Ely S. Simon

Dual tasking, gait rhythmicity, and Parkinson's disease: which aspects of gait are attention demanding?

Cognitive function and the performance of a secondary, dual task may affect certain aspects of gait, but the relationships between cognitive function and gait are not well understood. To better understand the motor control of gait and the relationship between cognitive function and gait, we studied cognitive function and the effects of different types of dual tasking on the gait of patients with Parkinsons disease (PD) and controls, contrasting measures of gait automaticity and rhythmicity with other features. Patients with idiopathic PD (n = 30; mean age 71.8 year) with moderate disease severity (Hoehn and Yahr Stage 2–3) were compared to age and gender‐matched healthy controls (n = 28). Memory and executive function were also assessed. In both groups, gait speed decreased in response to dual tasking, in a parallel fashion. For the PD group only, gait variability increased compared to usual walking. Executive function was significantly worse in the PD group, while memory was not different in the two groups. Executive function measures were significantly correlated with gait variability during dual tasking, but not during usual walking. These findings demonstrate that regulation of gait variability and rhythmicity is apparently an automatic process that does not demand attention in healthy adults. In patients with PD, however, this ability becomes attention‐demanding and worsens when subjects perform secondary tasks. Moreover, the associations between executive function and gait variability suggest that a decline in executive function in PD may exacerbate the effects of dual tasking on gait, potentially increasing fall risk.

Dual-tasking effects on gait variability: the role of aging, falls, and executive function.

The objectives of the present study were to test the hypothesis that the dual‐tasking effect on gait variability is larger in healthy older adults than it is in healthy young adults; that this effect is larger in idiopathic elderly fallers than it is in healthy older adults; and that the dual‐tasking effects on gait variability are correlated with executive function (EF). Young adults and older adults who were classified as fallers and nonfallers were studied. Gait speed, swing time, and swing time variability, a marker of fall risk, were measured during usual walking and during three different dual‐tasking conditions. EF and memory were evaluated. When performing dual tasks, all three groups significantly decreased their gait speed. Dual tasking did not affect swing time variability in the young adults and in the nonfallers. Conversely, dual tasking markedly increased swing time variability in the fallers. While memory was similar in fallers and nonfallers, EF was different. The faller‐specific response to dual tasking was significantly correlated with tests of EF. These findings demonstrate that dual tasking does not affect the gait variability of elderly nonfallers or young adults. In contrast, dual tasking destabilizes the gait of idiopathic elderly fallers, an effect that appears to be mediated in part by a decline in EF.

Walking is more like catching than tapping: gait in the elderly as a complex cognitive task

Walking is generally viewed as an automated, over-learned, rhythmic motor task and may even be considered the lower-limb analog of rhythmic finger tapping, another automated motor task. Thus, one might hypothesize that walking would be associated with a simple rhythmic task like tapping rather than with a complex motor task like catching. Surprisingly, however, we find that among older adults, routine walking has more in common with complex motor tasks, like catching a moving object, than it does with tapping. Tapping performance, including both the average tapping interval and the variability of tapping interval, was not significantly associated with any gait parameter (gait speed, average stride time and stride time variability). In contrast, catch game performance was significantly associated with measures of walking, suggesting that walking is more like catching than it is like tapping. For example, participants with a higher gait speed tended to have lower times to first move when catching, better catching accuracy, and less catching errors. Stride time variability was significantly associated with each of the measures of catching. Participants with a lower stride time variability (a more steady gait) had better catching accuracy, lower time to first move, fewer direction changes when moving the cursor to catch the falling object, and less catching errors. To understand this association, we compared walking performance to performance on the Stroop test, a classic measure of executive function, and tests of memory. Walking was associated with higher-level cognitive resources, specifically, executive function, but not with memory or cognitive function in general. For example, a lower (better) stride time variability was significantly associated with higher (better) scores on the Stroop test, but not with tests of memory. Similarly, when participants were stratified based on their performance on the Stroop test and tests of memory, stride time variability was dependent on the former, but not the latter. These findings underscore the interconnectedness of gait and cognitive function, indicate that even routine walking is a complex cognitive task that is associated with higher-level cognitive function, and suggest an alternative approach to the treatment of gait and fall risk in the elderly.

Validity of a novel computerized cognitive battery for mild cognitive impairment.

