# The Sensory Input from the External Cuneate Nucleus and Central Cervical Nucleus to the Cerebellum Refines Forelimb Movements

## TL;DR

This study shows that the external cuneate and central cervical nuclei send sensory input to the cerebellum, which is crucial for precise forelimb movements.

## Contribution

The study identifies the central cervical nucleus's termination in the medial cerebellar nucleus, a previously unclear anatomical connection.

## Key findings

- Inhibiting the external cuneate nucleus impaired reaching and grasping in rats.
- The central cervical nucleus projects to the medial cerebellar nucleus within the deep cerebellar nuclei.
- Sensory input from these nuclei is essential for accurate forelimb movement control.

## Abstract

Goal-directed reaching movements are extremely accurate to the point that the location, placement, and speed of the limbs are specific from trial to trial. These movements require descending motor commands and feedback modulation from ascending sensory information. The descending motor commands and ascending sensory information work in conjunction to ensure that the movement is accurate and precise through an error-corrected process that resides in the cerebellum. Disruptions to this information may cause errors in the precision of forelimb motor targeting. According to the previous literature, the external cuneate nucleus (ECN) and central cervical nucleus (CeCv) are responsible for conveying unconscious sensory information from the forelimbs, shoulders, and neck muscles to the cerebellum. Here, we examined the significance of the ECN and CeCv, separately, in forelimb function. In conjunction with inhibitory DREADDs (hM4Di), we observed an obstruction in single pellet reaching and grasping when ECN activity was repressed, both unilaterally and bilaterally, in normal rats. We also observed reduced reach in the grooming assessment bilaterally. We discovered that the CeCv terminates in the medial cerebellar nucleus (MCN), within the deep cerebellar nuclei (DCN), which, to the best of our knowledge, was previously not clearly defined. Together, this information provides evidence that the requirement of ascending sensory information is important in forelimb function.