STABILITY OF BEHAVIOURALLY RELATED DENDRITIC ACTIVITY PATTERNS ACROSS DAYS IN MOUSE MOTOR CORTEX

How sensorimotor information is represented by the synaptic inputs distributed across the dendritic trees of pyramidal cells is poorly understood. Recent work using calcium and glutamate imaging has identified various activity patterns including global cell-wide, hemi-tree and branch-specific activation events as well as sub-branch local events involving approximately five to more than ten spines. But, how these distributed patterns of activity are related to motor behaviour is not known. This is largely due to the difficulty of recording from entire dendritic trees at high temporal resolution in awake behaving animals. To overcome this we used 3D acousto-optic lens two-photon microscope equipped with real-time 3D brain motion compensation to measure calcium throughout dendritic trees of pyramidal cells in mouse primary motor cortex, a sensorimotor integration hub that plays a key role in modulating movements such as locomotion, whisking and limb movement. We investigated dendritic processing of behaviour-related variables in head-fixed mice by longitudinally imaging dendritic calcium in L2/3 cells, ultra-sparsely expressing GCaMP8m and extracted local dendritic tree modulation signals. Using linear and non-linear dimensionality reduction and regression approaches, we investigated the relationship between movements and dendritic modulation. We found that behaviour-related dendritic activity patterns were compartmentalised, and that those patterns were stable across days. We are currently investigating the synaptic basis of patterns of movement-related dendritic activity by simultaneously imaging RCaMP3 and iGluSnFR4s during the execution of a learned behaviour.