Transcranial Direct Current Stimulation Enhances Episodic Memory in Healthy Older Adults by Modulating Retrieval-Specific Activation

Abstract

Memory decline has become an issue of major importance in the aging society. Anodal transcranial direct current stimulation (atDCS) is a viable tool to counteract age-associated episodic memory deterioration. However, the underlying neural mechanisms are unclear. In this single-blind, sham-controlled study, we combined atDCS and functional magnetic resonance imaging to assess the behavioral and neural consequences of multiple-session atDCS in older adults. Forty-nine healthy older adults received either 10 sessions of anodal or sham stimulation over the left dorsolateral prefrontal cortex. Before and after stimulation, participants performed a source memory task in the MRI scanner. Compared to sham stimulation, atDCS significantly improved item memory performance. Additionally, atDCS significantly increased regional brain activity around the stimulation area in the prefrontal cortex and extended to the bilateral anterior cingulate cortex. Neural changes in the prefrontal cortex correlated with memory gains. Our findings therefore indicate that multiple-session offline atDCS may improve memory in older adults by inducing neural alterations.

Effects of Transcranial Direct Current Stimulation on Cognitive Function in Older Adults with and without Mild Cognitive Impairment: A Systematic Review and Meta-Analysis of Randomized Controlled Trials

“…A total of 991 participants participated in 9 RCTs [41‒45, 52‒55]. Fifteen task types were included: object-location learning, source memory task, item memory task, digit span forward task, Rivermead behavioral memory test, word memory task, auditory verbal learning test, wordlist learning task, logical memory, international shopping list test, one card-learning task, test de aprendizaje verbal España-Complutense, direct digits of the WAIS-III, and memory alteration test.…”

“…Lu et al [42] reported that the loss rate was 13.9%, so it was regarded as high risk. The remaining eight studies [41,[43][44][45][46][52][53][54][55] were considered low risk because the follow-up situation was clearly described or did not influence the meta-analysis result.…”

Enhancing Immediate Memory, Potential Learning, and Working Memory with Transcranial Direct Current Stimulation in Healthy Older Adults

“…Neuroplasticity is based on cortical and neuronal excitability, and stimulating excitability with tDCS enhances cognitive processes [35], through the forti cation of neural connections [36,37] and, therefore, a recon guration of brain networks [38]. For example, Huo et al (2020) found that tDCS was effective when stimulating the DLPFC because neural changes in the prefrontal cortex resulted in better memory performance [39].…”

Opposite pattern of transcranial direct current stimulation effects in middle-aged and older adults: Behavioral and neurophysiological evidence

“…The results regarding the cognitive effects of tDCS in aging are mixed, as the administration of atDCS has not consistently resulted in the enhancement of cognitive functions in older individuals. Some tDCS studies have reported memory improvement in healthy older adults when stimulating the prefrontal cortex ( Manenti et al, 2013 , 2017 ; Sandrini et al, 2014 , 2016 , 2019 ; Medvedeva et al, 2019 ; Huo et al, 2020 ) or the left temporoparietal cortex ( Antonenko et al, 2019 ). On the other hand, other studies applying tDCS over the prefrontal cortex reported no effects or even a worsening in aging ( Leach et al, 2016 , 2019 ; Peter et al, 2019 ; Habich et al, 2020a , b ).…”