Abstract
Motor cortex generates descending output necessary for executing a wide range of limb movements. Although movement-related activity has been described throughout motor cortex, the spatiotemporal organization of movement-specific signaling in deep layers remains largely unknown. Here, we recorded layer 5B population dynamics in the caudal forelimb area of motor cortex while mice performed a forelimb push/pull task and found that most neurons show movement-invariant responses, with a minority displaying movement specificity. Cell-type-specific imaging identified that movement-invariant responses dominated pyramidal tract (PT) neuron activity, with a small subpopulation representing movement type, whereas a larger proportion of intratelencephalic (IT) neurons displayed movement-specific signaling. The proportion of IT neurons decoding movement-type peaked prior to movement initiation, while for PT neurons this occurred during movement execution. Our data suggest that layer 5B population dynamics largely reflect movement-invariant signaling, with information related to movement-type being differentially routed through relatively small, distributed subpopulations of projection neurons.
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
1) Revised title, introduction and discussion. 2) Addition of cell-type-specific imaging of pyramidal tract (PT) and intratelencephalic (IT) neurons in layer 5 of motor cortex during task execution. 3) Inclusion of high-density silicone probe recordings of putative layer 5B projection neurons in the caudal forelimb area (CFA) of motor cortex to complement original imaging data. 4) Additional tracking of forelimb kinematics and correlation with movement-related fluorescence changes in layer 5B neurons. 5) Inclusion of anatomical mapping of muscimol diffusion in CFA and control injections to show the spatiotemporal specificity of pharmacological manipulations. 6) Additional quantification of the proportions of layer 5B neurons imaged per field of view, confirming that we recorded ∆F/F0 changes in the vast majority of neurons expressing genetically encoded calcium indicator.
