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Biology subjects

Sporn, S.

Publications and source records attributed to Sporn, S..

7 recordsLinked to original sources

bioRxiv2024

The effects of varying intensities of unilateral handgrip fatigue on bilateral movement

The human ability to maintain adequate movement quality despite muscle fatigue is of critical importance to master physically demanding activities of daily life and for retaining independence following motor impairments. Many real-life situations call for asymmetrical activation of extremity muscles leading to unilateral manifestations of muscle fatigue. Repeated unilateral handgrip contractions at submaximal force have been shown to be associated with neural dynamics in both contralateral and ipsilateral cortical motor areas and improved response times of the contralateral, unfatigued homologue in a button-press task. However, it remains unclear whether the observed improvement in contralateral response latency translates into higher-level benefits in movement quality. To investigate this, 30 healthy participants underwent unilateral handgrip fatiguing tasks at 5%, 50%, and 75% of maximum voluntary contraction (MVC) force. Subsequently, bimanual movement quality was assessed in an object-hit task using a Kinarm robot. The protocol at 50% and 75% of MVC elicited clear signs of muscle fatigue compared to the control condition (5%) measured by a decline in force, post-exercise deterioration in MVC, characteristic changes in surface electromyography magnitudes, and increases in ratings of perceived exertion. No change was observed on kinematic measures in the object-hit task for both arms indicating that unilateral handgrip fatigue did not elicit measurable effects on higher-level movement quality on the ipsilateral or contralateral homologue. Previously reported improvements on contralateral response latency were not found to translate into advanced movement quality benefits.

neuroscience↗

bioRxiv2024

Use of the non-paretic arm reflects a habitual behaviour in chronic stroke

BackgroundA proportion of stroke survivors use their affected arm less than might be expected based on their level of impairment. The resulting non-use of the affected arm has a negative impact on participation in neurorehabilitation and functional independence. However, non-use remains poorly understood. One possibility is that prioritising the non-paretic arm reflects a habit, despite residual functional capacity in the paretic arm. Methods30 chronic stroke survivors (Mean FM: 28.9 {+/-} 11.3) participated in a simplified version of the forced response paradigm, which reliably identifies the presence of a habit. Participants were asked to choose which arm to use to maximise points scored during a reaching task. During half of the trials, the presumed habit of using the non-paretic arm yielded more points, whereas in the other half using the non-paretic arm incurred a loss of points. Participants completed two versions of this task, once with unlimited response time available and once without. ResultsParticipants scored fewer points in the limited response condition compared to the unlimited response conditions. This difference was driven by a selective increase in the use of the non-paretic arm in trials where the paretic arm yielded more points. The results were not mediated by former hand dominance. ConclusionsOur results demonstrate that not using the non-paretic arm may reflect a habit response that is more readily triggered in demanding (e.g. time-limited) situations. This may explain why successful neurorehabilitation does not always result in a more functionally useful arm. Our results pave the way for targeted interventions such as habit breaking techniques to be included in clinical practise.

neuroscience↗

bioRxiv2023

Reward-based improvements in motor sequence learning are differentially affected by dopamine

Reward is a powerful tool to enhance human motor behaviour with research showing that it promotes motor sequence learning through increases in both motor vigour and movement fusion. Specifically, during a sequential reaching movement, monetary incentive leads to increased speed of each movement (vigour effect), whilst reward-based performance feedback increases speed of transition between movements (fusion effect). Therefore, motor sequence learning can be driven by distinct reward types with dissociable underlying processes. The neurotransmitter dopamine has been implicated to modulate motor vigour and regulate movement fusion. However, in humans, it is unclear if the same dopaminergic mechanism underlies both processes. To address this, we used a complex sequential reaching task in which rewards were based on movement times (MT). Crucially, MTs could be reduced via : 1) enhanced speed of individual movements (vigour effect) and/or 2) enhanced speed of transition between movements (fusion effect). 92 participants were randomly assigned to a reward and no reward group and were given either 2.5mg of the dopamine antagonist haloperidol or a placebo. Our results demonstrate that haloperidol impaired the reward-based effects on motor vigour whilst not affecting movement fusion. Thus, we illustrate that whilst both strategies are reward sensitive, they rely on dissociable mechanisms.

neuroscience↗

bioRxiv2021

Age-Related Differences in Reward-Based Modulation of Sequential Reaching Performance

