Striatal firing rate reflects head movement velocity

Although the basal ganglia have long been implicated in the initiation of actions, their contribution to movement remains a matter of dispute. Using wireless multi-electrode recording and motion tracking, we examined the relationship between single-unit activity in the sensorimotor striatum and movement kinematics. We recorded single-unit activity from medium spiny projection neurons and fast-spiking interneurons while monitoring the movements of mice using motion tracking. In Experiment 1, we trained mice to generate movements reliably by water-depriving them and giving them periodic cued sucrose rewards. We found high correlations between single-unit activity and movement velocity in particular directions. This correlation was found in both putative medium spiny projection neurons and fast-spiking interneurons. In Experiment 2, to rule out the possibility that the observed correlations were due to reward expectancy, we repeated the same procedure but added trials in which sucrose delivery was replaced by an aversive air puff stimulus. The air puff generated avoidance movements that were clearly different from movements on rewarded trials, but the same neurons that showed velocity correlation on reward trials exhibited a similar correlation on air puff trials. These experiments show for the first time that the firing rate of striatal neurons reflects movement velocity for different types of movements, whether to seek rewards or to avoid harm.