Optimizing tDCS to Improve Dual Task Gait and Balance

Study Overview
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Brief Summary
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The objective of this study is to determine the acute effects of single sessions of personalized tDCS, traditional tDCS, and sham stimulation on dual task standing and walking in older adults who are free of overt disease yet who present with poor baseline dual task performance.

Detailed Description
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Standing and walking are almost always completed in unison with other cognitive tasks such as talking, reading or making decisions. The ability to perform this important type of dual tasking is critical to daily activities and dependent upon one's capacity to effectively activate appropriate brain networks that include the left dorsolateral prefrontal cortex (dlPFC). Transcranial direct current stimulation (tDCS) is a safe, noninvasive technology that can selectively modulate brain excitability (i.e., the likelihood of activation) by passing low-level currents between electrodes placed upon the scalp. The investigators have demonstrated through a series of studies that a single, 20-minute exposure of tDCS targeting the left dlPFC-administered via two large sponge electrodes-reduces dual task costs to metrics of standing postural control and gait, when tested immediately following stimulation. Still, the investigators and others have also observed relatively high between-subject variability in the effects of this 'traditional' bipolar form of tDCS. The investigators contend that this variability in effectiveness arises in part from relatively diffuse and unspecific current flow when using large sponge electrodes, in combination with individual variability in head and brain anatomy that significantly alters current flow and the generated electric field in the target brain region. In this project, the investigators will apply recent advances in tDCS modeling and administration to 1) model the electric fields generated by traditional tDCS in older adults using their individual structural brain MRIs, and 2) develop personalized tDCS-delivered via an array of eight small gel electrodes-by using optimization algorithms to determine electrode placement and current parameters needed to generate desired electrical field with the brain region of interest. The Specific Aim is to examine the immediate after-effects of personalized tDCS, traditional tDCS, and sham stimulation on dual task standing and walking in older adults. The study population will be older men and women without overt disease or illness, yet with poor baseline dual task performance defined as a dual task cost (i.e., reduction) to gait speed of at least 20% induced by simultaneously performing a serial subtraction task when walking. The investigators hypothesize that across participants, the effect of traditional tDCS on dual task standing and walking performance will correlate with a specific component of the electric field generated over the left dlPFC target. The investigators also hypothesize that personalized tDCS will induce A) greater effects on dual task standing and walking performance as compared to traditional tDCS and sham stimulation, and B) these effects will be more consistent across individuals as compared to traditional tDCS. This project will provide important insights into tDCS dosage that will enable the investigators and many other researchers to better understand, control, and optimize this form of noninvasive brain stimulation to individual head and brain anatomy. It is also expected to demonstrate that personalized tDCS, as compared to the traditional approach, significantly improves the size and consistency of observed benefits to dual task standing and walking in vulnerable older adults.

Official Title
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Optimizing Transcranial Direct Current Stimulation (tDCS) to Improve Dual Task Gait and Balance in Older Adults

Conditions
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Aging

Intervention / Treatment
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* Other: Traditional tDCS
* Other: Traditional Sham
* Other: Personalized tDCS
* Other: Personalized Sham


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: Men and women aged 65-85 years Poor dual task performance, defined as a preferred gait speed that is >20% slower when walking and simultaneously performing verbalized serial subtractions (i.e., dual tasking), as compared to walking normally (i.e. single tasking) Exclusion Criteria: Unwillingness to cooperate or participate in the study protocol An inability to walk or stand for 30 continuous seconds without an assistive device A diagnosis of a gait disorder, Parkinson's disease, Alzheimer's disease or dementia, multiple sclerosis, previous stroke or other neurodegenerative disorder Self-report of acute illness, injury or other unstable medical condition; Any report of severe lower-extremity arthritis or pain, physician-diagnosis of peripheral neuropathy, or other peripheral neuromuscular disease that may confound the effects of tDCS on gait or postural control Use of antipsychotics, anti-seizure, benzodiazepines, or other neuroactive medications Severe depression defined by a Geriatric Depression Scale score greater than 11; Any report or physician-diagnosis of schizophrenia, bipolar disorder or other psychiatric illness Contraindications to MRI or tDCS, including reported seizure within the past two years, use of neuro-active drugs, the risk of metal objects anywhere in the body, self-reported presence of specific implanted medical devices (e.g., deep brain stimulator, medication infusion pump, cochlear implant, pacemaker, etc.), or the presence of any active dermatological condition, such as eczema, on the scalp

