Abstract
Manual dexterity measures can be useful for early detection of age-related functional decline and for prediction of cognitive decline. However, what aspects of sensorimotor function to assess remains unclear. Manual dexterity markers should be able to separate impairments related to cognitive decline from those related to healthy aging. In this pilot study, we aimed to compare manual dexterity components in patients diagnosed with cognitive decline (mean age: 84 years, N = 11) and in age comparable cognitively intact elderly subjects (mean age: 78 years, N = 11). In order to separate impairments due to healthy aging from deficits due to cognitive decline we also included two groups of healthy young adults (mean age: 26 years, N = 10) and middle-aged adults (mean age: 41 years, N = 8). A comprehensive quantitative evaluation of manual dexterity was performed using three tasks: (i) visuomotor force tracking, (ii) isochronous single finger tapping with auditory cues, and (iii) visuomotor multi-finger tapping. Results showed a highly significant increase in force tracking error with increasing age. Subjects with cognitive decline had increased finger tapping variability and reduced ability to select the correct tapping fingers in the multi-finger tapping task compared to cognitively intact elderly subjects. Cognitively intact elderly subjects and those with cognitive decline had prolonged force release and reduced independence of finger movements compared to young adults and middle-aged adults. The findings suggest two different patterns of impaired manual dexterity: one related to cognitive decline and another related to healthy aging. Manual dexterity tasks requiring updating of performance, in accordance with (temporal or spatial) task rules maintained in short-term memory, are particularly affected in cognitive decline. Conversely, tasks requiring online matching of motor output to sensory cues were affected by age, not by cognitive status. Remarkably, no motor impairments were detected in patients with cognitive decline using clinical scales of hand function. The findings may have consequences for the development of manual dexterity markers of cognitive decline.
Highlights
Cognitive aging represents the reduction of mental abilities with age, such as attention, memory function, and information processing speed [1]
Post-hoc testing revealed that young adults (YA) had smaller errors compared to other groups (Table 2, p < 0.05)
Young adults had decreased error compared to elderly subjects (p = 0.03) and to subjects with cognitive decline (p = 0.001)
Summary
Cognitive aging represents the reduction of mental abilities with age, such as attention, memory function, and information processing speed [1]. The prevalence of Mild Cognitive Impairment (MCI) and Alzheimer’s disease (AD) increases strongly with age These conditions are common in approximately 10% of the population over 65 years of age. Markers of impaired manual dexterity have been used [3], and a recent longitudinal 4-year cohort study found that prolonged time taken in two simple manual dexterity tasks (including putting on and buttoning a shirt) was related to higher risk of developing cognitive decline [according to MMSE; [10]]. Performance measures previously used were most often global task-based measures, i.e., time taken to complete task [5, 6, 10] It remained unclear what aspect of sensorimotor control was being measured, making the rationale for detecting cognitive decline uncertain. It is likely that sensorimotor performance measures incorporating cognitive control would enhance discrimination and improve detection of cognitive decline
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