Topographic analysis of coherence and propagation of EEG activity during sleep and wakefulness

Overnight sleep EEG recorded from 21 derivations was studied in 8 healthy subjects. The vector autoregressive model was fitted to all 21 channels simultaneously. Ordinary, multiple and partial coherences and directed transfer functions were estimated for sleep stages and wakefulness. Ordinary coherences give rather trivial information that coherence decreases with distance. Partial coherences revealed specific structure that was well repeatable for the subjects studied. Differences in coherence patterns between sleep stages were found by means of statistical tests. An increase of coherence was found for sleep stages 2, 3 and 4. Directed transfer function made possible the identification of the main centers from which EEG activity is spreading during sleep and wakefulness. During sleep the influence of subcortical structures was manifested by propagation of activity from the fronto-central region. The range of this interaction was highest in sleep stages 3 and 4. An EEG analysis, based on the approach of treating time series as a realization of one process and on the simultaneous (not pair-wise) evaluation of signals offers new possibilities in the investigation of synchronization and functional relations in the brain.     

Spectral characteristics of sleep EEG in chronic insomnia

To determine whether the spectral characteristics of the sleep electroencephalogram (EEG) of insomniacs differ from that of healthy subjects, we compared in each of the first four non-rapid eye movement (NREM) and rapid eye movement (REM) episodes: (a) the time courses of absolute power, averaged over the subjects in each group, for the delta, theta, alpha, sigma and beta frequency bands; (b) the relationship between these time courses; and (c) the overnight trend of integrated power in each frequency band. The results show that NREM power, for all frequencies below the beta range, has slower rise rates and reaches lower levels in the insomniac group, whereas beta power is significantly increased. In REM, insomniacs show lower levels in the delta and theta bands, whereas power in the faster frequency bands is significantly increased. Thus, the pathophysiology of insomnia is characterized not only by the generally acknowledged slow wave deficiency, but also by an excessive hyperarousal of the central nervous system throughout the night, affecting both REM and NREM sleep. This hyperarousal is interpreted in terms of the neuronal group theory of sleep which provides a possible explanation for the discrepancies observed between subjective impressions and objective measures of sleep. Also, it is suggested that the progressive hyperpolarization of the thalamocortical neurons as sleep deepens is slower in the patient population and that this may explain the observed slow wave deficiency. The homeostatic control of slow wave activity, on the other hand, would appear to be intact in the patient population.     

Fronto-occipital EEG power gradients in human sleep

In the German healthcare system, two major trends contribute to the growing need for ambulatory care. One is the demographic increase of the older population; the other is the growing preponderance of chronic diseases. The required services often surpass the human resources of the family and ask for professional nursing service. The combination of lay caregiving and professional work is a necessary growing phenomenon that calls for new concepts in home care. In this perspective the idea of the so called "Sozialstation" (social center), which started their work in 1970, is an interesting concept towards more systematic planning and interdisciplinary cooperation and reversing the trend towards hospitalization. This literature-based article looks critically at accomplishments and limitations of Sozialstationen.     

Changes in EEG power density during sleep laboratory adaptation

First- and second-night effects on the electroencephalogram (EEG) were investigated by means of polygraphic sleep recordings and all-night spectral analysis. Eighteen normal subjects were studied for three consecutive nights in a hospital sleep laboratory. Visual sleep scoring showed that there was a first-night effect in normal subjects similar to that reported previously [increased wakefulness; decreased total sleep time, sleep efficiency, and rapid eye movement (REM) sleep]. Spectral analysis of the sleep EEG revealed important changes, most of which occurred in REM sleep. Increased delta, theta, and beta1 power densities accompanied by decreased mean frequency were seen in REM sleep in the second night. On the basis of REM sleep deprivation results previously published, our data suggest that the second night could be affected by partial REM sleep deprivation that occurred in the first night. Delta and theta power density values decreased in the first non-rapid eye movement episode of nights 1 and 2; this could result from increased REM sleep pressure. The overall consistency of spectral data in the first and second night with REM sleep findings derived from visual scoring in the first night lends further support to this hypothesis. The sleep disturbance experienced during the first night in a sleep laboratory may be a useful and valid model of transient insomnia. Therefore, we conclude that data from all nights recorded should be included in assessing a subject's sleep.     

