eLife Assessment
This important study records basal ganglia output neurons in the substantia nigra pars reticulata of head-fixed mice performing self-timed reaching and licking tasks. Contrary to simple predictions of action selection and inhibitory gating by basal ganglia output, the authors report that most substantia nigra pars reticulata neurons modulate congruently across reaching, licking, and reaches to different targets. Optogenetic identification of substantia nigra pars reticulata neurons projecting to the central and lateral, orofacial superior colliculus shows that these congruent signals are routed to both output zones. Evidence from the recordings is convincing, while that from the projection-specific experiments is solid but rests on few animals and would be strengthened by increased power and clearer criteria for unit identification.