Rehearsal by eye movement improves visuomotor performance in cerebellar patients

Oculomotor Impairments in Children After Posterior Fossa Tumors Treatment

Posterior fossa tumors (PFT) are the most common pediatric brain tumors, and the study of the somatic and cognitive status of PFT survivors still remains a critical problem. Since cerebellar damage can affect eye movement centers located in the vermis and hemispheres, such patients suffer from disturbances in visual perception, visual-spatial functions, reading, etc. Our investigation aimed at describing oculomotor impairments in PFT survivors linked to core oculomotor functions assessed through eye tracking method: gaze holding, reflexive saccades, and organization of voluntary saccades and their dependency on age at tumor diagnosis. Also, we investigated the relationship between oculomotor functions and ataxia measured with International Cooperative Ataxia Rating Scale (ICARS). A total of 110 children (patients and age-matched healthy controls, aged 9-17 years old) participated in the study. We found that the earlier the child had a tumor, the more impaired gaze holding (p = 0.0031) and fewer isometric saccades (p = 0.035) were observed at the time of examination. The above-mentioned functions in healthy controls improved with age. Visual scanning was also impaired compared to controls but was not related to age at diagnosis. A positive correlation between ICARS scores and number of hypermetric saccades (r = 0.309, p = 0.039), but no correlation with the number of hypometric saccades (r = - 0.008, p = 0.956). Furthermore, number of hypometric saccades did not differ between patients and controls (p = 0.238). Thus, primarily hypermetric saccades can be considered a prominent oculomotor symptom of cerebellar tumors. Our study provides basis for new methods of PFT diagnosis and rehabilitation procedure evaluation, both playing essential roles in modern pediatric neurooncology.

Assessment and tailored physical rehabilitation approaches in persons with cerebellar impairments targeting mobility and walking according to the International Classification of Functioning: a systematic review of case-reports and case-series

PURPOSE

Cerebellar impairment (CI) manifests from different etiologies resulting in a heterogenic clinical presentation affecting walking and mobility. Case-reports were reviewed to provide an analytical clinical picture of persons with CI (PwCI) to differentiate cerebellar and non-cerebellar impairments and to identify interventions and assessments used to quantify impact on walking and mobility according to the International Classification of Functioning, Disability and Health (ICF).

MATERIALS AND METHODS

Literature was searched in PubMed, Web Of Science and Scopus. Case-reports conducting physical rehabilitation and reporting at least one outcome measure of ataxia, gait pattern, walking or mobility were included.

RESULTS

28 articles with a total of 38 different patients were included. Etiologies were clustered to: spinocerebellar degenerations, traumatic brain injuries, cerebellar tumors, stroke and miscellaneous. The interventions applied were activity-based, including gait and balance training. Participation based activities such as tai chi, climbing and dance-based therapy had positive outcomes on mobility. Outcomes on body function such as ataxia and gait pattern were only reported in 22% of the patients.

CONCLUSIONS

A comprehensive test battery to encompass the key features of a PwCI on different levels of the ICF is needed to manage heterogeneity. Measures on body function level should be included in interventions.

Gaze behaviour during walking in young adults with developmental coordination disorder

BACKGROUND

Individuals with Developmental Coordination Disorder (DCD) experience difficulty with motor coordination and this affects their daily functioning. Research indicated inferior visuospatial processing and oculomotor control in DCD. As visual information is essential for locomotor control, more insight in the gaze behaviour of this population during walking is required and crucial for gaze training interventions as a possible means to improve daily functioning of children and adults with DCD.

AIM

This study explored differences and similarities in gaze behaviour during walking between typically developing young adults and those with DCD.

METHODS AND PROCEDURES

Ten young adults with DCD (age: 22.13 ± 0.64) and ten typically developing individuals (age: 22.00 ± 1.05) completed a walking task in which they had to place their feet on irregularly placed targets wearing eye tracking glasses.

OUTCOMES AND RESULTS

Individuals with DCD walked slower and demonstrated a different gaze strategy compared to their neurotypical peers as they fixated almost each and every target sequentially. Typically developing individuals, on the other hand, directed gaze further along the path and often fixated areas around the targets.

