Biology subjects

Miall, R. C.

Publications and source records attributed to Miall, R. C..

9 recordsLinked to original sources

bioRxiv2026

Gaze Direction During Bimanual Reaching Is Associated with Changes in Relative Hand Speed

The control of visually guided bimanual movements is thought to represent a compromise between the drive for synchrony that characterizes many bimanual movements and the competing demands that characterize the constituent unimanual movements. As a result, while visually guided bimanual movements are found to be ostensibly synchronized, they also demonstrate subtle asynchronies. Here, we conducted a fine-grained analysis of bimanual reaching movements focusing on their relative synchrony as movements unfold and the relationship with gaze behavior. Our novel analysis revealed that participants frequently shifted their gaze laterally several times during bimanual reaches and that these gaze shifts were systematically associated with changes in the speed ratio of the two limbs. More specifically, we observed a strong association between gaze shifts and the speed ratio shifting toward the limb on the attended side. This pattern of behavior was seen regardless of hand dominance and target difficulty, suggesting that it may reflect a common visuomotor strategy during bimanual reaching.

neuroscience↗

bioRxiv2026

Cortico-cerebellar beta-band dynamics predict flexible motor timing

Flexible motor control requires that movements adapt to changing temporal contexts. Here, we test whether flexible timing is driven by context-dependent encoding across cortico-cerebellar circuits and how neural dynamics within these circuits enable accurate performance. To overcome the signal-to-noise limitations of conventional electro- and magnetoencephalography, we recorded whole-head neural dynamics using optically pumped magnetometer arrays (OPM-MEG). Participants learned a context-dependent task, executing manual button presses at time intervals 800 ms (T1) and 1,600 ms (T2), respectively, to avoid a periocular air puff, which was associated with an implicit conditioned eyeblink. We found that the motor cortex contralateral to the hand and bilateral cerebellar lobule VI dynamically encoded these intervals through beta-band (13-30 Hz) event-related desynchronisation (ERD) that precisely scaled with T1 and T2. The cerebellar trial-by-trial latency of the beta-band ERD predicted the timing of explicit manual actions. Finally, partial directed coherence revealed that baseline bidirectional beta-band coupling across the network transiently weakened from the ipsilateral cerebellum to the contralateral motor cortex during finger movement execution. Our findings show that cortico-cerebellar coupling functions as a gating mechanism and suggest that cerebellar circuits modulate cortical motor activity for flexible, accurate motor timing.

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bioRxiv2023

Implicit motor adaptation and perceived hand position without proprioception: A kinesthetic error may be derived from efferent signals

Implicit sensorimotor adaptation keeps our movements well-calibrated amid changes in the body and environment. We have recently postulated that implicit adaptation is driven by a perceptual error: the difference between the desired and perceived movement outcome. According to this perceptual re-alignment model, implicit adaptation ceases when the perceived movement outcome - a multimodal percept determined by a prior belief conveying the intended action, the motor command, and feedback from proprioception and vision - is aligned with the desired movement outcome. Here, we examined the role of proprioception in implicit motor adaptation and perceived movement outcome by examining individuals who lack proprioception. We used a modified visuomotor rotation task designed to isolate implicit adaptation and probe perceived outcome throughout the experiment. Surprisingly, implicit adaptation and perceived outcome were minimally impacted by deafferentation, posing a challenge to the perceptual re-alignment model of implicit adaptation.

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bioRxiv2022

Multi-session tDCS paired with passive mobilisation increases thalamo-cortical coupling during command following.

BackgroundTherapeutic options for patients with prolonged disorder of consciousness (PDOC) are limited. PDOC patients often exhibit a dissociation between their retained level of (covert) cognitive ability and their (overt) behavioural responses (cognitive-motor dissociation; CMD). This is linked to reduced coupling between thalamus and the primary motor cortex. ObjectiveTo assess whether pairing tDCS with a concurrent passive mobilisation protocol (designed to be feasible in PDOC) can influence thalamo-M1 dynamics and whether these changes are enhanced after multiple stimulation sessions. MethodsWe used Dynamic Causal Modelling (DCM) on functional magnetic resonance imaging (fMRI) data from 22 healthy participants to assess tDCS changes on effective connectivity within motor network areas during command-following. ResultsWe found that a single anodal tDCS session (paired with passive mobilisation of the thumb) decreased self-inhibition in the motor cortex, with five sessions further enhancing this effect. In addition, anodal tDCS increased thalamo-M1 excitation as compared to cathodal stimulation, with the effects maintained after 5 sessions. In turn, cathodal tDCS had opposing effects on these connections after one session but became more similar to anodal after 5. ConclusionsTogether, our results suggest that pairing anodal tDCS with passive mobilisation across multiple sessions may facilitate behavioural command-following in PDOC patients with CMD. More broadly, they offer a mechanistic window into the neural underpinnings of the cumulative effects of multi-session tDCS.

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bioRxiv2022

Neural activity in human eyeblink conditioning: an optically pumped magnetometer-based MEG study

There is a profound lack of electrophysiological data from the cerebellum in humans, as compared to animals, because the pervading perception is that it is difficult to record human cerebellar activity non-invasively using magnetoencephalography (MEG) or electroencephalography (EEG). We used on-scalp MEG based on optically pumped magnetometers (OP-MEG) to detect learning related cerebellar signals in a classical eyeblink conditioning paradigm. In four healthy human adults, we observed unconditioned stimulus-related evoked responses locating in the cerebellum. These evoked responses diminished during the acquisition of conditioned responses, which corresponds with previous observed changes of Purkinje cell activities in animals. We also observed evoked responses immediately before conditioned blinks in 3 out of 4 participants, which were also located in the cerebellum. We discuss the potential nature of these cerebellar evoked responses and future applications of OP-MEG to the studies of human cerebellar physiology.

