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Abstract
The ability to initiate and cancel actions is a basic requirement for motor control in humans. Rapid movements to stationary targets over single joints are characterized by triphasic bursts of electromyographic (EMG) activity. While analysis of reaction time in motor activation tasks, in relation to different modalities of sensory inputs, has studied, its diametrically opposite task of motor cancellation has not been adequately addressed. We studied 9 normal right-handed subjects using biceps (agonist) and triceps (antagonist) EMG recordings. Each underwent 3 motor activation and 3 motor cancellation tasks to light, sound and dual stimuli (6 blocks). The former consisted of ballistic elbow flexion over 45 degrees, while the latter involved dropping of the forearm from a 45-degree elbow flexion angle. For motor activation, onset latencies and duration of agonist (Lat1, Dur1) and antagonist (Lat2, Dur2) muscles were recorded. For motor cancellation, onset latencies and duration of agonist (Lat1 only) and antagonist (Lat2, Dur2) were noted. Motor cancellation showed significantly shorter Dur2 EMG bursts (p < .0005) for all 3 stimuli conditions. Lat1 and Lat2 demonstrated significant correlation (p < 0.0005 for all), with the exception of dual stimulus condition during motor cancellation (p = 0.089). While dual stimulus during motor cancellation resulted in significantly shorter Lat2 (p = .013) in comparison with light and sound stimuli, this was not evident for motor activation tasks. The findings suggest that while a common central program exists for executing motor activation and cancellation, generation of antagonist activity in the latter may involve distinct neural pathways specifically robust to the effects of intersensory facilitation. This is discussed in relation to reciprocal motor oscillatory activity manifestations at the level of single joint movements.