Nonnekes, J. | Search bioRxiv

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.

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bioRxiv2022

The effect of walking with reduced trunk motion on dynamic stability in healthy adults

BackgroundMost people with Parkinsons Disease (PD) walk with a smaller mediolateral base of support (BoS) compared to healthy people, but the underlying mechanisms remain unknown. According to the extrapolated center of mass (XCoM) concept, a decrease in mediolateral XCoM excursion would require a smaller mediolateral BoS to maintain a constant margin of stability (MoS) and remain stable. As people with PD typically walk with reduced trunk motion, we hypothesized that the mediolateral MoS might stay the same despite a smaller BoS. Research questionAs proof of principle, we assess whether walking with reduced trunk motion results in a smaller step width in healthy adults, without altering the mediolateral MoS. MethodsFifteen healthy adults walked on a treadmill at preferred comfortable walking speed in two conditions. First, the regular walking condition without any instructions, and second, the reduced trunk motion condition with the instruction: Keep your trunk as still as possible. Treadmill speed was kept the same in the two conditions. Trunk kinematics, step width, mediolateral XCoM excursion and mediolateral MoS were calculated and compared between the two conditions. ResultsWalking with the instruction to keep the trunk still significantly reduced trunk kinematics. Walking with reduced trunk motion resulted in significant decreases in step width and mediolateral XCoM excursion, but not in the mediolateral MoS. Furthermore, step width and mediolateral XCoM excursion were strongly correlated during both conditions (r=0.887 and r=0.934). SignificanceThis study shows that walking with reduced trunk motion leads to a gait pattern with a smaller BoS in healthy adults, without altering the mediolateral MoS. Our findings indicate a strong coupling between CoM motion state and the mediolateral BoS. We expect that people with PD who walk narrow-based, have a similar mediolateral MoS as healthy people, which will be further investigated.

neuroscience↗