PLASTICITY AND REGULATION OF PROPRIOCEPTIVE REPRESENTATIONS IN THE MOUSE FORELIMB CORTEX

Proprioception is essential for perceiving body position and movement in space. While comparative evolutionary studies have suggested that proprioceptive cortex organization reflects limb use rather than mere innervation density, the extent of this plasticity within individuals remains unclear. We investigated this principle by analysing proprioceptive neuronal activity in the forelimb somatosensory cortex (fS1) of mice across two scales: individual-level experience-related plasticity via extensive motor training, and group-level developmental plasticity through environmental enrichment.
We longitudinally tracked the proprioceptive responses of fS1 neurons to passive forelimb displacements, comparing their tuning properties during reach-to-grasp motor training. Their functional properties, both directional preference and spatial selectivity, perdured over weeks in expert mice. Similarly, when investigating developmental plasticity, we found that enriched housing did not reorganize the cortical proprioceptive activation map. However, enriched-housed mice exhibited enhanced spatial selectivity and finer distribution of preferred directions. Notably, we observed that directional preference of proprioceptive fS1 neurons is topographically organized and maintains its topographic properties regardless of housing conditions.
Our findings suggest that adult motor experience does not drive functional changes in proprioceptive cortical neurons, as evidenced by the spatial tuning stability over time. However, developmental limb use refines neuronal selectivity within a stable topographic map, suggesting that the environment shapes individual tuning properties rather than reorganizing the cortical sensory representation. Our ongoing experiments investigate the circuit mechanisms underlying this refinement. Given that the superior colliculus (SC) contains sensorimotor maps involved in coordinate transformations, we hypothesize that the lateral SC modulates the spatial tuning properties observed in fS1.