Transcranial electrical stimulation during sleep enhances declarative (but not procedural) memory consolidation: Evidence from a meta-analysis

This meta-analysis summarizes research examining whether transcranial electrical stimulation (transcranial direct current stimulation with oscillating and constant currents; transcranial alternating current stimulation), administered during sleep, can modulate declarative and procedural memory consolidation. Included in the meta-analysis were 13 experiments that represented data from 179 participants. Study findings were summarized using standardized mean difference (SMD) which is an effect size that summarizes differences in standard deviation units. Results showed electrical stimulation during sleep could enhance (SMD = 0.447; p=.003) or disrupt (SMD= -0.476, p =.030) declarative memory consolidation. However, transcranial electric stimulation does not appear to be able to enhance (SMD =0.154, p = .279) or disrupt (SMD = 0.076, p=.675) procedural memory consolidation. This meta-analysis provides strong evidence that TES is able to modulate some consolidation processes. Additional research is required to determine the mechanisms by which transcranial electrical stimulation is able to influence declarative memory consolidation. Finally, it is yet to be determined whether transcranial electrical stimulation can modulate procedural memory consolidation. Crown Copyright (C) 2016 Published by Elsevier Ltd. All rights reserved.