Does articulation contribute to modifications of postural control during dual-task paradigms?

Many studies have been carried out to investigate the attentional resources required for postural control, using a 'dual-task' methodology in which performance on mental and postural control tasks is compared when these are carried out separately and concurrently. Most mental tasks used in these dual-task studies have employed verbal responses. However, changes in respiration during speech production are known to produce changes in postural control. Hence, the goal of this study was to determine whether articulation might contribute to the changes found in postural sway when a spoken mental task is being performed and to determine if the type of postural control measurement might also have an impact on the outcome of the study. Twenty young healthy participants were asked to stand on a force platform while executing secondary tasks that were performed silently or required a verbal response, and that required high or low levels of attention. Vision and postural task difficulty were manipulated. Performance of all tasks produced an increased sway frequency and decreased sway amplitude relative to the no task baseline. However, tasks that required articulation resulted in a more pronounced increase in postural sway frequency and sway path than did the tasks that did not require any articulation. These findings could imply that the addition of a secondary task results in increased stiffness, whereas articulation results in a further increased frequency of sway, which leads to an increase in sway path. We conclude that changes in the various parameters of sway that accompany performance of secondary tasks are complex, and are not always wholly attributable to attentional load, but may also be partly due to the motor requirements of the task, such as those involved in articulation.     

Disruption of sitting balance after stroke: influence of spoken output

OBJECTIVES: To identify the extent of dual task interference between cognitive and motor tasks, (cognitive motor interference (CMI)) in sitting balance during recovery from stroke; to compare CMI in sitting balance between stroke and non-stroke groups; and to record any changes to CMI during sitting that correlate with functional recovery. METHOD: 36 patients from stroke rehabilitation settings in three NHS trusts. Healthy control group: 21 older volunteers. Measures of seated postural sway were taken in unsupported sitting positions, alone, or concurrently with either a repetitive utterance task or an oral word category generation task. Outcome measures were variability of sway area, path length of sway, and the number of valid words generated. RESULTS: Stroke patients were generally less stable than controls during unsupported sitting tasks. They showed greater sway during repetitive speech compared with quiet sitting, but did not show increased instability to posture between repetitive speech and word category generation. When compared with controls, stroke patients experienced greater dual task interferences during repetitive utterance but not during word generation. Sway during repetitive speech was negatively correlated with concurrent function on the Barthel ADL index. CONCLUSIONS: The stroke patients showed postural instability and poor word generation skills. The results of this study show that the effort of verbal utterances alone was sufficient to disturb postural control early after stroke, and the extent of this instability correlated with concomitant Barthel ADL function.     

Dual-task study of cognitive and postural interference in 7-year-olds and adults

The study examined, in children aged 7 and adults, the postural control when a cognitive task (modified Stroop) of varying level of difficulty is executed simultaneously. Postural difficulty also varied (with or without vibrations of the ankle joint). We hypothesized that children's performance was more affected than adults', when the difficulty of the cognitive and postural tasks increased. Results (i) demonstrated that the presence of a concurrent cognitive task affected postural sway at all ages; (ii) confirmed that the interference between mental activity and postural control can be attributed mainly to general capacity limitations and (iii) showed a degradation of the postural criteria in children but not of the cognitive ones, when the postural condition was constraining.     

Postural sway changes during static standing with concurrent task in children with traumatic brain injury