Ages Eligible for Study
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Minimum Age: 65 Years
Maximum Age: 85 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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Accepts Healthy Volunteers

Study Plan
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How is the study designed?
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Design Details

Primary Purpose: Basic Science
Allocation: Randomized
Intervention Model: Single Group Assignment
Interventional Model Description: The investigators will conduct a within-subject, double-blinded, randomized controlled study comparing the after-effects of single sessions of traditional tDCS, personalized tDCS, and two different sham conditions on dual task performance in men and women aged 65-85 years with poor baseline dual task performance. Participants will complete a structural brain MRI. They will then complete four visits during which they will receive one of the four interventions in random order.
Masking: Quadruple


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Experimental: Traditional tDCS<br>At the beginning of stimulation, the current will be increased manually from 0.1 mA, in 0.1 mA increments over 60 seconds, up to a maximum of 1.8 mA. Participants will be instructed to notify study personnel if and when they feel any uncomfortable sensation. The ramp-up will be stopped at this point and for the remainder of the session tDCS will be delivered at an intensity of 0.1 mA below the highest level reached. At the end of each session, current will be automatically ramped down to 0.0 mA over a 60 second period. | Other: Traditional tDCS<br>* The participant will receive a single-session of traditional tDCS for 20 minutes.<br>|
| Sham Comparator: Traditional Sham<br>A traditional sham will be used to maximize blinding of traditional sponge-based stimulation. The same sponge placement, ramp-up procedure, and session duration as described with the Traditional tDCS will be used; however, current will automatically be ramped down 60 seconds after ramp-up. | Other: Traditional Sham<br>* The participant will receive a single-session of traditional sham for 20 minutes.<br>|
| Experimental: Personalized tDCS<br>Baseline MRI's will enable personalization of tDCS via current flow modeling and optimized to each participant with the goal of generating an average nE over the dlPFC of the same size as the one delivered by a traditional montage using sponges in an average subject at 1.5 mA of current. The direct current delivered by any one electrode will however never exceed 2.0 mA; the total amount of current from all electrodes will not exceed 4 mA. Each 20- minute session will begin and end with a 60-second ramp up/down of current amplitude to maximize comfort. | Other: Personalized tDCS<br>* The participant will receive a single-session of personalized tDCS for 20 minutes.<br>|
| Sham Comparator: Personalized Sham<br>An active sham will be used in which very low-level currents (0.5mA max) are transferred between the same electrodes used in the active condition throughout the entire 20-minute session. This intervention will be optimized to each participant to deliver currents designed to not significantly influence their cortical tissue, but still mimic the cutaneous sensations induced by tDCS. | Other: Personalized Sham<br>* The participant will receive a single-session of personalized sham for 20 minutes.<br>|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Dual task cost to gait speed | Assesses the percent difference in gait speed between single and dual task walking conditions. | Change from baseline to immediate post-tDCS follow-up | 
| Dual task cost to postural sway speed | Assesses the percent difference in postural sway speed between single and dual task standing conditions. | Change from baseline to immediate post-tDCS follow-up | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Dual task cost to stride time variability | Assesses the percent difference in stride time variability between single and dual task walking conditions. | Change from baseline to immediate post-tDCS follow-up | 
| Single task gait speed | Assesses gait speed within single task walking conditions | Change from baseline to immediate post-tDCS follow-up | 
| Dual task gait speed | Assesses gait speed within dual task walking conditions | Change from baseline to immediate post-tDCS follow-up | 
| Single task stride time variability | Assesses stride time variability within single task walking conditions | Change from baseline to immediate post-tDCS follow-up | 
| Dual task stride time variability | Assesses stride time variability within dual task walking conditions | Change from baseline to immediate post-tDCS follow-up | 
| Dual task cost to postural sway area | Assesses the percent difference in postural sway elliptical area between single and dual task standing conditions | Change from baseline to immediate post-tDCS follow-up | 
| Single task postural sway speed | Assesses postural sway speed within single task standing conditions | Change from baseline to immediate post-tDCS follow-up | 
| Dual task postural sway speed | Assesses postural sway speed within dual task standing conditions | Change from baseline to immediate post-tDCS follow-up | 
| Single task postural sway area | Assesses postural sway area within single task standing conditions | Change from baseline to immediate post-tDCS follow-up | 
| Dual task postural sway area | Assesses postural sway area within dual task standing conditions | Change from baseline to immediate post-tDCS follow-up | 

 Terms related to the study
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Keywords Provided by Centre Hospitalier Valida
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Mobility, Dual Task