Abstract
Episodic memory is critical to daily life functioning. This type of declarative memory declines with age and is the earliest cognitive function to be compromised in Alzheimer’s disease (AD). Subjective memory complaints are commonly reported by older adults and have been considered a risk factor for developing AD. The possibilities for prevention of memory disorders in older adults have increased substantially in recent years. Previous studies have shown that anodal transcranial Direct Current Stimulation (tDCS) applied over the left lateral prefrontal cortex (PFC) after a contextual reminder strengthened existing verbal episodic memories, conceivably through reconsolidation, in elderly people. In this study, we hypothesized that anodal tDCS applied over the left lateral PFC after a contextual reminder would improve delayed memory retrieval relative to placebo (sham) stimulation in elderly individuals with SMC. Twenty-two subjects learned a list of words. Twenty-four hour later, tDCS (anodal or placebo) was applied over the left lateral PFC after a contextual reminder. Memory retrieval was tested 48h and 30 days later. These findings showed that anodal tDCS over the left lateral PFC strengthened existing episodic memories, a behavioral effect documented by improved recognition up to 30 days, relative to placebo stimulation. This study suggests that tDCS after a contextual reminder can induce long-lasting beneficial effects by facilitating the consolidation processes and opens up the possibility to design specific non-invasive interventions aimed at preventing memory decline in this at-risk population.
Highlights
There is evidence that episodic memory declines with age (Spencer and Raz, 1995; Balota et al, 2000; Salthouse, 2010; Rhodes and Katz, 2017; Solesio-Jofre et al, 2017)
Episodic memory is critical to daily life functioning (Tulving, 1983) and several clinical works have reported that this type of long-term memory relies on the integrity of the medial temporal lobe (MTL) (Dickerson and Eichenbaum, 2010)
– Inclusion: persons aged 60 or over, education between 5 and 18 years, Mini Mental State Examination (MMSE) score from 27 to 30 (Folstein et al, 1975), a score of more than 1.0 SD at Everyday Memory Questionnaire (EMQ) above the mean score obtained in a group of healthy older participants, normal objective memory performance on neuropsychological tests, normal objective cognitive performance in all the administered tests, normal scores in functional assessment, absence of mood and anxiety disorders, absence of criteria for a diagnosis of dementia according to DSM-V (American Psychiatric Association, 2014)
Summary
There is evidence that episodic memory declines with age (Spencer and Raz, 1995; Balota et al, 2000; Salthouse, 2010; Rhodes and Katz, 2017; Solesio-Jofre et al, 2017). Evidence supporting the critical role of lateral PFC in episodic memory along the life span comes from clinical neuropsychology (Jetter et al, 1986; Janowsky et al, 1989a,b; Incisa Della Rocchetta and Milner, 1993; Eslinger and Grattan, 1994; Gershberg and Shimamura, 1995; Mangels, 1997; Alexander et al, 2003; Duarte et al, 2005), functional magnetic resonance imaging (Cabeza et al, 1997, 2000; Fletcher and Henson, 2001; Dennis et al, 2007, 2008), and transcranial magnetic stimulation studies (Rossi et al, 2001, 2004, 2011; Sandrini et al, 2003; Floel et al, 2004; Kohler et al, 2004; Innocenti et al, 2010; Manenti et al, 2010a, 2011, 2012; Gagnon et al, 2011; Blumenfeld et al, 2014)
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