Altered slow wave activity in major depressive disorder with hypersomnia: A high density EEG pilot study

https://doi.org/10.1016/j.pscychresns.2012.03.001Get rights and content

Abstract

Hypersomnolence in major depressive disorder (MDD) plays an important role in the natural history of the disorder, but the basis of hypersomnia in MDD is poorly understood. Slow wave activity (SWA) has been associated with sleep homeostasis, as well as sleep restoration and maintenance, and may be altered in MDD. Therefore, we conducted a post-hoc study that utilized high density electroencephalography (hdEEG) to test the hypothesis that MDD subjects with hypersomnia (HYS+) would have decreased SWA relative to age- and sex-matched MDD subjects without hypersomnia (HYS-) and healthy controls (n = 7 for each group). After correction for multiple comparisons using statistical non-parametric mapping, HYS+ subjects demonstrated significantly reduced parieto-occipital all-night SWA relative to HYS- subjects. Our results suggest hypersomnolence may be associated with topographic reductions in SWA in MDD. Further research using an adequately powered prospective design is indicated to confirm these findings.

Introduction

Sleep disturbance commonly occurs in major depressive disorder (MDD) and plays an important role in the natural history of the disorder. Diagnostic criteria for sleep-related complaints associated with MDD include either insomnia, broadly defined as difficulty initiating or maintaining sleep despite adequate opportunity, or hypersomnia, defined as excessive sleepiness or increased total sleep time (American Psychiatric Association, 2000). Self-report of insomnia and hypersomnia occurs in roughly 80 and 30 percent of MDD patients, respectively (Armitage, 2007, Kaplan and Harvey, 2009). Although a sizeable literature has examined the role of insomnia in MDD (Baglioni et al., 2011), relatively little research has examined the role of hypersomnia in the disorder. Since hypersomnia increases the risk of incident depression (Breslau et al., 1996, Roberts et al., 2000), is a highly treatment-resistant symptom (Worthington et al., 1995, Zimmerman et al., 2005), increases the risk of depressive relapse (Kaplan and Harvey, 2009, Kaplan et al., 2011), and increases the risk of suicide (Goldstein et al., 2008), further research regarding the epidemiology and pathophysiology of hypersomnia in MDD is a crucial, yet neglected area in mood disorders research.

Polysomnography has been widely employed to study sleep in MDD, demonstrating alterations in sleep continuity, rapid eye movement (REM) sleep, and slow wave sleep (SWS) (Benca et al., 1992, Steiger and Kimura, 2010). Slow wave activity (SWA), the power density of low frequency delta activity during sleep, more accurately reflects slow oscillations than traditional sleep staging, and has been established as a marker of sleep homeostasis that is also associated with sleep restoration, maintenance, and quality (Borbély, 1982, Achermann et al., 1993, Dijk, 2009). Several investigations have examined SWA in depression; however, findings have not been consistent across studies, with decreases (Borbély et al., 1984, Hoffmann et al., 2000), increases (Schwartz et al., 2001), and non-significance (Mendelson et al., 1987, Armitage et al., 1992) reported, with differential effects of age and sex (Armitage et al., 2000a, Armitage et al., 2000b, Armitage et al., 2001). Notably, spectral analysis in prior studies was limited to central EEG derivations, and none examined SWA in the context of clinical sleep disturbance.

Therefore, the primary aim of this study was to examine SWA in MDD segregated into subtypes based on the presence or absence of hypersomnia. This study utilized high density electroencephalography (hdEEG), which yields superior spatial resolution compared to standard montages when examining SWA topography. Because reductions in SWS/SWA have been described in other central nervous system disorders associated with hypersomnolence, including idiopathic hypersomnia (Sforza et al., 2000) and paramedian thalamic stroke (Bassetti et al., 1996, Fonseca et al., 2011), we hypothesized that MDD subjects with hypersomnia would demonstrate decrements in all-night SWA relative to controls and MDD subjects without hypersomnia.

Section snippets

Subjects

All subjects were right-handed, free of psychotropic medications for ≥ 6 months, and drawn post-hoc from larger studies of sleep homeostasis in neuropsychiatric disorders, conducted at the University of Wisconsin-Madison. MDD was diagnosed via the Structured Clinical Interview for DSM-IV Axis I disorders (SCID) (First et al., 2002a). Healthy comparison subjects were evaluated with the non-patient SCID (First et al., 2002b) to rule out current or past psychiatric disorders. All MDD subjects were

Results

Participant characteristics and polysomnographic data are presented in Table 1. Each group consisted of age- and sex-matched subjects (4/7 female). Three HYS+ subjects and 1 HYS- subject met criteria for atypical depression. No MDD subjects were characterized as having a seasonal pattern to their illness. Depression severity as measured by HRSD did not differ significantly between HYS+ and HYS- MDD groups (t = 0.89, p = 0.39). One-way ANOVA demonstrated an effect of sleep onset latency (F2,18 = 4.17,

Discussion

This study demonstrates parieto-occipital decreases in all-night SWA in MDD subjects with hypersomnia. These findings are important in the context of mood and sleep disorders research because they suggest SWA is differentially regulated within sleep-related subtypes of MDD, and that the clinical sleep complaint of hypersomnolence may be a marker of decreased SWA in the disorder.

The literature examining SWA in MDD has been inconsistent, with decreased (Borbély et al., 1984, Hoffmann et al., 2000

Acknowledgements

This research was funded by the National Institute of Mental Health (5P20MH077967 to GT and RMB, and F30MH082601 to EL) and the National Alliance for Research on Schizophrenia and Depression Young Investigator Award to MJP. We thank Drs. Brady Riedner and Vlad Vyazovskiy for their technical assistance, and Miss Seugnet Miller who assisted with preparation of the manuscript.

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