Quincy J. Almeida

Freezing of gait in Parkinson's disease: a perceptual cause for a motor impairment?

While freezing of gait (FOG) is typically considered a motor impairment, the fact that it occurs more frequently in confined spaces suggests that perception of space might contribute to FOG. The present study evaluated how doorway size influenced characteristics of gait that might be indicative of freezing. Changes in spatiotemporal aspects of gait were evaluated while walking through three different-sized doorways (narrow (0.675 m wide × 2.1 m high), normal (0.9 m wide × 2.1 m high) and wide (1.8 m wide × 2.1 m high)) in three separate groups: 15 individuals with Parkinsons disease confirmed to be experiencing FOG at the time of test; 16 non-FOG individuals with Parkinsons disease and 16 healthy age-matched control participants. Results for step length indicated that the FOG group was most affected by the narrow doorway and was the only group whose step length was dependent on upcoming doorway size as indicated by a significant interaction of group by condition (F(4,88)=2.73, p<0.034). Importantly, the FOG group also displayed increased within-trial variability of step length and step time, which was exaggerated as doorway size decreased (F(4,88)=2.99, p<0.023). A significant interaction between group and condition for base of support measures indicated that the non-FOG participants were also affected by doorway size (similar to Parkinsons disease FOG) but only in the narrow doorway condition. These results support the notion that some occurrences of freezing may be the result of an underlying perceptual mechanism that interferes with online movement planning.

Symptom and gait changes after sensory attention focused exercise vs aerobic training in Parkinson's disease.

The current study compared lower‐limb aerobic training and sensory attention focused exercise (PD SAFEx) to a non‐exercise control group with the overall objective of determining which strategy would have a greater benefit for Parkinsons disease (PD) symptoms and gait. PD SAFEx was developed to focus on sensorimotor deficits identified in PD with the aim of increasing sensory feedback and body awareness, while the lower‐limb aerobic training utilized a specially designed semi‐recumbent elliptical device. Intervention groups (PD SAFEx, n = 18; aerobic, n = 13) exercised three times/week for 10–12 weeks, while nonexercise control participants (n = 15) maintained their regular activity level for 12 weeks. Outcome measures included the Unified Parkinsons disease rating scale motor section (UPDRS) administered by a blinded clinician; a posture and gait (PG) score (total of UPDRS items 27–31); the Timed‐Up‐and‐Go (TUG); and spatiotemporal aspects of self‐paced gait. PD SAFEx resulted in an improved UPDRS, PG score, and TUG (reached significance when participants with poor attendance were excluded) but not self‐paced gait. The lower‐limb aerobic training led to increased step length and velocity but had no change to disease severity. Since gait improvements were not combined with symptomatic changes, lower‐limb aerobic exercise may not be optimal for individuals with PD. Conversely, sensory‐based exercise (PD SAFEx) was beneficial, and led to improvement in symptoms and functional movement control.

Dopaminergic modulation of timing control and variability in the gait of Parkinson's disease

The basal ganglia have been implicated in timing control, yet the nature of timing disturbances in Parkinsons disease (PD) is poorly understood. We evaluated the influence of timing cues on spatiotemporal aspects of gait control and its variability, and the impact of dopaminergic treatment on timing. Three separate groups: 19 PD (OFF state); 24 PD (ON state); and 30 control participants were tested. Participants walked on a computerized carpet at four randomized and metronome‐controlled rates: self‐paced, 60, 80, or 100 steps/min. To our knowledge, this is the first study to demonstrate that medicated PD patients had poorer timing control than patients withdrawn from medication and healthy participants when modulating timing to an external stimulus. Increased step‐to‐step timing variability and deficits in mean temporal gait characteristics revealed that the medicated PD group (in contrast to nonmedicated PD group) performed least like healthy participants. This was observable in externally‐cued conditions, but not during self‐paced gait. Similar to previous research, step length contributed to overall slowness in PD, while temporal characteristics of gait did not. Interestingly, healthy participants increased stride length with each increase in cue rate, whereas both PD groups locked their step length regardless of temporal demand. Step‐to‐step variability differences between PD and healthy (e.g. step and double‐support time measurements) may be indicative of specific basal ganglia involvement in temporal control of gait.

