# Organization and development of bilateral somatosensory feedback projections in mice

## TL;DR

This study maps how the somatosensory cortex in mice sends bilateral feedback to brainstem regions, with a developing preference for one side.

## Contribution

The study reveals a dynamic bilateral feedback system in the somatosensory pathway and its modulation by feedforward laterality.

## Key findings

- Bilateral feedback projections from the somatosensory cortex to brainstem exist in mice.
- A contralateral bias in feedback projections emerges by postnatal day 7.
- Feedback laterality is modulated by feedforward pathway laterality, not evoked activity.

## Abstract

Sensory information travels from the periphery to the cortex across relays. Each of these stations receives feedback projections which gate and tune the transmission of feedforward information. We used whole brain imaging combined with viral strategies and single axon tracings to reveal the existence of a bilateral feedback projection from the somatosensory cortex to brainstem relays processing whisker information. Initially, after birth in mice, this feedback loop projects equally to both sides of the brainstem. Then, the projection strengthens preferentially toward the contralateral side while maintaining its ipsilateral component. We found that manipulating the laterality of the feedforward pathway from the brainstem to the opposite cortex altered the laterality preference of the descending feedback projections. This suggests a dynamic interplay between ascending and descending pathways in shaping sensory processing. This study highlights the presence of bilateral integration within the somatosensory system’s feedback projections.

•3D mapping in mice of the barrel cortex projections to the brainstem•These projections are bilateral with a contralateral bias emerging from P7 onwards•The contralateral bias is independent of evoked activity•The contralateral bias is modulated by the laterality of feedforward pathways

3D mapping in mice of the barrel cortex projections to the brainstem

These projections are bilateral with a contralateral bias emerging from P7 onwards

The contralateral bias is independent of evoked activity

The contralateral bias is modulated by the laterality of feedforward pathways

Biological sciences; Natural sciences; Neuroanatomy; Neuroscience; Systems neuroscience