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bioRxiv2021

Residual errors in visuomotor adaptation persist despite extended motor preparation periods

A consistent finding in sensorimotor adaptation is a persistent undershoot of full compensation, such that performance asymptotes with residual errors greater than seen at baseline. This behaviour has been attributed to limiting factors within the implicit adaptation system, which reaches a sub-optimal equilibrium between trial-by-trial learning and forgetting. However, recent research has suggested that allowing longer motor planning periods prior to movement eliminates these residual errors. The additional planning time allows required cognitive processes to be completed before movement onset, thus increasing accuracy. Here we looked to extend these findings by investigating the relationship between increased motor preparation time and the size of imposed visuomotor rotation (30{degrees}, 45{degrees} or 60{degrees}), with regards to the final asymptotic level of adaptation. We found that restricting preparation time to 0.35 seconds impaired adaptation for moderate and larger rotations, resulting in larger residual errors compared to groups with additional preparation time. However, we found that even extended preparation time failed to eliminate persistent errors, regardless of magnitude of cursor rotation. Thus, the asymptote of adaptation was significantly less than the degree of imposed rotation, for all experimental groups. Additionally, there was a positive relationship between asymptotic error and implicit retention. These data suggest that a prolonged motor preparation period is insufficient to reliably achieve complete adaptation and therefore our results provide support for the proposal that limitations within the implicit learning system contributes to asymptotic adaptation levels. New & NoteworthyResidual errors in sensorimotor adaptation are commonly attributed to an equilibrium between trial-by-trial learning and forgetting. Recent research suggested that allowing sufficient time for mental rotation eliminates these errors. In a number of experimental conditions, we show that while restricted motor preparation time does limit adaptation - consistent with mental rotation - extending preparation time fails to eliminate the residual errors in motor adaptation.

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bioRxiv2020

Adaptation of reach action to a novel force-field is not predicted by acuity of dynamic proprioception in either older or younger adults

Healthy ageing involves degeneration of the neuromuscular system which impacts movement control and proprioception. Yet the relationship between these sensory and motor deficits in upper limb reaching has not been examined in detail. Recently, we reported that age-related proprioceptive deficits were unrelated to accuracy in rapid arm movements, but whether this applied in motor tasks more heavily dependent on proprioceptive feedback was not clear. To address this, we have tested groups of younger and older adults on a force-field adaptation task under either full or limited visual feedback conditions and examined how performance related to dynamic proprioceptive acuity. Adaptive performance was similar between the age groups, regardless of visual feedback condition, although older adults showed increased after-effects. Physically inactive individuals made larger systematic (but not variable) proprioceptive errors, irrespective of age. However, dynamic proprioceptive acuity was unrelated to adaptation and there was no consistent evidence of proprioceptive recalibration with adaptation to the force-field for any group. Finally, in spite of clear age-dependent loss of spatial working memory capacity, we found no relationship between memory capacity and adaptive performance or proprioceptive acuity. Thus, non-clinical levels of deficit in dynamic proprioception, due to age or physical inactivity, do not affect force-field adaptation, even under conditions of limited visual feedback that might require greater proprioceptive control.

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bioRxiv2018

Using optically-pumped magnetometers to measure magnetoencephalographic signals in the human cerebellum

We test the feasibility of an optically pumped magnetometer (OPM)-MEG system for the measurement of human cerebellar activity. We show that the OPM system allows for excellent coverage of this structure by decreasing the average sensor-to-cerebellum distance by around 33% (16mm), compared to a standard MEG helmet. This closer proximity to the cerebellum approximately doubles the signal-to-noise ratio (SNR). As a proof of principle, we used an air-puff stimulus to the eyeball in order to elicit cerebellar evoked and induced responses that are well characterized in non-human models. In three subjects, we observed an evoked component at 50ms post stimulus, which originates in the cerebellum (predominantly ipsilateral). This response was followed by a second component at 100ms post stimulus (predominantly contra-lateral). Sensory stimulation also elicited an event-related broadband spectral power change in the ipsilateral cerebellum at ~100ms in all subjects. We conclude that the OPM-MEG technology offers a promising way to advance the understanding of the information processing mechanisms in the human cerebellum.

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bioRxiv2018

Proprioceptive Deficits in Inactive Older Adults are not Reflected in Discrete Reaching Performance

During normal healthy ageing there is a decline in the ability to control simple movements, characterised by increased reaction times, movement durations and variability. There is also growing evidence of age-related proprioceptive loss which may contribute to these impairments. However this relationship has not been studied in detail for the upper limb. We recruited 20 younger adults (YAs) and 31 older adults (OAs) who each performed 2 tasks on a 2D robotic manipulandum. The first assessed dynamic proprioceptive acuity using active, multi-joint movements towards visually presented targets, with movement constrained by the robot to a predefined path. Participants made perceptual judgements of the lateral position of the unseen arm. The second was a rapid motor task which required fast, accurate movements to the same targets in the absence of hand position visual feedback, and without constraint by the robot. We predicted that the variable proprioceptive error (uncertainty range) from Task 1 would be increased in physically inactive OAs and would predict increased movement variability in Task 2. Instead we found that physically inactive OAs had larger systematic proprioceptive errors (bias). Neither proprioceptive acuity nor bias was related to motor performance in either age group. We suggest that previously reported estimates of proprioceptive decline with ageing may be exaggerated by task demands and that the extent of these deficits is unrelated to discrete, ballistic movement control. The relationship of dynamic proprioceptive acuity with movement control in tasks which emphasise online proprioceptive feedback for performance is still unclear and warrants further investigation.

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