CONCLUSIONS AND IMPLICATIONS

Despite adequate walking performance in daily situations in young adults with DCD, fundamental control deficits persist into adulthood. WHAT THIS PAPER ADDS?: This paper is the first to demonstrate differences in gaze behaviour between young adults with DCD and typically developing individuals in a task that resembles a task of daily living, as previous research focused on laboratory tasks. This is a valuable finding as DCD has a clear impact on the daily life. Furthermore, this study demonstrated that the fundamental control deficits of DCD persist into adulthood despite frequent performance and practice of these daily tasks. Lastly, these findings might contribute to the therapeutic potential of gaze training interventions to improve the daily functioning of children and adults with DCD.

Guidelines on the diagnosis and management of the progressive ataxias

The progressive ataxias are a group of rare and complicated neurological disorders, knowledge of which is often poor among healthcare professionals (HCPs). The patient support group Ataxia UK, recognising the lack of awareness of this group of conditions, has developed medical guidelines for the diagnosis and management of ataxia. Although ataxia can be a symptom of many common conditions, the focus here is on the progressive ataxias, and include hereditary ataxia (e.g. spinocerebellar ataxia (SCA), Friedreich’s ataxia (FRDA)), idiopathic sporadic cerebellar ataxia, and specific neurodegenerative disorders in which ataxia is the dominant symptom (e.g. cerebellar variant of multiple systems atrophy (MSA-C)). Over 100 different disorders can lead to ataxia, so diagnosis can be challenging. Although there are no disease-modifying treatments for most of these entities, many aspects of the conditions are treatable, and their identification by HCPs is vital. The early diagnosis and management of the (currently) few reversible causes are also of paramount importance. More than 30 UK health professionals with experience in the field contributed to the guidelines, their input reflecting their respective clinical expertise in various aspects of ataxia diagnosis and management. They reviewed the published literature in their fields, and provided summaries on “best” practice, including the grading of evidence available for interventions, using the Guideline International Network (GIN) criteria, in the relevant sections.

A Guideline Development Group, consisting of ataxia specialist neurologists and representatives of Ataxia UK (including patients and carers), reviewed all sections, produced recommendations with levels of evidence, and discussed modifications (where necessary) with contributors until consensus was reached. Where no specific published data existed, recommendations were based on data related to similar conditions (e.g. multiple sclerosis) and/or expert opinion. The guidelines aim to assist HCPs when caring for patients with progressive ataxia, indicate evidence-based (where it exists) and best practice, and act overall as a useful resource for clinicians involved in managing ataxic patients. They do, however, also highlight the urgent need to develop effective disease-modifying treatments, and, given the large number of recommendations based on “good practice points”, emphasise the need for further research to provide evidence for effective symptomatic therapies.

These guidelines are aimed predominantly at HCPs in secondary care (such as general neurologists, clinical geneticists, physiotherapists, speech and language therapists, occupational therapists, etc.) who provide care for individuals with progressive ataxia and their families, and not ataxia specialists. It is a useful, practical tool to forward to HCPs at the time referrals are made for on-going care, for example in the community.

The Relationship between Saccades and Locomotion

Human locomotion involves a complex interplay among multiple brain regions and depends on constant feedback from the visual system. We summarize here the current understanding of the relationship among fixations, saccades, and gait as observed in studies sampling eye movements during locomotion, through a review of the literature and a synthesis of the relevant knowledge on the topic. A significant overlap in locomotor and saccadic neural circuitry exists that may support this relationship. Several animal studies have identified potential integration nodes between these overlapping circuitries. Behavioral studies that explored the relationship of saccadic and gait-related impairments in normal conditions and in various disease states are also discussed. Eye movements and locomotion share many underlying neural circuits, and further studies can leverage this interplay for diagnostic and therapeutic purposes.

