The paper reviewed here is ‘Dual-tasking and Gait in People with Mild Cognitive Impairment. The effect of working memory’ by Chertkow and colleagues and is freely available here. In the abstract the authors write that
‘Our findings suggest that cortical control of gait is associated with decline in working memory in people with MCI‘
In the introduction, the authors cite one study in which the inability to walk and talk simultaneously (a form of dual task cognition) predicted falls. The authors argue that it is difficult to understand the relationship between cognitive domains and gait in dementia as there is a global deterioration in cognitive functioning. For this reason they have focused on Mild Cognitive Impairment (MCI) in which single as well as multiple cognitive domains may be affected.
Subjects from an ongoing longitudinal study were identified. Subjects were 65 years or older, dementia was excluded and they scored 1.5 standard deviations or more below the norm for the memory tasks. The inclusion criteria for the ongoing study weren’t clear from this paper i.e how were the participants originally recruited to the study. The authors do state that the subjects in this part of the study were contacted by telephone but that is presumably only after they have been recruited into the original study. A score of >5 on the Geriatric Depression Scale was also an exclusion criteria.
The Montreal Cognitive Test and the Mini-Mental State Examination were used. The researchers explain that high MMSE and low MCT scores are associated with Mild Cognitive Impairment. Gait assessment was performed using the Gait Velocity Test which is a simple measure of gait velocity. Subjects were asked to either count backwards and walk or else to name animals aloud and walk. There were minimum pilot trials to enable the subjects to familiarise themselves with the task while attempting to avoid the confounding effects of trial learning on subsequent performance. A power calculation was performed and the relevant number of subjects (i.e 60) were included in the study.
Average age was 77.7 years, there was a mean of 12.1 years of education and an average MMSE score of 26.8. Gait velocity was reduced with both dual task conditions compared to single gait velocity although the confidence intervals overlapped between for all three tasks. There was also found to be a significant correlation between performance on the Trail Masking Task B and single gait velocity. There was also a significant correlation between the performance on the counting and verbal fluency tasks.
The authors concluded that there was a significant correlation between both executive function and gait velocity as well as working memory and gait velocity. They suggest that there may be some overlap in the cortical areas generating gait as well as working memory or executive functioning. There are a number of areas involved in gait and presumably this overlap might be occurring at the ideational stage i.e where the plans for movements are constructed rather than where the finer details of which muscle groups should be allocated to the movement. The most obvious location would be within the frontal cortex. Indeed this would most likely be in the dorsolateral prefrontal cortex. The researchers also draw the conclusion that impaired executive functioning may be the confounder that explains the relationship between gait velocity and performance on cognitive tasks.
This is a small cross-sectional study (occurring within a prospective longitudinal study) which provides evidence that working memory and executive functioning impact on gait velocity in subjects with MCI and possibly share the same neural substrate. This suggests that executive functioning may be related to falls and this would benefit from further testing.
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