Measurement instruments to assess posture, gait, and balance in Parkinson's disease: Critique and recommendations

Disorders of posture, gait, and balance in Parkinsons disease (PD) are common and debilitating. This MDS‐commissioned task force assessed clinimetric properties of existing rating scales, questionnaires, and timed tests that assess these features in PD.

A positive influence of vision on motor symptoms during sensory attention focused exercise for Parkinson's disease†

This study evaluated the effect of increased attention to sensory feedback during exercise. Two 12‐week exercise programs that differed only in the presence (PD SAFEx™) or absence (non‐SAFE control group) of increased attention focused on sensory feedback were compared. Participants were assessed symptomatically using the Unified Parkinsons Disease Rating Scale (UPDRS) before the start of the exercise program, immediately following the 12‐week program and after a 6‐week nonexercise washout period. Secondary outcome measures included the Timed‐Up‐and‐Go (TUG), Grooved Pegboard (GP) and velocity and step length of self‐paced gait. Both groups significantly improved on the TUG, GP, velocity, and step length, and this was maintained after a 6‐week washout period. Of additional interest, only the PD SAFEx™ program significantly improved motor symptoms (UPDRS). These gains were maintained in the PD SAFEx™ group 6 weeks after the exercise was stopped, while motor symptoms significantly worsened in the non‐SAFE group. These results suggest that increasing awareness of sensory feedback may be a critical factor that specifically impacts motor symptoms. Future work should strive to uncover the underlying neurophysiological mechanism behind this effect.

The relationship between motor planning and freezing of gait in Parkinson's disease

Objective To examine how a cued change in motor plan influences Parkinsons disease (PD) patients with freezing of gait (FOG) (PD FOG; n=10), compared with those without FOG (PD non-FOG; n=10) and healthy controls (n=10). Methods Participants walked through a doorway in three experimental conditions: no cue; cue before gait initiation; and cue after gait initiation. The light cue was presented at the end of the pathway and signified that individuals must walk to the cue, turn around and return to starting position. Results Step-to-step variability (a known precursor to FOG) revealed a significant main effect of group (F2,27=32.83, p<0.001), where PD FOG walked with greater step length variability than PD non-FOG and the control group. A significant interaction (F4,54=3.035, p=0.025) demonstrated that only the PD FOG group was most variable when the cue was present before gait initiation. Conclusion This study concludes that motor planning deficits affect gait, specifically in individuals who experience FOG. This may have important implications for the design of therapeutic interventions in PD FOG.

Plantar cutaneous sensory stimulation improves single-limb support time, and EMG activation patterns among individuals with Parkinson's disease.

Parkinsons disease is a chronic neurological disorder that results in gait and posture impairment. There is increasing evidence that these motor impairments may be partially due to deficits within the sensory system. In this study, the effects of a facilitatory insole that provides increased plantar sensory stimulation, was evaluated during gait, in a group of individuals with Parkinsons disease in comparison with healthy age-matched controls. Spatial-temporal parameters of gait were evaluated using an instrumented carpet, and muscle activation patterns were evaluated using surface EMG. All participants were tested with both a facilitatory (ribbed) insole and a conventional (flat) insole while walking 20 feet. Results indicated that the use of the facilitatory insole produced a significant increase in single-limb support time. Additionally, the muscle activation sequence of the tibialis anterior was normalized by the facilitatory insole, at the time of initial ground contact. These changes may lead to an overall improvement in gait pattern and stability, and suggest that the use of this type of facilitatory insole may be a useful treatment strategy for improving the gait of individuals with Parkinsons disease. This also provides support for the role of facilitation of the sensory system in improving motor output in individuals with Parkinsons disease.

Could Sensory Mechanisms Be a Core Factor That Underlies Freezing of Gait in Parkinson’s Disease?