Cerebellar ataxia

The cerebellum plays an integral role in the control of limb and ocular movements, balance, and walking. Cerebellar disorders may be classified as sporadic or hereditary with clinical presentation varying with the extent and site of cerebellar damage and extracerebellar signs. Deficits in balance and walking reflect the cerebellum's proposed role in coordination, sensory integration, coordinate transformation, motor learning, and adaptation. Cerebellar dysfunction results in increased postural sway, hypermetric postural responses to perturbations and optokinetic stimuli, and postural responses that are poorly coordinated with volitional movement. Gait variability is characteristic and may arise from a combination of balance impairments, interlimb incoordination, and incoordination between postural activity and leg movement. Intrinsic problems with balance lead to a high prevalence of injurious falls. Evidence for pharmacologic management is limited, although aminopyridines reduce attacks in episodic ataxias and may have a role in improving gait ataxia in other conditions. Intensive exercises targeting balance and coordination lead to improvements in balance and walking but require ongoing training to maintain/maximize any effects. Noninvasive brain stimulation of the cerebellum may become a useful adjunct to therapy in the future. Walking aids, orthoses, specialized footwear and seating may be required for more severe cases of cerebellar ataxia.

Controlling Posture and Vergence Eye Movements in Quiet Stance: Effects of Thin Plantar Inserts

The purpose of this study was to assess properties of vergence and saccade eye movements as well as posture in quiet stance, and the effects of thin plantar inserts upon postural and oculomotor control. The performances of 36 young healthy subjects were recorded by a force platform and an eye tracker in three testing conditions: without plantar stimulation, with a 3 millimetre-thick plantar insert, either a Medial or a Lateral Arch Support (MAS/LAS). The results showed a decrease of the Surface and Variance of Speed and a more posterior position of the CoP with either stimulation compared with the control condition. The fractal analysis showed a decrease with MAS. Wavelet analysis in the time-frequency domain revealed an increase in the Cancelling Time of the low frequency band with MAS. These results suggest a better stability for a lower energy cost. Concerning eye movements, the inserts influenced only vergence (not saccades): MAS caused an increase of the phasic amplitude of divergence, and conversely a decrease of the tonic amplitude. In contrast, LAS caused an increase of the tonic amplitude of convergence. Thus, MAS renders divergence less visually driven, while LAS renders convergence more visually driven. We conclude that the CNS uses the podal signal for both postural and vergence control via specific mechanisms. Plantar inserts have an influence upon posture and vergence movements in a different way according to the part of the foot sole being stimulated. These results can be useful to clinicians interested in foot or eye.

Sensorimotor processing for balance in spinocerebellar ataxia type 6

Background

We investigated whether balance impairments caused by cerebellar disease are associated with specific sensorimotor processing deficits that generalize across all sensory modalities. Experiments focused on the putative cerebellar functions of scaling and coordinate transformation of balance responses evoked by stimulation of single sensory channels.

Methods

Vestibular, visual, and proprioceptive sensory channels were stimulated in isolation using galvanic vestibular stimulation, moving visual scenery, and muscle vibration, respectively, in 16 subjects with spinocerebellar ataxia type 6 (SCA6) and 16 matched healthy controls. Two polarities of each stimulus type evoked postural responses of similar form in the forward and backward directions. Disease severity was assessed using the Scale for Assessment and Rating of Ataxia.

Results

Impaired balance of SCA6 subjects during unperturbed stance was reflected in faster than normal body sway (P = 0.009), which correlated with disease severity (r = 0.705, P < 0.001). Sensory perturbations revealed a sensorimotor processing abnormality that was specific to response scaling for the visual channel. This manifested as visually evoked postural responses that were approximately three times larger than normal (backward, P < 0.001; forward P = 0.005) and correlated with disease severity (r = 0.543, P = 0.03). Response direction and habituation properties were no different from controls for all three sensory modalities.

Conclusion

Cerebellar degeneration disturbs the scaling of postural responses evoked by visual motion, possibly through disinhibition of extracerebellar visuomotor centers. The excessively high gain of the visuomotor channel without compensatory decreases in gains of other sensorimotor channels provides a potential mechanism for instability of the balance control system in cerebellar disease. © 2015 The Authors. Movement Disorders published by Wiley Periodicals, Inc. on behalf of International Parkinson and Movement Disorder Society.

