Older adults get episodic memory boosting from noninvasive stimulation of prefrontal cortex during learning

Abstract

Episodic memory displays the largest degree of age-related decline, a process that is accelerated in pathological conditions such as amnestic mild cognitive impairment and Alzheimer's disease. Previous studies have shown that the left lateral prefrontal cortex (PFC) contributes to the encoding of episodic memories along the life span. The aim of this randomized, double-blind, placebo-controlled study was to test the hypothesis that anodal trascranial direct current stimulation (tDCS) over the left lateral PFC during the learning phase would enhance delayed recall of verbal episodic memories in elderly individuals. Older adults learned a list of words while receiving anodal or placebo (sham) tDCS. Memory recall was tested 48 hours and 1 month later. The results showed that anodal tDCS strengthened episodic memories, an effect indicated by enhanced delayed recall (48 hours) compared to placebo stimulation (Cohen's d effect size = 1.01). The observation that PFC-tDCS during learning can boost verbal episodic memory in the elderly opens up the possibility to design-specific neurorehabilitation protocols targeted to conditions that affect episodic memory such as mild cognitive impairment.

Low intensity transcranial electric stimulation: Safety, ethical, legal regulatory and application guidelines

“…The incidence does not differ significantly between active and sham stimulation, indicating the effectiveness of the standard fade-in fade-out sham stimulation at least in naïve subjects (Hummel et al, 2010; Lindenberg et al, 2013; Manor et al, 2016; Parikh and Cole, 2014; Sandrini et al, 2014, 2016; Zimerman et al, 2013). Not surprisingly, the identification of the actually applied stimulation paradigm is more accurate after repeated sessions (Nilsson et al, 2015; Wallace et al, 2016).…”

“…About one-third of the studies published until 2016 in aging populations reported no occurrence of tDCS-related AEs without giving details (Table 7). The most commonly reported AEs were typical tingling and itching that usually occurred when stimulation began but were also reported under sham conditions, where stimulation was applied only for a short duration at the beginning of the session (Boggio et al, 2010; Fertonani et al, 2014; Gandiga et al, 2006; Harty et al, 2014; Hoff et al, 2015; Holland et al, 2011; Learmonth et al, 2015; Manenti et al, 2013; Parikh and Cole, 2014; Sandrini et al, 2014, 2016). …”

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

“…A noninvasive brain stimulation technique that can be used to modulate memory in physiological aging is transcranial Direct Current Stimulation (tDCS) [5,6]. TDCS has been used for two main purposes in memory research: (1) to test the causal relationship between activity of a cortical region and a memory function; and (2) to investigate whether tDCS might modulate memory formation and learning, an issue of relevance for research and neurorehabilitation [5,[7][8][9].…”

“…tDCS studies have shown that the left lateral prefrontal cortex (PFC) contributes to verbal episodic memories along the life span [8][9][10][11][12][13] and enhancement of these abilities has been reported in healthy older adults after the application of tDCS over this brain area [8,9,13]. Specifically, Sandrini and coworkers [8,9] showed that anodal tDCS strengthened memories when applied during the encoding phase or after the consolidation process in elderly individuals. However, an aspect that has not been directly investigated in previous studies is the optimal timing of stimulation to induce long-lasting positive effects on episodic memory function.…”

“…In the present study, we re-analyzed data acquired from two previous studies [8,9] in which we showed episodic memory enhancement in older adults when anodal tDCS was applied to the left PFC during the encoding phase [9] or after the memory consolidation process [24h after the encoding session, 8] using the same word-learning paradigm.…”