Auditory-Motor coupling to musical and non-musical rhythms during walking in persons with Multiple Sclerosis

This doctoral thesis is situated in the fields of musicology and rehabilitation sciences. Overall, the embodied music cognition theory1 in combination with task-oriented rehabilitation approaches have been used as umbrellas for studying auditory-motor couplings in patients with Multiple Sclerosis. Of particular interest were the underlying processes of entrainment and synchronisation when musical and non-musical rhythms were used to impact walking. Through my work in musicology and rehabilitation science, I aimed at contributing to epistemologies and methodologies of both disciplines: to musicology by expanding on the nature of auditory-motor couplings. In rehabilitation sciences, to investigate the application of auditory-motor coupling as a task-oriented rehabilitation approach for motor and cognitive impairments in persons with multiple sclerosis. Persons with Multiple Sclerosis with motor and cognitive impairments thereby provided a unique population where both the nature and application of auditory-driven entrainment – specific to music and metronomescould be studied. Evidence for using auditory-motor coupling in neurological rehabilitation to facilitate walking is increasing. In the context of this thesis, auditory-motor coupling can be conceived as the coupled interaction which occurs between person walking (the footfalls) and the auditory stimuli (the beats in music and metronomes). Nevertheless, evidence is still scarce for its applicability in rehabilitation of PwMS with motor and cognitive impairments. This interdisciplinary thesis aims address this niche. To reach this end, two systematic reviews and one large multi-session case-control observational study were performed. Thereby, with the work compiled in this thesis, first, I contributed towards understanding and expanding the current theories which underlie the process of auditory-motor coupling, called entrainment. Second I contributed in the understanding of applying auditory-motor coupling in persons with multiple sclerosis compared to healthy controls. I investigated if PwMS were able to couple to different tempi marking different motor and cognitive thresholds, as well as sustain coupling for a longer walking period. I investigated what were the effects of the coupling on their walking, gait dynamics, perceived physical and cognitive fatigue and motivation. I also investigated if the results of the above mentioned investigations yielded differences when coupling to music compared to metronomes. XVII A total of eight chapters are found in this thesis; two of which are general introduction (chapter 1) and general discussion (chapter 8). Below, the main aims of the investigations and results of remaining chapters are elaborated. Chapter 2 is a systematic literature review, which provides evidence of music-based interventions’ effectiveness for cognitive and motor rehabilitation in neurological populations. The review results revealed that music-based interventions did have positive effects on the cognitive and motor functions. The effects on motor functions were more extensively investigated than for cognitive functions. Yet studies were warranted to investigate cognition as well as motor and cognitive dysfunctions in combination, and a need to expand the investigations to neurological diseases other than Parkinson’s disease and stroke. Chapter 3 is a methodological systematic review. Here, six metrics were identified to capture the interaction between the human movement and the auditory stimuli. An explanation of these metrics as well as formulas of calculations were provided in order to facilitate including these metrics in auditory-motor studies, to enhance the current state of the art and practice across the neurological gait rehabilitation. In addition, some of these outcome measures have been used as primary outcome measures in the experimental study. Thereafter, I conducted a case-control multi-session observational experimental study in PwMS and Healthy Controls (HC). The protocol was designed such that each session consisted of separate research questions. Chapters 4-7 contain experiments conducted in each session of the multi-session observational experimental study. Chapter 4 presents an experiment, where I investigated spontaneous and intended auditorymotor coupling processes to different motor thresholds ranging from preferred baseline cadence up to +10% of the baseline cadence in PwMS and HC. The study results showed that spontaneous synchronisation was possible at ranges of entrainment basin (0 and +2% of preferred walking cadence); at tempo higher than this, instruction was needed for PwMS and HC. A conceptual model was proposed; from +4% of PWC, active cognitive processes were required to engage in the process of minimisation of prediction error in order to maintain auditory-motor entrainment. On the contrary, below +4%, passive cognitive processes were required to engage in the process of minimisation of prediction error. Chapter 5 presents an experiment, where I investigated coupling the motor and auditory systems at different tempi with music compared to metronomes, in PwMS and HC. Besides, I investigated whether the coupling to music and/or metronomes impacted perceived fatigue and gait in PwMS compared to HC. As the process of the coupling requires cognitive components66, I additionally explored if cognitive impairment posed to be a factor XVIII in the coupling. The study results showed that PwMS were able to synchronise and increase cadence at higher tempi (up to +10%) when coupling for three minutes with metronomes. They were able to synchronise and increase cadence up to +8% when coupling for three minutes with music. Walking to music was perceived cognitively and physically less fatiguing and more motivating when walking three minutes to music compared to metronomes at all tempi. In addition, cognitive impaired PwMS were not able to synchronise past +6% when walking 3 minutes to music and metronomes. However further studies are warranted to confirm this, taking into account other symptoms of MS such as fatigue, fatigability, depression, etc. Chapter 6 presents an experiment, where I investigated the effect on gait dynamics during the auditory-motor coupling (i.e. the entrainment process), when participants walked to music and metronomes at different tempi using detrended fluctuation analysis (DFA). I hypothesised that walking with music may result in more persistent gait dynamics compared to walking in time to an isochronous metronome due to the difference in auditory structures in both stimuli. The study results showed that the study of gait dynamics (fractal scaling of statistical probabilities of inter-step-interval time series) can provide valuable information in regards to control mechanisms to adjust into making necessary corrections during auditory-motor coupling. This study allowed to interpret the interactive dynamics of a coupled system, whereas walking to music is advised due to better gait dynamics. Chapter 7 presents an experiment, where I expanded our investigation to prolonged walking, given the ecological validity. In this chapter, I investigated if coupling could be sustained when walking for 12 minutes at an optimal tempo to music and metronomes in PwMS compared to HC. I also investigated the effects of the prolonged walking on perceived fatigue, motivation and gait when compared to walking for 12 minutes in silence. There was a difference in results seen between walking to three minutes to music/metronomes and 12 minutes (sustaining synchronisation for a longer time). When walking for 12 minutes, PwMS maintained synchronisation for longer when walking to music compared to metronomes, while perceiving less cognitive fatigue and higher motivation. Results reflected that coupling to metronomes may require more attention compared to coupling to music. To conclude, the results of my work compiled in this thesis contributed into developing a conceptual model and expanding the current framework of auditory-motor coupling and entrainment. In addition, the work provided evidence to support the notion that auditorymotor coupling- and more so with the use of music as the auditory stimuli- could be used for functional walking training in PwMS with cognitive and motor impairments.

Publication year:2020

Accessibility:Embargoed