Frontal Eeg Synchronization in Young Women with Depression

1699 EEG Activity Markers in Depression—Birchler-Pedross et al be quantified by spectral EEG correlates in the low-frequency range (1-7 Hz) during sleep and wakefulness.13-19 The intensity of low-frequency EEG activity at the beginning of sleep is proportional to the duration of prior wakefulness, and is considered to reflect the homeostatic aspect of sleep regulation.20-22 During sustained wakefulness, EEG activity in the 1-7 Hz range increases and can predict the subsequent homeostatic increase in slow wave activity (SWA, EEG power density 0.75-4.5 Hz) during sleep,16,23,24 a phenomenon that is particularly pronounced in frontal brain regions.23,24 This increased propensity in frontal low-frequency EEG activity (FLA) during sustained wakefulness suggests that frontal regions are more susceptible to sleep deprivation effects than other cortical regions.23,25 The process S deficiency hypothesis for MDD has rarely been tested in either sleep or waking EEG. An early study found lower delta waves during sleep in depressed patients,10 which was later documented only in males with MDD.9 In untreated middle-aged depressives, there was no difference from controls in SWA during sleep.26 Similarly, EEG studies during wakefulness in depression are contradictory and inconclusive.27 It is surprising that this has not received more attention, since waking EEG-derived indices are a desirable biological measure in psychiatric disorders, given its practicability, low budget, and possibility of a greater number of recording sites.27 Thus, here we aimed at investigating sleep-homeostat and circadianrelated differences in the EEG during extended wakefulness in MDD and healthy women under very stringently controlled laboratory conditions. INTRODUCTION Major depressive disorder (MDD) is often associated with a dysregulation in circadian rhythmicity and/or sleep regulation. Abnormal circadian rhythms in many variables have been reported over the years, ranging from core body temperature, neurotransmitters, and hormones to physiology of the sleepwake cycle itself.1,2 Characteristics of the circadian system (amplitude, phase, and/or endogenous period) can be measured under very stringent laboratory conditions using markers such as core body temperature or melatonin. Although both delayed and advanced phases have been found in patients with MDD, several studies using highly controlled protocols such as the constant routine3,4 or forced desynchrony5,6 could not confirm circadian phase changes in MDD. However, reduced circadian amplitude seems to be generally present.2,4,7,8 The process S deficiency hypothesis postulates a deficiency in the homeostatic build-up of sleep pressure during wakefulness in MDD, leading to a shallower dissipation rate of process S during sleep.4,9-12 Changes in homeostatic sleep regulation can FRONTAL EEG SYNCHRONIZATION IN YOUNG WOMEN WITH DEPRESSION