Biomedical subjects

J Röschke

Publications and source records attributed to J Röschke.

At least 37 records · Page 2Linked to original sources

PubMed1998

Effects of Lorazepam on the automatic online evaluation of sleep EEG data in healthy volunteers.

In earlier publications we described an automatic algorithm to detect rapid eye movement (REM) sleep from a single-channel EEG recording without using EMG or EOG information. This system consisted of an artificial neural network operating on the basis of preprocessed EEG data and was composed to provide a maximum of robustness for online applications. In the present study the influence of acute administration of lorazepam on the performance of the REM detection procedure was evaluated. Following an adaptation to laboratory conditions, sleep EEG data were obtained from healthy subjects in three nights each. On the evening of the second night the volunteers received a single dosage of 2.5 mg Lorazepam; the other two nights were drug-free. The sleep profile and the quantitative EEG data reflected the known changes following acute administration of benzodiazepines: during the treatment night the amount of non-REM sleep and the relative power of the EEG signal in the beta and gamma frequency bands was increased relative to the first night, while the amount of REM sleep was reduced. The night of drug discontinuation still showed some characteristics of the treatment night. The discordance rate of the REM detection algorithm relative to the manual evaluation ranged from 9% to 14.2% for the different nights. Surprisingly, the percentage of correctly classified time periods was even higher for the lorazepam night as compared to the other nights.

Adult↗

PubMed1998

No effects of pulsed high-frequency electromagnetic fields on heart rate variability during human sleep.

The influence of pulsed high-frequency electromagnetic fields emitted by digital mobile radio telephones on heart rate during sleep in healthy humans was investigated. Beside mean RR interval and total variability of RR intervals based on calculation of the standard deviation, heart rate variability was assessed in the frequency domain by spectral power analysis providing information about the balance between the two branches of the autonomic nervous system. For most parameters, significant differences between different sleep stages were found. In particular, slow-wave sleep was characterized by a low ratio of low- and high-frequency components, indicating a predominance of the parasympathetic over the sympathetic tone. In contrast, during REM sleep the autonomic balance was shifted in favor of the sympathetic activity. For all heart rate parameters, no significant effects were detected under exposure to the field compared to placebo condition. Thus, under the given experimental conditions, autonomic control of heart rate was not affected by weak-pulsed high-frequency electromagnetic fields.

Adult↗

PubMed1998

Effects of pulsed high-frequency electromagnetic fields on the neuroendocrine system.

The influence of pulsed high-frequency electromagnetic fields emitted from a circularly polarized antenna on the neuroendocrine system in healthy humans was investigated (900 MHz electromagnetic field, pulsed with 217 Hz, average power density 0.02 mW/cm2). Nocturnal hormone profiles of growth hormone (GH), cortisol, luteinizing hormone (LH) and melatonin were determined under polysomnographic control. An alteration in the hypothalamo-pituitary-adrenal axis activity was found with a slight, transient elevation in the cortisol serum level immediately after onset of field exposure which persisted for 1 h. For GH, LH and melatonin, no significant effects were found under exposure to the field compared to the placebo condition, regarding both total hormone production during the entire night and dynamic characteristics of the secretion pattern. Also the evaluation of the sleep EEG data revealed no significant alterations under field exposure, although there was a trend to an REM suppressive effect. The results indicate that weak high-frequency electromagnetic fields have no effects on nocturnal hormone secretion except for a slight elevation in cortisol production which is transient, pointing to an adaptation of the organism to the stimulus.

Adolescent↗

PubMed1998

Human sleep under the influence of pulsed radiofrequency electromagnetic fields: a polysomnographic study using standardized conditions.

To investigate the influence of radiofrequency electromagnetic fields (EMFs) of cellular phone GSM signals on human sleep electroencephalographic (EEG) pattern, all-night polysomnographies of 24 healthy male subjects were recorded, both with and without exposure to a circular polarized EMF (900 MHz, pulsed with a frequency of 217 Hz, pulse width 577 micros, power flux density 0.2 W/m2. Suppression of rapid eye movement (REM) sleep as well as a sleep-inducing effect under field exposure did not reach statistical significance, so that previous results indicating alterations of these sleep parameters could not be replicated. Spectral power analysis also did not reveal any alterations of the EEG rhythms during EMF exposure. The failure to confirm our previous results might be due to dose-dependent effects of the EMF on the human sleep profile.

Adolescent↗

PubMed1997

Time course of human 40 Hz EEG activity accompanying P3 responses in an auditory oddball paradigm.

In order to quantify the time course of auditory P3-related gamma activity, root mean square (RMS) values were calculated from band-filtered (30-45 Hz) target and non-target responses in an auditory oddball experiment. Evoked (phase locked) gamma activity was evaluated from the time domain averages, whereas induced (not necessarily phase locked) activity was analyzed on the basis of single trials. Gamma RMS values were integrated across different time windows, namely the prestimulus, N50/P50, N100, pre P3, P3 and post P3 window. The single trial P3 window hereby was defined by a maximum amplitude criterion. In accordance with other studies, we found a pronounced increase of evoked gamma activity in the time window up to 80 ms after stimulus onset. In contrast, induced gamma activity as revealed by single trial analysis decreased markedly after stimulus presentation. Starting with the P3 window, induced activity recovered to baseline level for the non-target trials, whereas it remained significantly suppressed for the target responses.

