Discovery of phosphatidylcholines and sphingomyelins as biomarkers for ovarian endometriosis.

BACKGROUND: Current non-invasive diagnostic methods for endometriosis lack sensitivity and specificity. In search for new diagnostic biomarkers for ovarian endometriosis, we used a hypothesis-generating targeted metabolomics approach. METHODS: In a case-control study, we collected plasma of study participants and analysed their metabolic profiles. We selected a group of 40 patients with ovarian endometriosis who underwent laparoscopic surgery and a control group of 52 healthy women who underwent sterilization at the University Clinical Centre Ljubljana, Slovenia. Over 140 targeted analytes included glycerophospholipids, sphingolipids and acylcarnitines. The analytes were quantified by electrospray ionization tandem mass spectrometry. For assessing the strength of association between the metabolite or metabolite ratios and the disease, we used crude and adjusted odds ratios. A stepwise logistic regression procedure was used for selecting the best combination of biomarkers. RESULTS: Eight lipid metabolites were identified as endometriosis-associated biomarkers due to elevated levels in patients compared with controls. A model containing hydroxysphingomyelin SMOH C16:1 and the ratio between phosphatidylcholine PCaa C36:2 to ether-phospholipid PCae C34:2, adjusted for the effect of age and the BMI, resulted in a sensitivity of 90.0%, a specificity of 84.3% and a ratio of the positive likelihood ratio to the negative likelihood ratio of 48.3. CONCLUSIONS: Our results suggest that endometriosis is associated with elevated levels of sphingomyelins and phosphatidylcholines, which might contribute to the suppression of apoptosis and affect lipid-associated signalling pathways. Our findings suggest novel potential routes for therapy by specifically blocking highly up-regulated isoforms of phosphpolipase A2 and lysophosphatidylcholine acyltransferase 4.

Mycorrhizosphere responsiveness to atmospheric ozone and inoculation with Phytophthora citricola in a phytotron experiment with spruce/beech mixed cultures.

The aim was to analyze functional changes in the mycorrhizosphere (MR) of juvenile spruce and beech grown in a mixture under ambient and twice ambient ozone and inoculated with the root pathogen Phytophthora citricola. The phytotron experiment was performed over two vegetation periods, adding the pathogen at the end of the first growing season. Root biomass data suggest that the combined treatment affected spruce more than beech and that the negative influence of ozone on stress tolerance against the root pathogen P. citricola was greater for spruce than for beech. In contrast, beech was more affected when the pathogen was the sole stressor. The functional soil parameter chosen for studies of MR soil samples was activity of extracellular enzymes. After the first year of ozone exposure, MR soil samples of both species showed increased activity of almost all measured enzymes (acid phosphatase, chitinase, beta-glucosidase, cellobiohydrolase) in the O3 treatment. Species-specific differences were observed, with a stronger effect of P. citricola on beech MR and a stronger ozone effect on spruce MR. In the second year, the effects of the combined treatment (ozone and P. citricola) were a significant increase in the activity of most enzymes (except cellobiohydrolase) for both tree species. The results indicated that responsiveness of MR soils towards ozone and P. citricola was related to the severity of infection of the plants and the reduction of belowground biomass, suggesting a strong, direct influence of plant stress on MR soil enzyme activity. Additional research is needed using different species and combined stresses to determine the broader ecological relevance of shifts in rhizosphere enzymes.

Regression analysis of time trends in perinatal mortality in Germany 1980-1993.

