Recruitment of attentional resources during visuomotor tracking: effects of Parkinson's disease and age

Age-related changes in the interference between cognitive task components and concurrent sensorimotor coordination

Continuous sensorimotor coordinations (CSCs) such as driving, walking, using control interfaces or maintaining the body's balance are often performed alongside concurrent cognitive tasks involving attention and executive function. A range of these task combinations show interference, particularly in older adults, but the timing, direction and reciprocity of interference is not yet understood at the level of the tasks' information-processing operations. This paper compares the chronometry of dual task interference between a visual oddball task and a continuous visuomanual tracking task performed by young and older adults. The oddball task's constituent operations were identified using electrophysiological correlates, and deviations in the tracking task reflected perturbations to state monitoring and adjustment characteristics of CSC tasks. Despite instructions to give equal priority to both tasks, older participants maintained a high level of resourcing of the oddball task when dual tasking whereas young participants reduced resourcing to accommodate the demands of the tracking task. Older participants had a longer period of tracking inaccuracy during the executive function component of the oddball task, and unlike in young participants, this decrement was also observed when the stimulus was not a target and the executive function of updating the target tally was not required. These detailed chronometric results clarify that age-related amplification of CSC-cognitive interference are largely due to greater inflexibility in task prioritization. Prioritization of the cognitive task over the CSC in this type of dual tasking may have safety implications in everyday task settings.

Straying Off Course: The Negative Impact of Mind Wandering on Fine Motor Movements

The goal of this study was to examine how various degrees of perceptual decoupling during mind wandering affect fine motor control. We hypothesized that while under normal circumstances attention ensures an optimal control strategy that leads to accurate motor performance, during mind wandering the process becomes disrupted. In this study, we conducted a computer-based experiment with a tracking task. During mind wandering, motor movements were more erratic and less variable, indicative of reduced attentiveness to the continuous demands of the external task. Importantly, the deeper the reported mind wandering, the less accurate and less variable were the mouse movements, suggesting that perceptual decoupling may take place in a graded rather than in an all or nothing manner. Greater movement intermittency was associated with higher tracking accuracy, suggesting that more corrective movements toward a moving target were functional to task performance. Moreover, greater variance in velocity was negatively correlated with tracking accuracy. These findings suggest that periods of inattention to the task have a negative impact on fine motor movement control by making behavior unpredictable, providing support for the idea that there is a decoupling of sensory-motor processes during mind wandering.

Strength or Motor Control: What Matters in High-Functioning Stroke?

Background: The two primary motor impairments that hinder function after stroke are declines in strength and motor control. The impact of motor impairments on functional capacity may vary with the severity of stroke motor impairments. In this study, we focus on high-functioning stroke individuals who experience mild to moderate motor impairments and often resume prior activities or return to work. These tasks require the ability to move independently, placing high demands on their functional mobility. Therefore, the purpose of this study was to quantify impairments in strength and motor control and their contribution to functional mobility in high-functioning stroke.

Methods:Twenty-one high-functioning stroke individuals (Fugl Meyer Lower Extremity Score = 28.67 ± 4.85; Functional Activity Index = 28.47 ± 7.04) and 21 age-matched healthy controls participated in this study. To examine motor impairments in strength and motor control, participants performed the following tasks with the paretic ankle (1) maximum voluntary contractions (MVC) and (2) visuomotor tracking of a sinusoidal trajectory. Strength was quantified as the maximum force produced during ankle plantarflexion and dorsiflexion. Motor control was quantified as (a) the accuracy and (b) variability of ankle movement during the visuomotor tracking task. For functional mobility, participants performed (1) overground walking for 7 meters and (2) simulated driving task. Functional mobility was determined by walking speed, stride length variability, and braking reaction time.

