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Article

Bi-Temporal Anodal Transcranial Direct Current Stimulation during Slow-Wave Sleep Boosts Slow-Wave Density but Not Memory Consolidation

1
Cognitive Neuroscience of Memory and Consciousness, Institute of Psychology, University of Bern, 3012 Bern, Switzerland
2
Department of Neurosurgery and Neurotechnology, Institute for Neuromodulation and Neurotechnology, University of Tübingen, 72076 Tübingen, Germany
3
Translational Research Center, University Hospital of Psychiatry and Psychotherapy, University of Bern, 3000 Bern, Switzerland
4
Department of Psychiatry, Psychotherapy and Psychosomatics, University Hospital of Psychiatry, University of Zurich, 8032 Zurich, Switzerland
*
Author to whom correspondence should be addressed.
Academic Editor: David Conversi
Brain Sci. 2021, 11(4), 410; https://doi.org/10.3390/brainsci11040410
Received: 11 January 2021 / Revised: 15 March 2021 / Accepted: 22 March 2021 / Published: 24 March 2021
Slow-wave sleep (SWS) has been shown to promote long-term consolidation of episodic memories in hippocampo–neocortical networks. Previous research has aimed to modulate cortical sleep slow-waves and spindles to facilitate episodic memory consolidation. Here, we instead aimed to modulate hippocampal activity during slow-wave sleep using transcranial direct current stimulation in 18 healthy humans. A pair-associate episodic memory task was used to evaluate sleep-dependent memory consolidation with face–occupation stimuli. Pre- and post-nap retrieval was assessed as a measure of memory performance. Anodal stimulation with 2 mA was applied bilaterally over the lateral temporal cortex, motivated by its particularly extensive connections to the hippocampus. The participants slept in a magnetic resonance (MR)-simulator during the recordings to test the feasibility for a future MR-study. We used a sham-controlled, double-blind, counterbalanced randomized, within-subject crossover design. We show that stimulation vs. sham significantly increased slow-wave density and the temporal coupling of fast spindles and slow-waves. While retention of episodic memories across sleep was not affected across the entire sample of participants, it was impaired in participants with below-average pre-sleep memory performance. Hence, bi-temporal anodal direct current stimulation applied during sleep enhanced sleep parameters that are typically involved in memory consolidation, but it failed to improve memory consolidation and even tended to impair consolidation in poor learners. These findings suggest that artificially enhancing memory-related sleep parameters to improve memory consolidation can actually backfire in those participants who are in most need of memory improvement. View Full-Text
Keywords: memory consolidation; hippocampus; sleep; slow wave; transcranial direct current stimulation; temporal lobe memory consolidation; hippocampus; sleep; slow wave; transcranial direct current stimulation; temporal lobe
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MDPI and ACS Style

Ruch, S.; Fehér, K.; Homan, S.; Morishima, Y.; Mueller, S.M.; Mueller, S.V.; Dierks, T.; Grieder, M. Bi-Temporal Anodal Transcranial Direct Current Stimulation during Slow-Wave Sleep Boosts Slow-Wave Density but Not Memory Consolidation. Brain Sci. 2021, 11, 410. https://doi.org/10.3390/brainsci11040410

AMA Style

Ruch S, Fehér K, Homan S, Morishima Y, Mueller SM, Mueller SV, Dierks T, Grieder M. Bi-Temporal Anodal Transcranial Direct Current Stimulation during Slow-Wave Sleep Boosts Slow-Wave Density but Not Memory Consolidation. Brain Sciences. 2021; 11(4):410. https://doi.org/10.3390/brainsci11040410

Chicago/Turabian Style

Ruch, Simon, Kristoffer Fehér, Stephanie Homan, Yosuke Morishima, Sarah M. Mueller, Stefanie V. Mueller, Thomas Dierks, and Matthias Grieder. 2021. "Bi-Temporal Anodal Transcranial Direct Current Stimulation during Slow-Wave Sleep Boosts Slow-Wave Density but Not Memory Consolidation" Brain Sciences 11, no. 4: 410. https://doi.org/10.3390/brainsci11040410

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