Peri-head distance coding in the mouse brainstem.

Perceiving the location of nearby objects relative to the body is essential for guiding movement and avoiding danger. Many organisms use touch to estimate object distance, yet how somatosensory circuits extract distance from tactile inputs remains unclear. Here, we investigate how neurons in the mouse whisker brainstem compute peri-head distance. Using extracellular recordings in awake mice during wall-passing stimulation, we find two coding schemes that tile peri-head space: "proximity," showing monotonically increasing activity as objects approach the face, and "map," showing peaked tuning at specific distances. The map code enables a more precise readout of peri-head distance. Perturbations suggest that long-range internuclear inhibition is important for generating the map code, subtracting heterogeneous peripheral signals from different whiskers or within the same whisker. These findings reveal an underappreciated computational role for brainstem circuits, where inhibition acts as a neural comparator to transform multiplexed peripheral inputs into a stable representation of peri-head distance.