Variability of response to exercise‐primed tDCS in those with mild cognitive impairment and Alzheimer’s disease (the EXPRESS study): a preliminary analysis

Abstract

AbstractBackgroundStudies investigating the use of transcranial direct current stimulation (tDCS) to improve outcomes in patients with Alzheimer’s disease (AD) and mild cognitive impairment (MCI) have reported mixed findings. Such variability may be explained by inter‐individual differences such as demographics or disease pathology. Given the increased prevalence of cardiovascular risk factors with aging and the potential changes in neurobiology of those exhibiting additional vascular etiology, we evaluate the influence of etiology on tDCS outcomes in patients with mild AD or MCI.MethodParticipants were diagnosed with mild or major neurocognitive disorder due to AD or mixed AD/vascular disease according to The Diagnostic and Statistical Manual of Mental Disorders (DSM–5) criteria. Participants completed a 2‐week, blinded, randomized trial examining the effects of exercise primed tDCS where they were randomized to receive either exercise with tDCS, exercise with sham tDCS, or tDCS only. Cognitive tests assessing episodic memory (ADAS‐Cog Word Recognition and Word Recall Tasks) and working memory (N‐Back) were administered before and after intervention. Independent t‐tests were used to assess for differences in demographics between groups, and paired t‐tests were used to evaluate the influence of etiology on tDCS outcomes.ResultOf the 28 participants (17 males [58.6%], mean [±SD] age 74.8±8.9 years, education 16.3±2.2 years) included, 17 participants had mixed vascular/AD etiology and 11 participants had AD (without vascular) etiology. Both groups did not differ significant in demographics. Participants with mixed vascular/AD etiology showed significant improvement in episodic memory (Word Recognition 1.71±2.97, t(16) = 2.365, p = 0.031; Word Recall 0.65±1.12, t(16) = 2.257, p = 0.038), while those without vascular etiology did not (Word Recognition 0.36±2.80, t(10) = 0.43, p = 0.676; Word Recall ‐0.09±0.63, t(10) = ‐0.472, p = 0.647). No significant improvement in working memory in either group was observed.ConclusionFactors such as etiology should be taken into consideration when considering the efficacy of tDCS on improving cognition in patients diagnosed with AD/MCI. Further analyses upon unblinding will confirm whether patients with mixed AD/vascular etiology respond differently to tDCS.