Numerous investigations have been carried out on the possible impact of the Chernobyl accident on the prevalence of anomalies at birth and on perinatal mortality. In many cases the studies were aimed at the detection of differences of pregnancy outcome measurements between regions or time periods. Most authors conclude that there is no evidence of a detrimental physical effect on congenital anomalies or other outcomes of pregnancy following the accident. In this paper, we report on statistical analyses of time trends of perinatal mortality in Germany. Our main intention is to investigate whether perinatal mortality, as reflected in official records, was increased in 1987 as a possible effect of the Chernobyl accident. We show that, in Germany as a whole, there was a significantly elevated perinatal mortality proportion in 1987 as compared to the trend function. The increase is 4.8% (p = 0.0046) of the expected perinatal death proportion for 1987. Even more pronounced levels of 8.2% (p = 0. 0458) and 8.5% (p = 0.0702) may be found in the higher contaminated areas of the former German Democratic Republic (GDR), including West Berlin, and of Bavaria, respectively. To investigate the impact of statistical models on results, we applied three standard regression techniques. The observed significant increase in 1987 is independent of the statistical model used. Stillbirth proportions show essentially the same behavior as perinatal death proportions, but the results for all of Germany are nonsignificant due to the smaller numbers involved. Analysis of the association of stillbirth proportions with the (137)Cs deposition on a district level in Bavaria discloses a significant relationship. Our results are in contrast to those of many analyses of the health consequences of the Chernobyl accident and contradict the present radiobiologic knowledge. As we are dealing with highly aggregated data, other causes or artifacts may explain the observed effects. Hence, the findings should be interpreted with caution, and further independent evidence should be sought.

European stillbirth proportions before and after the Chernobyl accident.

BACKGROUND: Numerous investigations have been carried out concerning the possible impact of the Chernobyl accident, in April 1986, on the prevalence of anomalies at birth and on perinatal mortality. The accident has contaminated Eastern Europe more heavily than Western Europe. If there was an effect of the radioactive contamination on perinatal mortality or stillbirth proportions one would expect to find it more pronounced in Eastern Europe as compared to Western Europe. We therefore studied long-term time trends in European stillbirth proportions. METHODS: Linear logistic regression was applied to model the time trends in stillbirth proportions. Dummy variables were used to account for effects that can be associated with certain years or locations. A synoptic logistic regression model is suggested for the western, central, and eastern parts of Europe. RESULTS: There is a marked differential effect in the long-term stillbirth time trends between Western Europe (Belgium, France, Great Britain, Iceland, Ireland, Luxembourg, Portugal, Spain), Central Europe (Austria, Denmark, Germany, Italy, Norway, Switzerland), and Eastern Europe represented by four countries (Greece, Hungary, Poland, Sweden). In contrast to the western and central European trends, the eastern European trend exhibits an absolute increase of the stillbirth proportion in 1986 as compared with 1985 and an apparent upward shift of the whole trend line from 1986 on. CONCLUSION: Our results are in contrast to those of many analyses of the health consequences of the Chernobyl accident and contradict the present radiobiological knowledge. As we are dealing with highly aggregated data, other causes or artefacts may explain the observed effects. Hence, the findings should be interpreted with caution and further independent evidence should be sought.

Frequency distributions and density functions of distances with simulated linear track structures.

Track structures of high-LET particles can be simulated by various linear approaches. The distribution of distances seems to be an important parameter in understanding the type of interactions which occur and the biological effects which these excitations and ionizations will create; therefore, the distance distributions of these simulated track structures were calculated. Three presentations show that their exact appearance depends on the scaling parameter: the number of classes. In one approach the theoretical density of the distances was calculated by the techniques of convolution and by forming mixed distributions which confirm the findings of the simulation.

Correlation between spectral EEG parameters and intelligence test variables in school-age children.

