Dorothy Cowie

Doorway-Provoked Freezing of Gait in Parkinson’s Disease

Freezing of gait in Parkinsons disease can be difficult to study in the laboratory. Here we investigate the use of a variable‐width doorway to provoke freeze behavior together with new objective methods to measure it. With this approach we compare the effects of anti‐parkinsonian treatments (medications and deep‐brain stimulation of the subthalamic nucleus) on freezing and other gait impairments. Ten “freezers” and 10 control participants were studied. Whole‐body kinematics were measured while participants walked at preferred speed in each of 4 doorway conditions (no door present, door width at 100%, 125%, and 150% of shoulder width) and in 4 treatment states (offmeds/offstim, offmeds/onstim, onmeds/offstim, onmeds/onstim). With no doorway, the Parkinsons group showed characteristic gait disturbances including slow speed, short steps, and variable step timing. Treatments improved these disturbances. The Parkinsons group slowed further at doorways by an amount inversely proportional to door width, suggesting a visuomotor dysfunction. This was not improved by either treatment alone. Finally, freeze‐like events were successfully provoked near the doorway and their prevalence significantly increased in narrower doorways. These were defined clinically and by 2 objective criteria that correlated well with clinical ratings. The risk of freeze‐like events was reduced by medication but not by deep‐brain stimulation. Freeze behavior can be provoked in a replicable experimental setting using the variable‐width doorway paradigm, and measured objectively using 2 definitions introduced here. The differential effects of medication and deep‐brain stimulation on the gait disturbances highlight the complexity of Parkinsonian gait disorders and their management.

Children’s Responses to the Rubber-Hand Illusion Reveal Dissociable Pathways in Body Representation

The bodily self is constructed from multisensory information. However, little is known of the relation between multisensory development and the emerging sense of self. We investigated this question by measuring the strength of the rubber-hand illusion in young children (4 to 9 years old) and adults. Intermanual pointing showed that children were as sensitive as adults to visual-tactile synchrony cues for hand position, which indicates that a visual-tactile pathway to the bodily self matures by at least 4 years of age. However, regardless of synchrony cues, children’s perceived hand position was closer to the rubber hand than adults’ perceived hand position was. This indicates a second, later-maturing process based on visual-proprioceptive information. Furthermore, explicit feelings of embodiment were related only to the visual-tactile process. These findings demonstrate two dissociable processes underlying body representation in early life, and they call into question current models of body representation and ownership in adulthood.

Doorway-provoked freezing of gait and its treatment in Parkinson’s disease.

Freezing of gait in Parkinsons disease can be difficult to study in the laboratory. Here we investigate the use of a variable‐width doorway to provoke freeze behavior together with new objective methods to measure it. With this approach we compare the effects of anti‐parkinsonian treatments (medications and deep‐brain stimulation of the subthalamic nucleus) on freezing and other gait impairments. Ten “freezers” and 10 control participants were studied. Whole‐body kinematics were measured while participants walked at preferred speed in each of 4 doorway conditions (no door present, door width at 100%, 125%, and 150% of shoulder width) and in 4 treatment states (offmeds/offstim, offmeds/onstim, onmeds/offstim, onmeds/onstim). With no doorway, the Parkinsons group showed characteristic gait disturbances including slow speed, short steps, and variable step timing. Treatments improved these disturbances. The Parkinsons group slowed further at doorways by an amount inversely proportional to door width, suggesting a visuomotor dysfunction. This was not improved by either treatment alone. Finally, freeze‐like events were successfully provoked near the doorway and their prevalence significantly increased in narrower doorways. These were defined clinically and by 2 objective criteria that correlated well with clinical ratings. The risk of freeze‐like events was reduced by medication but not by deep‐brain stimulation. Freeze behavior can be provoked in a replicable experimental setting using the variable‐width doorway paradigm, and measured objectively using 2 definitions introduced here. The differential effects of medication and deep‐brain stimulation on the gait disturbances highlight the complexity of Parkinsonian gait disorders and their management.

Urinary incontinence following deep brain stimulation of the pedunculopontine nucleus

Low-frequency deep brain stimulation (DBS) of the pedunculopontine nucleus (PPN) has been reported to improve akinesia and gait difficulties in patients with Parkinson’s disease (PD). We report on a patient with PD and L-dopa refractory gait symptoms who developed detrusor over-activity immediately after right PPN DBS. Proximity between caudal PPN and brainstem structures implicated in control of micturition is a possible explanation.

Development of visual control in stepping down.

