Summary: Researchers investigating sensory circuits in fruit flies have found that nerve cells responsible for sensing leg movement are actively suppressed when the insect walks or grooms. This state-dependent silencing acts like a switch, allowing the nervous system to move between a mode that stabilizes posture and one that supports rapid, dynamic behavior. A particular class of interneurons mediates this switch, ensuring flies maintain balance while remaining highly responsive to external disturbances.
The study shows that proprioceptive feedback is not fixed but flexibly gated: movement-related signals are inhibited during self-generated actions but remain available when limbs are moved passively. Insights from this mechanism help clarify how nervous systems balance stability and agility and may guide future approaches to treating motor disorders and enhancing rehabilitation strategies after injury.
Key Facts
- Proprioception Switch: In behaving flies, leg-motion sensors are silenced during active behaviors such as walking and grooming.
- Circuit Identified: A defined group of interneurons provides presynaptic inhibition that toggles sensory feedback between postural stabilization and ongoing movement.
- Clinical Potential: Understanding how proprioceptive signals are flexibly controlled could inform therapies for sensorimotor disorders and improve rehabilitation methods.
Source: University of Washington
In fruit flies, nerve cells that detect limb motion are turned off during walking and grooming. This on-off gating appears to let the insect’s nervous system switch between two complementary modes: one that enforces stabilizing reflexes and another that supports dynamic, voluntary movement.
John Tuthill, a neuroscientist at UW Medicine, used a human analogy to explain the functional significance: “Stabilizing reflexes let us stay upright on a swaying train, while an active mode allows us to move confidently across uneven ground.” Proprioception—the internal sense of body position and motion—underlies both types of control, and this work reveals how those signals are flexibly managed in a behaving animal.
Tuthill, a professor of neurobiology and biophysics at the University of Washington School of Medicine, leads a lab focused on the cells, signals and circuits that govern proprioception and motor control in Drosophila. The study, led by former postdoctoral researcher Chris Dallmann, was published Sept. 17 in Nature.
Using cell-type–specific calcium imaging in freely behaving flies, the team found that proprioceptors encoding joint position remain active across many behaviors, whereas the axons of proprioceptors that encode limb movement are specifically suppressed when the fly walks or grooms. This selective inhibition reduces self-generated motion signals while preserving sensitivity to external perturbations.
The researchers combined functional imaging with connectomic analysis to identify the circuit mechanism behind this gating. They found a class of GABAergic interneurons that provide presynaptic inhibition to movement-encoding proprioceptor axons. These interneurons act as a relay between descending brain inputs and the sensory axons, allowing context-dependent, leg-specific suppression of movement signals.
Importantly, the inhibition is linked to active, self-initiated movements and does not occur when a fly’s leg is passively moved. Imaging of the interneurons and their descending inputs showed activity correlated with self-generated motion but not with passive displacement, indicating the suppression is specifically tied to the animal’s own motor commands. Additional observations suggest the gating can be predictive: interneurons may become active before leg motion begins, following descending signals from the brain.
By selectively removing movement-related sensory signals during self-motion, flies may become more attuned to unexpected external events that could destabilize them, allowing faster corrective responses. This flexible tuning of proprioceptive feedback strikes a balance between the competing demands of stability and mobility and represents a fundamental principle for motor control across species.
“Understanding how proprioception is used to control the body is important for developing treatments for sensorimotor disorders and supporting rehabilitation after injury,” Tuthill said. The study’s demonstration of a clear anatomical and functional pathway for presynaptic inhibition of proprioception provides a mechanistic framework that could inspire future translational research.
Dallmann, now a Marie Sklodowska-Curie Fellow at the University of Wuerzburg in Germany, continues to explore how neural circuits shape movement control. The present work advances basic knowledge about how sensory feedback is gated in behaving animals and sets the stage for comparative studies in other systems.
About this neuroscience research news
Author: Leila Gray
Source: University of Washington
Contact: Leila Gray – University of Washington
Image: The image is credited to Neuroscience News
Original Research: Open access.
“Selective presynaptic inhibition of leg proprioception in behaving Drosophila” by John Tuthill et al. Nature
Abstract
Selective presynaptic inhibition of leg proprioception in behaving Drosophila
Coordinating limb movements requires continuous feedback from proprioceptive sensory neurons that detect joint position and motion. These feedback signals must be flexibly tuned depending on behavioral context, but the circuit mechanisms that implement such tuning have remained unclear.
Using calcium imaging in behaving Drosophila, we show that axons of position-encoding leg proprioceptors remain active across a broad range of behaviors, while axons of movement-encoding proprioceptors are specifically suppressed during walking and grooming.
Connectomic analysis reveals a class of interneurons that provide GABAergic presynaptic inhibition onto the axons of movement-encoding proprioceptors. These interneurons receive convergent input from parallel excitatory and inhibitory descending pathways, positioning them to drive context- and leg-specific suppression.
Calcium imaging of both the interneurons and their descending inputs confirms activity correlated with self-generated, but not passive, leg movements. Together, these results identify a neural circuit that selectively suppresses particular proprioceptive signals during self-initiated movements, revealing a mechanism for state-dependent control of sensory feedback.