OBJECTIVES: The objective of the study was to investigate the relationship between the degree of intelligence and spectral electroencephalographic (EEG) parameters and to find out which EEG variables are relevant for this correlation. METHODS: Bipolar 1 min EEG recordings were derived for the fronto-central and parieto-occipital leads from 155 clinically healthy 10-year-old children in vigilance state awake with eyes closed. Relative spectral power parameters were calculated by Fast Fourier Transform. Two-group t tests according to the score values of the 'WISC-R' intelligence test as well as univariate and multiple correlation analyses between spectral and intelligence test variables were carried out. RESULTS: A statistically significant positive correlation of the intelligence test variables with the spectral alpha power and a significant negative correlation with the spectral power of lower frequency bands was observed. Predicting the spectral parameters by means of intelligence test variables, significant multiple correlation coefficients were revealed in the frequency ranges: 0.5-1.5, 3.0-5.0 and 9.0-10.5 Hz. The highest significance (P<0.0001) was found for the spectral value at 9.0 Hz. CONCLUSIONS: The results of t tests and correlation analyses confirm the strong relationship between spectral EEG parameters and the degree of intelligence indicating that the 'EEG recordings do reflect intellectual abilities'. It may be supposed that the amount of the intelligence quotient is correlated with the degree of EEG maturation and thus reflects the active number of synapses and the degree of differentiation of the neuronal controlling system.

A cluster of childhood leukaemias near two neighbouring nuclear installations in Northern Germany: prevalence of chromosomal aberrations in peripheral blood lymphocytes.

PURPOSE: Between 1990 and 1991 a leukaemia cluster was observed in children living close to the combined site of a nuclear power plant and a nuclear research facility in Elbmarsch, a region in Lower Saxony (Germany). We aim to investigate the prevalence of presumably radiation-induced chromosomal aberrations in peripheral blood lymphocytes of children in Elbmarsch and children of a control region in order to find out whether there was an uncontrolled release of radioactive material which resulted in a substantial exposure. MATERIALS AND METHODS: The frequency of dicentric and ring chromosomes in lymphocytes of the peripheral blood in 42 children in Elbmarsch and 30 children in Plön was investigated. Children in both groups had been permanent residents of the study area. RESULTS: The mean frequency of dicentric and ring chromosomes in Elbmarsch was 14/32580 cells (=0.430 x 10(-3); 95% CI 0.24-0.70 x 10(-3) cells), and in Plön it was 17/24065 cells (=0.706 x 10(-3); 95% CI 0.42-1.10 x 10(-3) cells). CONCLUSIONS: No difference in the frequency of dicentric and ring chromosomes was observed between children in Elbmarsch living close to a combined site of a nuclear power plant and a nuclear research facility and children living in the control area Plön. The power of the study to detect a threefold or higher increase in the aberration frequency was at least 0.86.

Pentachlorophenol in indoor environments. Correlation of PCP concentrations in air and settled dust from floors.

The investigation of settled dust is a proven and simple screening-method for considering indoor contamination for semivolatile compounds. Here we investigate the correlation of PCP concentrations in air and freshly settled dust from floors. Air and dust samples were taken from 75 rooms in 30 buildings with suspicion of an application of PCP-containing wood preservatives. Sampling was repeated four times within 18 months. PCP air concentrations were found in the range of <0.3-576 ng m-3 (mean value 25.3 ng m-3, median 2.5 ng m-3). PCP dust concentrations were found in the range of 0.083-79 microg g-1 (mean value 3.5 microg g-1, median 1.1 microg g-1. A weak highly significant correlation (P < 0.0001) with a correlation coefficient of R2 = 0.433, of the PCP concentration in dust with the PCP concentration in air, was observed. Measurement of PCP concentrations in dust, therefore, is a suitable screening method for the evaluation of indoor contamination with PCP. Due to the high dispersion of the data it is not possible to calculate PCP concentrations in air from concentrations in dust although a highly significant correlation of the PCP concentrations in air and dust was found.

Kinetic analyses of plant water relocation using deuterium as tracer - reduced water flux of Arabidopsis pip2 aquaporin knockout mutants.

