The encoding of touch by somatotopically aligned dorsal column subdivisions

Abstract

The somatosensory system decodes a range of tactile stimuli to generate a coherent sense of touch. Discriminative touch of the body depends on signals conveyed from peripheral mechanoreceptors to the brain via the spinal cord dorsal column and its brainstem target the dorsal column nuclei (DCN)1, 2. Models of somatosensation emphasize that fast-conducting low- threshold mechanoreceptors (LTMRs) innervating the skin drive the DCN3, 4. However, post- synaptic dorsal column neurons (PSDCs) within the spinal cord dorsal horn also collect mechanoreceptor signals and form a second major input to the DCN5-7. The significance of PSDCs and their contributions to the coding of touch have remained unclear since their discovery. Here, we show that direct LTMR inputs to the DCN convey vibrotactile stimuli with high temporal precision, whereas PSDCs primarily encode touch onset and the intensity of sustained contact into the high force range. LTMR and PSDC signals topographically re-align in the DCN to preserve precise spatial detail. Different DCN neuron subtypes have specialized responses that are generated by unique combinations of LTMR and PSDC inputs. Thus, LTMR and PSDC subdivisions of the dorsal column encode different tactile features and differentially converge in the DCN to generate unique ascending sensory processing streams.