Reward can increase the speed and accuracy of movements in both simple and sequential reaching tasks. Two mechanisms are thought to be responsible for this: an increase in maximum velocity, due to increased muscle stiffness, resulting in faster, but energetically inefficient, individual movements; or coarticulation - the blending of sub-movements into single, smoother, more energetically efficient movements. Older adults have shown reduced sensitivity to reward in decision paradigms, but there is little research relating reward and motor performance in older adults. Using a novel online sequential reaching task, we compared the effects of reward on motor performance between young (18-23 years) and older (65-79 years) participants. We found that movement time decreased across training in all groups, and reward invigorated this decrease in both age groups. This suggests that reward is a viable facilitator of motor performance to compensate for age-related motor decline and has the potential for use in the design of rehabilitation programmes for age-related motor deficits or disease.

neuroscience↗

bioRxiv2021

The dissociable effects of reward on sequential motor behaviour

Reward has consistently been shown to enhance motor performance however its beneficial effects appear to be largely unspecific. While reward has been shown to invigorate performance, it also enhances learning and/or retention. Therefore, a mechanistic account of the effects of reward on motor behaviour is lacking. Here we tested the hypothesis that these distinct reward-based improvements are driven by dissociable reward types: explicit reward (i.e. money) and performance feedback (i.e. points). Experiment 1 showed that explicit reward instantaneously improved movement times (MT) using a novel sequential reaching task. In contrast, performance-based feedback led to learning-related improvements. Importantly, pairing both maximised MT performance gains and accelerated movement fusion. Fusion describes an optimisation process during which neighbouring sequential movements blend together to form singular actions. Results from experiment 2 served as a replication and showed that fusion led to enhanced performance speed whilst also improving movement efficiency through increased smoothness. Finally, experiment 3 showed that these improvements in performance persist for 24 hours even without reward availability. This highlights the dissociable impact of explicit reward and performance feedback, with their combination maximising performance gains and leading to stable improvements in the speed and efficiency of sequential actions.

neuroscience↗

bioRxiv2020

Reward-based invigoration of sequential reaching

Seeking reward is a powerful tool for shaping human behaviour. While it has been demonstrated that reward invigorates performance of simple movements, its effect on more complex sequential actions is less clear. In addition, it is unknown why reward-based improvements for discrete actions are transient, i.e. performance gains are lost once reward is removed, but appear long lasting for sequential actions. We show across three experiments that reward invigorates sequential reaching performance. Driven by a reward-based increase in speed, movements also exhibited greater coarticulation, smoothness and a closer alignment to a minimum jerk trajectory. Critically, these performance gains were maintained across multiple days even after the removal of reward. We propose that coarticulation, the blending together of sub-movements into a single continuous action, provides a mechanism by which reward can invigorate sequential performance whilst also increasing efficiency. This change in efficiency appears essential for the retention of reward-based improvements in motor behaviour.

neuroscience↗

bioRxiv2018

Bursts and variability of beta oscillations mediate the effect of anxiety on motor exploration and motor learning

Anxiety results in sub-optimal motor performance and learning; yet, the precise mechanisms through which these modifications occur remain unknown. Using a reward-based motor sequence learning paradigm, we show that concurrent and prior anxiety states impair learning by biasing estimates about the hidden performance goal and the stability of such estimates over time (volatility). In an electroencephalography study, three groups of participants completed our motor task, which had separate phases for motor exploration (baseline) and reward-based learning. Anxiety was manipulated either during the initial baseline exploration phase or while learning. We show that anxiety induced at baseline reduced motor variability, undermining subsequent reward-based learning. Mechanistically, however, the most direct consequence of state anxiety was an underestimation of the hidden performance goal and a higher tendency to believe that the goal was unstable over time. Further, anxiety decreased uncertainty about volatility, which attenuated the update of beliefs about this quantity. Changes in the amplitude and burst distribution of sensorimotor and prefrontal beta oscillations were observed at baseline, which were primarily explained by the anxiety induction. These changes extended to the subsequent learning phase, where phasic increases in beta power and in the rate of long (> 500 ms) oscillation bursts following reward feedback were linked to smaller updates in predictions about volatility, with a higher anxiety-related increase explaining the biased volatility estimates. These data suggest that state anxiety alters the dynamics of beta oscillations during general performance, yet more prominently during reward processing, thereby impairing proper updating of motor predictions when learning in unstable environments.

neuroscience↗