Consensus paper: management of degenerative cerebellar disorders

Treatment of motor symptoms of degenerative cerebellar ataxia remains difficult. Yet there are recent developments that are likely to lead to significant improvements in the future. Most desirable would be a causative treatment of the underlying cerebellar disease. This is currently available only for a very small subset of cerebellar ataxias with known metabolic dysfunction. However, increasing knowledge of the pathophysiology of hereditary ataxia should lead to an increasing number of medically sensible drug trials. In this paper, data from recent drug trials in patients with recessive and dominant cerebellar ataxias will be summarized. There is consensus that up to date, no medication has been proven effective. Aminopyridines and acetazolamide are the only exception, which are beneficial in patients with episodic ataxia type 2. Aminopyridines are also effective in a subset of patients presenting with downbeat nystagmus. As such, all authors agreed that the mainstays of treatment of degenerative cerebellar ataxia are currently physiotherapy, occupational therapy, and speech therapy. For many years, well-controlled rehabilitation studies in patients with cerebellar ataxia were lacking. Data of recently published studies show that coordinative training improves motor function in both adult and juvenile patients with cerebellar degeneration. Given the well-known contribution of the cerebellum to motor learning, possible mechanisms underlying improvement will be outlined. There is consensus that evidence-based guidelines for the physiotherapy of degenerative cerebellar ataxia need to be developed. Future developments in physiotherapeutical interventions will be discussed including application of non-invasive brain stimulation.

Training balance with opto-kinetic stimuli in the home: a randomized controlled feasibility study in people with pure cerebellar disease

Objective:

To investigate the feasibility of a randomized controlled trial of a home-based balance intervention for people with cerebellar ataxia.

Design:

A randomized controlled trial design.

Setting:

Intervention and assessment took place in the home environment.

Participants:

A total of 12 people with spinocerebellar ataxia type 6 were randomized into a therapy or control group. Both groups received identical assessments at baseline, four and eight weeks.

Interventions:

Therapy group participants undertook balance exercises in front of optokinetic stimuli during weeks 4–8, while control group participants received no intervention.

Main measures:

Test–retest reliability was analysed from outcome measures collected twice at baseline and four weeks later. Feasibility issues were evaluated using daily diaries and end trial exit interviews.

Results:

The home-based training intervention with opto-kinetic stimuli was feasible for people with pure ataxia, with one drop-out. Test–retest reliability is strong (intraclass correlation coefficient >0.7) for selected outcome measures evaluating balance at impairment and activity levels. Some measures reveal trends towards improvement for those in the therapy group. Sample size estimations indicate that Bal-SARA scores could detect a clinically significant change of 0.8 points in this functional balance score if 80 people per group were analysed in future trials.

Conclusions:

Home-based targeted training of functional balance for people with pure cerebellar ataxia is feasible and the outcome measures employed are reliable.

The influence of early aging on eye movements during motor simulation

Movement based interventions such as imagery and action observation are used increasingly to support physical rehabilitation of adults during early aging. The efficacy of these more covert approaches is based on an intuitively appealing assumption that movement execution, imagery and observation share neural substrate; alteration of one influences directly the function of the other two. Using eye movement metrics this paper reports findings that question the congruency of the three conditions. The data reveal that simulating movement through imagery and action observation may offer older adults movement practice conditions that are not constrained by the age-related decline observed in physical conditions. In addition, the findings provide support for action observation as a more effective technique for movement reproduction in comparison to imagery. This concern for imagery was also seen in the less congruent temporal relationship in movement time between imagery and movement execution suggesting imagery inaccuracy in early aging.

Saccadic eye movements are related to turning performance in Parkinson disease

BACKGROUND

Persons with Parkinson disease (PD) experience difficulty turning, leading to freezing of gait and falls. We hypothesized that saccade dysfunction may relate to turning impairments, as turns are normally initiated with a saccade.

OBJECTIVE

Determine whether saccades are impaired during turns in PD and if characteristics of the turn-initiating saccade are predictive of ensuing turn performance.

METHODS

23 persons with PD off medication and 19 controls performed 90 and 180 degree in-place turns to the right and left. Body segment rotations were measured using 3-D motion capture and oculomotor data were captured using a head-mounted eye tracking system and electrooculography. Total number of saccades and the amplitude, velocity, and timing of the first saccade were determined.

RESULTS

Turn performance (turn duration, number of steps to turn) was impaired in PD (p<0.05). PD performed more saccades, and the velocity and timing of the first saccade was impaired for both turn amplitudes (p<0.05). Amplitude of the first saccade was decreased in PD during 180 degree turns. Turn duration correlated with oculomotor function. Characteristics of the first saccade explained 48% and 58% of the variance in turn duration for 90 and 180 degree turns, respectively.

