title: Deepening sleep by hypnotic suggestion.
abstract: OBJECTIVE
  Slow wave sleep (SWS) plays a critical role in body restoration and promotes brain plasticity; however, it markedly declines across the lifespan. Despite its importance, effective tools to increase SWS are rare. Here we tested whether a hypnotic suggestion to "sleep deeper" extends the amount of SWS.
  
  
  METHODS
  Within-subject, placebo-controlled crossover design.
  
  
  METHODS
  Sleep laboratory at the University of Zurich, Switzerland.
  
  
  METHODS
  Seventy healthy females 23.27 ± 3.17 y.
  
  
  METHODS
  Participants listened to an auditory text with hypnotic suggestions or a control tape before napping for 90 min while high-density electroencephalography was recorded.
  
  
  RESULTS
  After participants listened to the hypnotic suggestion to "sleep deeper" subsequent SWS was increased by 81% and time spent awake was reduced by 67% (with the amount of SWS or wake in the control condition set to 100%). Other sleep stages remained unaffected. Additionally, slow wave activity was significantly enhanced after hypnotic suggestions. During the hypnotic tape, parietal theta power increases predicted the hypnosis-induced extension of SWS. Additional experiments confirmed that the beneficial effect of hypnotic suggestions on SWS was specific to the hypnotic suggestion and did not occur in low suggestible participants.
  
  
  CONCLUSIONS
  Our results demonstrate the effectiveness of hypnotic suggestions to specifically increase the amount and duration of slow wave sleep (SWS) in a midday nap using objective measures of sleep in young, healthy, suggestible females. Hypnotic suggestions might be a successful tool with a lower risk of adverse side effects than pharmacological treatments to extend SWS also in clinical and elderly populations.
authors.affiliation: University of Zurich, Institute of Psychology, Division of Biopsychology, Zurich, Switzerland, Binzmühlestrasse 14/5, 8050 Zürich.
authors.forename: Maren J
authors.initials: MJ
authors.lastname: Cordi
authors.affiliation: University of Tübingen, Department of Psychology, Division of Clinical Psychology and Psychotherapy, Tübingen, Germany.
authors.forename: Angelika A
authors.initials: AA
authors.lastname: Schlarb
authors.affiliation: University of Zurich, Institute of Psychology, Division of Biopsychology, Zurich, Switzerland, Binzmühlestrasse 14/5, 8050 Zürich ; Zurich Center for Interdisciplinary Sleep Research (ZiS), University of Zurich, Zurich, Switzerland ; University of Fribourg, Department of Psychology, Division of Cognitive Biopsychology and Methods, Fribourg, Switzerland.
authors.forename: Björn
authors.initials: B
authors.lastname: Rasch
mesh_terms: D000161:Acoustic Stimulation; D000293:Adolescent; D000328:Adult; D018592:Cross-Over Studies; D004569:Electroencephalography; D005260:Female; D006801:Humans; D006990:Hypnosis / Q000379:methods*; D012890:Sleep / Q000502:physiology*; D012894:Sleep Stages / Q000502:physiology; D013557:Switzerland; D013826:Theta Rhythm; D014851:Wakefulness / Q000502:physiology; D055815:Young Adult
keywords: high-density EEG; hypnosis; sleep; slow wave sleep