Objectives:To investigate the effects of concurrent tasks (motor and cognitive) on postural control performance in children with traumatic brain injury (TBI) compared to typically developing (TD) control subjects.Methods:Sixteen children with TBI (aged 11.63±1.89 years) and 22 TD controls (aged 11.41±2.24 years) participated in this case-control study. This study was conducted between May 2016 and March 2017. Each child performed static standing under 3 different conditions: single, concurrent motor, and concurrent cognitive task. Postural control performance measure includes sway area, anterior-posterior (AP) sway velocity, medio-lateral (ML) sway velocity, AP sway distance and ML sway distance as measured using the APDM® Mobility Lab (Oregon, Portland). A repeated-measure analysis of variance was used to analyse the data.Results:We found that children with TBI showed significantly more deterioration in postural control performance than TD children (p<0.05). Both concurrent tasks (motor and cognitive) significantly decreased postural control performance in both groups with more pronounced changes in children with TBI than that of the TD controls.Conclusion:The results demonstrated that, performing concurrent tasks (motor and cognitive) during upright standing resulted in deterioration of postural control performance. The existence of cognitive and balance impairment in children with TBI will possibly cause concurrent tasks to be more complex and demands greater attention compared to single task.

Traumatic brain injury is frequently referred to as a ‘silent epidemic’, with the majority of society being unaware on the magnitude a TBI can cause on an individual’s function.1 It remains a leading cause of death and long-term disability in children worldwide with approximately 3 million children experiencing TBI annually.2 Consequently, TBI may lead to neurological impairment which contributes to long-term disability among this group of children.With the cognitive and behavioral deficit, individuals with TBI are faced with a long-term functional disability including postural control instability.3,4 Postural control refers to the act of maintaining, achieving or restoring the line of gravity or centre of mass (COM) within the base of support (BOS).5 It is a complex collaboration of sensory, motor, and central nervous system. Disruption of any components such as visual, vestibular sensory inputs, muscle weakness and loss of proprioception will result in postural control instability. This impairment could seriously interfere with the child’s level of independence and lead to increased risk of falls.5The maintenance and control of posture and balance, whether in static or dynamic conditions, are essential requirements for daily activity. Postural control requires a lot of cognitive resources.6 The more challenging postural task required more cognitive processing in order to sustain the position. Children with TBI have both cognitive and information processing deficits that impact attention and functional abilities.7,8 In daily life, children encounter situations in which they must perform cognitive and motor tasks simultaneously, such as responding to verbal instructions or manipulating objects while sitting or standing. These situations may be complex and challenging for children with TBI as they present with both attention and information processing deficit. Using dual-task methodology, it can examine the effect of adding a concurrent task during a motor task. Trials using dual-task paradigm are commonly used in a clinical setting to measure automatic control of movement indirectly. It is crucial to understand the effects of a concurrent task on postural control performance while designing a dual-task paradigm intervention program in this population. The dual-task intervention during postural control could be more challenging and may improve the postural stability better as compared to single task intervention.Since attention is a limited resource, it may become overloaded by competing for attention demands and subsequently might lead to reduced performance in one or all tasks.9 Children with TBI may need more attention during postural control and as a result might be more vulnerable to falls while doing concurrent task. A recent study among healthy children and youth 5-18 years old showed concurrent cognitive task resulted in decreased postural stability.10 Comparing the effects of different surface (firm vs. foam surface) on postural stability during concurrent cognitive task reveals that the foam surface caused greater interference in postural stability.10 A normative database was created as a result of this study, which may benefit future investigations of post-concussion performances with potential to assess post-concussion severity. In addition, it also focuses on assessing both motor and cognitive domains simultaneously. This study also reports information regarding the effect of cognitive task on postural stability in healthy children & youth. The examined effect of concurrent cognitive and motor task conditions on postural control in children with TBI is limited. Therefore, the objective of the present study was to investigate the postural control performance under concurrent tasks in children with TBI and TD controls. We hypothesized that both concurrent motor and cognitive tasks would cause significant postural control deterioration compared to single task condition.     

