The striatal way of encoding information about locomotor speed

Movement execution relies on the activity of the striatum, but there are current unknowns on how the striatum selects actions and controls their speed. The “discrete encoding model” posits that striatal neurons generate a burst of activity at the beginning and the end of a movement. By contrast, the “continuous encoding model” posits that striatal neurons fire continuously during movement execution, to encode information about the sensory and/or motor state of an animal. In this work, the authors tested the validity of these two models. They performed experiments in which they obtained single and multi-unit recordings from the dorsomedial striatum of mice in an open field. By analyzing neuronal firing rates during bouts of locomotor activity, they showed that 18% of all recorded units increased their firing near the start of locomotion, and 15% of them increased firing near the end of it. The changing in firing rates in these cohorts of neurons reflected changes in locomotor speed. A close comparison of the firing activity of striatal neurons during head-fixed and free-moving locomotion suggest that the speed representation features of most striatal neurons may show continuous changes in firing rates and might be context-dependent. One of the main caveats of in vivo experiments on head-restrained mice is that the vestibular inputs are not comparable to those of freely moving mice. In addition, we wondered whether the results might change depending on the selection criteria used to identify neurons that encode locomotor information (as opposed to other types of movements like grooming, rearing or digging). Therefore, this interpretation holds for locomotor activity at speeds greater than 5 cm/s, it may or may not hold true for at slower speeds. Future works may shed light on the behavior of striatal neurons over all ranges of speed.

Nurat Affinnih and Haley Chesbro

Reference
Fobbs WC, Bariselli S, Licholai JA, Miyazaki NL, Matikainen-Ankney BA, Creed MC, Kravitz AV (2020). Continuous representations of speed by striatal medium spiny neurons. J Neurosci 40(8):1679-1688.