Abstract
Gait analysis involving cognitive-motor dual task (DT) is a diagnostic tool in geriatrics. Cognitive-motor interference effects during DT, such as decreased walking speed and increased step-to-step variability, have a high predictive value for fall risk and cognitive decline. Previously we showed the feasibility of DT during functional magnetic resonance imaging (fMRI) using an MRI-compatible stepping device. Here, we improved the DT-fMRI protocol with respect to task difficulty and signal robustness, making it more suitable for individualized analysis to better understand the neuronal substrates of cognitive-motor interference effects. Thirty healthy elderly subjects performed cognitive and motor single tasks (ST; stepping or finger tapping), as well as combined cognitive-motor DT during fMRI. After whole brain group level analysis, a region-of-interest (ROI) analysis and the computation of dual task costs (DTC = activation difference ratio ST/DT) at individual level were performed. Activations in the primary (M1) and secondary motor as well as in parietal and prefrontal cortex were measured at the group level during DT. Motor areas showed decreased activation whereas parietal and prefrontal areas showed increased activation in DT vs. ST. Stepping yielded more distinctive activations in DT vs. ST than finger tapping. At the individual level, the most robust activations (based on occurrence probability and signal strength) were measured in the stepping condition, in M1, supplementary motor area (SMA) and superior parietal lobule/intraparietal sulcus (SPL/IPS). The distribution of individual DTC in SPL/IPS during stepping suggested a separation of subjects in groups with high vs. low DTC. This study proposes an improved cognitive-motor DT-fMRI protocol and a standardized analysis routine of functional neuronal markers for cognitive-motor interference at the individual level.
Highlights
Clinical Use of Cognitive-Motor dual task (DT)Performance decline during DT in one or both tasks is indicated by DT interference effects resulting from competing resources used by both tasks
Based on these previous results, the aims of the present study were (1) to improve the functional magnetic resonance imaging (fMRI) protocol developed in Burki et al (2017) in terms of robustness of the fMRI signal to make it better suitable for individual analysis, (2) to target brain areas sensitive to cognitive-motor interference effects during DT which could be used to stratify elderly subjects in different DT impairment levels (3) to evaluate if a finger tapping movement instead of stepping ensures similar results in the DT context, knowing it to be less prone to movement artifacts in the MRI
The analysis of motion parameters showed that none of the subjects exhibited movements larger than > 5 mm translation or > 1◦ rotation during the tapST, cognitive single task (cognST), and tapping and naming/counting (tapDT) fMRI tasks
Summary
Performance decline during DT in one or both tasks is indicated by DT interference effects resulting from competing resources used by both tasks. This can be operationalized as the performance difference between the single and dual task, the socalled dual task costs (DTC). The DTC have been shown to be age dependent. Overall, decreased gait speed and increased step-to-step variability as well as larger DTC are associated with older age (Springer et al, 2006; YogevSeligmann et al, 2010; Holtzer et al, 2014b) and the presence of neurodegenerative disorders such as pre-stages of Alzheimer’s disease (AD), e.g., mild cognitive impairment (MCI; Bridenbaugh and Kressig, 2015; Montero-Odasso et al, 2017)
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