Summary: Why does motor coordination continue to improve into adulthood when the brain’s motor circuits appear structurally mature by early adolescence? New research identifies a crucial piece of the puzzle: astrocytes. These star-shaped support cells undergo a late-adolescent transition in the cerebellum, taking over persistent inhibitory signaling (GABA) via Best1 channels. That cellular handoff reduces interference between neuronal populations and enables the independent, flexible, and precise movements characteristic of adult motor skill.
By shifting tonic inhibition from a neuron-dominated source to an astrocyte-driven mechanism, the brain stabilizes motor networks in a way that lets different muscle groups operate more independently. This change underlies improvements in agility, dexterity, and adaptive motor control that continue to develop after the basic wiring of the cerebellum has formed.
Key Facts
- Adolescent transition: During late adolescence in mice, the principal source of tonic GABA in cerebellar granule cells moves from neuronal spillover to astrocyte release through Bestrophin-1 (Best1) channels.
- Greater independence: Astrocyte-driven tonic inhibition reduces cross-talk between granule cell populations, allowing separate groups to process inputs with lower mutual interference.
- Persistent background signal: Tonic inhibition differs from phasic synaptic inhibition by providing a continuous background that stabilizes excitability across the network.
- Best1 is essential: Mice lacking Best1 fail to develop the adult pattern of diverse limb coordination and remain behaviorally similar to younger animals with more rigid movement coupling.
- Broader implications: The findings shift emphasis from neuron-only models of development to neuron–astrocyte interaction frameworks, with implications for understanding motor disorders and inspiring biologically informed control systems in robotics.
Source: Institute for Basic Science
Astrocytes drive late-stage maturation of coordinated movement
A collaborative team led by C. Justin Lee and Sungho Hong at the Institute for Basic Science (Center for Memory and Glioscience) together with Erik De Schutter of the Okinawa Institute of Science and Technology investigated how inhibitory signaling in the cerebellum changes across development and how that change affects motor coordination. Their experiments and computational modeling reveal that astrocytes become the dominant source of tonic GABA during late adolescence, and that this shift promotes more independent processing across cerebellar granule cell populations.
Motor coordination depends on combining movements across different body parts in flexible, context-dependent ways. Although cerebellar circuits reach structural maturity relatively early, behavioral coordination continues to improve well into adulthood. To address this apparent mismatch, the team examined tonic inhibition in cerebellar granule cells, one of the brain’s most numerous neuron types. Tonic inhibition—mediated by ambient GABA—provides a steady modulatory backdrop distinct from fast synaptic inhibition and is important for controlling neuronal excitability and information fidelity.
Electrophysiological recordings from young (3–4 week) and adult (8–12 week) mice showed that the magnitude of tonic current in granule cells remained broadly similar with age. However, the dominant cellular origin of that tonic GABA shifted markedly. In young mice, tonic GABA predominantly arose from spillover of synaptic release by inhibitory neurons. In adult mice, astrocytes contributed the principal tonic GABA through Best1 channels, an activity-independent release pathway.
The investigators also observed age-dependent changes in GABA transporter (GAT) activity. Increased GAT-mediated clearance in adults reduces the impact of neuron-derived spillover, favoring a steady astrocytic source of GABA. To test how this cellular rebalancing affects circuit computation, they built a large-scale computational model of the cerebellar network using physiological measurements from their experiments. Simulations showed that when tonic inhibition becomes astrocyte-driven, mutual inhibition between granule cell clusters weakens, making those clusters more independent in processing inputs.
Behavioral testing supported the model. Using a deep-learning posture analysis system that reconstructs three-dimensional mouse movement, the team found that adult mice display a wider repertoire of limb coordination patterns than younger animals. Adult mice lacking Best1 did not show this increased diversity: their limb movements remained more tightly coupled, resembling the less flexible coordination seen in juvenile animals. This confirms that astrocyte-mediated tonic inhibition is essential for the late-stage emergence of flexible motor skills.
Lee emphasizes that these results expand the traditional neuron-centric view of brain maturation to include critical astrocyte contributions. Understanding how astrocytes shape network dynamics may offer new avenues for studying developmental and degenerative motor disorders and could inform the design of movement control strategies in robotics that mimic the stabilizing, background role of astrocytes.
Key Questions Answered
Q: Why might you feel more coordinated in your 20s than at 13?
A: During late adolescence astrocytes increase their release of GABA, creating a persistent stabilizing background (tonic inhibition) that reduces signal interference between motor-related neuron groups. This allows body segments to move more independently and supports smoother, more flexible coordination.
Q: What happens if astrocytes fail to make this transition?
A: Without the astrocyte-driven source of tonic inhibition, animals retain more rigid, tightly coupled limb movements and show reduced ability to switch between different movement strategies—outcomes observed in Best1-deficient mice.
Q: Could this insight inform robotics or AI?
A: Possibly. Adding an astrocyte-like stabilization layer that provides continuous background modulation, alongside neuron-like processing units, could help engineered systems achieve more fluid and adaptable motor control.
Editorial Notes
- This article was edited by a Neuroscience News editor.
- The journal paper was reviewed in full by the editorial team.
- Additional contextual information was added by staff for clarity.
About this neuroscience research news
Author: William Suh
Source: Institute for Basic Science
Contact: William Suh – Institute for Basic Science
Image: The image is credited to Neuroscience News
Original Research: Open access. Title: “Cerebellar tonic inhibition orchestrates the maturation of information processing and motor coordination” by Jea Kwon, Sunpil Kim, Junsung Woo, Keiko Tanaka-Yamamoto, Oliver James, Erik De Schutter, Sungho Hong & C. Justin Lee. DOI: 10.1038/s12276-026-01657-8
Abstract
Tonic inhibition in cerebellar granule cells is crucial for maintaining information coding fidelity during motor coordination. It arises from both activity-dependent and activity-independent mechanisms, and the interplay of these mechanisms changes with age. While the net tonic inhibitory current remains stable, the primary source of ambient GABA shifts from synaptic spillover to astrocytic Best1-mediated release across adolescence (4–8 weeks) in mice. Computational modeling based on experimental data demonstrates that this switch reduces internally generated network activity that produces mutual inhibition between granule cell clusters receiving different inputs, thereby enhancing their independence. Consistent with model predictions, three-dimensional posture analysis shows an age-dependent increase in independent limb movements during spontaneous behavior, a change that is impaired in Best1-knockout mice. These findings highlight a late-stage developmental role for astrocyte-mediated tonic inhibition in shaping complex motor coordination.