NEURONAL ACTIVITY OF THE CEREBELLAR NUCLEI AT THE POPULATION LEVEL ACROSS FORELIMB RELATED BEHAVIOURS

Smooth motor control relies on cerebellar processing. While information processing in the cerebellar cortex is becoming better understood, much less is known about the deep cerebellar nuclei (CN), which constitute the sole output of the cerebellum. Characterizing how neuronal subpopulations within the Anterior Interposed Nucleus (IntA) encode and process upper-limb movements in vivo will help us understand how the cerebellar output influences its numerous targets during natural and perturbed movement. In this study, we combined two-photon microscopy with a three-dimensional acousto-optic lens (AOL) and online movement correction to monitor neuronal populations in vivo through a GRIN lens. Preliminary ground-truth experiments were conducted in vitro to determine whether the GCaMP8m variant was suitable for reporting rate-coded activity, as CN neurons are known to exhibit high baseline firing rates modulated by movement. By coupling loose-patch electrophysiological recordings with two-photon AOL calcium imaging, we confirmed that GCaMP8m reliably reports CN neuronal activity and can be used to infer spike rates through calcium trace deconvolution. In vivo imaging was then performed in head-fixed mice performing upper-limb motor tasks. Movement kinematics were tracked using a combination of markerless pose-estimation approaches and correlated with normal and perturbed behaviour. This constitutes the first population imaging recording of CN neurons, and provides a framework to dissect how cerebellar output populations coordinate motor control in behaving animals.