Summary: Gnawing is more than a mechanical necessity for rodents; it is also a rewarding, motivated behavior. New research identifies a neural circuit that links sensory input from the teeth directly to midbrain dopamine neurons. This pathway explains how oral sensations drive repetitive chewing behaviors and how those behaviors are reinforced by the brain’s reward system.
The discovery sheds light on why animals like dogs enjoy chewing and why some people persist in nail-biting or tooth-grinding (bruxism). It also points to potential new directions for addressing oral health problems tied to conditions that affect dopamine signaling, such as autism, depression, and Parkinson’s disease.
Key Facts
- Reward circuit: Touch-sensitive neurons around the teeth relay signals to the midbrain, prompting dopamine release during gnawing.
- Survival motivation: Beyond reflexive tooth maintenance, a motivation pathway encourages rodents to gnaw sufficiently to prevent harmful tooth overgrowth and jaw misalignment.
- Human relevance: Similar neural mechanisms may underlie repetitive oral habits in people—like bruxism and nail-biting—even though human teeth do not grow continuously.
- Clinical implications: Disorders that alter dopamine function are associated with higher rates of malocclusion and oral habits, suggesting a neurological contribution to these problems.
- Behavioral reinforcement: The study shows that basic maintenance behaviors are actively reinforced by brain reward centers, ensuring their persistence.
Source: University of Michigan
Researchers at the University of Michigan discovered that rodents’ persistent gnawing activates dopamine release in the brain via a previously unknown neural circuit, making gnawing a motivated, rewarding action rather than a purely mechanical reflex.
Although the experiments were conducted in mice, the investigators suggest the circuit may operate across other mammals. These findings add to growing evidence that oral sensation and brain reward systems are closely linked, with implications for both animal behavior and human oral health.
“Historically, gnawing was viewed as a passive, mechanically driven action,” said Bo Duan, associate professor in the U-M Department of Molecular, Cellular and Developmental Biology, who led the study with Joshua Emrick of the U-M School of Dentistry. “Our work shows gnawing is a motivated behavior with a defined neural circuit connecting tooth sensation to dopamine neurons in the midbrain.”
Identifying this circuit helps explain why repetitive oral behaviors persist over time and why animals and people engage in chewing, biting, or grinding even when the mechanical need is limited. The researchers note that this sensory-to-reward link may underlie everyday habits such as nail-biting as well as clinical problems like bruxism and malocclusion.
On the clinical side, dopamine regulation is implicated in a range of oral issues. Bruxism refers to involuntary grinding or clenching of the teeth, while malocclusion describes misalignment between upper and lower teeth. Both can have significant effects on dental health and quality of life.
Published in the journal Neuron, the study explains how touch-sensitive neurons in the tissue around incisors project to a central relay that branches into two functional pathways: one to motor neurons that control jaw movement and tooth positioning, and another to midbrain dopamine centers that provide motivational drive. When the motivational pathway is blocked, mechanical tooth maintenance remains possible but becomes inefficient, increasing risk for tooth overgrowth and malocclusion in rodents.
“For animals with continuously growing incisors, motivation is essential to keep teeth and jaws properly aligned for survival,” Duan said. “Although human teeth do not grow lifelong, the same circuitry could still promote repetitive oral behaviors and influence oral health.”
The researchers point to clinical observations linking conditions that affect motivation and dopamine—such as autism, depression, and Parkinson’s disease—with elevated rates of malocclusion and bruxism. Parkinson’s treatments that increase dopamine availability can sometimes lead to new or worsened teeth grinding, consistent with the idea that dopamine-driven motivation contributes to these oral behaviors.
Emrick emphasized the translational potential: “Understanding this sensory-reward pathway offers a biological target for therapies. Rather than only protecting teeth mechanically with guards, future treatments might address the motivational signals in the brain that sustain damaging oral habits.”
The team is now exploring whether similar touch-reward circuits regulate other repetitive behaviors and whether targeting these pathways could help when such behaviors become maladaptive. Researchers from across the University of Michigan—spanning the Life Sciences Institute, Mechanical Engineering, Cell and Developmental Biology, and Molecular and Integrative Physiology—also contributed to the work. Federal support included funding from NIH institutes focused on neurological disorders and dental research.
Always be chomping
Rodents—mice, rats, squirrels, beavers, groundhogs and capybaras—gnaw constantly because their incisors grow without stopping. Regular gnawing wears teeth down to maintain a functional length and jaw alignment; without it, eating becomes difficult or impossible. The new research reframes this essential behavior as an outcome of sensorimotor and motivational integration rather than mere reflex.
Key Questions Answered:
A: Repetitive oral behaviors can activate a sensory-to-reward circuit that releases dopamine. When you bite your nails, the mouth and jaw sensations feed into a pathway that produces a feel-good response, making the habit hard to break.
A: Chewing provides oral sensory stimulation and helps maintain jaw musculature and oral tone. The same neural hardware that rewards gnawing in animals may make chewing soothing or habit-forming in people, even though it is not required to control tooth length.
A: Potentially. By showing that bruxism is driven in part by a brain circuit that motivates grinding, the findings open opportunities for treatments that target motivational signals rather than only protecting teeth mechanically.
Editorial Notes:
- This article was edited by a Neuroscience News editor.
- The referenced journal paper was reviewed in full.
- Additional context was added by staff to clarify human health implications.
About this sensory neuroscience research news
Author: Matt Davenport
Source: University of Michigan
Contact: Matt Davenport, University of Michigan
Image credit: Neuroscience News
Original research: Open access. Title: “A Touch-Guided Neural Circuit Regulates Motivated Gnawing to Maintain Dental Alignment,” published in Neuron. DOI: 10.1016/j.neuron.2026.01.021
Abstract
A Touch-Guided Neural Circuit Regulates Motivated Gnawing to Maintain Dental Alignment
How hindbrain circuits combine peripheral touch signals with central processing to regulate complex oral behaviors has been unclear. In rodents, gnawing produces localized tooth wear that offsets lifelong incisor growth. Whether this process depends on specific sensory inputs and active neural regulation was unresolved.
The study identifies somatostatin-expressing neurons in the spinal trigeminal nucleus oralis as a central relay that distributes tactile information to both motor and motivational circuits. These neurons receive input from S100b-positive Aβ low-threshold mechanoreceptors that innervate the incisor periodontium and project to jaw-closing motor neurons and, via the parabrachial nucleus, to the ventral tegmental area. Disrupting this pathway abolished gnawing and caused severe malocclusion, while activation elicited dopamine release in the nucleus accumbens. The findings redefine dental alignment as an active, touch-dependent, circuit-governed process and suggest malocclusion can be viewed as a disorder of sensorimotor-motivational integration.