Cognitive requirements for vestibular and ocular motor processing in healthy adults and patients with unilateral vestibular lesions

This study investigated the role of cognition in the vestibulo-ocular reflex (VOR) and ocular pursuit using a dual-task paradigm in patients with unilateral peripheral vestibular loss and healthy adults. We hypothesized that cognitive resources are involved in successful processing and integration of vestibular and ocular motor sensory information, and this requirement would be greater in patients with vestibular dysfunction. Sixteen well-compensated patients with surgically confirmed absent unilateral peripheral vestibular function and 16 healthy age- and sex-matched controls underwent seven combinations of vestibular-only, visual-only, and visual-vestibular stimuli while performing three different information processing tasks. Visual-vestibular stimuli included a semicircular canal and an otolith stimulus provided through seated chair rotations; fixation on a laser target and sinusoidal smooth pursuit while still; and fixation on a head-fixed laser target during chair rotations. The information processing tasks were three different auditory reaction time (RT) tasks: (1) simple RT, (2) disjunctive RT, and (3) choice RT. Our results showed increases in RTs in both patients and controls under all vestibular-only stimulation conditions and during ocular pursuit. Patients showed greater increases in RTs during vestibular stimulation and the more complex disjunctive and choice RT tasks. No differences between the groups were found during the visual-only or visual-vestibular interaction conditions. These results reveal interference between vestibulo-ocular processing and a concurrent RT task, suggesting that the VOR and the ocular motor system are dependent upon cognitive resources to some extent, and thus, are not fully automatic systems. We speculate that this interference with cognition occurs as a result of the sensory integration required for resolving inputs from multiple sensory streams. The particularly large decrement in information processing task performance of the patients compared with controls during vestibular stimulation suggests that compensation for unilateral vestibular loss requires continued cognitive resources.     

Effect of cognitive and motor tasks on postural stability in Parkinson's disease: a posturographic study.

To analyse the effect of concomitant cognitive or motor task performance on balance control in Parkinson's disease (PD), we performed a posturographic study in 24 PD patients and in 20 sex- and age-matched control subjects. Postural sway was measured with eyes open (EO) and eyes closed (EC) during quiet stance and during performance of calculation or motor sequence of thumb opposition to the other fingers. No difference of centre of foot pressure (COP) parameters was observed during quiet standing (either EO or EC) between patients and controls, but visual deprivation induced in both groups a worsening of postural stability. COP area was significantly increased in PD patients during dual task performance, whereas no difference of COP path and x-y axes was observed. The effects induced by the performance of cognitive or motor task were significantly more evident in PD patients with clinical evidence of postural instability (presence of prior falls in the history). This study demonstrates that dual task interference on postural control can be observed in PD patients during performance of cognitive as well as motor tasks. The balance deterioration during dual task performance was significantly enhanced in patients with history of prior falls. These findings have some implications for the strategies to be used in reducing the risk of fall in PD.     

Influence of sensory manipulation on postural control in Parkinson''s disease.

Postural control was assessed on a tilting platform system in 20 patients with idiopathic Parkinson's disease and 20 age-matched controls. The amount of information provided by vision and lower limb proprioception was varied during the experiment to investigate the influence of changes in sensory cues on postural control. The patient group with clinical evidence of impaired postural control (Hoehn and Yahr III) had significantly higher sway scores over all sensory conditions than either the Hoehn and Yahr II group or controls. The pattern of sway scores indicated that no obvious deficit in the quality, or processing, of sensory information was responsible for the postural instability observed in this group. The patients in both Hoehn and Yahr groups were also able to respond appropriately to potentially destabilising sensory conflict situations and significantly improved their sway scores when provided with visual feedback of body sway. The results indicate that in Parkinson's disease, the main site of dysfunction in postural control is likely to be at a central motor level.     