Changes in EEG power density of non-REM sleep in depressed patients during treatment with trazodone

Recently, it was hypothesized that acute or cumulative suppression of non-REM sleep intensity might be related to the therapeutic effects of antidepressants. This intensity has been proposed to be expressed in the EEG power density in non-REM sleep. In the present study, the relationship was examined between the changes of EEG power density in non-REM sleep and the changes in clinical state in 8 depressed patients during treatment with trazodone. A 1-week wash-out period was followed by 1 week of placebo administration, a medication period of 5 weeks and a 1-week placebo period. To minimize systematic influences of sleep duration and non-REM-REM sleep alterations, EEG power was measured over the longest common amount of non-REM sleep stages 2-4 (168.5 min), accumulated from sleep onset onwards. During trazodone treatment, the 13- and 14-Hz bins showed a significant reduction in EEG power. No clear-cut change, however, was observed in the EEG power of the delta frequency range (1-4 Hz) which is considered to be the principle manifestation of non-REM sleep intensity. Furthermore, no overall significant relationship between EEG power suppression and clinical improvement could be demonstrated.     

Aberrant functional organization in schizophrenia: analysis of EEG coherence during rest and photic stimulation in drug-naive patients

Participation in bronchial asthma pathogenesis of the epithelium, bronchial wall, effector cells of inflammation at various periods of the disease are described. Morphology of the bronchi between the attacks, at the height of the attack and at the experimental model of the bronchospasm is presented. The hypotheses of the bronchospasm and respiratory tract obstruction are discussed.     

Regional changes in EEG power and coherence during cognition: Intensive study of two individuals.

Studied whether EEG power is relevant to cognitive performance by conducting weekly EEG recordings on 2 adult male volunteers who were living for several months in a controlled laboratory environment. Data from an 8-channel EEG during a resting period and during performance of 2 cognitive tasks (word fluency and mental imagery) were subjected to spectral analysis. Statistical analyses on power and coherence were conducted for each S separately. Although substantial individual differences were observed, particularly for the theta band, both Ss showed changes in the spectral information over the anterior left hemisphere during the word fluency task. (26 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Spectral analysis in cyclic changes of human sleep evaluation

In this study cyclic changes of human sleep structure were examined. For whole-night polysomnograms of 35 healthy volunteers of both sexes, manual hypnograms were created and divided into NREM-REM cycles. EEG signals from C3-A2 derivation were analysed by computer using a Fast Fourier Transform (FFT). For consecutive NREM-REM cycles of individual sleep stages, EEG power density contents for delta, theta, alpha, sigma and beta waves were analysed. For consecutive sleep cycles, a clear decrease in NREM sleep duration, especially slow wave sleep duration, was obtained. In addition, a decrease in power density of delta waves was observed. For consecutive sleep cycles, increases in REM sleep duration and in power density of theta and alpha waves were obtained. In consecutive sleep cycles, high amplitude delta slow waves are replaced by higher frequency and lower amplitude waves. Thus stages of NREM sleep are replaced by stages of REM.     

Citalopram: differential sleep/wake and EEG power spectrum effects after single dose and chronic administration

