Biology subjects

Weerdesteyn, V.

Publications and source records attributed to Weerdesteyn, V..

5 recordsLinked to original sources

bioRxiv2025

Effects of aging on upper body express visuomotor responses while reaching under varying postural demands

Humans can react remarkably quickly to novel or displaced visual stimuli when time is of the essence. Such movements are thought to be initiated by a subcortical fast visuomotor network, but it is unclear how this network declines with age. Past work in the upper limb has detailed delayed reaching corrections to jumped visual stimuli in the elderly, but the underlying mechanisms contributing to these changes of the fast visuomotor network are poorly understood. Conversely, work in the lower limb has reported delayed muscle recruitment during obstacle avoidance, but such findings may be confounded by age-related challenges in postural control. The output of the fast visuomotor network can be quantified by measuring express visuomotor responses (EVRs), which are the earliest and very short-latency bursts of muscle activity that follow visual target presentation. Here, we compare the prevalence, latency, and magnitude of EVRs in elderly (58-80 years old) and younger (18-25 years old) participants performing visually-guided reaches. We also investigated the impact of postural stability by having participants reach either while seated on a stable chair, or on a wobble stool. Both the elderly and younger cohorts expressed EVRs, but EVRs in the elderly were comparatively less frequent, and had longer latencies and smaller magnitude. Postural instability had no effects on these outcomes. Our results suggest age-related declines in the fast visuomotor network, potentially resulting from deterioration of underlying circuits and a prioritization of stability over speed. This study serves as an important standard for future research investigating clinical populations. HighlightsO_LIDo aging and postural stability affect express visuomotor responses (EVRs)? C_LIO_LIEVRs were recorded from the pectoralis muscle during rapid goal-directed reaches C_LIO_LIEVRs were smaller and delayed, and movement was slower, in elderly participants C_LIO_LIAge-related differences were independent of our postural stability manipulation C_LIO_LIOur results suggest age-related declines of the fast visuomotor network C_LI

neuroscience↗

bioRxiv2024

Cortical dynamics underlying initiation of rapid steps with contrasting postural demands

Our ability to flexibly initiate rapid visually-guided stepping movements can be measured in the form of express visuomotor responses (EVRs), which are short-latency ([~]100ms), goal-directed bursts of lower-limb muscle activity. Interestingly, we previously demonstrated that recruitment of anticipatory postural adjustments (APAs) interacted with the subcortically-generated EVRs in the lower limb, suggesting context-dependent top-down modulation. We investigated the associated cortical dynamics prior to and during rapid step initiation towards a salient visual target in twenty-one young, healthy individuals. We adopted two contrasting postural conditions by manipulating the stepping direction. Anterolateral steps involved low postural demands, whereas anteromedial stepping involved high postural demands. We recorded high-density EEG, surface electromyography from gluteus medius and ground-reaction forces. Independent component analysis and time-frequency statistics revealed significant, yet relatively modest differences between conditions in preparatory cortical dynamics, most evidently in primary motor areas. Following target presentation, we observed stronger theta and alpha power enhancement in the supplementary motor area, and stronger alpha and beta power decrease in primary motor, parietal and occipital clusters during APA recruitment that preceded steps under high postural demands. We found no differences in (pre)frontal areas associated with the observed EVR suppression in the high postural demand condition. Together, our findings point towards greater cortical involvement in step initiation under high postural demands as compared to more reflexive, stimulus-driven steps. This notion may be particularly relevant for populations where postural control is impaired by age or disease, as more cortical resources may need to be allocated during stepping.

neuroscience↗

bioRxiv2024

Lower-limb express visuomotor responses are spared in Parkinson's Disease during step initiation from a stable position

While motor impairments have been extensively studied in Parkinsons Disease, rapid visuomotor transformations for flexible interaction with the environment have received surprisingly little attention. In recent years, such rapid visuomotor transformations have been studied in the form of express visuomotor responses (EVRs), which are goal-directed bursts of muscle activity that are thought to originate from superior colliculus, reaching the periphery via the tecto-reticulospinal pathway. Here, we examined EVRs in the lower limbs during goal-directed step initiation in 20 people with Parkisons Disease (PwPD) and 20 age-matched healthy control participants (HC). As lower-limb EVRs in the young have been shown to interact with postural control - which is often affected in PwPD - we manipulated the postural demands by varying initial stance width and target location. In the low postural demand condition, EVRs were robustly present in both the PwPD (17/20) and HC (16/20) group. However, when postural demands were high, EVRs were largely absent in both groups and, instead, strong anticipatory postural adjustments (APAs) were required prior to foot off. EVR magnitudes were, on average, stronger in PwPD compared to HC, but they decreased with increasing disease severity, suggesting that the EVR network may become compromised or down-regulated in later stages of the disease. While APA magnitudes were smaller in PwPD compared to HC, subsequent stepping performance (step reaction time, duration, size, velocity) was remarkably similar between the two groups. We suggest that the EVR network may be upregulated in the early stages of Parkinsons disease in order to compensate for some of the emerging motor deficits experienced in daily life.