Results: Compared with the controls, the stroke group showed decreased plantarflexion strength, decreased accuracy, and increased variability of ankle movement. In addition, the stroke group demonstrated decreased walking speed, increased stride length variability, and increased braking reaction time. The multiple-linear regression model revealed that motor accuracy was a significant predictor of the walking speed and braking reaction time. Further, motor variability was a significant predictor of stride length variability. Finally, the dorsiflexion or plantarflexion strength did not predict walking speed, stride length variability or braking reaction time.

Conclusions: The impairments in motor control but not strength predict functional deficits in walking and driving in high-functioning stroke individuals. Therefore, rehabilitation interventions assessing and improving motor control will potentially enhance functional outcomes in high-functioning stroke survivors.

Target-distractor synchrony affects performance in a novel motor task for studying action selection

The study of action selection in humans can present challenges of task design since our actions are usually defined by many degrees of freedom and therefore occupy a large action-space. While saccadic eye-movement offers a more constrained paradigm for investigating action selection, the study of reach-and-grasp in upper limbs has often been defined by more complex scenarios, not easily interpretable in terms of such selection. Here we present a novel motor behaviour task which addresses this by limiting the action space to a single degree of freedom in which subjects have to track (using a stylus) a vertical coloured target line displayed on a tablet computer, whilst ignoring a similarly oriented distractor line in a different colour. We ran this task with 55 subjects and showed that, in agreement with previous studies, the presence of the distractor generally increases the movement latency and directional error rate. Further, we used two distractor conditions according to whether the distractor’s location changes asynchronously or synchronously with the location of the target. We found that the asynchronous distractor yielded poorer performance than its synchronous counterpart, with significantly higher movement latencies and higher error rates. We interpret these results in an action selection framework with two actions (move left or right) and competing ‘action requests’ offered by the target and distractor. As such, the results provide insights into action selection performance in humans and supply data for directly constraining future computational models therein.

Subthalamic nucleus deep brain stimulation does not improve visuo-motor impairment in Parkinson's disease

OBJECTIVE

To evaluate how bilateral subthalamic nucleus deep brain stimulation (STN-DBS) affects visuo-motor coordination (VMC) in patients with Parkinson's disease (PD).

BACKGROUND

VMC involves multi-sensory integration, motor planning, executive function and attention. VMC deficits are well-described in PD. STN-DBS conveys marked motor benefit in PD, but pyscho-cognitive complications are recognized and the effect on VMC is not known.

METHODS

Thirteen PD patients with bilateral STN-DBS underwent neurological, cognitive, and mood assessment before VMC testing with optimal DBS stimulation parameters ('on-stimulation') and then, on the same day without any medication changes, after DBS silencing and establishing motor function deterioration ('off-stimulation'). Twelve age-matched healthy controls performed 2 successive VMC testing sessions, with a break of similar duration to that of the PD group. The computer cursor was controlled with a dome-shaped 'mouse' hidden from view that minimized tremor effects. Movement duration, hand velocity, tracking continuity, directional control variables, and feedback utilization variables were measured. MANOVA was performed on (1) clinically measured motor function, (2) VMC performance and (3) mood and attention, looking for main and interaction effects of: (1) group (controls/PD), (2) test-order (controls: first/second, PD: on-stimulation/off-stimulation), (3) path (sine/square/circle) and (4) hand (dominant/non-dominant).

RESULTS

Unified PD Rating Scale (UPDRS) Part III worsened off-stimulation versus on-stimulation (mean: 42.3 versus 21.6, p = 0.02), as did finger tapping (p = 0.02), posture-gait (p = 0.01), upper limb function (p<0.001) and backwards digit span (p = 0.02). Stimulation state did not affect mood. PD patients performed worse in non-velocity related VMC variables than controls (F(5,18) = 8.5, p<0.001). In the control group there were significant main effects of hand (dominant/non-dominant), path (sine/square/circle) and test-order (Test_1/Test_2). In the PD group, hand and path effects, but no test-order (on-stimulation/off-stimulation), were found.

CONCLUSIONS

'Low-level' clinically-measured motor function responds to STN-DBS but 'high-level' motor and cognitive functions relating to VMC may be unresponsive to STN-DBS.

