The optimal timing of stimulation to induce long-lasting positive effects on episodic memory in physiological aging

Abstract

Episodic memory displays the largest degree of age-related decline. A noninvasive brain stimulation technique that can be used to modulate memory in physiological aging is transcranial Direct Current Stimulation (tDCS). However, an aspect that has not been adequately investigated in previous studies is the optimal timing of stimulation to induce long-lasting positive effects on episodic memory function. Our previous studies showed episodic memory enhancement in older adults when anodal tDCS was applied over the left lateral prefrontal cortex during encoding or after memory consolidation with or without a contextual reminder. Here we directly compared the two studies to explore which of the tDCS protocols would induce longer-lasting positive effects on episodic memory function in older adults. In addition, we aimed to determine whether subjective memory complaints would be related to the changes in memory performance (forgetting) induced by tDCS, a relevant issue in aging research since individuals with subjective memory complaints seem to be at higher risk of later memory decline. The results showed that anodal tDCS applied after consolidation with a contextual reminder induced longer-lasting positive effects on episodic memory, conceivably through reconsolidation, than anodal tDCS during encoding. Furthermore, we reported, providing new data, a moderate negative correlation between subjective memory complaints and forgetting when anodal tDCS was applied after consolidation with a contextual reminder. This study sheds light on the best-suited timing of stimulation to induce long-lasting positive effects on memory function and might help the clinicians to select the most effective tDCS protocol to prevent memory decline.

Effects of tDCS on motor learning and memory formation: A consensus and critical position paper

“…-decreasing the threshold for hyperpolarization of neurons on one side of a gyrus but depolarization on the other). Systematic determination of the optimal timing of stimulation for inducing long-lasting effects, and how this varies across individuals, is another avenue where more research is needed (Manenti, Sandrini, Brambilla, & Cotelli, 2016;Martin, Liu, Alonzo, Green, & Loo, 2014). Indeed, a more coordinated effort where experimental parameters and modeling assumptions are iteratively refined is required (Bestmann, 2015;Brunoni et al, 2012).…”

Individual Differences and Long-term Consequences of tDCS-augmented Cognitive Training

“…Jeon and Han (2012) ;Park, Seo, Kim, and Ko (2014);and Jones, Stephens, Alam, Bikson, and Berryhill (2015) all found continued improvements to WM performance from a week to 2 months after stimulation. Persistent, long-term changes have also been detected as a function of learning or training in other domains as well, such as motor skill training (Reis et al, 2009), math training (Looi et al, 2016), and episodic memory retrieval (Manenti, Sandrini, Brambilla, & Cotelli, 2016). However, to our knowledge, no other study of combined tDCS and cognitive training has examined whether these follow-up effects are maintained for periods in excess of 2-3 months after the intervention.…”

Effects of tDCS on motor learning and memory formation: a consensus and critical position paper

“…-decreasing the threshold for hyperpolarization of neurons on one side of a gyrus but depolarization on the other). Systematic determination of the optimal timing of stimulation for inducing long-lasting effects, and how this varies across individuals, is another avenue where more research is needed (Manenti, Sandrini, Brambilla, & Cotelli, 2016;Martin, Liu, Alonzo, Green, & Loo, 2014). Indeed, a more coordinated effort where experimental parameters and modeling assumptions are iteratively refined is required (Bestmann, 2015;Brunoni et al, 2012).…”