Browsing by Subject "hidasaalto"

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  • Yli-Kyyny, Iikka (Helsingfors universitet, 2016)
    Objectives: In recent years, scientific inquiry has been able to dig into the effects of sleep on memory. More specifically, slow oscillations (SO) detected with EEG during deep sleep, have been found to reactivate memory representations which further enhances their processing and consolidation into long-term memory. In previous studies, auditory stimulation during deep sleep has been found to strengthen the brain's natural SO cycles and enhance consolidation of declarative memory but it has also been found to have unwanted side-effects on mood. This study is part of a research project, Sound Deep Sleep, where the objective is to develop a non-pharmacological method for home use to enhance the positive effects of deep sleep using auditory stimulation. In this study the effects of different auditory stimuli and their duration on memory consolidation and mood was investigated. Methods: 21 healthy adult volunteers took part in the study. The subjects slept in a sleep research lab in the Institute of Occupational Health for four nights with electrodes attached to the scalp and their memory performance and mood was tested once every evening and once every morning. Memory performance was tested with paired associative words, face-name test and with sequential finger tapping. Subject's mood was tested with POMS questionnaire and task load with NASA-TLX. During the four nights, subjects were presented with brief auditory noise or percussion sounds for the whole night of for the first four hours or with no auditory stimulation in a randomized order. The auditory stimulation was time locked to SO cycles according to online detection by a previously developed algorithm. The volume of the sound was adjusted according to online detection of sleep depth by the same algorithm. Results and conclusions: Auditory stimulation did not affect memory consolidation, mood, task load or subject's sleep architecture. The results on memory consolidation are contradictory to previously published data and possible explanations for the contradiction are discussed. The fact that this study had larger sample size and almost identical design than previous studies casts doubt that the effects size of auditory stimulation on memory consolidation might be smaller than previously expected or that it concerns only a sub-population of people. Based on the results of this study, suggestions for future research designs are introduced.