Assessment of fine motor control in individuals with Parkinson's disease using force tracking with a secondary cognitive task

BACKGROUND AND PURPOSE

Motor symptoms of Parkinson's disease (PD) are typically assessed using clinical scales such as the Unified Parkinson's Disease Rating Scale, but clinical scales are insensitive to subtle changes early in the disease process. The goal of this project was to use current sensing technology to develop a quantitative assessment tool to document fine motor deficits in PD based on the ability to control grip force output. The assessment was designed to challenge deficits commonly encountered as a result of PD, including dual-task performance of a motor task and a cognitive task simultaneously.

METHODS

Two force sensors were used to measure the isometric pinch grip force between the thumb and index finger in 30 individuals with PD and 30 control participants of similar age without disability. Participants performed a target force tracking task with each of two different target waveforms (sinusoidal or pseudorandom) under each of three different cognitive load conditions (none, subtract 1, and subtract 3). Dependent variables calculated from the force sensor data included root mean square error, tremor integral, and lag.

RESULTS

In general, individuals with PD showed significantly less accuracy in generating the target forces as shown by larger root mean square error compared with controls (P < 0.001). They also showed greater amounts of tremor and lag compared with controls (P = 0.001 and <0.001, respectively). Deficits were more pronounced during the cognitive multitasking component of the test.

DISCUSSION AND CONCLUSIONS

These results will serve as a preliminary work for the development of a clinical biomarker for PD that may help to identify subtle deficits in fine motor control early in the disease process and facilitate tracking of disease progression with time.

Assessing cognition in Parkinson disease: use of the cognitive linguistic quick test

OBJECTIVE

To evaluate the Cognitive Linguistic Quick Test (CLQT) as a cognitive screening tool in Parkinson disease (PD).

METHODS

A total of 93 patients with PD were evaluated with the Mini-Mental State Examination (MMSE) and the CLQT. The CLQT provides separate ratings for 5 cognitive domains. Descriptive statistics, correlations between the tests, and diagnostic value for dementia were analyzed.

RESULTS

Cognitive Linguistic Quick Test correlated well with MMSE. Diagnostic values for dementia were similar for the 2 instruments. Unlike the MMSE, the CLQT also provided domain-specific information on cognitive deficits. Cognitive domains were differentially affected between and within the demented and nondemented patient groups with PD: memory was the weakest domain in the demented group and attention in the nondemented.

CONCLUSIONS

The CLQT is a valuable instrument in assessing cognitive dysfunction in PD. The CLQT is superior to the MMSE as it also provides cognitive domain-specific information.

Visuo-motor coordination deficits and motor impairments in Parkinson's disease

Background

Visuo-motor coordination (VMC) requires normal cognitive executive functionality, an ability to transform visual inputs into movement plans and motor-execution skills, all of which are known to be impaired in Parkinson's disease (PD). Not surprisingly, a VMC deficit in PD is well documented. Still, it is not known how this deficit relates to motor symptoms that are assessed routinely in the neurological clinic. Such relationship should reveal how particular motor dysfunctions combine with cognitive and sensory–motor impairments to produce a complex behavioral disability.

Methods and Findings

Thirty nine early/moderate PD patients were routinely evaluated, including motor Unified Parkinson's Disease Rating Scale (UPDRS) based assessment, A VMC testing battery in which the subjects had to track a target moving on screen along 3 different paths, and to freely trace these paths followed. Detailed kinematic analysis of tracking/tracing performance was done. Statistical analysis of the correlations between measures depicting various aspects of VMC control and UPDRS items was performed. The VMC measures which correlated most strongly with clinical symptoms represent the ability to organize tracking movements and program their direction, rather than measures representing motor-execution skills of the hand. The strong correlations of these VMC measures with total UPDRS score were weakened when the UPDRS hand-motor part was considered specifically, and were insignificant in relation to tremor of the hand. In contrast, all correlations of VMC measures with the gait/posture part of the UPDRS were found to be strongest.