CONCLUSIONS

Turning performance is impaired in PD and may be influenced by saccade dysfunction. An association between saccade function and turning performance may be indicative of the key role of saccades in initiating proper turning kinematics. Future work should focus on improving saccade performance during functional tasks and testing the effects of therapeutic interventions on related outcomes.

Upper limb activity in children with unilateral spastic cerebral palsy: the role of vision in movement strategies

This article reviews the capacity of children with unilateral spastic cerebral palsy (USCP) to (re)organize the available degrees of freedom and to use visual information in interceptive actions during motion with either the impaired or the less-impaired hand. Atypical reaching movements, such as increased trunk movement or slower wrist velocity, are considered adaptive coordination patterns that are the result of a change in the constraints. It is argued that manipulation of the task context facilitates children with USCP to enhance performance. For example, when reducing the time available to intercept a ball, the children are found to exceed their usual maximum walking speed and to increase range of motion of the elbow. In addition, the children appear to rely on a visual information strategy similar to typically developing children ('bearing angle'), although more variability is observed when using the impaired arm. The implications for interventions are, it should be recognized, that these children adapt to the impairment by reorganizing the movement system and that this process can be influenced by changing the task context. Attention should be paid to the importance of using correct visual cues for initiation and guidance of interceptive actions, which may be provoked by using external visual triggers.

Cerebellar ataxia: pathophysiology and rehabilitation

This series of articles for rehabilitation in practice aims to cover a knowledge element of the rehabilitation medicine curriculum. Nevertheless they are intended to be of interest to a multidisciplinary audience. The competency addressed in this article is 'The trainee consistently demonstrates a knowledge of management approaches for specific impairments including spasticity, ataxia.'

Quiet eye training facilitates competitive putting performance in elite golfers

The aim of this study was to examine the effectiveness of a brief quiet eye (QE) training intervention aimed at optimizing visuomotor control and putting performance of elite golfers under pressure, and in real competition. Twenty-two elite golfers (mean handicap 2.7) recorded putting statistics over 10 rounds of competitive golf before attending training individually. Having been randomly assigned to either a QE training or Control group, participants were fitted with an Applied Science Laboratories Mobile Eye tracker and performed 20 baseline (pre-test) putts from 10 ft. Training consisted of video feedback of their gaze behavior while they completed 20 putts; however the QE-trained group received additional instructions related to maintaining a longer QE period. Participants then recorded their putting statistics over a further 10 competitive rounds and re-visited the laboratory for retention and pressure tests of their visuomotor control and putting performance. Overall, the results were supportive of the efficacy of the QE training intervention. QE duration predicted 43% of the variance in putting performance, underlying its critical role in the visuomotor control of putting. The QE-trained group maintained their optimal QE under pressure conditions, whereas the Control group experienced reductions in QE when anxious, with subsequent effects on performance. Although their performance was similar in the pre-test, the QE-trained group holed more putts and left the ball closer to the hole on missed putts than their Control group counterparts in the pressure test. Importantly, these advantages transferred to the golf course, where QE-trained golfers made 1.9 fewer putts per round, compared to pre-training, whereas the Control group showed no change in their putting statistics. These results reveal that QE training, incorporated into a pre-shot routine, is an effective intervention to help golfers maintain control when anxious.

Effectiveness of physiotherapy for adults with cerebellar dysfunction: a systematic review

Objective: To systematically review the literature investigating the effectiveness of physiotherapy in adults with cerebellar dysfunction and to document treatment strategies currently employed in the physiotherapy management of this patient population.

Data sources: Eight electronic databases were searched to source English-language studies published up to December 2007. Secondary searching of reference lists was also undertaken.

Review methods: Studies were included if they used a quantitative research design to investigate the effect of physiotherapy on adults with diagnosed cerebellar dysfunction. Three reviewers were involved in study selection. Eligible studies were assessed for methodological quality. Data pertaining to the participants, interventions received, outcomes measured, and the effectiveness of the intervention were systematically extracted and synthesised in a narrative format.

Results: Nine studies were included in the review. The majority of the studies (n = 7) were case studies or case series. The median quality score was 8/16 (range 4—10). The studies were heterogeneous in terms of patient characteristics, interventions received and outcomes measured. All studies reported positive effects of physiotherapy over a range of outcomes measured, in particular balance, gait and function.