The sleep/wake effects of the selective serotonin re-uptake inhibitor citalopram were studied in both a single-dose study with three dose levels (0.5, 2.0 and 5.0 mg/kg), and a 5-week chronic administration study (15 mg/kg/24 h). Single doses of citalopram resulted in a dose-dependent inhibition of rapid eye movement (REM) sleep. After chronic citalopram treatment there was a sustained REM sleep inhibition. Single doses of citalopram resulted in only minor changes in non-REM (NREM) sleep as well as in NREM EEG power spectral density. Chronic administration resulted in a major shift from SWS-2 to SWS-1. The observed corresponding changes in EEG power density were regional. A 30 to 40 percent reduction of power density in the 0.5-15 Hz range in the fronto-parietal EEG derivation was seen for the whole 8-h registration period. In the fronto-frontal EEG derivation only minor changes were seen. A decreasing trend in NREM sleep power density between 0.5 and 7 Hz, usually seen during the course of the light period, was not observed in the chronic condition, but was seen in control and single-dose condition, suggesting altered diurnal distribution of slow wave activity in the chronic condition. The data indicate that acute and chronic administration of citalopram shows clear differences in sleep effect, which may be caused by alteration of serotonergic transmission, and may be related to the antidepressant effect.     

Power spectral analysis of EEG in a multiple-bedroom, multiple-polygraph sleep laboratory

Although scientific and policy statements regarding drugs often suggest that there are grave problems of drug use within America's inner cities, the evidence that supports these statements is often based on anecdotal or incomplete data. This study of African-American adults from the Woodlawn study followed longitudinally partially fills that gap, at least for learning more about those who spend some or all of their childhood within an inner city neighborhood. We found few differences between the lifetime prevalence of drug use and a national representative sample of adults of the same age range. Furthermore, a national household survey of African-Americans of similar age living in six central cities also reported low lifetime rates of illicit drug use. Nevertheless, those from the Woodlawn cohort had higher rates of use of illicit drugs in the past year than the national sample, especially those still living in areas with high rates of poverty. Additionally, reports of heavy drug trafficking were much greater in the inner city areas than in the suburbs.     

EEG coherence following acute and chronic clozapine in treatment-resistant schizophrenics.

Electroencephalographic (EEG) coherence is an index of brain regional coupling that has been found to be abnormal in people with schizophrenia but has not been systematically examined in response to neuroleptics. EEG coherence in slow (delta and theta) frequencies was assessed in 17 treatment-resistant people with schizophrenia at baseline, 2 hr after their first oral dose (25 mg) and after 6 weeks of clozapine treatment. Compared with EEG norms, participants exhibited significant interhemispheric and intrahemispheric coherence abnormalities prior to treatment. Both acute and chronic treatments altered coherence but differed with respect to their relationship to symptom reduction and their ability to normalize or augment pretreatment abnormalities. Findings are discussed in relation to "disconnection" theories of schizophrenia. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Spindle frequency activity in the sleep EEG: individual differences and topographic distribution

Focal magnetic transcranial stimulation (TCS) is employed for mapping of the motor cortical output to abductor digiti minimi (ADM) muscle. The aim of this study was to evaluate the interhemispheric asymmetries in normals. Motor maps were obtained through motor evoked potentials (MEPs) recordings from ADM muscle in 20 healthy subjects in right and left hemispheres TCS. Measurement of several indexes such as excitability threshold, MEPs amplitude, MEPs latency, and silent period duration did not show differences between the hemispheres. Moreover, no interhemispheric asymmetries were found when the amplitude ratio values were analyzed. The hand motor cortical area, as represented by the number of responsive sites (3.6 vs. 3.5) and the "hot spot" site localization presented a fairly symmetrical organization. Absolute values displayed a relatively wide intersubject variability, while their interhemispheric differences were extremely restricted. This observation can offer a new tool in diagnosing and following up neurological disorders affecting the central motor system, mainly for those concerning monohemispheric lesions.     

Abnormal functional connectivity in Alzheimer''s disease: intrahemispheric EEG coherence during rest and photic stimulation

