Alzheimer's Disease (AD) is associated with impairments in both gait and cognition, significantly increasing fall risk. Falls are a leading cause of injury-related disability in older adults, and individuals with AD experience a nearly threefold higher rate of falls compared to neurotypical older adults. There is an urgent need for fall prevention interventions tailored to the unique deficits of individuals with AD. Converging evidence suggests that interventions aiming to reduce fall risk in AD should target both gait and cognition. Rhythmic music interventions, such as Rhythmic Auditory Stimulation (RAS) can harness global brain activation and auditory-motor entrainment to facilitate high-intensity exercise to alleviate AD-related neurocognitive and gait dysfunction. This study aims to assess the neural correlates of gait dysfunction in people with AD, evaluate if baseline neurocognitive impairment is predictive of the effects of RAS, and evaluate RAS benefits for individuals with AD.

1. Background and Scientific Rationale: Alzheimer's Disease (AD) is a progressive neurodegenerative disorder characterized by the accumulation of amyloid-beta plaques and tau neurofibrillary tangles, leading to widespread cortical and subcortical atrophy. While memory impairment is the most recognized clinical feature, AD also profoundly disrupts motor systems - particularly gait - through degeneration of frontal-subcortical circuits that govern attentional control of movement. Gait deficits in AD include reduced speed, shortened stride length, increased stride variability, and disproportionate cognitive-motor interference during dual-task conditions. These impairments reflect underlying disruptions in prefrontal-motor connectivity and are strongly predictive of fall events.

   Rhythmic Auditory Stimulation (RAS) is an interventional technique that harnesses the coupling between the auditory and motor systems. Rhythmic auditory cues delivered as an isochronous beat (with or without music) activate auditory-motor entrainment pathways, recruiting motor planning circuits in the basal ganglia, supplementary motor area, and cerebellum to promote more stable and efficient gait. RAS has demonstrated efficacy in improving gait parameters in neurological populations including Parkinson's disease and stroke. Its application in AD is motivated by evidence that music-based rhythmic stimuli elicit broad, cross-regional brain activation, including areas relatively spared in early AD, and may therefore provide a viable sensory scaffold for augmenting motor control even as cognitive reserve declines.

2. Study Design and Overview: This is a single-session, non-randomized clinical trial enrolling 40 subjects -- 20 adults with a clinical diagnosis of AD (restricted to mild cognitive impairment, MCI) and 20 neurotypical older adults serving as a healthy comparison group. All participants complete one study visit conducted at the Boston University Neuromotor Recovery Laboratory (NRL) and/or affiliated BU clinical research facilities.

3. Specific Aims

   The study pursues three primary aims:

   1. To characterize the neural correlates of gait dysfunction in people with AD using simultaneous brain-body imaging during walking under typical and challenging conditions.
   2. To evaluate whether baseline neurocognitive profile (degree and domain of impairment) predicts individual responsiveness to RAS during walking.
   3. To quantify the acute effects of RAS on gait and functional brain connectivity in individuals with AD compared to neurotypical older adults.

4. Measurement Framework & Outcome Measures: Mobile Brain-Body Imaging (MoBI): A defining feature of this study is the use of a Mobile Brain-Body Imaging (MoBI) framework consisting of the concurrent capture of neural and biomechanical data during real-time ambulation. Brain activity is measured using functional near-infrared spectroscopy (fNIRS), a non-invasive optical neuroimaging technique that quantifies changes in cortical hemodynamics (oxy- and deoxy-hemoglobin concentration) as a proxy for regional neural activation. Unlike traditional neuroimaging modalities, fNIRS is tolerant of movement artifact, making it well-suited for ambulatory paradigms. Biomechanical gait data are collected concurrently using inertial measurement units (IMUs).

5. Walking Conditions: Participants will walk overground under multiple conditions designed to vary cognitive and sensorimotor demand: a) walking with and without RAS and b) walking on an altered, gait-destablizing surface (foam mat or rocker-bottom footwear) to increase sensorimotor challenge. These conditions are intended to elicit a gradient of gait and neural responses and to probe the extent to which RAS can attenuate dual-task interference and cognitive-motor coupling deficits characteristic of AD.

6. Cognitive Assessment: A standardized neuropsychological battery will be administered to all participants with AD to characterize baseline cognitive status and confirm MCI diagnosis. This battery includes the Montreal Cognitive Assessment (MoCA), Mini Mental Status Examination (MMSE), Consortium to Establish a Registry in Alzheimer's Disease (CERAD) delayed recall, Boston Naming Test (short form), Trail Making Test A and B, and verbal fluency measures. These assessments will be used to examine relationships between neurocognitive impairment profile and the magnitude of RAS benefit observed during walking.

7. Significance: This study will generate foundational data linking neural mechanisms of gait dysfunction in AD with behavioral responsiveness to an accessible, non-pharmacological auditory-motor intervention in a population at high fall risk and with limited therapeutic options. Findings are intended to inform participant selection criteria and outcome measure development for future RAS-based clinical trials targeting fall prevention in AD.

Inclusion Criteria:

General Inclusion (both healthy and AD populations):

• Community-dwelling
• Capable of walking short community distances (approximately 10-15 minutes at a time) without assistance from another person or a device (such as a cane).
• Able to communicate with researchers
• Age 50-90 (inclusive)

Population-specific Inclusion criteria:

• Healthy -

  • No diagnosis of AD

• AD population-

CERAD score of <1.5 SD from age + education adjusted norms on delayed recall domain or one or more other cognitive domains (i.e. language, attention).

MoCA score between 20-30 MMSE score between 25-30

Exclusion Criteria:

• Presence of significant hearing impairment
• Current orthopedic, neurologic or other medical condition that limits the ability to walk.

The MOCA, MMSE and CERAD tests will be completed in-person after the participant consents into the study. If the participant is determined to be ineligible based on their performance on these tests (compared to inclusion requirements listed above), they will be informed that they are not eligible for this study and the study visit will be cancelled. They will then be withdrawn from the study; their clinical tests and study documentation will be maintained for the purposes of completeness, but will not be used for any study analyses.

De-identified individual participant data underlying the results reported in publications arising from this study will be made available. Shared data may include participant demographics, clinical characteristics, gait and biomechanical measures, neurophysiological measures, metronome settings for delivery of RAS, and other study variables necessary to reproduce published findings. Data will be de-identified prior to sharing in accordance with applicable regulations and institutional policies.

Data will become available following publication of the primary study results or within 12 months of study completion, whichever occurs first, and will remain available for at least 5 years thereafter.

De-identified data and supporting documentation will be made available to qualified researchers for scientifically sound research purposes. Requests will be reviewed by the study investigators and may require a data use agreement. Access will be provided in accordance with participant consent, institutional policies, and applicable regulations.