The discovery comes from simultaneous quadruple-electrode recordings made while fruit flies performed feeding behavior. By monitoring several components of the motor circuit at once, the researchers were able to observe how neural activity moved through the chain that controls the fly’s feeding muscles. Their results reveal a feedforward disinhibition cascade, a circuit mechanism in which one active neuron releases another from inhibition, allowing activity to advance in a controlled direction.

Feeding in Drosophila depends on a series of rhythmic muscle contractions that move food through the animal’s feeding apparatus. These contractions must occur in the correct sequence: muscles involved in one stage of the action need to activate before those responsible for the next stage. If the timing is disrupted, the fly may continue making feeding movements, but the behavior can become inefficient or fail to transport food properly.

The study shows that the sequence begins when food-related sensory stimuli trigger rhythmic firing in a leading motor neuron. This neuron performs two functions at the same time. Through the release of glutamate, it directly excites its target muscle, contributing to the physical movement required for feeding. At the same time, it acts on a premotor element in the circuit in a way that reduces inhibitory control over the next motor neuron. The result is a precisely timed transition from one stage of the motor pattern to the next.

This arrangement is known as disinhibition because the crucial signal is not simply an excitatory command directed at the next neuron. Instead, the active motor neuron suppresses or bypasses an inhibitory influence, effectively opening a gate for the following motor neuron to fire. Once recruited, that neuron activates its own muscle target and promotes the release of the next step in the chain. The circuit therefore behaves like a wave, with activity traveling forward through the motor system rather than being imposed independently on every muscle.

The finding expands the conventional view of motor neurons. In many textbook descriptions, motor neurons sit at the end of a hierarchy: sensory information and brain circuits generate a command, premotor neurons shape it, and motor neurons transmit the final instruction to muscles. The new work suggests that at least some motor neurons are active organizers of behavior. They can combine direct control of muscle contraction with circuit-level regulation of downstream neurons, helping construct the motor pattern as it unfolds.

The researchers also examined whether the neural sequence was simply a reflection of how quickly the fly was pumping. Feeding movements can vary in rate depending on the animal’s behavioral context, the strength of the food stimulus, or the stage of the action. Yet behavioral measurements and computational modeling indicated that the ordered motor-neuron sequence remained distinct from the pumping rate. In other words, the circuit appears to preserve the identity and order of the feeding pattern even when the overall tempo changes.

That separation may be important for biological robustness. A motor system that tied every element of a sequence rigidly to one fixed rhythm could fail whenever an animal needed to speed up, slow down, pause, or adjust its behavior. By using a propagating circuit pattern that is partly independent of the absolute pumping rate, the fly may retain reliable coordination across changing circumstances. The same underlying sequence can potentially be executed at different speeds without losing the relationships between successive muscle activations.

The work also highlights why recordings from behaving animals are essential for understanding neural circuits. Isolated preparations can reveal how individual synapses operate, but they may not show how those connections contribute to a natural action. By combining electrophysiology, behavioral analysis, and computational modeling, the researchers linked cellular signaling to the timing of an entire feeding sequence. Their results suggest that motor neurons are not passive endpoints of command pathways but dynamic components of neural computation—cells capable of initiating, shaping, and propagating the patterns that make coordinated behavior possible.

Subject of Research: Motor-neuron control and coordination of feeding sequences in Drosophila

Article Title: Motor neurons organize Drosophila feeding sequences via a disinhibitory cascade

Article References: Sui, XW., Yi, JJ., Zhou, Y. et al. “Motor neurons organize Drosophila feeding sequences via a disinhibitory cascade.” Nature Neuroscience (2026). https://doi.org/10.1038/s41593-026-02412-y

Image Credits: AI Generated

DOI: https://doi.org/10.1038/s41593-026-02412-y

Keywords: Drosophila, motor neurons, feeding behavior, disinhibition, glutamate, premotor circuits, muscle coordination, neural sequences, motor control, computational modeling

The team explored how synchronous activation of CFs — those axonal projections originating from the inferior olive — modulates MLI activity and PCs’ calcium dynamics. Prior research acknowledged that synchronous CF activity occurs in vivo within parasagittal bands of PCs during sensory input, yet the mechanistic implications of such synchrony remained elusive. Utilizing a combination of in vivo recordings, optogenetics, multiphoton calcium imaging, and computational modeling, the investigators dissected the interplay between CF synchrony and disinhibitory circuits to unravel how this dynamic turns excitation into an enhanced plasticity trigger.