BackgroundThe NeuroTrax Mindstreams computerized cognitive assessment system was designed for widespread clinical and research use in detecting mild cognitive impairment (MCI). However, the capability of Mindstreams tests to discriminate elderly with MCI from those who are cognitively healthy has yet to be evaluated. Moreover, the comparability between these tests and traditional neuropsychological tests in detecting MCI has not been examined.MethodsA 2-center study was designed to assess discriminant validity of tests in the Mindstreams Mild Impairment Battery. Participants were 30 individuals diagnosed with MCI, 29 with mild Alzheimers disease (AD), and 39 healthy elderly. Testing was with the Mindstreams battery and traditional neuropsychological tests. Receiver operating characteristic (ROC) analysis was used to examine the ability of Mindstreams and traditional measures to discriminate those with MCI from cognitively healthy elderly. Between-group comparisons were made (Mann-Whitney U test) between MCI and healthy elderly and between MCI and mild AD groups.ResultsMindstreams outcome parameters across multiple cognitive domains significantly discriminated among MCI and healthy elderly with considerable effect sizes (p < 0.05). Measures of memory, executive function, visual spatial skills, and verbal fluency discriminated best, and discriminability was at least comparable to that of traditional neuropsychological tests in these domains.ConclusionsMindstreams tests are effective in detecting MCI, providing a comprehensive profile of cognitive function. Further, the enhanced precision and ease of use of these computerized tests make the NeuroTrax system a valuable clinical tool in the identification of elderly at high risk for dementia.

Risk factors for dementia, depression and psychosis in long-standing Parkinson's disease

Summary.Objectives. To study the relationships between clinical features of Parkinsons disease (PD) and the development of dementia, depression or psychosis in patients with long-standing disease. Background. The natural history of dementia and depression in PD, and its relation to psychosis in long standing PD, are unclear. Method. 172 consecutive patients (99 men and 73 women, mean age at symptoms onset 58.3 ± 13.2 years) with 5 years or more of PD (mean symptom duration of 11.8 ± 5.6 years) were studied. Clinical data were collected during the last office visit through physical examination, detailed history, review of patient charts and outside documents. Dementia and depression were diagnosed according to DSM-IV criteria, while psychosis was diagnosed if hallucinations or delusions were present. Chi-square and t tests were used to compare the patient characteristics among those with vs. those without mental complications of the disease at different disease stages. Logistic regression was used for the comparison of associations between the presence of dementia or depression (dependent variable) and age at onset of PD, duration of PD and disease staging (explanatory variables). Results. The study population consisted of 45 patients at Hoehn & Yahr (H&Y) stage ≤2.5 (26%), 104 patients at stage 3 (60.5%) and 23 patients at H&Y stage 4–5 (13.5%). Sixty one patients (36%) had dementia, 55 patients had depression (33%) and 50 patients (27%) had psychosis. Dementia and depression were significantly associated with disease severity as reflected in the H&Y scale (P = 0.0003, Z = 3.59; P = 0.006, Z = 3.22, respectively). These associations were significant also for the older age of PD onset (≥59 years n = 89) subgroup (p = 0.001, Z = 3.2 for dementia and p = 0.02, Z = 2.9 for depression), but not for younger onset cases (<59 years n = 83). Dementia was significantly associated with older age of PD onset (β = 0.04, p = 0.009) while depression was inversely associated with age of PD onset (β = −0.04, p = 0.02). The presence of dementia was also significantly associated with depression (β = 1.49, p = 0.0006). Dementia and depression were found to be independent explanatory variables for the development of psychosis (logistic regression, odds ratio (OR) = 26.0, p < 0.0001; OR = 10.2, p < 0.0001, respectively). In patients with younger age of PD onset, depression more than dementia was strongly correlated with the appearance of psychosis. Conclusion. Dementia in PD was related to older age of symptoms onset and old age. Depression was associated with dementia or early age of PD onset. Depression seemed to contribute to the appearance of psychosis even more than dementia, especially in patients with younger age of symptoms onset.