Effect of bilateral subthalamic nucleus stimulation on balance and finger control in Parkinson's disease

We aimed to quantify the effects of bilateral subthalamic nucleus (STN) stimulation in Parkinson's disease (PD) on stance and gait ("axial"motor control), and related this to effects on finger movements ("appendicular" motor control). Fourteen PD patients and 20 matched controls participated. Subjects completed several balance and gait tasks (standing with eyes open or closed, on a normal or foam surface; retropulsion test; walking with eyes closed; walking up and down stairs; Get Up and Go test). Postural control was quantified using trunk sway measurements (angle and angular velocity) in the roll and pitch directions. Subjects further performed a pinch grip reaction time task, where we measured isometric grip forces, as well as movement and reaction times. Patients were examined with STN stimulators switched on or off (order randomised across patients), always after a supramaximal levodopa dosage. STN stimulation improved postural control, as reflected by a reduced trunk sway tremor during stance, a reduced duration for all gait tasks, an increased trunk pitch velocity while rising from a chair, and improved roll stability. STN stimulation also improved finger control, as reflected by a reduced time to reach maximum grip force, without altering reaction times and maximum force levels. Improvements in finger control timing did not correlate with reduced task durations during gait. We conclude that STN stimulation affords improvement of postural control in PD, over and above optimal drug treatment. STN stimulation also provides a simultaneous effect on distal and axial motor control. Because improvements in distal and axial motor control were not correlated, we assume that these effects are mediated by stimulation of different structures within the STN.     

Effect of articulatory and mental tasks on postural control

The present study sought to determine whether the increased postural instability produced by a spoken mental task was due to competing demands for attentional resources or perturbation of posture by articulation. Postural sway was measured in 36 normal subjects under the following conditions: repeating a number aloud (articulation), counting backwards aloud in multiples of seven (articulation and attention), counting backwards silently (attention), and no mental task (neither articulation nor attention). Articulation resulted in a significant increase in sway, whereas no effect of attention was observed. We conclude that in order to accurately assess the effect of attentional demands on postural control, it is important to eliminate or control the effects of articulation.     

Postural sway and effect of levodopa in early Parkinson's disease

OBJECTIVE: To characterize postural stability control and levodopa responsiveness in early Parkinson's disease (PD). METHODS: Postural sway was studied during quiet stance in ten patients within six years of PD onset, both before (OFF) and after (ON) regular oral levodopa dosing. Postural sway was recorded using a force platform during 30 sec with eyes open, and six dependent variables were examined. RESULTS: Mild baseline subclinical changes in postural sway were recorded in our patients. Clear benefit was observed in five out of six characteristics (mean sway, transversal sway, sagittal sway, sway intensity, and sway area) in the ON condition. CONCLUSION: Postural control mechanisms are affected early in PD and modulated by dopamine.     

Cerebellar networks in individuals at ultra high‐risk of psychosis: Impact on postural sway and symptom severity

Despite known deficits in postural control in patients with schizophrenia, this domain has not been investigated in youth at ultra high‐risk (UHR) for psychosis. This is particularly relevant as postural control implicates dysfunction in the cerebellum‐a region implicated in cognitive dysmetria conceptions of schizophrenia but poorly understood in the prodrome. Here, we extended our understanding of movement abnormalities in UHR individuals to include postural control, and have linked these deficits to both symptom severity and cerebello‐cortical network connectivity. UHR and healthy control participants completed an instrumentally based balance task to quantify postural control along with a resting state brain imaging scan to investigate cerebellar networks. We also quantified positive and negative symptom severity with structured clinical interviews. The UHR group showed overall increased postural sway and decreased cerebello‐cortical resting state connectivity, relative to controls. The decreased cerebello‐cortical connectivity was seen across multiple networks. Postural sway was also correlated with cerebellar connectivity in this population and uniquely positively correlated with the severity of negative symptoms. Finally, symptom severity was also associated with cerebellar connectivity. Together, our results point to a potential deficit in sensory integration as an underlying contributor to the increased postural sway, and provide evidence of cerebellar abnormalities in UHR individuals. These results extend our understanding of the motor abnormalities of UHR individuals beyond striatum‐based dyskinesias to include postural control and sensory integration deficits, and implicate the cerebellum as a distinct neural substrate preceding the onset of psychosis. Taken together, our results extend the cognitive dysmetria framework to UHR populations. Hum Brain Mapp 35:4064–4078, 2014. © 2014 Wiley Periodicals, Inc .     

