Population-level encoding of somatosensation in mouse sensorimotor cortex

Dexterous limb movements rely on somatosensation (touch and proprioception), which provides the sense of the body’s posture, movement, and interaction with objects. The heterogeneous responses of single neurons in sensorimotor cortex to somatosensation have led to disparate views of the computa-tional role of this brain area in somatosensory processing. Here, we use population-level analyses of neural activity recorded during active and passive limb movements to assess the structure and sum-marize the properties of neural encoding in sensorimotor cortex. We used 2-photon imaging to record the activity of thousands of neurons in these brain areas from eight anesthetized mice during passive deflections of each limb. We additionally analyzed neural responses to passive limb movements in eight awake mice, sourced from an open dataset [1], and neural responses to spontaneous limb movements in eight mice, collected during a previous study [2]. To conduct the population-level analyses, we found the principal components of the time-varying neural population activity matrix in each set of experi-ments. Across all three datasets and behavioral conditions, a small fraction of principal components explained a large fraction of variance in the neural responses. These low-dimensional representations of single and multi-limb movements were well conserved across animals, including orthogonal represen-tations of ipsilateral and contralateral limbs. This organization of somatosensory information mirrors the well-known structure of neural encoding of motor commands. Furthermore, while the activity of in-dividual neurons and small populations best encoded intrinsic variables, larger populations of neurons additionally encode extrinsic variables — a representational structure that is commonly associated with higher-level brain areas. Together, these analyses demonstrate that population-level encoding of somatosensory information in mouse sensorimotor cortex is structured to facilitate sensorimotor integration across the brain.