The main objective of this study was to determine how manipulating the amount of sensory information available about the body and surrounding environment influenced freezing of gait (FOG), while walking through a doorway. It was hypothesized that the more limited the sensory information, the greater the occurrence of freezing of gait. Nineteen patients with Parkinsoǹs disease who experience freezing of gait (PD-FOG) walked through a doorway or into open space in complete darkness. The three doorway conditions included: (i) FRAME (DARK) – walking through the remembered door frame; (ii) FRAME - walking through the door with the door frame illuminated; (iii) FRAME+BODY - walking through the door (both the door and the limbs illuminated). Additionally, two conditions of walking away from the doorway included: (iv) NO FRAME (DARK) - walking into open space; (v) NO FRAME+BODY - walking into open space with the limbs illuminated, to evaluate whether perception (or fear) of the doorway might account for FOG behaviour. Key outcome measures included: the number of freezing of gait episodes recorded, total duration of freezing of gait, and the percentage of time spent frozen. Significantly more freezing of gait episodes occurred when participants walked toward the doorway in complete darkness compared to walking into open space (p<0.05). Similar to previous studies, velocity (p<0.001) and step length (p<0.0001) significantly decreased when walking through the door in complete darkness, compared to all other conditions. Significant increases in step width variability were also identified but only when walking into open space (p<0.005). These results support the notion that sensory deficits may have a profound impact on freezing of gait that need to be carefully considered.

Proprioceptive deficits in Parkinson's disease patients with freezing of gait.

Recent research has proposed that proprioceptive deficits may exist in Parkinsons disease (PD); however, proprioception has not been studied in those who experience freezing of gait (FOG). Proprioception was investigated through stimulation of proprioceptive receptors via patellar tendon vibration. In a force matching task to either 10% or 30% maximal voluntary contraction, response to vibration with and without vision of a force target was compared between 15 PD with FOG (PD-FOG), 16 PD without FOG (PD non-FOG), and 15 non-PD control participants (Controls). In a 15-s trial, vision of the target was provided for the first 10 s but in the last 5 s, four conditions were possible: (i) vision, no vibration; (ii) vision, vibration; (iii) no vision, no vibration; or (iv) no vision, vibration. The expected healthy response to vibration was an overshoot of the target. Controls and PD non-FOG did not perform significantly different with or without: vibration or vision. PD-FOG performed similarly to Controls and PD non-FOG in the baseline condition (i). Errors by PD-FOG on the other conditions (ii-iv) were significantly different from the baseline condition but were not significantly different from each other. The PD-FOG group significantly undershot the target when vibration was added [F((2,36))=4.8376, P<0.02] and when vision was removed [F((2,36))=4.8376, P<0.02]. It is suggested that any deviation from normal sensory availability contributes to severe deficits in PD-FOG.

Dissociating between sensory and perceptual deficits in PD: more than simply a motor deficit.

Although Parkinsons disease (PD) is traditionally considered a motor output disorder, recent evidence suggests that people with PD may have sensory and perceptual impairments that may underlie movement impairments. Yet there has not been any direct testing of perceptual judgments, especially when manipulating the sensory feedback on which these judgments are made. The present study investigated how perception might be influenced by sensory feedback to contribute to height estimations and obstacle stepping in PD relative to healthy age‐matched control participants. Perceptual judgment accuracy was evaluated by judging 3 typically encountered obstacle heights in 2 sensory feedback conditions: (1) vision of foot available and (2) without vision of foot (reliance on proprioceptive feedback to estimate height). Then participants proceeded to walk and step over the obstacle. Fifteen individuals with PD and 15 healthy control participants completed the task. As seen with toe elevation, toe elevation variability, and toe error measures, individuals with PD overestimated the obstacle height and were significantly more variable when relying solely on proprioception (in contrast to when vision was available) compared with healthy controls, although no differences between groups in obstacle crossing were found. These results support the notion that sensory deficits may contribute to inaccuracy of perceptual judgment and has the potential to contribute to gait behaviors such as tripping and falling, especially when vision is not available. Future studies should carefully consider the impact of sensory and perceptual deficits that might contribute to movement planning problems and consequentially movement impairments.