Attentional demands of continuously monitoring orientation using vestibular information.

The aim of this series of experiments was to determine whether attention is normally required for continuously processing vestibular information concerning orientation, or is required only when orientation is disrupted (eg by vestibular dysfunction or by conflicting visual and vestibular orientation cues). In the first two studies, healthy subjects were passively oscillated, and indicated when they perceived they were passing through their starting position. There was only weak evidence for interference between performance on this 'continuous orientation monitoring task' and on concurrent mental tasks. However, a third study showed that when patients with vestibular imbalance carried out the continuous orientation monitoring task their performance on a concurrent mental arithmetic task was substantially impaired. This dual task interference was correlated with inaccuracy in judging orientation on the continuous orientation monitoring task, which in turn correlated with severity of recent vestibular symptomatology (assessed by questionnaire). In a fourth experiment, disorientation was induced in healthy subjects by rotating the visual field about the line of sight. Bidirectional interference was observed between monitoring orientation (assessed by accuracy in setting a rod to the perceived vertical) and performance of an arithmetic task. Dual task interference was correlated with baseline levels of disorientation induced by the visual field, as indicated by inaccuracy in judging the visual vertical. These findings suggest that monitoring orientation makes significant demands upon cortical processing resources when disorientation is induced, whether the disorientation results from deficient sensory functioning or from ambiguous perceptual information.     

The "posture second" strategy: a review of wrong priorities in Parkinson's disease

Falls are common in Parkinson's disease. It remains difficult to predict these falls, presumably because clinical balance tests assess single components of postural control, whereas everyday fall mechanisms are typically more complicated. A substantial proportion of everyday falls appears to occur while Parkinson patients attempt to perform multiple tasks at the same time. Furthermore, little attention is generally paid to the possible contribution of cognitive impairments to falls. The importance of mental dysfunction is supported by the fact that cognitive loading while walking or balancing can lead to marked deteriorations in postural performance, and there is some evidence to suggest that such "dual tasking" is particularly difficult for elderly persons with dementia or depression. We examined what strategies Parkinson patients used when a basic walking task became increasingly challenging by adding additional tasks (both motor and cognitive). Most patients could perform a simple "dual task" test: simultaneously walking and answering simple questions. However, as the walking task became more complex, patients' performance began to deteriorate. Interestingly, this was reflected not only by failure to answer questions, but also by an increasing number of blocks in motor performance (walking and balancing). This behaviour was different from that of both young and elderly controls, who appeared to sacrifice performance on the cognitive task in order to optimise their gait and balance ("posture first" strategy). Preliminary evidence suggest that impaired multiple task performance is associated with a two-fold increased risk of sustaining falls in daily life. We conclude that Parkinson patients are less inclined than healthy persons to maintain a safe gait. Instead, Parkinson patients use a "posture second" strategy and treat all elements of a complex task with equal priority, which in daily life may go at the expense of maintaining balance and lead to falls.     

Errors in cognitive performance trigger postural instability in Parkinson's disease

BackgroundGlobally, postural stability and cognitive performance are intimately linked in Parkinson's disease (PD). However, a fundamental gap exists in understanding the precise relationship between a disruption in executive function and its impact on postural stability.ObjectiveThis project aimed to determine the precise effects of cognitive errors on postural stability under dual-task conditions in participants with PD and controls.MethodsTwenty-eight individuals with PD and 27 healthy controls completed a series of postural stability tests under single- and dual-tasks. The dual-task required maintenance of balance while performing an audio number discrimination task.ResultsIn general, postural stability in PD and control subjects was similar across single-task conditions. In controls, an error in the cognitive task during dual-task conditions did not impact measures of postural sway. In contrast, in PD, postural sway increased in epochs surrounding cognitive errors relative to epochs without errors.ConclusionsPostural task selection plays a critical role when testing for balance deficits in PD compared to healthy controls. Furthermore, time synchronized analysis of cognitive and balance data revealed the greatest episodes of postural instabilities occurred around cognitive errors. The measurement and evaluation of cognitive-motor linkages, relative to postural stability, could provide a patient-specific fingerprint of balance function and provide more sensitive measures for fall risk in PD.     

