DISSECTING THE NEURAL CIRCUITS OF MOTOR CONTROL IN THE MOUSE SUPERIOR COLLICULUS

Adapting behaviour to changing external contingencies is essential for operating in a dynamic environment. The mouse superior colliculus (SC), a central hub for visually guided orienting movements, is well positioned to modify ongoing behaviour through downstream interactions with circuits involved in motor planning and execution. Two anatomically distributed output pathways are of particular importance: one targeting the hindbrain and the other ascending to the thalamus. How visually guided motor commands derived in the SC are orchestrated in tandem with ongoing motor activity remains unclear.
To interrogate the outputs of the SC we focus on Lypd1 neurons, a population of glutamatergic projection neurons, labelled with a Cre line. We show Lypd1 neurons project to motor thalamus, an interface with the basal ganglia, and hindbrain nuclei, providing them with broad access to motor circuits. In vivo optogenetic activation elicited robust contralateral orienting, pupil dilation and orofacial movement implicating this population in the control of movement and arousal state. We next evaluated their role in goal-directed behaviour using a trained pursuit task. Silencing Lypd1 neurons during pursuit caused a transient disruption of performance, from which mice recovered within the stimulation period, suggesting the engagement of parallel mechanisms supporting behaviour.
These findings suggest that Lypd1 neurons in the SC are well equipped to shape ongoing movements. Dissecting the distinct contributions of ascending and descending SC output pathways will be essential for understanding how visually guided motor commands are integrated with ongoing motor activity to support adaptive behaviour.