Context-specific early recruitment of small motor units in the shoulder muscle reflects a reach movement plan.

Understanding how motor plans are transformed into appropriate patterns of muscle activity is a central question in motor control. Although muscle activity during the delay period has not been reported using conventional electromyographic (EMG) approaches, we isolated motor unit activity using a high-density surface EMG signal from the anterior deltoid muscle to test whether heterogeneity in motor units could reveal early preparatory activity. Consistent with our previous work (Rungta SP, Basu D, Sendhilnathan N, Murthy A.

Preparatory activity links the frontal eye field response with small amplitude motor unit recruitment of neck muscles during gaze planning.

A hallmark of intelligent behavior is that we can separate intention from action. To understand the mechanism that gates the flow of information between motor planning and execution, we compared the activity of frontal eye field neurons with motor unit activity from neck muscles in the presence of an intervening delay period in which spatial information regarding the target was available to plan a response. Although spatially specific delay period activity was present in the activity of frontal eye field neurons, it was absent in motor unit activity.