Selective interference reveals dissociation between auditory memory for location and pitch

Effects of interfering task-irrelevant tones varying in location or pitch on auditory location and pitch n-back tasks were investigated to study whether there is segregation of spatial and non-spatial information processing in the auditory working memory. The subjects performed spatial and non-spatial auditory 1- and 2-back tasks with and without location or pitch interference. In the 1-back tasks, location but not pitch interference significantly impaired location task performance whereas pitch but not location interference disrupted pitch task performance. In the 2-back tasks, neither the location nor the pitch task performance was differentially disrupted by the distractors, suggesting that there is memory load-dependent segregation in the handling of location and pitch information in the neuronal networks engaged in auditory working memory.     

Postural sway in patients with early Parkinson’s disease performing cognitive tasks while standing

Objectives: We investigated postural sway in patients with early Parkinson’s disease (PD) to test the hypothesis that the postural control system was affected already at an early stage of PD. Moreover, we identified cases of dysfunction of stereopsis in PD patients.

Methods: We examined 23 patients with early PD and 23 healthy, sex- and age-matched control subjects. Postural sway was measured with an accelerometer at the center of mass at the lower spine. Subjects were asked to stand quietly for 30 s under two usual conditions (eyes open and eyes closed) and two dual tasks conditions (eyes open with dual task, eyes closed with dual task). Stereopsis was assessed using the Titmus fly test.

Results: In the usual conditions, no differences were found between the control group and PD group. With increasing task difficulty, PD patients showed an increase of RMS values of sway acceleration, compared to control subjects. These differences reached significance during cognitive task performance. PD patients showed larger JERK values with increasing difficulty of the sway task which also reached significance during cognitive task performance. Relative to controls, PD patients showed decreased stereopsis function. But, there were no statistically significant correlations between log seconds of arc of the Titmus test and JERK, even during cognitive task performance.

Conclusion: Our results indicate that patients with early PD have subtle signs of postural instability when their attention is diverted or reduced. In addition, deficits of stereopsis may be common in early PD patients. St

Abbreviations: ACC: Accelerometers; ANOVA: Analysis of variance; AP: Antero-posterior; COP: Center of pressure; EC: Eyes closed; ECDT: eyes closed with dual task; EO: Eyes open; EODT: Eyes open with dual task; GDS: Geriatric depression scale; JERK: Jerkiness of sway; ML: Medio-lateral; MMSE: Mini mental state examination; MoCA: Montreal cognitive assessment; PD: Parkinson’s disease; PDAbS: PD Patients with abnormal stereopsis; PDNrS: PD Patients with normal stereopsis; PIGD: Postural instability and gait disorder; RMS: Root mean square; UPDRS: Unified Parkinson’s disease rating scale.     

Postural inflexibility in parkinsonian subjects.

In order to identify the types of postural deficits seen in parkinsonian patients with postural instability, we compared the performance of parkinsonian subjects with young and old control subjects in 3 aspects of postural control: (1) the use of sensory information for postural orientation, (2) the coordination of postural movement patterns in response to surface displacements, and (3) the flexible modification of postural response patterns to changes in support conditions. Parkinsonian subjects had very small sway, even under altered sensory conditions. Postural response latencies to displacements were also normal. Postural instability was associated with abnormal patterns of postural responses including excessive antagonist activity and inflexibility in adapting to changing support conditions. Some parkinsonian subjects appeared to have difficulty sequencing motor programs for postural correction. The parkinsonian subjects appeared stiffer since the rate-of-change of sway in response to displacements was reduced. Levodopa improved postural coordination but not the flexible adaptation to changing support conditions.     

