Visual Cues Promote Head First Strategies During Walking Turns in Individuals With Parkinson's Disease.

Anticipatory eye movement promotes cranio-caudal sequencing during walking turns. Clinical groups, such as Parkinson's disease (PD), do not produce anticipatory eye movements, leading to increased risk of falls. Visual cues may promote anticipatory eye movement by guiding the eyes into the turn. This study examined if visual cues could train anticipatory eye movement. Ten neurotypical young adults and 6 adults with PD completed three blocks of walking trials. Trials were blocked by visual condition: non-cued baseline turns (5 trials), visually cued turns (10 trials), and non-cued post turns (5 trials). A Delsys Trigno (Delsys, Boston, MA) recorded horizontal saccades at 1024 Hz via electrooculography (EOG). Two Optotrak cameras (Northern Digital Inc., ON, Canada) captured body segment kinematics at 120 Hz. Initiation of segment rotation with respect to ipsilateral foot contact (IFC1) prior to the turn was calculated. Neurotypical young adults (NYA) produced typical cranio-caudal rotation sequences during walking turns. Eyes led (407 ms prior to IFC1), followed by the head (50 ms prior to IFC1), then trunk and pelvis. In contrast, PD produced no anticipatory eye or segment movement at baseline. During pre-trials the eyes moved 96 ms after IFC1 and segment movement was initiated by the pelvis followed by trunk and head segments. After visual cue training however, PD produced anticipatory eye movements 161 ms prior to IFC1, followed by the head 88 ms following IFC1 but ahead of trunk and pelvis onset. These results suggest visual cues assist in producing cranio-caudal control during walking turns in PD.

Increased obstacle clearance in people with ARCA-1 results in part from voluntary coordination changes between the thigh and shank segments.

Obstacle clearance can be a hazardous locomotor task if not coordinated with the utmost accuracy. The current study explored changes in leading limb segment coordination during obstacle clearance in a population with cerebellar ataxia using the planar law of intersegmental coordination. Eight participants with ARCA-1, caused by mutations in the SYNE-1 gene, and eight healthy adults stepped over obstacles. Healthy adults walked at natural speeds, as well as a velocity similar to the participants with cerebellar ataxia, resulting in three groups [healthy (H), matched velocity (MV) and cerebellar ataxia (CA)]. Elevation angles of the foot, shank and thigh in the sagittal plane were calculated. A principal component analysis was applied to limb segment trajectories, and a Fourier harmonic series was further used to determine temporal phase differences between adjacent segments. Although obstacle clearance was greater in the CA group, the planar nature of the 3D covariance plot of segment elevation angles, the covariance loop width and orientation did not differ between the CA, H and MV groups, suggesting that the planar patterns between elevation angles may not be heavily influenced by the cerebellum. Further analysis led to the observation of a nonlinear relationship between covariance loop width and thigh-shank fundamental harmonic phase difference, and a decrease in covariance loop width was observed when the fundamental harmonic phase difference between the thigh and shank segments is >90°. This study supports previous work that a greater safety margin is used in people with cerebellar ataxia when stepping over obstacles, but reveals a mechanism of segmental coordination to facilitate this increase in toe clearance. Further work is required to determine whether ataxia severity has an effect on the observed coordination variables.