Fractal auditory stimulation has greater benefit for people with Parkinson's disease showing more random gait pattern

Background: Healthy gait dynamics are characterized by the presence of fractal, persistent stride-to-stride variations, which become more random with Parkinson's disease (PD). Rhythmic auditory stimulation with fractal beat-to-beat variations can change gait dynamics in people with PD toward more persistence. Research question: How does gait in people with PD change when synchronizing steps with fractal melodic metronomes with different step-to-beat ratios, and which stimulus do they prefer? Methods: In this cross-sectional study, 15 people with PD and 15 healthy older adults walked over-ground in three conditions: self-paced, paced by a fractal auditory stimulus with a 1:1 step-to-beat ratio (‘metronome’), and fractal auditory stimulus with a 1:2 step-to-beat ratio (‘music’). Gait dynamics were recorded with instrumented insoles, and detrended fluctuation analysis (DFA) was applied to the series of stride time intervals. Stimuli preference was assessed using Likert-like scales and open-ended questions. ANOVAs were used to compare mean, coefficient of variation, α-DFA, and the responses from the continuous Likert scales. Pearson correlations were used to assess the relationship between ‘music’ and ‘metronome’ enjoyment or difficulty with gait outcomes, and to determine the association between baseline α-DFA and changes due to the stimuli. Results: Our major findings are that (i) stride-to-stride variations were more persistent with the ‘metronome’ compared to baseline for both groups, (ii) the effect was greater for people with lower α-DFA at baseline (i.e., more random stride-to-stride variations), and (iii) both groups found the ‘metronome’ less difficult to synchronize with. Significance: This study showed that people with PD and healthy older adults walk with higher statistical persistence in their stride-to-stride variations when instructed to synchronize their steps with a fractal stimulus. Participants with lower persistence at baseline benefited the most from the fractal ‘metronome’, highlighting the importance to develop patient-centered tests and interventions.