tDCS-Induced Memory Reconsolidation Effects: Analysis of Prominent Predicting Factors

Abstract

BackgroundMemory impairment is among one of the greatest cognitive complaints in midlife and in old age. Considering the importance of good memory functioning in everyday life, it is crucial to study interventions that can reduce the natural decline in this cognitive function. Transcranial Magnetic Stimulation (TMS) studies have demonstrated that the lateral prefrontal cortex (PFC) plays a causal role in enhancing episodic memory recall through reconsolidation. Using a similar paradigm with transcranial direct current stimulation (tDCS) over the left lateral PFC, facilitation effects were observed in delayed memory retrieval in older adults with subjective memory complaints (SMCs) and amnestic Mild Cognitive Impairment (aMCI). However, it remains unclear which potential factors (i.e., tDCS group, cognitive reserve, education level, diagnosis and encoding performance) directly and/or indirectly modulate the tDCS-induced memory reconsolidation effects.MethodsWe reanalyzed data acquired in our previous tDCS studies with 22 SMC and 18 aMCI participants from the perspective of predicting delayed memory retrieval performance. These studies included a learning session on Day 1, a reactivation by a contextual reminder followed by 15 min of tDCS session on Day 2 (24 h after Day 1), and two retrieval sessions (free recall and recognition) tested on Days 3 and 30 (48 h and 30 Days after Day 1).ResultsUnivariate models showed that tDCS group (sham vs. active) significantly predicted memory recognition (but not free recall), evidenced by higher scores in the active tDCS group than in sham group, confirming our previous results. Encoding performance and diagnosis (SMC vs. aMCI) significantly predicted memory retrieval, suggesting higher performances in individuals with SMC than in those with aMCI. Regarding cognitive reserve, higher leisure time activity subscores significantly predicted better memory recognition. Finally, multiple models did not show any tDCS group × predictor interaction effects, indicating that the effects of the predictors on retrieval occurred irrespective of tDCS group.ConclusionOur results shed light on predicting factors of episodic memory retrieval in this reconsolidation paradigm in individuals with SMC and aMCI. The findings suggest that multifactorial interventions program may be most promising to slow cognitive decline and delay the onset of dementia.

Cognitive reserve predicts episodic memory enhancement induced by transcranial direct current stimulation in healthy older adults

“…In a recent study, we reanalysed the data acquired in our previous studies with Subjective Memory Complaints (SMC) and aMCI participants with the aim of investigating how the tDCS-induced reconsolidation effects could be modulated by individual factors such as age, CR, education level, diagnosis and encoding performance in these AD-risk populations. Our main finding was that the higher leisure time subscore of the Cognitive Reserve Index questionnaire (CRI-q 31 ) predicted better delayed retrieval performances, but none of the individual factors analysed modulated the tDCS-induced memory enhancement effects, indicating that the effects of the predictors on retrieval performance occurred regardless of the tDCS group (Anodal vs. Sham) 32 .…”

“…The Anodal tDCS condition involved the application of current for 15 min at an intensity of 1.5 mA with a 10-s ramp at the beginning and at the end of the tDCS session. For the Sham condition, the current was turned off 10 s after the start of stimulation and turned on again for 10 s at the end of the stimulation period 13 – 15 , 21 , 32 , 58 , 59 . The current density (0.043 mA/cm 2 ) was kept below the safety limits 53 , 54 .…”

“…The variable “Free Recall Day 3” was normally distributed, while “Free Recall Day 30” displayed a right-skewed distribution and was analysed with generalized linear models. A set of predictors was chosen (based on former study evidence 17 , 32 ), thus inference on them did not need to be adjusted for multiple testing 63 , 64 .…”

Effects of repetitive transcranial magnetic stimulation on episodic memory in patients with subjective cognitive decline: study protocol for a randomized clinical trial

“…One previous research has demonstrated that the application of anodal tDCS on the left lateral prefrontal cortex (PFC) enhances pre-existing episode memories, with the effect persisting for a period of 30 days in elderly individuals with SCD (Manenti et al, 2017). Nonetheless, these results demonstrate the ability of the interventions to transiently influence brain function and did not identify them as therapeutic tools for individuals with memory impairment who performed poorly on neuropsychological tests (Solé-Padullés et al, 2006;Vaqué-Alcázar et al, 2021;Cotelli et al, 2022). Thus, to date, the efficacy of rTMS as a therapeutic tool for patients with SCD requires further investigation.…”