Due to reduced evaporation and diffusion of water molecules containing heavier isotopes, leaf water possesses an elevated (18)O or (2)H steady-state content. This enrichment has been exploited in plant physiology and ecology to assess transpiration and leaf water relations. In contrast to these studies, in this work the (2)H content of the medium of hydroponically grown Arabidopsis thaliana was artificially raised, and the kinetics of (2)H increase in the aerial parts recorded during a short phase of 6-8 h, until a new equilibrium at a higher level was reached. A basic version of the enrichment models was modified to establish an equation that could be fitted to measured leaf (2)H content during uptake kinetics. The fitting parameters allowed estimation of the relative water flux q(leaf) into the Arabidopsis rosette. This approach is quasi-non-invasive, since plants are not manipulated during the uptake process, and therefore, offers a new tool for integrated analysis of plant water relations. The deuterium tracer method was employed to assess water relocation in Arabidopsis pip2;1 and pip2;2 aquaporin knockout plants. In both cases, q(leaf) was significantly reduced by about 20%. The organ and cellular expression patterns of both genes imply that changes in root hydraulic conductivity, as previously demonstrated for pip2;2 mutants, and leaf water uptake and distribution contributed in an integrated fashion to this reduced flux in intact plants.

Impairment of germline transmission after blastocyst injection with murine embryonic stem cells cultured with mouse hepatitis virus and mouse minute virus.

The aim of this study was to determine the susceptibility of murine embryonic stem (mESCs) to mouse hepatitis virus (MHV-A59) and mouse minute virus (MMVp) and the effect of these viruses on germline transmission (GLT) and the serological status of recipients and pups. When recipients received 10 blastocysts, each injected with 10(0) TCID(50) MHV-A59, three out of five recipients and four out of 14 pups from three litters became seropositive. When blastocysts were injected with 10(-5) TCID(50) MMVp, all four recipients and 14 pups from four litters remained seronegative. The mESCs replicated MHV-A59 but not MMVp, MHV-A59 being cytolytic for mESCs. Exposure of mESCs to the viruses over four to five passages but not for 6 h affected GLT. Recipients were seropositive for MHV-A59 but not for MMVp when mESCs were cultured with the virus over four or five passages. The data show that GLT is affected by virus-contaminated mESCs.

[Data protection and data access (II): Physician's responsibility for confidentiality, federal statistics law and data collection by authorization with reference to implementing occupational medicine epidemiologic studies in Germany]. / Datenschutz und Datenzugang (II): Arztliche Schweigepflicht, Bundesstatistikgesetz und Datenerhebung durch einen Treuhänder unter dem Gesichtspunkt der Durchführung arbeitsmedizinisch-epidemiologischer Studien in der Bundesrepublik Deutschland.

The additional legal rulings governing access to personal data for epidemiological research are the medical professional secrecy regulators and the federal statistics law. These permit access to personal data only if the individual has given his or her informed constant. Beyond this, both laws contain clauses governing the transfer of anonymous data for research and science. Thus anonymized data may be transferred on request to authorized persons or institutions, such as a physician or the regional statistics office. Finally, a custodian model is presented which provides further possibilities for research in occupational medicine and epidemiology within this very restrictive legal framework.

[Data protection and data access (I): federal data protection law and the social welfare code with reference to carrying out occupational medicine epidemiologic studies in Germany]. / Datenschutz und Datenzugang (I): Bundesdatenschutzgesetz und Sozialgesetzbuch unter dem Aspekt der Durchführung arbeitsmedizinisch-epidemiologischer Studien in der Bundesrepublik Deutschland.

The regulations applicable to research in occupational epidemiology are the federal data protection (confidentiality) law (BDSG), the social welfare code (SGB), medical professional secrecy regulations and the federal statistics law (BStatG). The SGB, medical professional secrecy, and BStatG codes take precedence over BDSG rulings. This paper discusses BDSG and SGB. Medical professional secrecy and BStatG will be the topic of another publication (Datenschutz and Datenzugang II). The BDSG permits processing and utilization of personal data only if 1. this is permitted by BDSG or a law with higher priority, or 2. if the individual concerned has given her or his informed consent. According to the BDSG private research institutes can have access to personal data collected within non-public institutions only via section 28 (2) without consent of the individual. The "research paragraph" section 40 governs the processing and utilisation of personal data by research institutions. As a rule, the SGB permits access to epidemiological data sources only with the informed consent of the individuals concerned. The exception is section 75 SGBX. This paragraph permits disclosure of personal data without the individual's consent by the relevant public institution only if public interest considerably outweighs the private concerns. To our knowledge, however, this clause has had no practical significance. The concept of "informed consent" is discussed in detail, including the requirements for a legal form for informed consent. The legal codes of the BDSG, professional secrecy, and BStatG permit the transfer of personal data if the individuals concerned remain anonymous. This paper deals in detail with the concept of "anonymity".(ABSTRACT TRUNCATED AT 250 WORDS)