Tolbutamide is a sulfonylurea oral hypoglycaemic agent with suspected teratogenicity in humans and demonstrated teratogenicity in laboratory animals, but the underlying mechanism is unknown. This study examined maternal-to-conceptus tolbutamide transfer on gestational days 9.5 and 10.5 and drug concentration in embryonic head, heart, and trunk regions on gestational day 10.5 after maternal dosing in mouse. Embryos exposed to tolbutamide in vitro on gestational day 8.5 were assayed for glucose uptake, glycolysis, and protein content after 6, 12, and 24 hr. Dose-dependent tolbutamide transfer from maternal serum to extraembryonic fluid occurred on gestational day 9.5 and 10.5, with highest tolbutamide levels in embryonic heart on gestational day 10.5. In vitro tolbutamide exposure on gestational day 8.5 decreased glycolysis at 6 hr, increased glycolysis at 24 hr, and had no effect on glucose uptake at 6, 12, or 24 hr. Embryonic protein content reflected growth retardation after 24 hr tolbutamide exposure. Thus, mouse embryos are directly exposed to tolbutamide after maternal dosing on gestational day 9.5 and 10.5, with concentration of drug within embryonic heart. Tolbutamide-induced changes in glucose metabolism are less apparent in whole embryos than reported in adult tissues.     

EEG slow waves and sleep spindles: windows on the sleeping brain

Slow waves and sleep spindles are prominent features of the EEG in non-REM sleep and some of the neurophysiological mechanisms underlying their genesis have been elucidated. In humans, slow-wave activity in non-REM sleep increases and EEG activity in the frequency range of sleep spindles decreases when wakefulness prior to sleep is varied from 2 to 40 h. The opposite changes are observed in the course of sleep, even when sleep is scheduled out of phase with the circadian rhythm of sleep propensity. Within non-REM sleep episodes the association between slow waves and sleep spindles is bi-phasic: both activities are correlated positively at the beginning and end of non-REM sleep episodes whereas in the middle part of non-REM sleep episodes high values of slow-wave activity coincide with low levels of spindle activity. An extension of wakefulness enhances the rise rate of slow-wave and spindle activity at the onset of sleep. Since macroscopic slow waves and sleep spindles both are dependent on hyperpolarization and synchronization of neurons in thalamo-cortical and cortical circuits, the sleep deprivation induced changes in these EEG activities may be related to reduced activating input to thalamo-cortical and cortical neurons, local facilitation of their hyperpolarization or facilitation of their synchronization. The precise regulation of slow-wave and spindle activity as a function of the duration and intensity of prior sleep and wakefulness demonstrates that these EEG oscillations are accurate indicators of non-REM-sleep homeostasis and suggests that they are fundamental to the sleeping brain.     

Interhemispheric asymmetry of human sleep EEG in response to selective slow-wave sleep deprivation.

Recent evidence suggests that the human sleep electroencephalogram (EEG) shows regional differences over both the sagittal and coronal planes. In the present study, in a group of 10 right-handers, the authors investigated the presence of hemispheric asymmetries in the homeostatic regulation of human sleep EEG power during and after selective slow-wave sleep (SWS) deprivation. The SWS deprivation was slightly more effective over the right hemisphere, but the left hemisphere showed a markedly larger increase of EEG power in the 1.00-24.75 Hz range during recovery-night non-REM sleep, and a larger increase of EEG power during both deprivation-night and recovery-night REM sleep. These results support the greater need for sleep recuperative processes of the left hemisphere, suggesting that local sleep regulation processes may also act during REM sleep. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Joint time and time-frequency optimal detection of K-complexes in sleep EEG

Automated detection of waveforms such as delta and K-complex in the EEG is an important component of sleep stage monitoring. The K-complex is a key feature that contributes to sleep stages assessment. However, its automated detection is still difficult due to the stochastic nature of the EEG. In this paper, we propose a detection structure which can be interpreted as joint linear filtering operations in time and time-frequency domains. We also introduce a method of obtaining the optimum detector from training data, and we show that the resulting receiver offers better performances than the one obtained via the Fisher criterion maximization. The efficiency of this approach for K-complexes detector design is explored. It results from this study that the obtained receiver is potentially the best one which can be found in the literature. Finally, it is emphasized that this methodology can be advantageously used to solve many other detection problems.     

