Optimizing tDCS to Improve Dual Task Gait and Balance

Not Applicable

Completed

Conditions: Aging

Interventions: Other: Traditional tDCS
Other: Personalized Sham
Other: Traditional Sham
Other: Personalized tDCS

Registration Number: NCT04295798

Lead Sponsor: Hebrew SeniorLife

Brief Summary: The objective of this study is to determine the acute effects of single sessions of optimized tDCS, conventional 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: 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. We have demonstrated through a series of studies that a single, 20-minute exposure of 'conventional' 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, we and others have also observed relatively high between-subject variability in the effects of this conventional bipolar form of tDCS. We 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, we will 1) apply recent advances in tDCS modeling and administration to model the electric fields generated by conventional tDCS in older adults using their individual structural brain MRIs, and 2) develop and test an multi-channel tDCS montage designed to optimize current flow to the left dlPFC (i.e., 'optimized' tDCS). Our Specific Aim is to examine the immediate after-effects of conventional tDCS, optimized tDCS, and sham stimulation on dual task standing and walking in older adults. Our 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 10% induced by simultaneously performing a serial subtraction task when walking. We hypothesize that across participants, the effect of conventional tDCS on dual task standing and walking performance will correlate with a specific component of the electric field generated over the left dlPFC target. We also hypothesize that optimized tDCS will induce A) greater effects on dual task standing and walking performance as compared to conventional tDCS and sham stimulation, and B) these effects will be more consistent across individuals as compared to conventional tDCS.

This project will provide important insights into tDCS "dosage" that will enable us 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 optimized tDCS, as compared to the conventional approach, significantly improves the size and consistency of observed benefits to dual task standing and walking in vulnerable older adults.

Recruitment & Eligibility

Status: COMPLETED

Sex: All

Target Recruitment: 29

Inclusion Criteria

Men and women aged 65-85 years
Poor dual task performance, defined as a preferred gait speed that is >10% 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

Study & Design

Study Type: INTERVENTIONAL

Study Design: CROSSOVER

Arm && Interventions

Group	Intervention	Description
Traditional tDCS	Traditional tDCS	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.
Personalized Sham	Personalized Sham	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.
Traditional Sham	Traditional Sham	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.
Personalized tDCS	Personalized tDCS	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.

Primary Outcome Measures

Name	Time	Method
Absolute Change in Dual Task Cost to Gait Speed From Baseline to Immediately Post Intervention	Change from baseline to immediately post-tDCS, up to 60 minutes	Prior to testing, participants were outfitted with wireless biosensors, each containing a triaxial accelerometer, goniometer and magnetometer, on the low back and feet to record gait kinematics (Mobility Lab™, APDM Inc). Six 25-meter walking trials were completed pre and post tDCS. Two at a preferred speed while walking quietly (single task), two at a preferred speed while performing a cognitive task (dual task) and two fast walking trials. The cognitive task during the dual task condition was verbalized serial subtractions of 3's from a random three-digit number. The absolute change was then calculated using post-intervention dual task cost minus baseline dual task cost. The outcome was calculated by averaging the dual task costs of the four trials. Negative numbers demonstrate lower (i.e., better) dual task cost post intervention. The preferred Unit of Measure is unitless.
Absolute Change in Dual Task Cost to Standing Postural Sway Speed From Baseline to Immediately Post Intervention	Change from baseline to immediately post-tDCS, up to 60 minutes	Postural sway speed was assessed by measuring standing postural sway (ie., center-of pressure fluctuations) during six, 45-second trials of standing with eyes open (single task), eyes closed, or performing a cognitive task (dual task standing) on a stationary force platform (Kistler, Amherst, NY). The cognitive task was verbalized serial subtractions of 3's from a random three-digit number between 200 and 999. Participant responses during each trial were recorded. The absolute change was then calculated using post-intervention dual task cost minus baseline dual task cost. The outcome was obtained by averaging the dual task costs of the four trials. Negative numbers demonstrate lower (i.e., better) dual task cost post intervention. The preferred Unit of Measure is unitless.

