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."
In your coverage, please use this URL to provide access to the freely available paper in PLOS Biology: https://plos.io/3DEEBcK
Citation: Hage P, Fakharian MA, Shoup AM, Pi JS, Sedaghat-Nejad E, Orozco SP, et al. (2025) Purkinje cells of the cerebellum control deceleration of tongue movements. PLoS Biol 23(4): e3003110. https://doi.org/10.1371/journal.pbio.3003110
Author countries: United States
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.
