Summary: Researchers studying marmosets discovered that Purkinje cells in the cerebellum help regulate tongue movement by signaling when to stop as the tongue nears its target. These cells were highly engaged during precision tasks, like inserting the tongue into narrow tubes, but not during casual grooming.
When researchers suppressed these cells, the tongue overshot its target or slowed in retraction, revealing how crucial Purkinje cell activity is to coordination. The findings shed light on how the cerebellum contributes to precise motor control and could inform treatments for speech and swallowing disorders.
Key Facts:
- Motor Precision: Purkinje cells in the cerebellar vermis signal to stop tongue movement near targets.
- Functional Disruption: Suppressing these cells caused overreach or slowed tongue return.
- Clinical Relevance: Insights may aid therapies for speech, swallowing, and vocal disorders.
Source: PLOS
By studying the skilled movements of marmoset tongues, researchers have discovered that Purkinje cells (P-cells) in a brain region called the cerebellum signal to stop protrusion as the tongue approaches its target, according to a study published April 10th in the open-access journal PLOS Biology by Reza Shadmehr from Johns Hopkins School of Medicine, U.S., and colleagues.
We use our tongue to shape the air and generate sounds to communicate, and we use our tongue to evaluate food morsels and transport them through the oral cavity when eating.
These skillful acts involve coordination of more than 100 muscles, producing movements that are fundamental to our existence. Damage to the cerebellum disrupts these movements, resulting in abnormal muscle activation patterns. Yet it has not been clear how the cerebellum controls tongue movements.
To answer this question, Shadmehr and colleagues used an animal model that has a long tongue and can skillfully direct it to small targets. Marmosets have a 21mm tongue which they use to burrow into small holes and retrieve insects and sap. Indeed, they have an extraordinary ability to control their tongue, vocalizing to label other marmosets during two-way communication.
The researchers observed that marmosets could naturally bend and twist their tongues and insert them into small tubes, even when the tubes were placed at sharp angles with respect to their mouths.
To quantify how the cerebellum contributes to the control of the tongue, the researchers recorded the activity of P-cells in a cerebellar structure called the vermis. When a P-cell was suppressed during protraction, the tongue’s trajectory became hypermetric, overshooting the intended target during movements.
When the suppression took place during retraction, the tongue’s return to the mouth was slowed. Both effects were amplified when two P-cells were simultaneously suppressed. Suppression of P-cells in the vermis disrupted the forces that would normally decelerate the tongue as it approached the target.
The results suggest that P-cells signal to downstream structures to stop the movement as the tongue approaches its target. This strong engagement of the P-cells was present when the tongue was aiming for a small tube – a movement that requires precision — but not when the tongue was used to groom the face.
According to the authors, treatments or cures for symptoms linked to cerebellar dysfunction, such as vocal muscle spasms, problems with swallowing, or speech disorders, will require a much better understanding of how the cerebellum contributes to the control and learning of tongue movements.
Because marmosets are exceptionally skilled at shaping and twisting their tongues, using them almost like fingers, they are an attractive animal model to study the neural control of a body part that is essential for our existence.
The authors add, “During dexterous licking, a climbing fiber induced suppression of Purkinje cells in the lingual vermis inhibited the forces that would otherwise retract the tongue, resulting in hypermetria during protraction and slowing during retraction.
“Because the direction of these forces aligned with the direction of motion specified by the olivary input, a pattern that is also present for P-cells in the oculomotor region of the cerebellum, the results imply a general computation for P-cells during control of targeted movements.”
Funding: The work was supported by grants from the National Institutes of Health (https://www.ninds.nih.gov/) (R01-EB028156 to RS, R37-NS128416 to RS) and the National Science Foundation (https://www.nsf.gov/) (CNS-1714623 to RS). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
About this neuroscience research news
Author: Claire Turner
Source: PLOS
Contact: Claire Turner – PLOS
Image: The image is credited to Neuroscience News
Original Research: Open access.
“Purkinje cells of the cerebellum control deceleration of tongue movements” by Reza Shadmehr et al. PLOS Biology
Abstract
Purkinje cells of the cerebellum control deceleration of tongue movements
We use our tongue much like our hands: to interact with objects and transport them. For example, we use our hands to sense properties of objects and transport them in the nearby space, and we use our tongue to sense properties of food morsels and transport them through the oral cavity.
But what does the cerebellum contribute to control of tongue movements?
Here, we trained head-fixed marmosets to make skillful tongue movements to harvest food from small tubes that were placed at sharp angles to their mouth.
We identified the lingual regions of the cerebellar vermis and then measured the contribution of each Purkinje cell (P-cell) to control of the tongue by relying on the brief but complete suppression that they experienced following an input from the inferior olive.
When a P-cell was suppressed during protraction, the tongue’s trajectory became hypermetric, and when the suppression took place during retraction, the tongue’s return to the mouth was slowed.
Both effects were amplified when two P-cells were simultaneously suppressed. Moreover, these effects were present even when the pauses were not due to the climbing fiber input. Therefore, suppression of P-cells in the lingual vermis disrupted the forces that would normally decelerate the tongue as it approached the target.
Notably, the population simple spike activity peaked near deceleration onset when the movement required precision (aiming for a tube), but not when the movement was for the purpose of grooming.
Thus, the P-cells appeared to signal when to stop protrusion as the tongue approached its target.