Conclusions

Our apparently counterintuitive findings suggest that the VMC deficit pertains more strongly to a PD related change in cognitive-executive control, than to a reduction in motor capabilities. The recently demonstrated relationship between gait/posture impairment and a cognitive decline, as found in PD, concords with this suggestion and may explain the strong correlation between VMC dysfunction and gait/posture impairment. Accordingly, we propose that what appears to reflect a motor deficit in fact represents a multisystem failure, dominated by a cognitive decline.

Effect of ropinirole on visuo-motor test in newly diagnosed Parkinson's disease patients

OBJECTIVES

The aim of this study was to assess the sensitivity of the visuo-motor test (VMT) compared with the Unified Parkinson's Disease Rating Scale (UPDRS) in newly diagnosed Parkinson's disease (PD) patients.

METHODS

VMT and UPDRS were carried out in 20 patients before treatment onset, 2 weeks after treatment with ropinirole 1.5 mg/day and 2 weeks following increasing the dose of ropinirole to 3.0 mg/day.

RESULTS

Improvement in clinical status was seen in all patients, with a mean UPDRS reduction of 16.6% following treatment with ropinirole 1.5 mg/day, and 38.9% reduction in UPDRS observed with ropinirole 3.0 mg/day. Initial improvement was not correlated with severity of PD, although further improvement with ropinirole 3.0 mg/day correlated linearly with patient's baseline UPDRS. Improvement in the ability to control the direction of the moving hand during tracing is expressed by the reduction of VMT variables following treatment. Mean VMT variables were 36.2% at baseline, 34.0% with ropinirole 1.5 mg/day and 31.7% with ropinirole 3.0 mg/day. Although changes in VMT variables were less uniform across patients, on average, it did correlate with patients UPDRS.

CONCLUSIONS

We suggest that VMT can be useful in the assessment of treatment effect on high-level motor planning and cognitive capabilities in newly diagnosed PD patients, added to the UPDRS which does not appropriately comply with those skills.

Unimpaired negative but enhanced positive priming in Parkinson's disease: Evidence from an identity and a location priming task

Mechanisms of selective attention are frequently reported to be impaired in Parkinson's disease (PD). Fundamental to selective attention is attending to relevant information and, concurrently, ignoring irrelevant information. Both processes can be assessed by positive priming (PP) and negative priming (NP) tasks, respectively. Unlike previous studies, in the present experiment, two separate identity- and location-based priming tasks were applied to 48 PD patients and 48 sex- and age-matched healthy controls. Results indicated that identity and location PP were reliably enhanced in PD patients compared to controls. Both groups showed significant location NP of almost identical magnitude but no identity NP. However, there was evidence for a positive functional relationship between severity of bradykinesia and identity NP. Furthermore, with increasing depression scores, location NP was enhanced in PD patients but not in controls. These findings suggest that disturbed selective attention associated with PD is due to changed mechanisms mediating attention to relevant information rather than due to mechanisms involved in inhibition of irrelevant information.

Backward inhibition in Parkinson's disease

Parkinson's disease has been associated with executive dysfunction, especially task-switching deficits. One factor contributing to task-switching costs is backward inhibition, as measured by less efficient performance when switching back to a task from which one has recently switched away. This alternating-switch cost is considered to be due to persisting inhibition of elements of the previous task set after a switch. In this study, patients with mild to moderate Parkinson's disease and controls performed three tasks (A-C) in an intermixed fashion. Patients with mild to moderate Parkinson's disease and controls showed equivalent response times. However, the patients made significantly more errors during an alternating switch (i.e., ABA) than did control participants. In contrast, there was no group difference in accuracy in the comparable condition of two consecutive switches between different tasks (i.e., CBA). In addition, accuracy for the two groups was similar for trials in which the task was repeated. These data suggest that Parkinson's disease is associated with either increased backward inhibition, or a reduced ability to overcome this inhibition when reactivating a recently abandoned task set.