The brain mechanisms underlying walking in complex situations in healthy older adults and persons with parkinson's disease


Introduction: The ability to walk safely and independently is a fundamental component of daily living activities. Walking while dual tasking and obstacle negotiation are two tasks that have been used to investigate walking in complex situations. Deficits in cognitive domains and sensory-motor processes associated with aging and neurodegeneration impair the ability to successfully assess the environment and react to it. These changes in the ability to walk are modulated via neural circuits. However, the actual neural circuits of the brain involved in the control of locomotion in different challenging situations are still poorly understood. Methods: Two groups of subjects; 20 healthy older adults (mean age 69.7±1.3 yrs, 50% females) and 47 persons with PD (mean age 71.7±1.1 yrs, 32% females) were studied. The protocol included real and imagined walking while negotiating obstacles and dual tasking. Walking conditions were performed while being monitored with fNIRS and imagined walking were assessed in the MR scanner. A repeated measures design (condition x group) was conducted with two levels; within group and between groups. Results: Significant differences in brain activation were observed in the fMRI and fNIRS. Between groups comparison showed that persons with PD had a significantly higher activation in frontal, parietal, occipital, and cerebellum regions during usual walking compared to healthy older adults (p<0.048). Comparison between the walking tasks within each group revealed (1) increased activation during walking while negotiating obstacles in both groups (p<0.023) and (2) increased activation during walking while dual tasking only in healthy older adults (p<0.035). Correlations between brain activation and performance in motor-cognitive tests were found in both groups however, healthy older adults presented inverse correlation and persons with PD positive correlation. Conclusions: These findings indicate that subjects with PD activate larger brain areas than healthy older adults even during usual walking. Perhaps, this increased activation is a compensatory strategy to enhance performance. The increased activation already during usual walking task may limit the ability to increase activation or recruit additional brain areas during the more complex walking tasks and may contribute to the high prevalence of falls and the dual tasking difficulty in persons with PD.

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