Abstract Representation of Movement Parameters in Basal Ganglia Output

An attractive hypothesis is that the basal ganglia (BG) are implicated in controlling and adapting movement kinematics to different behavioral contexts. We explored this possibility by recording substantia nigra pars reticulata (SNr) spiking activity in freely moving rats during movement execution using two behavioral protocols with different spatiotemporal content. First, animals were trained to perform locomotion runs constrained to a spatiotemporal range of meters and a few seconds (∼7 s). Then, the same animals were trained to perform forelimb movements restricted to 3-10 cm in the order of hundreds of milliseconds. We found that the spiking activity of SNr neurons recorded in both tasks was mainly and linearly correlated with movement position and velocity, with these representations scaling across different spatiotemporal contexts. That is, the minimum and maximum firing rates were proportionally adjusted to the corresponding ranges of velocity/position in each task. Finally, execution representations, their scaling properties, and the behavioral effects of pathway-specific optogenetic manipulations were similar across SNr subpopulations. Our data suggest that the SNr integrates upstream information into a common, scalable velocity/position output signal that is broadcast to multiple target structures, supporting the idea that the BG contribute to the abstract representation of movement kinematic control.