Conclusion: There is some evidence that supports the effectiveness of physiotherapy in adults with cerebellar dysfunction. However, these results need to be interpreted with caution due to the low volume, quality and clinical applicability of this evidence. There is a need for further high-quality research in this area.

Balance and eye movement training to improve gait in people with progressive supranuclear palsy: quasi-randomized clinical trial

BACKGROUND AND PURPOSE

Although vertical gaze palsy and gait instability are cardinal features of progressive supranuclear palsy (PSP), little research has been done to address oculomotor and gait rehabilitation for PSP. The purpose of this study was to compare the benefits of a program of balance training complemented with eye movement and visual awareness training versus balance training alone to rehabilitate gait in people with PSP.

PARTICIPANTS

Nineteen people moderately affected by the disease were assigned to either a treatment group (balance plus eye movement exercises, n=10) or a comparison group (balance exercises only, n=9) in a quasi-random fashion.

METHODS

The baseline characteristics assessed were diagnosis (possible versus probable), sex, age, time of symptom onset, dementia, and severity of symptoms. Within-group, between-group, and effect size analyses were performed on kinematic gait parameters (stance time, swing time, and step length) and clinical tests (8-ft [2.4-m] walk test and Timed "Up & Go" Test).

RESULTS

The within-group analysis revealed significant improvements in stance time and walking speed for the treatment group, whereas the comparison group showed improvements in step length only. Moderate to large effects of the intervention were observed for the treatment group, and small effects were observed for the comparison group. The between-group analysis did not reveal significant changes for either group.

DISCUSSION AND CONCLUSION

These preliminary findings support the use of eye movement exercises as a complementary therapy for balance training in the rehabilitation of gait in people with PSP and moderate impairments. Additional studies powered at a higher level are needed to confirm these results.

Saccade to stepping delays in elders at high risk for falling

BACKGROUND AND AIMS

Visually guided stepping is an essential function in many normal activities of daily living requiring the coordination of eye movements with precise foot placement. The objective of this investigation was to compare the saccade-footlift latency in community dwelling elderly identified as high-risk for falling with elderly who are at a low-risk of falling during a walking task that requires precise foot placement.

METHODS

A non-randomized between-group repeated measures design was employed using independently living elderly volunteers from the Minneapolis, MN community. Thirty older adults volunteered to participate in the study; fifteen who had a history of a fall in the previous 12 months or a prolonged score on a fall risk screening instrument (Timed Up and Go test), and fifteen elders who had not fallen and had a negative score on the screening instrument. Subjects were required to walk along a pathway of 4 irregularly spaced stepping targets. The time between horizontal saccadic eye movement to the initiation of footlift (saccade-footlift latency) was the primary dependent measure.

RESULTS

The mean saccade- footlift latency between high-risk (H-R) elderly and low-risk (L-R) elderly was statistically different (mean H-R 940 ms, L-R 825 ms; F1,3=7.45, p=0.006). The H-R elderly also performed more slowly on the cognitive test - Trail Making Test Part B (mean H-R 195 s, L-R 129 s; F1,2=7.21, p=0.01). The results suggest that there is an association between horizontal saccades, stepping and cognition for elderly at risk for falling.

CONCLUSIONS

The timing of saccades and precise foot placement in older persons living in the community are associated with fall risk status and cognitive status. The prolonged time for saccade-footlift in H-R elderly may be attributed to greater central nervous system processing time necessary to plan precise foot placements or volitional processing delays in postural control due to fall risk status. In addition, age related changes in cognitive functions appear to be associated with saccade stepping interaction when performing a visually guided stepping pattern and may influence the ability to coordinate precise lower extremity movements.

Alcohol badly affects eye movements linked to steering, providing for automatic in-car detection of drink driving

Driving is a classic example of visually guided behavior in which the eyes move before some other action. When approaching a bend in the road, a driver looks across to the inside of the curve before turning the steering wheel. Eye and steering movements are tightly linked, with the eyes leading, which allows the parts of the brain that move the eyes to assist the parts of the brain that control the hands on the wheel. We show here that this optimal relationship deteriorates with levels of breath alcohol well within the current UK legal limit for driving. The eyes move later, and coordination reduces. These changes lead to bad performance and can be detected by an automated in-car system, which warns the driver is no longer fit to drive.

