High definition transcranial direct current stimulation as an intervention for cognitive deficits in Alzheimer's dementia: A randomized controlled trial

BACKGROUND: Recent disease-modifying treatments for Alzheimer's disease show promise to slow cognitive decline, but show no efficacy towards reducing symptoms already manifested. OBJECTIVES: To investigate the efficacy of a novel noninvasive brain stimulation technique in modulating cognitive functioning in Alzheimer's dementia (AD). DESIGN: Pilot, randomized, double-blind, parallel, sham-controlled study SETTING: Clinical research site at UT Southwestern Medical Center PARTICIPANTS: Twenty-five participants with clinical diagnoses of AD were enrolled from cognition specialty clinics. INTERVENTION: Treatment consisted of high definition transcranial direct current stimulation (HD-tDCS) delivered for 20 min over the medial prefrontal cortex. Ten sessions of sham, 1 mA, or 2 mA stimulation were received. MEASUREMENTS: Cognitive outcomes were measured at baseline, after the last HD-tDCS session, and 8-weeks post-treatment. The primary outcome was change in total learning and delayed recall on the Rey Auditory Verbal Learning Test (RAVLT) immediately post-treatment and at 8-weeks. Secondary outcomes included measures of language, processing speed, and executive functioning. A multi-stage approach was used to examine cognitive outcomes, which included evaluation of effect sizes, statistical effects, and rate of clinically meaningful responses. RESULTS: In this pilot trial, no statistically significant differences on cognitive outcomes were found between sham and active HD-tDCS immediately post-treatment (p's > 0.05). However, moderate-to-large effect sizes were identified for enhanced RAVLT total learning (Cohen's d = 0.69-0.93) and phonemic fluency (d = 1.08-1.49) for both active HD-tDCS conditions compared to sham, with rates of clinically relevant improvement between 25 and 33%. Meaningful enhancement persisted to 8 weeks only for the 1 mA condition. CONCLUSIONS: Multiple sessions of HD-tDCS over the medial prefrontal cortex appears to have potential to produce meaningful cognitive enhancements in a proportion of patients having AD with improvements maintained for at least 8 weeks in some. TRIAL REGISTRATION INFORMATION: ClinicalTrials.gov (NCT05270408). Registered December 30, 2021.