Transcranial Direct Current Stimulation in Aging Research

As we age, the brain not only undergoes structural changes, but also a cascade of neurophysiological and neurochemical changes. These age-related changes result in declines in cognition, motor, and sensory function, even in the absence of neurological or neurodegenerative disease. Transcranial direct current stimulation-based effects on neuronal activity, neuroplastic response of tissue, and modulation of hyper vs. hypo active brain systems may have significant benefit for ameliorating symptoms of advanced aging in the brain. However, there are significant practical, technical and methodological considerations necessary for appropriately designing and implementing tDCS in aging populations. In this chapter, we will discuss the impact of brain atrophy and comorbid age-related conditions on tDCS, as well as potential modifying effects of medications commonly used in older adults. This chapter will describe appropriate considerations for selection of functional outcomes for tDCS studies in older adults. This will include discussion of relevant changes in motor and cortical excitability with age that can impact tDCS outcomes. We then review evidence for effects of tDCS on age-related cognitive, physical and motor function, and sensory processing while paying special attention to methodological challenges in these domains. This chapter will also cover special considerations for the adjunctive use of tDCS with electrophysiology and functional magnetic resonance imaging in older adults, and specific ethical consideration of tDCS use in this population. Finally, the chapter will examine additional considerations for the application of tDCS for purposes of enhancing function in healthy seniors in the absence of disease states.