Dynamical properties of the sleep EEG in different frequency bands

The information concerning the dynamic behavior of the sleep process gained by the usual evaluation of sleep EEGs according to the criteria of Rechtschaffen and Kales is limited. Therefore a new methodical approach is presented, which is a special case of spectral analyzed data processing. After digital band-pass filtering of the sleep EEG the root-mean-square (RMS) value of successive 20 s EEG epochs is calculated in defined frequency ranges. This procedure ensures to take into account the influence of the phase relation between different frequency components. The temporal course of these RMS values during the night reveals smooth curves with continuous transitions between different sleep states. In all frequency bands slow oscillations according to the sleep cycles are observable. Whereas the slow frequency bands have a temporal course with local maxima during non-REM and local minima during REM sleep, the fast frequency bands beta and gamma show the opposite behavior revealing higher RMS values during REM sleep. The relationship between the activities in different frequency bands is evaluated calculating the cross correlation coefficient. Taken together the procedure allows an objective and automated quantitative analysis of the sleep EEG. The main advantage of this approach is the characterization of the sleep cycle as a dynamic and continuous process. Compared to the classical analysis it provides a more detailed analysis of the sleep process, especially concerning the dynamics and microstructure of sleep.     

Spectral EEG during short-term discontinuation of antiepileptic medication in partial epilepsy

The effect of short-term discontinuation of antiepileptic drugs (AEDs) on spectral analysis of EEG background activity (spectral EEG) was studied in patients undergoing preoperative evaluation for epilepsy surgery. We also wished to clarify whether AED discontinuation would provide lateralizing evidence in spectral EEGs of patients with temporal lobe epilepsy (TLE). Spectral EEGs were performed in 15 patients receiving their regular medication regimen and again after a 1-week period during AED withdrawal. A subgroup of 9 patients who had previously undergone temporal lobectomies (TLE group) was studied separately. In this group, we evaluated the effect of preceding seizures on spectral EEG derived from temporal neocortical areas. In all patients, spectral EEG changes were detected even after a short-term AED withdrawal. The total amount of absolute delta activity was reduced and occipital peak frequency and relative alpha activity were increased as compared with baseline values. In TLE patients with habitual seizures occurring < 20 h before the spectral EEG recording, lateralization was correctly identified by the greater amount of absolute delta activity ipsilateral to the epileptogenic focus. Epileptic seizures are accompanied by subtle focal slowing in spectral EEG for a much longer period than has been assumed. In addition, postictal spectral EEG over the temporal lobes may have lateralizing value. Further studies in larger numbers of patients are needed to evaluate the role of spectral EEG in the preoperative evaluation of patients for temporal lobe surgery.     

EEG coherence changes during finger tapping in acallosal and normal children: a study of inter- and intrahemispheric connectivity

The EEG inter- and intrahemispheric coherences (ICoh and HCoh) in the theta, alpha and beta bands were studied in an acallosal group (ACCG) of five children and a normal group of 30 sex- and age-matched children (NG) during resting and tapping conditions. Being functionally deficient, tapping in the ACCG was characterized by increased intertap intervals and variability (in right-hand tapping) and by variability together with decreased synchronization (in bimanual tapping). In the ACCG, frontal, central and parietal ICohs were shown to be smaller, while temporal ICohs were larger under all conditions (see also Koeda, T., Knyazeva, M., Jonkman, J., Njiokiktjien, C., De Sonneville, L., Vildavsky, V., 1995. The resting EEG in acallosal children: compensatory left hemisphere mechanisms? Electroencephalogr. Clin. Neurophysiol. 95, 397-407). The effect was most pronounced in the EEG beta band. The sagittal HCohs, including fronto-central, fronto-parietal, and centro-parietal HCohs within both hemispheres, were larger in the ACCG, whereas temporal HCoh (fronto-temporal, centro-temporal, parieto-temporal and occipito-temporal) were smaller, suggesting rearrangement of intracortical activity associated with callosal agenesis. Tapping induced an increase in ICoh and HCoh between frontal, central and parietal areas in the NG, and weak enhancement only in the left temporal HCoh in the ACCG. The beta band, the most reactive band in the NG, was 'silent' in the ACCG, suggesting deviant cortical function during motor activity as well.