[Cleft lip and cleft palate birth rate in Bavaria before and after the Chernobyl nuclear power plant accident]. / Spaltgeburtenrate in Bayern vor und nach dem Reaktorunfall in Tschernobyl.

BACKGROUND: Cleft lip and palates (CLP) occur with a frequency of between 1 and 2 cases in 1000 live births and thus belong to the most frequent congenital anomalies. In the former German Democratic Republic (GDR), records covering 1967-1989 for CLP newborns show a 9.4% increase of the prevalence of CLP from 1987 to 1989, possibly due to Chernobyl. DATA AND STATISTICAL METHOD: In Bavaria, all congenital malformations in children's hospitals have been recorded from 1984 to 1991. Among these data, 1324 cases with CLP were found. A spatial-temporal analysis aimed at uncovering a possible association of the CLP occurrence with the Chernobyl fallout on a district level, as well as a synoptic analysis of the GDR and Bavarian data, were carried out. RESULTS: In Bavaria, from October 1986 to December 1990, the CLP frequency increased by 9.5% (p=0.10) relative to the trend as computed from the remaining years. The association of CLP rates with fallout on a district level is reflected by a significant relative risk (RR) per kBq/m(2) of RR=1.008 (p=0.03). A synoptic analysis of the Bavarian data and the GDR data restricted to the overlapping time window from 1984 to 1989 discloses a simultaneous significant jump of the CLP prevalence by 8.6% (p=0.02) after 1986. CONCLUSION: The presumption of a long-term increase of CLP after exposure to Chernobyl fallout is corroborated by the analysis of the Bavarian congenital malformation data.

[Statistical description of health complaints after pyrethroid exposure--a comparison of exposed groups]. / Statische Deskription von Gesundheitsbeschwerden nach Pyrethroidexposition--ein Belastungsgruppenvergleich.

In respect of 128 pyrethroid-exposed persons, data on subjective health impairment were collected by applying a self-administered questionnaire. Participants--83 female and 45 male--determined their health status using a scale for the strength of their complaints. Health complaints were measured by 70 variables and were divided into 6 symptom groups. A low exposure and a high exposure group was defined by the number of pyrethroid applications (once versus several). We computed mean values for all 70 variables stratified according to gender and exposure group. Comparison shows that for nearly all variables highly exposed women reported stronger health complaints than low exposed women. This uniform trend is not seen in men. For a condensed presentation of differing health complaints between exposure groups, we defined standardised scores for each of the 6 symptom classes. Women with elevated exposure show increased scores for all 6 symptom groups, one difference being significant (p = 0.018) and two differences being of borderline significance (p = 0.061 and p = 0.073). For highly exposed men only two scores are elevated and none is significant. However, it is pointed out that the high-exposure group comprises only 9 men.

[Statistical description of health complaints after pyrethroid exposure]. / Statistische Deskription von Gesundheitsbeschwerden nach Pyrethroidexposition.

