Optimizing tDCS to Improve Dual Task Gait and Balance
Condition: Aging
Study type: Interventional

Summary: 
      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: 
      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.
    

Intervention name(s): Traditional tDCS; Traditional Sham; Personalized tDCS; Personalized Sham
Intervention type(s): Other; Other; Other; Other
Intervention description(s): The participant will receive a single-session of traditional tDCS for 20 minutes.; The participant will receive a single-session of traditional sham for 20 minutes.; The participant will receive a single-session of personalized tDCS for 20 minutes.; The participant will receive a single-session of personalized sham for 20 minutes.
Allocation: Randomized
Intervention model: Single Group Assignment
Intervention 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 (Participant, Care Provider, Investigator, Outcomes Assessor)
Primary purpose: Basic Science
Keywords: Mobility; Dual Task