Functional imaging of NREM recovery sleep slow waves in young and older subjects : preliminary results

Abstract

Introduction During non-rapid eye movement (NREM) sleep, the level of neural synchronization is mainly reflected on the electroencephalogram (EEG) by large-amplitude slow waves (SW). Factors such as age and sleep homeostasis modify SW characteristics and their underlying neural processes. Recent neuroimaging studies have identified brain regions recruited by SW mechanisms in young, non-sleep-deprived humans. In these preliminary analyses, we aimed to identify brain regions implicated in SW onset and SW amplitude in young and older subjects during a recovery morning sleep following prolonged wakefulness. Materials and methods Thirty-one healthy, right-handed volunteers were divided in two age groups: young ( n = 16; 7 females; 20–30 years, M = 23.06, SD = 3.34) and older ( n = 15; 9 females; 52–69 years, M = 59.47, SD = 5.89). Subjects underwent 26 h of sleep deprivation before the recording session. Sleep was recorded in the morning for a maximum of 90 min, using simultaneous EEG and fMRI acquisitions. EEG data were corrected for gradient and ballistocardiographic artifacts, sleep stages were identified, and SW were detected using an automatic algorithm. Event-related fMRI analyses were performed on functional volumes corresponding to periods of uninterrupted N2 and N3 sleep. SW events were modeled as one onset regressor and one parametric modulator accounting for the wave’s amplitude, both convolved with the hemodynamic response function basis set. Individual t -maps (first level analysis) were included in an ANOVA with basis set and age group as factors (second level analysis). Significant voxels ( p p Results In young subjects, SW onset was associated to significant BOLD changes in the cerebellum, whereas older participants showed BOLD changes in the pons, thalamus, caudate nucleus and putamen. SW amplitude significantly modulated BOLD changes in the insula and in frontal, temporal and supramarginal regions in older subjects, but not in the young. Conclusion After prolonged wakefulness, SW onsets in young and older subjects are mostly associated to changes in subcortical brain regions. SW amplitudes in older subjects modulate neural activity in several cortical and subcortical areas. Acknowledgements This work was supported by the Canadian Institutes of Health Research and the Fonds de Recherche en Sante du Quebec.