Secondary Outcome Measures

Name	Time	Method
Absolute Change in Dual Task Cost to Stride Time Variability From Baseline to Immediately Post Intervention	Change from baseline to immediately post-tDCS, up to 60 minutes	Stride time variability is a measure of how consistent limb movements are during walking and is expressed as the coefficient of variation. Prior to testing, participants were outfitted with wireless biosensors, each containing a triaxial accelerometer, goniometer and magnetometer to record gait kinematics (Mobility Lab™, APDM Inc). Six 25-meter walking trials were completed. Two at a preferred speed while walking quietly (single task), two at a preferred speed while performing a cognitive task (dual task) and two fast walking trials. The cognitive task during the dual task condition was verbalized serial subtractions of 3's. The absolute change was then calculated using post-intervention dual task cost minus baseline dual task cost. Negative numbers demonstrate lower (i.e., better) dual task cost post intervention. The preferred Unit of Measure is unitless.
Absolute Change in Single Task Gait Speed From Baseline to Immediately Post Intervention	Change from baseline to immediately post-tDCS, up to 60 minutes	Prior to testing, participants were outfitted with wireless biosensors, each containing a triaxial accelerometer, goniometer and magnetometer, on the low back and feet to record gait kinematics (Mobility Lab™, APDM Inc). Six 25-meter walking trials were completed pre and post tDCS. Two at a preferred speed while walking quietly (single task). The absolute change from baseline to immediately post intervention was calculated by averaging the single task gait speeds (m/s) pre and post.
Absolute Change in Dual Task Gait Speed From Baseline to Immediately Post Intervention	Change from baseline to immediately post-tDCS, up to 60 minutes	Prior to testing, participants were outfitted with wireless biosensors, each containing a triaxial accelerometer, goniometer and magnetometer, on the low back and feet to record gait kinematics (Mobility Lab™, APDM Inc). Six 25-meter walking trials were completed pre and post tDCS. Two at a preferred speed while performing a cognitive task (dual task). The cognitive task during the dual task condition was verbalized serial subtractions of 3's from a random three-digit number between 200 and 999. Participant responses during each trial were recorded. The absolute change from baseline to immediately post intervention was calculated by averaging the dual task gait speeds (m/s) pre and post.
Absolute Change in Single Task Stride Time Variability From Baseline to Immediately Post Intervention	Change from baseline to immediately post-tDCS, up to 60 minutes	Stride time variability (STV) is a measure of how consistent limb movements are during walking. It's expressed as the coefficient of variation (CoV) and calculated from the mean and standard deviation of stride time. Prior to testing, participants were outfitted with wireless biosensors, each containing a triaxial accelerometer, goniometer and magnetometer, on the low back and feet to record gait kinematics (Mobility Lab™, APDM Inc). Six 25-meter walking trials were completed. Two at a preferred speed while walking quietly (single task). The absolute change from baseline to immediately post intervention was calculated by averaging the single task stride time variability pre and post.
Absolute Change in Dual Task Stride Time Variability From Baseline to Immediately Post Intervention	Change from baseline to immediately post-tDCS, up to 60 minutes	Stride time variability (STV) is a measure of how consistent limb movements are during walking. It's expressed as the coefficient of variation (CoV) and calculated from the mean and standard deviation of stride time. Prior to testing, participants were outfitted with wireless biosensors, each containing a triaxial accelerometer, goniometer and magnetometer, on the low back and feet to record gait kinematics (Mobility Lab™, APDM Inc). Six 25-meter walking trials were completed. Two at a preferred speed while performing a cognitive task (dual task). The cognitive task during the dual task condition was verbalized serial subtractions of 3's from a random three-digit number between 200 and 999. Participant responses during each trial were recorded. The absolute change from baseline to immediately post intervention was calculated by averaging the dual task stride time variability pre and post.
Absolute Change in Dual Task Cost to Standing Postural Sway Area From Baseline to Immediately Post Intervention	Change from baseline to immediately post-tDCS, up to 60 minutes	Postural sway area was assessed by measuring postural sway elliptical area during six, 45-second trials of standing with eyes open (single task), eyes closed, or performing a cognitive task (dual task standing) on a stationary force platform (Kistler, Amherst, NY). The cognitive task was verbalized serial subtractions of 3's from a random three-digit number between 200 and 999. Participant responses during each trial were recorded. The absolute change was then calculated using post-intervention dual task cost minus baseline dual task cost. The outcome was obtained by averaging the dual task costs of the four trials. Negative numbers demonstrate lower (i.e., better) dual task cost post intervention. The preferred Unit of Measure is unitless.
Absolute Change in Single Task Postural Sway Speed From Baseline to Immediately Post Intervention	Change from baseline to immediately post-tDCS, up to 60 minutes	Postural sway speed was assessed by measuring standing postural sway (ie., center-of pressure fluctuations) during two, 45-second trials of standing with eyes open (single task) on a stationary force platform (Kistler, Amherst, NY) pre and post intervention. The absolute change from baseline to immediately post intervention was calculated by averaging the single task postural sway speed (m/s) pre and post.
Absolute Change in Dual Task Postural Sway Speed From Baseline to Immediately Post Intervention	Change from baseline to immediately post-tDCS, up to 60 minutes	Postural sway speed was assessed by measuring standing postural sway (ie., center-of pressure fluctuations) during two, 45-second trials of standing with eyes open while performing a cognitive task (dual task) on a stationary force platform (Kistler, Amherst, NY) pre and post intervention. The cognitive task was verbalized serial subtractions of 3's from a random three-digit number between 200 and 999. Participant responses during each trial were recorded. The absolute change from baseline to immediately post intervention was calculated by averaging the dual task postural sway speed (m/s) pre and post.
Absolute Change in Single Task Postural Sway Area From Baseline to Immediately Post Intervention	Change from baseline to immediately post-tDCS, up to 60 minutes	Postural sway area was assessed by measuring postural sway elliptical area during two, 45-second trials of standing with eyes open (single task) on a stationary force platform (Kistler, Amherst, NY) pre and post intervention. The absolute change from baseline to immediately post intervention was calculated by averaging the single task postural sway area pre and post.
Absolute Change in Dual Task Postural Sway Area From Baseline to Immediately Post Intervention	Change from baseline to immediately post-tDCS, up to 60 minutes	Postural sway area was assessed by measuring postural sway elliptical area during two, 45-second trials of standing with eyes open while performing a cognitive task (dual task) on a stationary force platform (Kistler, Amherst, NY) pre and post intervention. The cognitive task was verbalized serial subtractions of 3's from a random three-digit number between 200 and 999. Participant responses during each trial were recorded. The absolute change from baseline to immediately post intervention was calculated by averaging the dual task postural sway area pre and post.