Extended Data Fig. 10: A model for sensory representation in the hindlimb dorsal column system.

a, Mechanical stimuli in a small area of skin are detected by LTMRs and HTMRs. LTMRs ascend the dorsal column and synapse onto neurons in the DCN, forming the direct pathway. LTMRs also form collaterals within the spinal cord dorsal horn. PSDCs in the spinal cord dorsal horn receive mechanical information from LTMRs and HTMRs, either directly or through local interneurons. PSDC axons ascend the dorsal column, forming the indirect pathway. PSDCs of the indirect pathway signal the intensity of sustained stimuli and the onset/offset of stimuli, as well as low-frequency vibratory stimuli. LTMRs of the direct pathway signal rapid movements and high-frequency vibratory stimuli, in addition to the onset/offset of stimulation. These two pathways converge somatotopically such that individual DCN neurons can encode multiple features in a small patch of skin. b, Different contributions from PSDCs and LTMRs drive distinct response properties in DCN neuron types. Left: VPL-PNs have small RF sizes and commonly have inhibitory surrounds driven by DCN Vgat-INs. Direct LTMR input drives phase-locked spiking up to ~150 Hz. VPL-PNs can also commonly encode sustained stimuli at high forces mediated by indirect PSDC input. Thus, VPL-PNs receive prominent direct and indirect pathway input. Middle: Local Vgat-INs have varying receptive field sizes and can entrain to vibrations up to 150 Hz. They can, in some cases, be activated by high-frequency stimulation, but typically do not entrain their firing. Vgat-INs rarely fire in response to the sustained component of stimuli and thus poorly encode the intensity of sustained stimuli. Inhibitory surrounds in other DCN neurons that are generated by Vgat-INs are not strongly driven by indirect input, and are not driven by Calca⁺ HTMR activation. Right: The most common type of IC-PNs (vibration-tuned) have very large receptive field sizes and can entrain to high-frequency vibratory stimuli up to 500 Hz. These high-frequency responses are likely generated exclusively by direct LTMR (Aβ-RA2-LTMR) input. They can encode sustained stimuli, but not as well as VPL-PNs. They receive some input from HTMRs, likely through PSDCs, but only to a subset of their receptive field.