probability of choosing the nonpreferred leg was not significantly increased when the gait was initiated in response to a binaural auditory cue. An auditory cue in the ear contralateral to the preferred leg side weakens the preference for choosing the preferred leg as the initial swing leg in gait initiation when the side of the auditory cue is unpredictable.

Bimanual coordination of force enhances interhemispheric inhibition between the primary motor cortices.

The purpose of this study was to elucidate whether bimanual coordination of force affects interhemispheric inhibition (IHI) between the primary motor cortices (M1s). IHI with the index fingers isometrically abducted against a fixed plate (AAP task) was compared with IHI with the index fingers isometrically abducted against each other (AAF task). The index fingers were held stationary at the midline and activity levels of the first dorsal interosseous muscles were equalized between the tasks. The abduction force of each index finger was individually controlled during the AAP task, and bimanually coordinated during the AAF task. IHI during the AAF task was significantly higher than that during the AAP task. IHI between the M1s is related not only to the suppression of unwanted activity of the M1 contralateral to the active M1 but also to bimanual coordination of force.

Smooth pursuit eye movement preferentially facilitates motor-evoked potential elicited by anterior-posterior current in the brain.

Neural interaction between the eye and hand movement centers must be a critical part of the mechanism underlying eye-hand coordination. One of the previous findings supporting this view is smooth pursuit eye movement-induced suppression of motor-evoked potential (MEP) in the hand muscles. The purpose of this study was to determine which descending volleys contributing to MEP are preferentially modulated by smooth pursuit eye movement. MEP in the first dorsal interosseous muscle was elicited by different directions of current in the brain during the steady-state phase of smooth pursuit eye movement. Smooth pursuit eye movement facilitated MEP elicited by anterior-posterior (AP) current, but this effect was not seen in MEP elicited by lateromedial or posterior-anterior current. Latency of MEP elicited by AP current was significantly longer than latencies of MEPs elicited by other directions of current, indicating that AP current in the brain predominantly elicited later I-waves. We conclude that smooth pursuit eye movement in the steady-state phase preferentially facilitates MEP predominantly elicited by later I-waves generated by AP current in the brain.