Stimulating the aging brain.

S uccess in using noninvasive neural stimulation in humans has paved the way for several exciting additions to the ever-expanding toolkit used by cogni-tive neuroscientists to understand the relationship between brain and behavior (eg, transcranial magnetic stimulation and transcranial direct current stimulation [tDCS]). Although neuroimaging methods such as functional MRI and electroencephalography are not always strictly correlational, 1 the ability to modulate behavior via training and targeted brain stimulation provides critical causal data to inform psychological and neuroimaging findings (eg, Zanto et al 2). Moreover, these approaches have the additional potential to serve as effective cognitive enhancers to augment abilities in healthy populations , 3–5 as well as therapeutic interventions to remediate deficits in individuals with neurological and psychiatric conditions. 6–8 tDCS modulates neuronal excitability, putatively by increasing calcium levels at the site of anodal stimulation even at relatively weak currents of a few milliam-peres 9 , altering neuronal resting membrane potential, 10 and possibly increasing neuroplasticity by inducing long-term potentiation. 11 In humans, tDCS is usually applied at the scalp noninvasively at 1 to 2 mA for 10 to 30 minutes, during which time participants are asked to perform a behavioral task of interest. 12 The rapid adoption of tDCS by the neuroscientific community since 2000 is evident in the exponential increase in the number of tDCS-related papers indexed in PubMed over the years (Fig). It has been applied to basic cogni-tive neuroscience and cognitive enhancement in healthy adults, as well as for the potential treatment of diseases such as depression, 8 Parkinson disease, 13 and Alzheimer disease. 7 In this issue of the Annals of Neurology, Zimerman and colleagues put tDCS to excellent use in their study, ''Neuroenhancement of the Aging Brain: Restoring Skill Acquisition in Old Subjects.'' 14 As the authors note, the fastest growing segment of the labor market is persons older than 50 years. Despite high expectations of many older adults in terms of how they would like to perform , insidious impairments in cognitive abilities are a common phenomenon, with deficits spanning multiple cognitive domains, including attention, working memory , and perceptual abilities, 15,16 possibly due to widespread disruptions in neural communication. 17 Even a mild deficit in cognition can constrain an otherwise productive life and reduce independence. Such cognitive deficits are a cause of great distress to many older adults who feel that their ability to lead high-quality lives is negatively impacted, and …