Evoked potentials in motor cortical LFPs reflect task 1 timing and behavioral performance 2 3

22 Evoked potentials (EPs) are observed in motor cortical local field potentials (LFPs) during 23 movement execution (Movement Related Potentials, MRPs) and in response to relevant 24 visual cues (Visual Evoked Potentials, VEPs). Motor cortical EPs may be directionally 25 selective, but little is known concerning their relation to other aspects of motor behavior, such 26 as task timing and performance. We recorded LFPs in motor cortex of two monkeys during 27 performance of a pre-cued arm-reaching task. A time-cue at the start of each trial signaled 28 delay duration, and thereby the pace of the task and the available time for movement 29 preparation. VEPs and MRPs were strongly modulated by the delay duration; VEPs being 30 systematically larger in short delay trials and MRPs larger in long delay trials. Despite these 31 systematic modulations related to the task timing, directional selectivity was similar in short 32 and long trials. The behavioral reaction time (RT) was positively correlated with MRP size 33 and negatively correlated with VEP size, within sessions. In addition, the behavioral 34 performance improved across sessions, in parallel with a slow decrease in the size of VEPs 35 and MRPs. Our results clearly show the strong influence of the behavioral context and 36 performance upon motor cortical population activity during movement preparation and 37 execution.