Abstract
Gait is a basic cognitive purposeful action that has been shown to be altered in late stages of neurodegenerative dementias. Nevertheless, alterations are less clear in mild forms of dementia, and the potential use of gait analysis as a biomarker of initial cognitive decline has hitherto mostly been neglected. Herein, we report the results of a study of gait kinematic time series for two groups of patients (mild cognitive impairment and mild Alzheimer’s disease) and a group of matched control subjects. Two metrics based on permutation patterns are considered, respectively measuring the complexity and irreversibility of the time series. Results indicate that kinematic disorganisation is present in early phases of cognitive impairment; in addition, they depict a rich scenario, in which some joint movements display an increased complexity and irreversibility, while others a marked decrease. Beyond their potential use as biomarkers, complexity and irreversibility metrics can open a new door to the understanding of the role of the nervous system in gait, as well as its adaptation and compensatory mechanisms.
Highlights
Within the large family of neurocognitive disorders, neurodegenerative dementias [1] are receiving increasing attention from the scientific community, to some extent proportional to their increasing prevalence in our ageing societies
We have shown that permutation entropy (PE) and IRR of joint kinematic time series along the gait cycle are modified in two stages of cognitive decline
We have demonstrated that PE and IRR provide complementary properties to provide more in depth insight into the complexity of gait kinematics
Summary
Within the large family of neurocognitive disorders, neurodegenerative dementias [1] are receiving increasing attention from the scientific community, to some extent proportional to their increasing prevalence in our ageing societies. No attempt has yet been made to analyse gait signals as time series, for instance to assess their complexity, which should be altered or modified as a result of motor system lesion and system re-adaptation in patients with cognitive impairment The rationale behind this is that brain signals to the muscles which provoke joint movement may become less continuous and less coordinated; inefficient joint movement noise may be added as a consequence of failure of some neuronal networks; and those signals may produce poor configurations that may not respond (or may respond wrongly) to purposeful cognitive commands such as changing velocity.
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