Abstract
Individuals with insomnia present unique patterns of electroencephalographic (EEG) asymmetry between homologous regions of each brain hemisphere, yet few studies have assessed asymmetry within the same hemisphere. Increase in intrahemispheric asymmetry during rapid eye movement (REM) sleep in good sleepers (GS) and disruption of REM sleep in insomnia sufferers (INS) both point out that this activity may be involved in the pathology of insomnia. The objective of the present exploratory study was to evaluate and quantify patterns of fronto-central, fronto-parietal, fronto-occipital, centro-parietal, centro-occipital and parieto-occipital intrahemispheric asymmetry in GS and INS, and to assess their association with sleep-wake misperception, daytime anxiety and depressive symptoms, as well as insomnia severity. This paper provides secondary analysis of standard EEG recorded in 43 INS and 19 GS for three nights in a sleep laboratory. Asymmetry measures were based on EEG power spectral analysis within 0.3–60 Hz computed between pairs of regions at frontal, central, parietal and occipital derivations. Repeated-measures ANOVAs were performed to assess group differences. Exploratory correlations were then performed on asymmetry and sleep-wake misperception, as well as self-reported daytime anxiety and depressive symptoms, and insomnia severity. INS presented increased delta and theta F3/P3 asymmetry during REM sleep compared with GS, positively associated with depressive and insomnia complaints. INS also exhibited decreased centro-occipital (C3/O1, C4/O2) and parieto-occipital (P3–O1, P4/O2) theta asymmetry during REM. These findings suggest that INS present specific patterns of intrahemispheric asymmetry, partially related to their clinical symptoms. Future studies may investigate the extent to which asymmetry is related to sleep-wake misperception or memory impairments.
Highlights
Insomnia disorder is defined primarily by a sleep-related complaint, whether it is a difficulty to initiate or maintain sleep, or the perception of the absence of restful sleep [1]
We did not corroborate our initial hypothesis that INS would have higher fronto-parietal asymmetry during non-rapid eye movement (NREM) sleep only, instead we found quite the opposite: this effect is only significant in rapid-eye movement (REM) sleep
Insomnia presents a specific pattern of cortical asymmetry in the left fronto-parietal regions (F3/P3), where REM sleep is characterized by an increase in slow frequency asymmetry
Summary
Insomnia disorder is defined primarily by a sleep-related complaint, whether it is a difficulty to initiate or maintain sleep, or the perception of the absence of restful sleep [1]. Brain Sci. 2020, 10, 1014 to an increase in beta power, women with insomnia, but not men, displayed more low frequency activity (delta/theta) than GS [8] These results suggest higher cortical arousal, especially in the beta band in INS than in GS, at sleep-onset, during sleep as well as during wake [9]. Research has showed that compared to GS, INS present peculiarities in their rapid-eye movement (REM) sleep, known as REM sleep instability [10] The fragmentation of this sleep stage, among others, may interfere with basic processes such as emotional regulation, which could significantly increase the risk for an INS individual to exhibit depressive symptoms [10,11]. While we may not have identified a constant pattern of abnormal EEG activity during the night yet, we know that the whole architecture of sleep is impaired in INS and may possibly play a role in sleep perception or anxiety and depression symptoms
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