In 96 pyrethroid-exposed persons data on subjective health impairment were collected by means of a questionnaire. The present explorative statistical analysis is restricted to a subgroup of 51 out of the 96 persons for which pyrethroid concentrations in dust samples from residential dwellings or from work places could be determined. Since measurements were taken from dwellings or work places, there is in some cases only one common measured value for families or teams. In total, we have 34 independent measurements. Based on the type of measured exposures, the 51 participants can be divided into 3 groups: 26 cases exposed to permethrin and tetramethrin (type-I pyrethroids), 13 cases exposed to deltamethrin, cyfluthrin or cypermethrin (type-II pyrethroids), and 12 cases with mixed exposure to the mentioned type-I and type-II pyrethroids. For the 3 groups we computed weighted mean values of pyrethroid concentrations, each independent measurement being weighted with the number of corresponding persons. The mean values are 425.7, 56.1, and 958.9 mg pyrethroid/kg dust for the groups in the above order. After combining the two highly exposed groups into one new group with now 38 members and a mean pyrethroid concentration of 594.1 mg/kg, an increased frequency of health complaints was found as compared to the group exposed only to type-II pyrethroids.

Pentachlorophenol in indoor environments. Does a single measurement of air and dust concentrations represent the contamination?

In order to be able to make a decision, as to whether a room or building has a health-endangering pentachlorophenol (PCP) concentration, usually the PCP concentrations in air and settled dust are measured. The variability of the PCP concentration in indoor air and dust was studied. Air and dust samples were taken from 75 rooms in 30 buildings with suspicion of application of PCP-containing wood preservatives. Sampling was repeated four times within 18 months. Thirty-six rooms were reconstructed within the study; 39 rooms had unchanged contamination status during the study. The four times repeated measurements of PCP concentrations in air and dust in these rooms showed large variations of the measured values. The variability of the results is to a large extent in the same range as the measured values. The observed relative standard deviation of the PCP concentrations in air and dust does not depend on the average PCP concentration detected in the individual rooms.

Temporal order of nonlinear dynamics in human brain.

In previous spectral analysis investigations, we demonstrated that the spontaneous activity of the alpha EEG is not stationary but rather shows cyclic alterations with a circa 1-min periodicity. Following the conclusion that a power increase in the alpha band implies a neuronal synchronization, and vice versa, an associated decrease of the EEG complexity was postulated. Accordingly, a rhythmic variation, i.e., a temporal order of the nonlinear dynamics with similar period length, was expected. Bipolar 4-min EEG recordings were obtained from 20 awake subjects (mean age: 23.5+/-2.5 years) with eyes closed for the EEG leads C3, C4, Oz, and Fz according to the 10-20 system. For the automatic evaluation of spontaneous alterations of complexity, a sliding computation of the so-called correlation dimension, using an analysis window length of 20 s continuously shifted by 1 s, was performed. The time series of complexity exhibited an oscillatory behavior with a mean period length of 58.7 s; the Friedman test statistic revealed no significant topological differences. For the rejection of the null hypothesis that the observed periodicity is a random one, two-group t-tests and ANOVA with repeated measures were performed, comparing the corresponding amplitudes and period lengths with those derived from 20 pseudo-random signals (taken from a multivariate Gaussian normal distribution). The mean relative change of EEG complexity was highly significantly increased (P<0.0001) compared to that of random data. Likewise, the difference of mean period lengths was also significant (P<0.01). The results indicate that the coupling strength of the neural network of the brain changes periodically, with a cyclic alteration from a central to a parallel processing mode of information, reflecting state transitions from synchronized, low-complex EEG activity to desynchronized high-complex activity, and vice versa. Various neuronal control mechanisms that may be acting as pacemakers responsible for the temporal order of such transients are discussed. A disturbance of the temporal order may be of pathophysiological significance.

[Organochlorine compounds in human milk]. / Organochlorverbindungen in Frauenmilch.

