Biology subjects

Refy, O.

Publications and source records attributed to Refy, O..

4 recordsLinked to original sources

bioRxiv2026

Theory Note: Emergence of a Proportional-Derivative Control Law from Two Coupled Oscillating Brain Circuits Near Synchrony

Oscillations and oscillatory synchronization are pervasive in motor circuits, where their role in rhythm generation and entrainment is well established but their role in feedback control of movement remains unclear. Here I show analytically that two oscillators of any type, coupled through a delayed interaction that is an odd function of their phase difference, necessarily implement a proportional-derivative (PD) control law in the near-synchrony limit. The proportional gain follows from the slope of the coupling function and the derivative gain is set by the coupling delay, so that PD control emerges with no additional machinery. Simulations confirm that such oscillators reproduce ideal PD step responses near synchrony and that control quality degrades systematically away from it. This establishes a direct, model-independent bridge between oscillatory synchronization and feedback control, and suggests concrete experimental signatures for candidate systems.

neuroscience↗

bioRxiv2026

Spinal cord population activity lacks rotational dynamics during an alternating isometric task in macaque

Recent studies report rotational population dynamics in spinal cord neuronal activity during rhythmic movements, suggesting computational principles shared with motor cortex. Here we show that primate cervical spinal cord activity does not exhibit rotational dynamics during an alternating single-joint isometric wrist task, instead it displays low-dimensional alternating population patterns. Positive controls confirm presence of rotational structure in motor cortex activity during the same task, indicating distinct computational strategies across the motor axis. Cortical neurons with post-spike effects on motoneurons had activity with dynamics resembling cortical rather than spinal populations.

neuroscience↗

bioRxiv2024

Changes in Gait Asymmetry May Be Caused by Adaptation of Spinal Reflexes

In a recent human study, we found that adaptive changes in step length asymmetry (SLA) are correlated with similar changes in the H-reflex gains of the leg muscles during split-belt treadmill locomotion. While this observation indicated a closer link between gait asymmetry and spinal reflex adaptation, it did not reveal their causal relationship. To better understand this relationship, here we use a neuromuscular model of human walking whose control relies primarily on spinal reflexes. Subjecting the model to split-belt treadmill locomotion with different combinations of belt speed and reflex gain adaptation patterns, we find that belt speed changes increase the variability in SLA but do not result in consistent SLA patterns as observed in human experiments, whereas reflex gain adaptations do. Furthermore, we find that the model produces SLA patterns similar to healthy adults when its reflex gains are adapted in a way similar to the H-reflex changes we observed in our previous human study. The model also predicts SLA patterns similar to the ones observed for cerebellar degeneration patients when the reflexes do not adapt beyond a sudden dip at the time the ipsilateral belt speed is lowered. Our results suggest that SLA does not arise from imposing belt speed changes but requires the adaptation of the reflex gains, and that the dynamic adaptation of these gains may be an essential part of human gait control when encountering unexpected environment changes such as the uneven speed changes in split-belt treadmill locomotion.

neuroscience↗

bioRxiv2022

Does Functional Recovery Imply Stable Circuitry in the Spinal Animal?

Spinal animals can regain locomotor function through gait training. However, the neural processes involved in this recovery are poorly understood. Here we use computer simulation to address if the reorganization of spinal circuits associated with the functional recovery leads to meaningful, stable circuitry function. Specifically, we develop a neuromuscular model of a spinalized rat whose circuitry can adapt based on two alternative Hebbian learning strategies, one designed to guide the circuitry back to its normal pre-injury state and the other designed to destabilize it and drive it into saturation. Exposing the model to simulated gait training, we find that both strategies lead to recovery of locomotor function as defined by the outcome measures reported in studies with spinal rats. If anything, the results obtained with the destabilizing learning strategy seem to agree more with animal observations, since it produces similarly excessive amplitudes in muscle activity. Our results suggest that gait training of spinalized animals does not necessarily effect a meaningful recovery of their spinal circuitry function. More experimental work should be directed to clarify this point, as it may have grave implications for the potential of gait rehabilitation in patients with motor complete injuries of the spinal cord.

neuroscience↗