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

Abstract

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. Whereas we could infer spatially-specific delayed period activity from the activity of frontal eye field neurons, neck motor unit activity during the delay period could not be used to infer the direction of an upcoming movement, Nonetheless, motor unit activity was correlated with the time it took to initiate saccades. Interestingly, we observed a heterogeneity of responses amongst motor units, such that only units with smaller amplitudes showed a clear modulation during the delay period. These small amplitude motor units also had higher spontaneous activity compared to the units which showed modulation only during the movement epoch. Taken together, our results suggest that the temporal information is visible in the periphery amongst smaller motor units during eye movement planning and explains how the delay period primes muscle activity leading to faster reaction times. Significance statementThis study shows that the temporal aspects of a motor plan in the oculomotor circuitry can be accessed by peripheral neck muscles hundreds of milliseconds prior to the instruction to initiate a saccadic eye movement. The coupling between central and peripheral processes during the delay time is mediated by the recruitment pattern of motor units with smaller amplitude in the periphery. Besides giving insight into how information processed in cortical areas is read out by the muscles, these findings could be useful to decode intentional signals from the periphery to control brain machine interface devices.