The impact of life style characteristics and chemical exposure conditions of about 80 nursing women on the contents of Organochlorine compounds (OCC) in their breast milk is analyzed and described by a robust statistical procedure. Information on independent variables such as age, diet, smoking, occupation and chemical exposures is obtained by a questionnaire. Concentrations of HCB alpha-, beta-, gamma-HCH, Heptachlorepoxide, Dieldrin, DDE and PCB in milk samples are measured and serve as dependent variables. By logistic regression we quantify the influence of combinations of several independent variables on the probability of being extremely contaminated with at least one OCC. We also study the pattern in which OCC are associated with each other. There are distinct pairwise correlations of the four main contaminants: HCB, beta-HCH, DDE and PCB. These correlations entail that a woman with a high PCB concentration, for example, is more likely of being also contaminated above average with the remaining contaminants. We define a simple load score and compare its different theoretical distributions under the assumption of presence or absence of the correlations. By this we can show that the proportion of heavily contaminated women is underestimated, if the OCC associations are ignored. We therefore recommend that the pattern of OCC-correlations in human milk is further studied in more representative samples. These investigations should also comprise occupationally exposed women.

Genomewide scans of complex human diseases: true linkage is hard to find.

Many "complex" human diseases, which involve multiple genetic and environmental determinants, have increased in incidence during the past 2 decades. During the same time period, considerable effort and expense have been expended in whole-genome screens aimed at detection of genetic loci contributing to the susceptibility to complex human diseases. However, the success of positional cloning attempts based on whole-genome screens has been limited, and many of the fundamental questions relating to the genetic epidemiology of complex human disease remain unanswered. Both to review the success of the positional cloning paradigm as applied to complex human disease and to investigate the characteristics of the whole-genome scans undertaken to date, we created a database of 101 studies of complex human disease, which were found by a systematic Medline search (current as of December 2000). We compared these studies, concerning 31 different human complex diseases, with regard to design, methods, and results. The "significance" categorizations proposed by Lander and Kruglyak were used as criteria for the "success" of a study. Most (66.3% [n=67]) of the studies did not show "significant" linkage when the criteria of Lander and Kruglyak (1995) were used, and the results of studies of the same disease were often inconsistent. Our analyses suggest that no single study design consistently produces more-significant results. Multivariate analysis suggests that the only factors independently associated with increased study success are (a) an increase in the number of individuals studied and (b) study of a sample drawn from only one ethnic group. Positional cloning based on whole-genome screens in complex human disease has proved more difficult than originally had been envisioned; detection of linkage and positional cloning of specific disease-susceptibility loci remains elusive.

Inverse covariation of spectral density and correlation dimension in cyclic EEG dynamics of the human brain.

The responsiveness or excitability of the central nervous system (CNS) to external or internal stimuli is systematically altered corresponding to transient changes of the EEG background activity, mainly in the alpha range. We hypothesise that a transient alpha power increase is due to an underlying increase in synchronisation or coupling strength between various neuronal elements or cortical networks. Consequently, the 'network' of the CNS may be more ordered and, hence, less complex in the case of high spectral density, and vice versa. The goals of the present paper are (1) to prove the inverse covariation between spectral density and correlation dimension for a set of human EEG data, (2) to falsify the null hypothesis that the observed relationship is a random one, and (3) to propose a neuronal approach which may explain the observed correlations. A sliding computation of the spectral density and correlation dimension [Grassberger P, Procaccia I (1983) Physica D 9:189-208] of mid-occipital EEG recordings derived from eight awake subjects with eyes closed was performed. The similarity between the two time courses was quantified by similarity measures and descriptive correlation coefficients. The temporal pattern of dimensional complexity showed an inverse relationship with simultaneously computed spectral power changes most pronounced in the alpha range. The group means of similarity measures and correlation coefficients were compared with the corresponding means of a sample set established by 20 Gaussian random signals. Statistically significant differences were obtained at the 0.1% level, rejecting the null hypothesis that the observed relationship is a random one. The results support the idea that the dynamics of the EEG signals investigated reflect a chaotic deterministic process with state transitions from 'high-dimensional' to 'low-dimensional' non-linear dynamics, and vice versa. Adequate neuronal models and approaches to interpret the disclosed transients and the inverse covariation between spectral density and dimensional complexity are proposed, giving additional insight into the integrative functioning of the CNS with respect to the strategy of information processing.