Offline Bi-Frontal Anodal Transcranial Direct Current Stimulation Decreases Total Sleep Time Without Disturbing Overnight Memory Consolidation

Abstract

Objectives: A proposed replay of memory traces between the hippocampus and frontal cortical brain areas during sleep is of high relevance for overnight memory consolidation. Recently, we demonstrated that bi-frontal anodal transcranial direct current stimulation (tDCS) prior to sleep increases waking EEG gamma power and decreases total sleep time during the night. It is unclear whether this effect on cortical excitability has an influence on overnight memory consolidation. We hypothesized that bi-frontal evening tDCS interferes with overnight memory consolidation with a polarity specific impairment following anodal tDCS. Materials and Methods: Nineteen healthy participants underwent a within-subject, repeated-measures protocol in the sleep laboratory with bi-frontal tDCS applied prior to sleep according to the experimental protocol (anodal, cathodal, sham stimulation). Memory tasks for declarative and procedural memory were assessed prior to tDCS and on the following morning. Results: No deterioration of overnight memory consolidation following evening offline bi-frontal tDCS could be detected. Conclusion(s): The application of tDCS can be considered safe regarding overnight memory consolidation and represents a promising treatment approach in conditions of decreased vigilance and arousal.