Stepping down at a change of height is a fundamental part of human locomotion. At a novel step, this requires the transformation of visual information about a depth change into a stepping movement of appropriate size. However, little is known about this process or its development. We studied adults, 3- and 4-year-old children stepping down a single stair of variable height. We assessed how well stepping down was scaled to stair height using several kinematic measures. Of these, ‘kneedrop’ and ‘toedrop’ describe how far the leg has descended by the time it begins to ‘swing in’ in preparation for landing; and ‘toeheight (speedpeak)’ describes where the toe begins to decelerate. If visually controlled, their values should scale to the height of the stair. Under normal visual conditions, children scaled these movements to stair height as well as adults. In a second condition, participants closed their eyes just before stepping down to remove visual feedback during the step. Adults’ steps were barely affected. For 4-year olds, only toeheight (speedpeak) decreased. For 3-year olds, both toedrop and toeheight (speedpeak) scaled less well to stair height than normal. The results suggest that visuomotor processes for fine-tuned stepping control develop remarkably early, but are initially dependent on visual feedback.

Visual control of action in step descent

Visual guidance of forwards, sideways, and upwards stepping has been investigated, but there is little knowledge about the visuomotor processes underlying stepping down actions. In this study we investigated the visual control of a single vertical step. We measured which aspects of the stepping down movement scaled with visual information about step height, and how this visual control varied with binocular versus monocular vision. Subjects stepped down a single step of variable and unpredictable height. Several kinematic measures were extracted including a new measure, “kneedrop”. This describes a transition in the movement of the lower leg, which occurs at a point proportional to step height. In a within-subjects design, measurements were made with either full vision, monocular vision, or no vision. Subjects scaled kneedrop relative to step height with vision, but this scaling was significantly impaired in monocular and no vision conditions. The study establishes a kinematic marker of visually controlled scaling in single-step locomotion which will allow further study of the visuomotor control processes involved in stepping down.

Visually Guided Step Descent in Children with Williams Syndrome.

Individuals with Williams syndrome (WS) have impairments in visuospatial tasks and in manual visuomotor control, consistent with parietal and cerebellar abnormalities. Here we examined whether individuals with WS also have difficulties in visually controlling whole-body movements. We investigated visual control of stepping down at a change of level in children with WS (5-16-year-olds), who descended a single step while their movement was kinematically recorded. On each trial step height was set unpredictably, so that visual information was necessary to perceive the step depth and position the legs appropriately before landing. Kinematic measures established that children with WS did not use visual information to slow the leg at an appropriate point during the step. This pattern contrasts with that observed in typically developing 3- and 4-year-old children, implying severe impairment in whole-body visuomotor control in WS. For children with WS, performance was not significantly predicted by low-level visual or balance problems, but improved significantly with verbal age. The results suggest some plasticity and development in WS whole-body control. These data clearly show that visuospatial and visuomotor deficits in WS extend to the locomotor domain. Taken together with evidence for parietal and cerebellar abnormalities in WS, these results also provide new evidence for the role of these circuits in the visual control of whole-body movement.

The Development of Locomotor Planning for End-State Comfort

Walking through real-world environments involves using perceptual information to make complex choices between alternative routes, and this ability must develop through childhood. We examined performance and its development in one such situation. We used a novel ‘river-crossing’ paradigm analogous to manual ‘end-state comfort’ planning tasks, where an uncomfortable manoeuvre at the start of a movement is traded off for comfort at its end. Adults showed locomotor end-state comfort planning, adjusting feet at the start of a route in order to gain comfort at its end (crossing a manageable gap between two stepping stones). 3–6-year-olds also made this trade-off, but to a lesser degree than adults. The results suggest that end-state comfort is an important determiner of locomotor behaviour. Furthermore, they show that children as young as 3 years can use detailed visual information to form sophisticated locomotor plans.

Uncertainty, misunderstanding and the pedunculopontine nucleus

Human brain atlases reveal that the PPN straddles the pontomesencephalic junction and lies medial to the lemniscal system, 5 to 8 mm from the midline [1, 12, 13]. Our group has confirmed these lateral coordinates by an in-depth analysis of MRI-guided localisation of the PPN [18]. MRIguided and MRI-verified stereotactic targeting of the PPN in a cadaver has also provided histological proof of accurate anatomical targeting at 6 to 7 mm from the midline [19]. Our recent paper, the subject of this correspondence, provided meticulous postoperative proof of correct anatomical lead location using stereotactic MRI [2].

My true face : unmasking one's own face representation.

Face recognition has been the focus of multiple studies, but little is still known on how we represent the structure of ones own face. Most of the studies have focused on the topic of visual and haptic face recognition, but the metric representation of different features of ones own face is relatively unknown. We investigated the metric representation of the face in young adults by developing a proprioceptive pointing task to locate face landmarks in the first-person perspective. Our data revealed a large overestimation of width for all face features which resembles, in part, the size in somatosensory cortical representation. In contrast, face length was compartmentalised in two different regions: upper (underestimated) and bottom (overestimated); indicating size differences possibly due to functionality. We also identified shifts of the location judgments, with all face areas perceived closer to the body than they really were, due to a potential influence of the self-frame of reference. More importantly, the representation of the face appeared asymmetrical, with an overrepresentation of right side of the face, due to the influence of lateralization biases for strong right-handers. We suggest that these effects may be due to functionality influences and experience that affect the construction of face structural representation, going beyond the parallel of the somatosensory homunculus.