Sleeping Soundly: Effects of Auditory Closed-Loop Stimulation on Sleep and Memory

  • Julia Schneider

Student thesis: Phd


Sleep is a unique behavioural state, whose exact purpose remains an unsolved mystery. A wealth of evidence posits that sleep facilitates the consolidation of memories. In particular slow oscillations (SOs) during deep slow wave sleep are thought to play a vital functional role in driving this consolidation process by orchestrating phase-coupled thalamo-cortical sleep spindles. To elucidate functional mechanisms of these oscillations, a new experimental technique called auditory closed-loop stimulation has been trialled, which applies brief sound stimuli in phase with on-going endogenous oscillations, and thereby enhances both SO and spindle activity, as well as overnight memory consolidation. The aim of the work presented in this thesis was to use the technique's potential in combination with behavioural measures of declarative and procedural memory and overnight polysomnography (PSG) to investigate oscillatory dynamics and their functional purpose during sleep. In Chapter 2, we examined the applicability of auditory closed-loop stimulation in a cohort of healthy, late middle-aged adults, as SO and spindle activity naturally decline during the lifespan and have been linked to impaired memory. We further compared stimulation outcome in this group to an existing young adult cohort. While the ageing brain responded to the stimulation, its susceptibility was markedly decreased with age, with no favourable impact on overnight memory consolidation observed. Our results demonstrate the need for stimulation optimisation to translate functional protocols to different age groups prior to clinical application. In Chapter 3, we investigated whether slow and fast sleep spindle types could be differentially modulated by applying variations of auditory closed-loop stimulation protocols, as particularly the respective functional contribution of slow spindles in the consolidation process remains unclear. A multi-stimulus protocol was found to enhance slow spindles to a greater extent than fast spindles, and revealed further temporal differences which suggest slow and fast spindles may underlie different neural dynamics in their generation. Auditory closed-loop stimulation constitutes a useful non-invasive tool to probe their potential functional differences in future investigations. Finally in Chapter 4, we considered the psychological impact associated with receiving auditory closed-loop stimulation during sleep and asked whether merely anticipating specific effects in a placebo protocol would have an impact on sleep and cognition. We discovered placebo and nocebo effects in the form of transiently altered slow spindle activity throughout the night, and suggest psychological aspects of applying stimulation could present a crucial factor and require due consideration in future research designs. In conclusion, our results shed new insights on the potential of using customised auditory closed-loop stimulation protocols as a suitable technique in the investigation of sleep oscillation dynamics and their functional implications. However, we also highlight limitations of susceptibility in an older population, and provide evidence of psychological aspects presenting a potentially confounding variable in stimulation outcome.
Date of Award1 Aug 2019
Original languageEnglish
Awarding Institution
  • The University of Manchester
SupervisorWael El-Deredy (Supervisor) & Alex Casson (Supervisor)


  • Sleep
  • Memory Consolidation
  • Slow Oscillation
  • Sleep Spindle
  • Ageing
  • Placebo

Cite this