Single-neuron projectome reveals organization of somatosensory ascending pathways in the mouse brain

Relay of multimodal somatosensory information from the spinal cord to the brain is critical for sensory perception, but the underlying circuit organization remains unclear. We have reconstructed mouse cervical spinal projection neurons at single-cell resolution and identified 19 projectome-defined subtypes exhibiting diverse projection patterns. We also reconstructed the brain-wide axonal projections of central relay neurons that receive direct spinal inputs at the single-cell resolution. We discovered parallel, divergent, and convergent projection patterns for spinal projection neurons and central relay neurons. Our results revealed the diverse pathways channeling spinal information to the cortex. Furthermore, we identified parallel lateral and medial spinal-superior colliculus-brainstem pathways, which could be involved in orienting and defensive behaviors, respectively. These data allowed us to construct a wiring diagram for ascending somatosensory pathways with projectome-defined subtype resolution. Our single-cell projectome analysis provided a new framework for understanding the complex neural circuitry underlying coordinated processing of diverse somatosensory modalities.