Locomotion Adaptation Deficits in Older Adults With Mild Cognitive Impairment and Alzheimers Disease

In conjunction with cognitive impairments, older adults with Alzheimer's Disease (AD) and Mild Cognitive Impairment (MCI) show increased impairments in walking function throughout disease progression. The ability to walk without the risk of falling is necessary for independent community activity and participation for elderly individuals. However, the relationships between cognition, gait dysfunction, and fall risk in people with MCI and AD are poorly understood, warranting further study. The objective of this study is to test the researchers' central hypothesis that in people with MCI and AD, decreased capacity for locomotor adaptation can worsen disease progression, and lead to reduced motor-cognitive function, mobility, and quality of life.

Community-based walking function requires complex motor coordination, sensory feedback, dynamic balance, adaptation to changing environmental stimuli, while also engaging in attentional tasks such as crossing a busy street or talking over the phone. Unfortunately, cognitive dysfunction, the hallmark of MCI and AD, directly impacts the cognitive-motor neural resources needed to carry out activities of daily living. People with MCI and AD walk slower, fall more, and have deficits in gait performance variables such as stride symmetry, and step regularity. Importantly, gait disturbances have often been shown to precede cognitive decline. In this study, the researchers propose to test their hypothesis that a decline in locomotor adaptation capacity may explain gait and mobility deficits in people with MCI and AD. Locomotor adaptation is a fundamentally important process that enables humans to flexibility respond to environmental demands, enabling normal community walking function. Split-belt adaptation is a standardized, robust, well studied paradigm for quantifying a person's capacity for locomotor adaptation, but had not yet been evaluated in people with MCI and AD. Split-belt walking task assesses locomotor adaptation, i.e. the ability to adjust stepping movements to changing environmental demands via trial-and-error processing. The split-belt task is systematically assessed during treadmill walking, where the speed of each leg can be controlled independently such that one belt and the corresponding leg run at a different speed (e.g., twice as fast or a 2:1 speed ratio) than the other leg. In previous work, both the magnitude and rate of split-belt adaptation as well as de-adaptation (during the after-effect) have provided objective measures of an individual's locomotor adaptation capacity.

The researchers of this study hypothesize that decreased capacity for split-belt adaptation may be an important contributing factor and a potentially sensitive indicator of increased fall risk and cognitive decline in older individuals with MCI and AD.

The researchers will examine locomotor adaptation capacity with three study aims: Aims 1 and 2 are observational, assessing walking function among persons with MCI and AD and age-matched controls. In Aim 3, a clinical trial is performed to evaluate the feasibility of a split-belt walking intervention on walking function in older adults with MCI and AD. Ten participants (5 with MCI and 5 with AD) will complete 5 split-belt treadmill walking exercise sessions over a 2-week period. The primary and secondary outcome measures for this study are measured in evaluation sessions before (Pre-training) and after 5 training sessions (Post-training).

• Change in De-adaptation Magnitude Assessed as Peak Step Length Symmetry [Time frame: Baseline (Pre-training), Week 2 (Post-training)]
• Change in De-adaptation Rate Assessed as the Number of Steps to Reach Step Symmetry [Time frame: Baseline (Pre-training), Week 2 (Post-training)]
• Change in Timed Up and Go (TUG) Test [Time frame: Baseline (Pre-training), Week 2 (Post-training)]
• Change in Falls History [Time frame: Baseline (Pre-training), Week 2 (Post-training)]
• Change in Stride Duration [Time frame: Baseline (Pre-training), Week 2 (Post-training)]
• Change in Double-support Duration [Time frame: Baseline (Pre-training), Week 2 (Post-training)]
• Change in Executive Index Score (EIS) [Time frame: Baseline (Pre-training), Week 2 (Post-training)]
• Change in Trail Making Test Part B Score [Time frame: Baseline (Pre-training), Week 2 (Post-training)]
• Change in Step Length [Time frame: Baseline (Pre-training), Week 2 (Post-training)]
• Change in Step Length Variability [Time frame: Baseline (Pre-training), Week 2 (Post-training)]