Gaze control and foot kinematics during stair climbing: characteristics leading to fall risk in progressive supranuclear palsy

BACKGROUND AND PURPOSE

Does gaze control influence lower-extremity motor coordination in people with neurological deficits? The purpose of this study was to determine whether foot kinematics during stair climbing are influenced by gaze shifts prior to stair step initiation.

SUBJECTS AND METHODS

Twelve subjects with gaze palsy (mild versus severe) secondary to progressive supranuclear palsy were evaluated during a stair-climbing task in a cross-sectional study of mechanisms influencing eye-foot coordination. Infrared oculography and electromagnetic tracking sensors measured eye and foot kinematics, respectively. The primary outcome measures were vertical gaze fixation scores, foot lift asymmetries, and sagittal-plane foot trajectories.

RESULTS

The subjects with severe gaze palsy had significantly lower lag foot lift relative to lead foot lift than those with a mild form of gaze palsy. The lag foot trajectory for the subjects with severe gaze palsy tended to be low, with a heading toward contact with the edge of the stair.

SUBJECTS

with severe gaze palsy were 28 times more likely to experience "fixation intrusion" (high vertical gaze fixation score) during an attempted shift of gaze downward than those with mild ocular motor deficits (odds ratio [OR]=28.3, 95% confidence interval [CI]=6.4-124.8). Subjects with severe gaze shift deficits also were 4 times more likely to have lower lag foot lift with respect to lead foot lift than those with mild ocular motor dysfunction (OR=4.0, 95% CI=1.7-9.7).

DISCUSSION AND CONCLUSION

The small number of subjects and the variation in symptom profiles make the generalization of findings preliminary. Deficits in gaze control may influence stepping behaviors and increase the risk of trips or falls during stair climbing. Neural and kinematic hypotheses are discussed as possible contributing mechanisms.

Specific influences of cerebellar dysfunctions on gait

Cerebellar ataxic gait is characterized by unsteady movements and variable gait patterns. Previous studies have successfully identified pathological changes of balance-related gait parameters. However, it has been difficult to demonstrate deficits of joint coordination and the control of limb dynamics. This has motivated the hypothesis that cerebellar ataxic gait might be affected predominantly by balance impairments. We investigated the influences of different types of cerebellar dysfunction on the gait patterns of patients suffering from degenerative cerebellar disease (13 patients, five females, 50.4 +/- 14.4 years). Walking patterns were quantitatively analysed combining standard gait measures and novel measures for the characterization of the spatial and the temporal variability of intra-joint coordination patterns. The temporal variability of gait patterns was significantly correlated with a subscale of the clinical ataxia scale (ICARS) that rates deficits of the control of limb dynamics and intra-limb coordination for goal-directed movements. This suggests that common cerebellar mechanisms might be involved in coordination during voluntary limb control and ataxic gait. The tested standard gait parameters correlated predominantly with clinical measures for balance-related abnormalities. These results imply that ataxic gait is influenced by both balance-related impairments and deficits related to limb control and intra-limb coordination. Applying the same analysis to gait patterns from patients with peripheral vestibular failure (six patients, four females, 47.8 +/- 14.3 years) and Parkinson's disease (eight patients, two females, 60.7 +/- 10.6 years), we found comparable abnormalities in balance-related gait parameters and general gait variability, but significantly lower increases of temporal variability. This implies that increased temporal variability of intra-limb coordination is a specific characteristic of cerebellar dysfunction, which does not arise for other movement disorders that also cause balance deficits and increased gait variability.

Eye-steering coordination in natural driving

When driving along a winding road, eye movements and steering are tightly linked; the driver looks across to the inside kerb of an approaching bend some time before turning the steering wheel. With the eyes leading, the oculomotor controller assists the neural centres controlling steering; prevention of any eye movements correlated with steering impairs driving, so the coordination is crucial for safety. A key question is therefore what are the limits of acceptable variation in timing and degree of coordination. Over a period of continuous driving on the open road, how much does the relative timing and degree of coordination between eye and steering movements vary? A related question is how brief a period of driving will suffice to measure these coordination parameters. Drivers' eye movements and steering were measured over different time periods ranging from 15 s to 6 min epochs of natural driving along a winding country road to establish the variability in coordination and the minimum time period required to characterise it. We show here that brief periods of driving, 30 s or less, are inadequate for describing eye-steering coordination. But a minute of driving yields an accurate description much of the time; and 2 min is sufficient both to accurately describe this relationship and to show that it is highly consistent for a given individual, and for different people driving the same route.

