Spatial encoding of forelimb proprioception in the mouse somatosensory cortex

Conscious perception of limb movements depends on proprioceptive neural responses in the somatosensory cortex. In contrast to tactile sensations, proprioceptive cortical coding is barely studied in the mammalian brain and practically non-existent in rodent research. To understand the cortical representation of this important sensory modality we developed a passive forelimb displacement paradigm in behaving mice. We imaged the responses of layer 2/3 neurons with two-photon microscopy and tracked the 3D position of limb joints. In addition, mice were trained to perceptually discriminate proprioceptive stimuli allowing us to delineate the mouse proprioceptive cortex with optogenetic silencing experiments. Our results reveal that passive forelimb movements are preferentially encoded as a spatial direction vector that interfaces movements with behaviorally relevant targets. This neural representation of proprioception appears not to be limited to the somatosensory cortex.