At the heart of this system lie two distinct subclasses of MLIs—MLI1s and MLI2s—that differentially shape PC responses. CFs preferentially excite MLI2s through glutamate spillover, which subsequently inhibit MLI1s. Given that MLI1s themselves are inhibitory to PCs, this cascade effectively reduces inhibitory pressure on PCs, creating a temporal window for heightened excitability called disinhibition. The result is a pronounced elevation in the amplitude of CF-evoked dendritic calcium transients, integral for inducing long-term depression (LTD) at granule cell (GrC) to PC synapses.

A pivotal finding came from observing natural sensory stimulation via airpuff stimuli that reliably elicited synchronous complex spikes (CSs) in neighboring PCs within a narrow temporal window of 5 milliseconds. When multiple CFs simultaneously fired, the subsequent suppression of MLI1 firing was robust and proportionate to the number of coactive CF inputs. Computational simulations recreated these dynamics, underscoring the critical role of the CF–MLI2 spillover synapse. The model revealed that without MLI2-mediated inhibition of MLI1s, the net effect reverted to PC inhibition rather than disinhibition, highlighting the indispensability of this microcircuit.

To probe this phenomenon in situ, the researchers harnessed two-photon calcium imaging in awake, behaving mice, capturing dendritic calcium transients in PCs during sensory-evoked CF activity. These experiments demonstrated that when neighboring CFs fired in synchrony, dendritic calcium signals exhibited significantly greater amplitude and duration compared to isolated CF activation. Intriguingly, the magnitude of calcium enhancement diminished as the spatial separation between PCs increased, reflecting the confined reach of this disinhibitory effect within tight parasagittal microzones.

The disinhibitory amplification was not only observed during single CS events but was markedly heightened during trials where multiple CF spikes occurred, yielding prolonged calcium signals that could potentiate synaptic plasticity more effectively. Such patterns resonate with the cerebellum’s need for precise temporal coordination during sensory processing and motor learning, where bursts of synchronous input may serve as a biological mechanism to signal salient events requiring adaptive responses.

This research compellingly positions the CF–MLI2–MLI1–PC pathway as a key modulator of synaptic plasticity, bridging gaps between known cellular interactions and observed behavioral outcomes. It illuminates how the cerebellum transcends a simple feedforward excitatory-inhibitory schema by leveraging disinhibitory motifs common in other brain regions to enable flexible sculpting of neuronal responses.

Beyond basic neuroscience, these insights have substantial implications for understanding cerebellar dysfunction in disorders where plasticity is compromised. The dynamic modulation of PC calcium signaling via CF synchrony could inform therapeutic strategies targeting cerebellar microcircuits in conditions such as ataxias and autism spectrum disorders.

Moreover, the study’s demonstration that sensory-evoked CF activity is naturally synchronous within parasagittal bands aligns with the cerebellum’s modular organization, whereby distinct microzones orchestrate fine-tuned behavioral adaptations. This modular disinhibitory mechanism could thus support parallel processing streams crucial for coordinating diverse sensorimotor tasks.

Future endeavors are anticipated to delve deeper into the molecular underpinnings governing the selective excitation of MLI2s and the temporal kinetics of inhibition within the CF–MLI–PC axis. Additionally, the development of genetic tools permitting specific silencing of MLI2s in vivo will be instrumental in dissecting their precise roles and confirming the exclusivity of this disinhibitory mechanism.

In conclusion, this comprehensive investigation redefines climbing fibres not merely as straightforward excitatory drivers of Purkinje cell activity but as sophisticated architects of disinhibition. By recruiting MLI2-mediated suppression of MLI1s, CFs create an enhanced window for calcium-mediated plasticity, essential for cerebellar learning. The integration of sensory-evoked synchrony with such disinhibitory control elegantly reconciles previous observations of CF synchrony’s potency in inducing cerebellar-dependent learning and plasticity.

This groundbreaking work exemplifies how circuit-level disinhibitory motifs empower the cerebellum’s remarkable computational flexibility. The elucidation of this CF–MLI2–MLI1–PC microcircuit motif paves the way for novel insights into the neural substrates of learning and may inspire innovative interventions for neurodevelopmental and degenerative disorders impacting cerebellar function.

Subject of Research: Cerebellar microcircuits mediating climbing fibre-induced disinhibition and dendritic calcium signaling in Purkinje cells

Article Title: Climbing fibres recruit disinhibition to enhance Purkinje cell calcium signals

Article References: Santos-Valencia, F., Lackey, E.P., Norton, A. et al. Climbing fibres recruit disinhibition to enhance Purkinje cell calcium signals. Nature (2026). https://doi.org/10.1038/s41586-026-10220-4

Image Credits: AI Generated

DOI: https://doi.org/10.1038/s41586-026-10220-4

Keywords: Climbing fibres, Purkinje cells, molecular layer interneurons, disinhibition, calcium signaling, cerebellar plasticity, synaptic learning, neural circuits, complex spikes, cerebellar microzones