Browsing by Author "Luokkala, Sanni"

Aims of the study. The aim of this study was to examine how overnight sleep impacts emotional memory and how the lateralization of sleep oscillations - sleep spindles, SO-spindle coupling and frontal theta - relates to emotional memory performance. Sleep has been observed to have a beneficial effect for memory. Prior studies have found sleep to favor preservation of emotional memory content. Behind sleep-related memory benefits are oscillatory events such as sleep spindles and their synchronized occurrence together with slow oscillations (SOs), SO-spindle coupling. Lateralization studies in turn suggest emotional information processing to be heavily focused in the right hemisphere also in terms of memory performance. When the effects of sleep and lateralized processing are combined, current research indicates that right-lateralized frontal theta is a predictive of enhanced memory performance for emotional material. Whether sleep spindle and SO-spindle coupling express laterality and if this laterality further relates to emotional memory performance is not currently known. Methods. The sample of this study consisted of 34 participants that underwent an overnight polysomnography procedure. Sleep spindle density, SO-spindle coupling and theta power density were selected for further analysis, and the lateralization variables were computed out of these sleep oscillatory parameters by subtracting the left hemisphere activity from the right hemisphere activity. Prior to study night, the participants encoded negative and neutral picture stimuli. Memory was tested at three recognition memory retrievals: one taking place immediately after the encoding, one on the following morning (12h) and one at the end of the following day (24h). Mixed model analysis for repeated measures was applied to examine the development of recognition accuracy (d’) for emotional and neutral items across the retrieval tasks. Linear regression analyses were used to investigate the relationship between oscillatory lateralization and emotional memory performance. Results and conclusions. Recognition accuracy decreased across the memory retrieval tasks as a function of time. 24h after the encoding recognition accuracy was better for neutral than emotional material. Right-lateralized sleep oscillations predicted the observed neutral memory benefit. These findings offer preliminary evidence of sleep spindles and SO-spindle coupling relating to emotional memory performance in a lateralized manner and shed light onto how methodology might impact the emotional memory benefit commonly observed in prior research.