Evidence for a link between changes to gaze behaviour and risk of falling in older adults during adaptive locomotion

There is increasing evidence that gaze stabilization with respect to footfall targets plays a crucial role in the control of visually guided stepping and that there are significant changes to gaze behaviour as we age. However, past research has not measured if age-related changes in gaze behaviour are associated with changes to stepping performance. This paper aims to identify differences in gaze behaviour between young (n=8) adults, older adults determined to be at a low-risk of falling (low-risk, n=4) and older adults prone to falling (high-risk, n=4) performing an adaptive locomotor task and attempts to relate observed differences in gaze behaviour to decline in stepping performance. Participants walked at a self-selected pace along a 9m pathway stepping into two footfall target locations en route. Gaze behaviour and lower limb kinematics were recorded using an ASL 500 gaze tracker interfaced with a Vicon motion analysis system. Results showed that older adults looked significantly sooner to targets, and fixated the targets for longer, than younger adults. There were also significant differences in these measures between high and low-risk older adults. On average, high-risk older adults looked away from targets significantly sooner and demonstrated less accurate and more variable foot placements than younger adults and low-risk older adults. These findings suggest that, as we age, we need more time to plan precise stepping movements and clearly demonstrate that there are differences between low-risk and high-risk older adults in both where and when they look at future stepping targets and the precision with which they subsequently step. We propose that high-risk older adults may prioritize the planning of future actions over the accurate execution of ongoing movements and that adoption of this strategy may contribute to an increased likelihood of falls.

Eye movements coordinated with steering benefit performance even when vision is denied

When driving along a winding road, eye movements and steering are tightly linked. When approaching a bend, the driver looks across to the inside kerb (the tangent point) some time before turning the steering wheel. All drivers we have tested show this optimal coordination, without which driving is impaired. An intriguing question is how much of the benefit for steering arises just from moving the eyes in this coordinated way (ahead of steering and in the same direction), and how much from the visual information that the eyes move to acquire, in this instance the foveated tangent point. This can be answered by dissociating the two, by reducing visibility of the road ahead (and crucially of the tangent point) to a level at which drivers might or might not choose to move their eyes but, if they do, will not gain the information they seek. Twenty subjects repeatedly drove a simulated stage of the World Rally Championship. With full visibility, they exhibited the usual coordination of eye movements and steering. Subsequently, visibility was reduced on the left hand side. Drivers who persisted in making eye movements coordinated with steering to the left, despite the fact that they could no longer see the tangent point on that side, performed better than drivers who under the identical conditions did not look to the left. This confirms that the making of coordinated eye movements itself benefits steering, even when the eye movements do not yield the visual information sought.

Prevention of coordinated eye movements and steering impairs driving performance

When approaching a bend in the road, a driver looks across to the inside kerb before turning the steering wheel. Eye movements and steering are tightly linked, with the eyes leading, which means that the oculomotor controller can assist the neural centres controlling steering. This optimum coordination is observed for all drivers; but despite being the preferred solution to the motor-control problem of successfully steering along a winding road, the question remains as to how crucial such coordinated eye and steering movements are for driving performance. Twenty subjects repeatedly drove a simulated stage of the World Rally Championship, aiming to complete the course in the fastest possible time. For the first six repetitions they used the usual coordination of eye movements and steering; for drives 7--12 they were instructed to fixate on a small spot in the centre of the screen (centre gaze). Prevention of coordination in this way impaired their performance (drives 6 and 7 compared), dramatically increasing their time taken to complete the course, equivalent to slipping 19 places down the leader board in the actual rally stage. This indicates that the usual pattern of eye movements correlated with steering is crucial for driving performance. Further experiments are suggested to reveal whether any attentional demand associated with keeping the eyes still contributes to the loss in performance.