Vestibular information is necessary for maintaining metric properties of representational space: evidence from mental imagery

The vestibular system contributes to a wide range of functions, from postural and oculomotor reflexes to spatial representation and cognition. Vestibular signals are important to maintain an internal, updated representation of the body position and movement in space. However, it is not clear to what extent they are also necessary to mentally simulate movement in situations that do not involve displacements of the body, as in mental imagery. The present study assessed how vestibular loss can affect object-based mental transformations (OMTs), i.e., imagined rotations or translations of objects relative to the environment. Participants performed one task of mental rotation of 3D-objects and two mental scanning tasks dealing with the ability to build and manipulate mental images that have metric properties. Menière's disease patients were tested before unilateral vestibular neurotomy and during the recovery period (1 week and 1 month). They were compared to healthy participants tested at similar time intervals and to bilateral vestibular-defective patients tested after the recovery period. Vestibular loss impaired all mental imagery tasks. Performance varied according to the extent of vestibular loss (bilateral patients were frequently the most impaired) and according to the time elapsed after unilateral vestibular neurotomy (deficits were stronger at the early stage after neurotomy and then gradually compensated). These findings indicate that vestibular signals are necessary to perform OMTs and provide the first demonstration of the critical role of vestibular signals in processing metric properties of mental representations. They suggest that vestibular loss disorganizes brain structures commonly involved in mental imagery, and more generally in mental representation.     

Subthalamic nucleus stimulation selectively improves motor and visual memory performance in Parkinson's disease

Although the treatment of Parkinson's disease via subthalamic stimulation yields remarkable improvements in motor symptoms, its effects on memory function are less clear. In this context, we previously demonstrated dissociable effects of levodopa therapy on parkinsonian performance in spatial and nonspatial visual working memory. Here we used the same protocol with an additional, purely motor task to investigate visual memory and motor performance in 2 groups of patients with Parkinson's disease with or without subthalamic stimulation. In each stimulation condition, subjects performed a simple motor task and 3 successive cognitive tasks: 1 conditional color‐response association task and 2 visual (spatial and nonspatial) working memory tasks. The Parkinson's groups were compared with a control group of age‐matched healthy subjects. Our principal results demonstrated that (1) in the motor task, stimulated patients were significantly improved with respect to nonstimulated patients and did not differ significantly from healthy controls, and (2) in the cognitive tasks, stimulated patients were significantly improved with respect to nonstimulated patients, but both remained significantly impaired when compared with healthy controls. These results demonstrate selective effects of subthalamic stimulation on parkinsonian disorders of motor and visual memory functions, with clear motor improvement for stimulated patients and a partial improvement for their visual memory processing. © 2011 Movement Disorder Society     

Postural control in multiple sclerosis: effects of disability status and dual task

Persons with Multiple Sclerosis (PwMS) have postural control impairments. The simultaneous performance of a cognitive task while maintaining an upright posture (i.e. dual task) negatively influences postural control in PwMS with mild disability. This investigation compares the effect of simultaneous cognitive task performance on postural control in PwMS with mild and moderate disability. Forty-five PwMS were divided into groups based on Expanded Disability Status Scale (EDSS) scores: mild (EDSS: 2.0-3.5) and moderate (EDSS: 4.0-6.5) disbaility. Each participant underwent posturography testing during a quiet baseline condition and a cognitive task condition (i.e. dual task). The cognitive task was a word list generation (WLG) task. Median sway velocity, root mean square displacement, and sway area were calculated for each condition. The moderate disability group had significantly worse postural control than the mild disability group. There was an increase in postural sway in the dual task condition. There were no significant task-by-group interactions on postural control. Postural control declines with disability status and is negatively affected by a concurrent cognitive task in PwMS. The dual task cost during a balance task is not different between disability levels and this conflicts with findings for the effect of dual tasking during walking in PwMS.