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J Neurosci Methods. 2019 Mar 15;316:117-124. doi: 10.1016/j.jneumeth.2018.09.006. Epub 2018 Sep 5.

Insights on auditory closed-loop stimulation targeting sleep spindles in slow oscillation up-states.

Author information

1
School of Psychology, University of Birmingham, Birmingham B15 2TT, United Kingdom; Institute of Medical Psychology and Behavioral Neurobiology, University of Tübingen, Tübingen 72076, Germany.
2
Institute of Medical Psychology and Behavioral Neurobiology, University of Tübingen, Tübingen 72076, Germany.
3
Center of Brain, Behavior and Metabolism, University of Lübeck, Lübeck, Germany.
4
Institute of Medical Psychology and Behavioral Neurobiology, University of Tübingen, Tübingen 72076, Germany; Centre for Integrative Neuroscience, University of Tübingen, Tübingen 72076, Germany. Electronic address: jan.born@uni-tuebingen.de.

Abstract

BACKGROUND:

The consolidation of sleep-dependent memories is mediated by an interplay of cortical slow oscillations (SOs) and thalamo-cortical sleep spindles. Whereas an enhancement of SOs with auditory closed-loop stimulation has been proven highly successful, the feasibility to induce and boost sleep spindles with auditory stimulation remains unknown thus far.

NEW METHOD:

Here we tested the possibility to enhance spindle activity during endogenous SOs and thereby to promote memory consolidation. Performing a sleep study in healthy humans, we applied an auditory Spindle stimulation and compared it with an Arrhythmic stimulation and a control condition comprising no stimulation (Sham).

RESULTS:

With Spindle stimulation we were not able to directly entrain endogenous spindle activity during SO up-states. Instead, both Spindle and Arrhythmic stimulation evoked a resonant SO response accompanied by an increase in spindle power phase-locked to the SO up-state. Assessment of overnight retention of declarative word-pairs revealed no difference between all conditions.

COMPARISON WITH EXISTING METHODS:

Our Spindle stimulation produced oscillatory evoked responses (i.e., increases in SOs and spindle activity during SO up-states) quite similar to those observed after the auditory closed-loop stimulation of SOs in previous studies, lacking however the beneficial effects on memory retention.

CONCLUSION:

Our findings put the endeavour for a selective enhancement of spindle activity via auditory pathways into perspective and reveal central questions with regard to the stimulation efficacy on both an electrophysiological and a neurobehavioral level.

KEYWORDS:

Auditory stimulation; Closed-loop stimulation; Memory; Sleep; Sleep spindle; Slow oscillation

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