A Common Cognitive Profile in Elderly Fallers and in Patients with Parkinson’s Disease: The Prominence of Impaired Executive Function and Attention

The present study examined the cognitive profile of elderly fallers relative to healthy elderly controls and patients with Parkinsons disease (PD), a positive-control group, using a computerized battery. Fallers performed more poorly than controls on executive function, attention, and motor skills, but performed comparably on memory, information processing and the Mini-Mental State Examination. A similar profile was evident for PD patients. However, unlike PD patients, fallers were abnormally inconsistent in their reaction times. These findings indicate that elderly fallers may have a unique cognitive processing deficit (i.e., variability of response timing) and underscore the importance of executive function and attention as potential targets for fall risk screening and interventions.

Effects of methylphenidate on cognitive function and gait in patients with Parkinson's disease: a pilot study.

Abstract: Twenty-one patients with Parkinsons disease were studied before and 2 h after the administration of a single dose of 20 mg of methylphenidate. In response to methylphenidate, attention significantly improved, whereas memory and visual-spatial performance were unchanged. Gait speed, stride time variability, and Timed Up and Go times (demonstrated measures of fall risk) significantly improved. These findings suggest a new potential pharmacologic means of enhancing mobility and decreasing fall risk in Parkinsons disease.

Thalamic stimulation for parkinsonian tremor: correlation between regional cerebral blood flow and physiological tremor characteristics

We used (15)O-labeled water (H(2)(15)O) positron emission tomography (PET) to study eight Parkinsons disease (PD) patients with unilateral ventral intermediate (Vim) thalamic nucleus deep brain stimulation (DBS) for severe tremor. Triaxial accelerometry (TRIAX) was used during imaging to obtain on-line measures of tremor characteristics. Regional cerebral blood flow (rCBF) scans together with TRIAX recordings were collected in three stimulation conditions (OFF, MID, and ON, corresponding, respectively, to 0%, 50%, and 100% reductions in mean accelerometry signal). Statistical Parametric Mapping (SPM99) revealed significant rCBF reductions during stimulation in the ipsilateral sensorimotor cortex (SMC) and the contralateral cerebellum, as well as concurrent increases in the ipsilateral ventral thalamus (P < 0.05, corrected). Covariate analysis of rCBF with physiological tremor characteristics revealed that tremor acceleration correlated positively with changes in the SMC and supplementary motor cortex ipsilaterally (P < 0.05, uncorrected), and negatively with changes in the ipsilateral cuneus (P < 0.05, corrected). After removing tremor acceleration effects, changes in tremor frequency correlated negatively with changes in the contralateral dentate nucleus and pons (P < 0.05, uncorrected). Our results suggest that Vim DBS for PD tremor modulates the activity of cerebello-thalamo-cortical pathways. Specific tremor characteristics relate to activity in different nodes of this system.

Synchrony of rest tremor in multiple limbs in parkinson's disease: evidence for multiple oscillators.

Summary. Recent evidence points to involvement of central nervous system oscillators in Parkinsons disease (PD) rest tremor. It remains unknown whether one or multiple oscillators cause tremor in multiple limbs. Based on the prediction that multiple oscillators would cause low coherence even with similar average frequency, we studied 22 PD patients using accelerometers on multiple limbs. Records were digitized and spectral analysis was performed. Peak frequencies in the arms, legs, and chin were similar, indicating that biomechanical factors did not determine the frequency. Coherence between different axes of individual accelerometers and between different segments of the same limb was high. However, coherence between tremor in different limbs was low. There was no consistent pattern across patients of ipsi- vs. contralateral predominance of coherence. These data suggest that tremor in PD is generated by multiple oscillatory circuits, which operate on similar frequencies.

Computerized cognitive testing battery identifies mild cognitive impairment and mild dementia even in the presence of depressive symptoms

Cognitive and depressive symptoms co-occur, complicating detection of mild cognitive impairment (MCI) and early dementia. In this study, discriminant validity of a novel computerized cognitive battery for MCI detection was evaluated after covariation for depressive symptom severity. In addition to the computerized battery, participants at two sites received the 30-item self-administered Geriatric Depression Scale (GDS; n = 72); those at two other centers received the observer-administered Cornell Scale for Depression in Dementia (CSDD; n = 88). In both cohorts, a Global Cognitive Score and memory, executive function, visual spatial, and verbal index scores discriminated among cognitively healthy, MCI, and mild dementia groups after covariation for GDS or CSDD, respectively (p < 0.05). Thus, the computerized battery for detection of mild impairment is robust to comorbid depressive symptoms, supporting its clinical utility in identifying neurodegenerative disease even in elderly with depression.