The basal ganglia, and the striatum in particular, have been implicated in the generation of contraversive movements. The striatum projects to downstream basal ganglia nuclei through two main circuits, originating in striatonigral and striatopallidal neurons, and different models postulate that the two pathways can work in opposition or synergistically. Here we show striatonigral and striatopallidal neurons are concurrently active during spontaneous contraversive movements. Furthermore, we show that unilateral optogenetic inhibition of either or both projection pathways disrupts contraversive movements. Consistently, simultaneous activation of both neuron types produces contraversive movements. Still, we also show that imbalanced activity between the pathways can result in opposing movements being driven by each projection pathway. These data show that balanced activity in both striatal projection pathways is critical for the generation of contraversive movements and highlights that imbalanced activity between the two projection pathways can result in opposing motor output.
The striatum is required for evoking contraversive movements from each brain hemisphere, but it is unclear how. Here, Tecuapetla et al. use optogenetics to inhibit direct and indirect downstream striatal projection pathways, and show that activity in both pathways is necessary for contraversive movements.