The Short-term Effects of Noninvasive Electrical Brain Stimulation on Dual Tasking in Older Adults

Optimization of Transcranial Direct Current Stimulation (tDCS) for Dual Task Performance in Older Adults With and Without a History of Falls

The tDCS & Dual Tasking study will compare the effects of transcranial Direct Current Stimulation (tDCS) targeting three different cortical regions (as well as sham stimulation) on dual task standing and walking in older adults with and without a recent history of recurrent falls.

The ability to stand and walk safely, especially while performing additional cognitive tasks like talking, reading or decision making, is critical to the preservation of functional independence into old age. Such "dual tasking" often impairs balance, even in healthy older adults and those with greater dual task "costs" are more likely to suffer future falls. Transcranial direct current stimulation (tDCS) is a safe, noninvasive and inexpensive means of modulating activity across cortical networks. A single, 20-minute session of tDCS facilitates brain activity for up to 24 hours. Through Dr. Manor's previous research in healthy older adults, he has discovered that just 20 minutes of tDCS targeting the left dorsolateral prefrontal cortex (dlPFC)-a region involved in both cognitive and motor function-immediately reduces the dual task costs to balance when standing and walking, and improves performance in the timed up-and-go (TUG) test of mobility. However, there are several brain networks with known involvement in balance control and dual tasking, and the optimal brain region to target to improve dual task capacity has not been established. The proposed study will be a double-blinded, sham-controlled study in which older adults both with and without a history of falling undergo dual task assessments immediately before and after single, 20-minute sessions of tDCS designed to target several different brain regions with known involvement in dual tasking and the maintenance of balance.

Inclusion Criteria:

"Faller" group

• Aged 65 years and older
• Able to read, write and communicate in English
• Self-report of 2 or more falls within the past 6 months

"Non-Faller" Group

• Aged 65 years and older
• Able to read, write, and communicate in English
• Self-report of 1 or no (zero) falls within the past 6 months

Exclusion Criteria:

• Self-reported diagnosis of Parkinson's disease, Alzheimer's disease or dementia, multiple sclerosis, history of stroke or other neurodegenerative disorder.
• Self-reported active cancer for which chemo-/radiation therapy is being received.
• Hospitalization within the past 3 months due to acute illness or as a result of a musculoskeletal injury significantly affecting gait and balance.
• Montreal Cognitive Assessment score <18, or insufficient understanding of study procedures following review of the Informed Consent Form. Understanding will be assessed by asking the participant to answer the following three questions: 1) What is the purpose of this study? 2) What are the risks of study involvement? 3) If you decide to participate, are you allowed to withdraw from the study at any time? Answers will be recorded by study personnel on the "Assessment of Protocol Understanding" form (see attached). Insufficient understanding will be defined by one or more incorrect answers, as determined at the discretion of the investigator.
• Inability to stand or ambulate unassisted for at least 25 feet.
• Contraindications to tDCS, including a reported seizure within the past two years, use of neuro-active drugs, the risk of metal objects in the brain, skull, or head, self-reported presence of specific implanted medical devices (e.g., deep brain stimulator, medication infusion pump, cochlear implant), or the presence of any active dermatological condition, such as eczema, on the scalp (see appendix for standardized tDCS screening questionnaire).