Cortex-Wide Substrates for Body Schema and Action Awareness

The body schema, an internal model of the body’s configuration in space, is essential for embodied perception and voluntary action. Cortical lesions can disrupt the body schema; however, it remains unclear how the cortex efficiently represents the vast repertoire of body postures during natural behavior. Here, we unveil the representational format underlying the body schema by combining large-scale electrophysiology with 3D full-body motion capture in freely moving mice. Across posterior parietal (PPC) and sensorimotor cortices (SMC), neurons encoded diverse postural features in distinct reference frames: PPC neurons emphasize midline-referenced features related to left-right turning, whereas SMC neurons encode body elevation and pitch relative to the ground, revealing a gravicentric reference frame. Strikingly, beyond static posture encoding, we identified neural ensembles selectively activated during stereotyped actions such as walking, rearing, and grooming. These action ensembles fire in phase-locked sequences that tile the entire action cycle, providing a substrate for action awareness. A network model recapitulated these dynamics, showing that population activity clustered into action-specific subspaces. Together, these findings demonstrate that the cortex organizes the body schema around actions, compressing high-dimensional kinematics into an efficient, gravity-anchored, and action-aware neural code.