Biology subjects

Severson, K. S.

Publications and source records attributed to Severson, K. S..

3 recordsLinked to original sources

bioRxiv2025

Peri-Head Distance Coding in the Mouse Brainstem

Perceiving object distance in peri-personal space is essential for guiding movement and avoiding danger. During active sensation, distance information is often anchored to the body via touch; yet how early somatosensory circuits extract distance information from tactile inputs remains unclear. Here, we investigate how second-order neurons in the mouse whisker brainstem encode peri-head distance. Using in vivo extracellular recordings in awake mice in a naturalistic wall-passing paradigm, we find brainstem neurons employ two distance-coding schemes: a "proximity" code, where firing increases monotonically as objects approach the face; and a "map" code, where neurons exhibit peak tuning at specific distances to collectively tile peri-head space. The map code outperforms proximity code in population decoding of distance. Perturbation experiments reveal multi-whisker integration and internuclear inhibition contribute to the generation of map-like tuning. These findings highlight a previously underappreciated computational role for brainstem circuits, where inhibition acts as a neural comparator to transform proximity-based sensory inputs into a map-like representation of peri-personal space.

neuroscience↗

bioRxiv2025

Cortex-Wide Substrates for Body Schema and Action Awareness

The concept of the body schema originated from studies of patients with cortical lesions who were unable to localize their body parts in space or perceive passive movements (Head & Holmes, 1911). Current consensus defines the body schema as the brains internal representation of the body configuration in space used for both embodied perception and voluntary action (de Vignemont, 2010; Berlucchi & Aglioti, 2010; Vallar et al., 2025). Despite extensive research, how the cortex efficiently encodes the vast repertoire of body postures to support natural behavior remains poorly understood. Here, we reveal the representational format underlying the body schema by combining large-scale electrophysiological recordings with full-body 3D tracking and joint angle computation in freely behaving mice. Across cortical regions, neurons encoded diverse postural features in distinct reference frames: posterior parietal cortex (PPC) populations preferentially encoded body midline-referenced features, while sensorimotor cortices utilized a gravity-referenced frame. Strikingly, during performance of different stereotyped actions, distinct cortical ensembles were selectively activated. These action ensembles fired in phase-locked sequences that tiled the full action cycle, providing a neural substrate for action awareness. A network model recapitulated these dynamics and identified low-dimensional action subspaces within population activity. Together, these findings reveal that the cortex organizes the body schema around actions, compressing high-dimensional kinematics into an efficient, body-midline-and gravity-anchored, action-aware neural code.

neuroscience↗

bioRxiv2018

What can facial mechanoreceptors tell the mouse brain about whisking?

Haptic perception synthesizes touch with proprioception, or sense of body position. Humans and mice alike experience rich active touch of the face. Because most facial muscles lack proprioceptor endings, the sensory basis of facial proprioception remains unsolved. Facial proprioception may instead rely on mechanoreceptors that encode both touch and self-motion. In rodents, whisker mechanoreceptors provide a signal that informs the brain about whisker position. Whisking involves coordinated orofacial movements, so mechanoreceptors innervating facial regions other than whiskers could also provide information about whisking. To define all sources of sensory information about whisking available to the brain, we recorded spikes from mechanoreceptors innervating diverse parts of the face. Whisker motion was encoded best by whisker mechanoreceptors, but also by those innervating whisker pad hairy skin and supraorbital vibrissae. Redundant self-motion responses may provide the brain with a stable proprioceptive signal despite mechanical perturbations such as whisker growth and active touch.

neuroscience↗