neuroscience↗

bioRxiv2024

Startling acoustic stimuli hasten choice reaching tasks by strengthening, but not changing the timing of, express visuomotor responses

Responding to an external stimulus takes [~]200 ms, but this can be shortened to as little as [~]120 ms with the additional presentation of a startling acoustic stimulus. This phenomenon is hypothesized to arise from the involuntary release of a prepared movement (a StartReact effect). However, a startling acoustic stimulus also expedites rapid mid-flight, reactive adjustments to unpredictably displaced targets which could not have been prepared in advance. We surmise that for such rapid visuomotor transformations, intersensory facilitation may occur between auditory signals arising from the startling acoustic stimulus and visual signals relayed along a fast subcortical network. To explore this, we examined how a startling acoustic stimulus shortens reaction times in a task that produces express visuomotor responses, which are brief bursts of muscle activity that arise from a fast tectoreticulospinal network. We measured express visuomotor responses on upper limb muscles in humans as they reached either toward or away from a stimulus in blocks of trials where movements could either be fully prepared or not, occasionally pairing stimulus presentation with a startling acoustic stimulus. The startling acoustic stimulus reliably produced larger but fixed-latency express visuomotor responses in a target-selective manner, and also shortened reaction times, which were equally short for prepared and unprepared movements. Our results provide insights into how a startling acoustic stimulus shortens the latency of reactive movements without full motor preparation. We propose that the reticular formation is the likely node for intersensory convergence during the most rapid transformations of vision into targeted reaching actions. KEY POINTSO_LIA startling acoustic stimulus (SAS) shortens reaction times by releasing fully prepared motor programs (the StartReact effect), but can also hasten responses in reflexive tasks without any movement preparation C_LIO_LIHere we measure the effect of a SAS on reaction times and upper limb muscle recruitment in a reflexive reaching task, focusing on express visuomotor responses that are evoked by visual target presentation and demarcate activity along a subcortical tectoreticulospinal pathway C_LIO_LIA SAS robustly increased the magnitude of express visuomotor responses without changing their timing, and this increase was tightly related to the subsequent reaction time even in the absence of motor preparation C_LIO_LIOur results attest to intersensory facilitation within the tectoreticulospinal pathway, which provides the shortest pathway mediating visuomotor transformations for reaching C_LIO_LIThese results reconcile discrepant findings by emphasizing the importance of intersensory facilitation in SAS-induced hastening of reaction times in reflexive tasks C_LI

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bioRxiv2022

Evidence for an Intricate Relationship Between Express Visuomotor Responses, Postural Control and Rapid Step Initiation in the Lower Limbs

Recent work has described express visuomotor responses (EVRs) on the upper limb. EVRs are directionally-tuned bursts of muscle activity that occur within 100 ms of visual stimulus appearance, facilitating rapid reaching. Rapid stepping responses are also important in daily life, and while there is evidence of EVR expression on lower limbs, it is unknown whether lower-limb EVRs are influenced by increased postural demands. Here, we investigate the interaction between stepping-related EVRs and anticipatory postural adjustments (APAs) that typically precede step initiation. 16 healthy young subjects rapidly stepped towards visual targets presented in front of the left or right foot. We recorded bilateral surface EMG of gluteus medius (GM), a muscle involved in both APAs and stepping, and bilateral ground reaction forces. Two conditions were introduced: an anterolateral or anteromedial stepping condition with reduced or increased postural demands, respectively. In the anterolateral stepping condition, EVRs were robustly and strongly present in stance-side GM, and ground reaction forces revealed strongly decreased expression of APAs. Larger EVRs preceded shorter RTs, consistent with EVRs facilitating step initiation. In contrast, in the anteromedial stepping condition, EVRs were largely absent, and ground reaction forces revealed the consistent expression of APAs. When occasionally present, EVRs in the anteromedial stepping condition preceded larger APAs and longer RTs. Thus, while EVRs in lower limbs can facilitate rapid stepping, their expression is normally suppressed when postural stability is low. Failing to appropriately suppress EVRs in such situations disrupts postural stability, necessitating larger compensatory APAs and leading to longer stepping RTs. Key PointsO_LIExpress visuomotor responses (EVRs) are directionally tuned bursts of muscle activity that aid the rapid initiation of a goal-directed movement. They are thought to be relayed to the motor periphery along a rapid subcortical pathway involving the superior colliculus. C_LIO_LIWhile EVRs have predominantly been studied in reaching, it is unclear whether EVRs extend to the lower extremities and if so, whether increasing the postural demands of a stepping task interfere with lower-limb EVR expression. C_LIO_LIWe found that when postural demands were low, strong EVRs in the hip abductor muscle gluteus medius facilitated a rapid stepping response. Conversely, when postural demands were high, EVRs hindered a fast stepping response, as they necessitated larger, compensatory postural adjustments prior to step onset. C_LIO_LIThese results help us better understand the interaction between ultra-rapid visuomotor transformations in the EVR network, the postural demands of a given stepping task, and subsequent step initiation. C_LI

neuroscience↗