Acoustic Stimulation↗

PubMed1997

Intra- and interhemispheric electroencephalogram coherence in siblings discordant for schizophrenia and healthy volunteers.

Former studies had pointed to an increased electroencephalogram (EEG) coherence in schizophrenics, but it remained unsolved whether this deviation represents the premorbid state or is only a consequence of the current or previous schizophrenic episodes. To clarify this question, we tested the hypothesis that subjects at elevated risk also reveal higher coherences compared to healthy controls. For that, intra- and interhemispheric EEG coherences were investigated in untreated schizophrenics, their healthy siblings, and healthy controls. Differences were only found regarding the intrahemispheric coherences. Both in schizophrenics and, even though to a lesser degree, in their siblings significantly higher coherence estimates were found compared to the control group. The results are in accordance with the assumption that schizophrenia is predominantly a neurodevelopmental disease. Increased coherence might be assumed to be a vulnerability marker for schizophrenia reflecting maldevelopment of the brain before onset of the disorder.

Adult↗

PubMed1997

Differential pathophysiological mechanisms of reduced P300 amplitude in schizophrenia and depression: a single trial analysis.

In order to address basic mechanisms behind a reduced averaged P300 wave in schizophrenia and depression, 17 unmedicated schizophrenic and 11 unmedicated depressive subjects were tested in an 'oddball paradigm' against healthy controls matched for gender and age. The amplitude distributions of single trials' maximum positive deflections after stimulation (P300) for both target and nontarget stimuli were determined, which served as a basis for calculating the discrimination index d'. This index characterizes differences in the electrophysiological responses to target and nontarget stimuli of a subject being engaged in a discrimination task. As a main result d' was significantly lower for schizophrenics than for their controls. Directly compared to depressive subjects, schizophrenics also depicted a statistically significant decrease of the discrimination index, which could not be explained by differences in age. Although the averaged P300 signals did not show any significant differences between the two diagnostic groups, the approach of calculating d' on the basis of single trial analysis differentiated between schizophrenics and depressives. In conclusion, schizophrenic patients revealed different functional features when generating event-related potentials in an 'oddball paradigm' compared to healthy controls and depressives.

Adult↗

PubMed1997

Analysis of sleep EEG microstructure in subchronic paroxetine treatment of healthy subjects.

Paroxetine is a selective and potent serotonin reuptake inhibitor and its efficacy for the treatment of depression has been proven. Under acute and subchronical treatment regimens, disturbances of the regular sleep pattern are a reported side effect of the drug. The present study was therefore performed to investigate the impact of subchronic treatment with the selective serotonin reuptake inhibitor paroxetine on the microstructure of the sleep EEG. The study especially addressed the question of subchronic effects of paroxetine medication (30 mg/day) in eight healthy male volunteers in a double blind, placebo-controlled crossover design. Conventional sleep EEG parameters and a spectral power analysis for different sleep stages after 4 weeks of treatment were computed. Additionally, the correlation of certain EEG rhythms across the night was calculated in order to detect subtle dynamical EEG alterations, not necessarily obvious when regarding conventional EEG analysis. Although we could not detect any alterations of the spectral power values in certain frequency bands either during NREM nor during REM sleep following subchronic paroxetine medication, the dynamical EEG attributes across the night revealed a significant enhancement of the correlation between certain EEG rhythms mainly during NREM sleep.

Adult↗

PubMed1997

Non-linear dynamics of alpha and theta rhythm: correlation dimensions and Lyapunov exponents from healthy subject's spontaneous EEG.

The aim of the present paper was to analyze some non-linear dynamic properties of the resting EEG from healthy subjects under eyes closed conditions. For this purpose we digitally filtered the spontaneous EEG in the theta (3-8 Hz) and alpha frequency range (8-13 Hz) and considered these independent rhythms as signals from a deterministic system. Under certain conditions non-linear dynamic systems are able to generate deterministic chaos, which means that similar causes do not produce similar effects. This phenomenon is called sensitive dependence on initial conditions. From different lead positions (F3, F4, Cz, P3, P4, O1 and O2) we calculated the so-called correlation dimension D2, which is assumed to be an estimation of the system's complexity, and the Lyapunov exponent L, which appears to be a measure of the sensitive dependence on initial conditions. Our investigations revealed that the dimensionality of the theta- and alpha-rhythm varies within subjects across the experimental session in wide ranges. The degrees of freedom of the alpha and theta rhythms across the scalp are in the same order, indicating dynamic processes which can not be differentiated by applying the Grassberger-Procaccia algorithm. The Lyapunov-exponents, indicating 'how chaotic a deterministic process is', are in general smaller for the theta than for the alpha activity. Across the scalp there is no evidence for different dynamics of the theta rhythm. The dynamics of the alpha rhythm, on the contrary, appears to be different at various lead positions. It appears justified to state that the dynamics of the frontal alpha activity is functionally different from the alpha activity recorded at other topographic locations.

Algorithms↗

PubMed1997

Online detection of REM sleep based on the comprehensive evaluation of short adjacent EEG segments by artificial neural networks.

1. For scientific and clinical requirements the present objective is a robust automatic online algorithm to detect rapid eye movement (REM) sleep from single channel sleep EEG data without using EMG or EOG information. 2. For data preprocessing 20 seconds time periods of the continuous EEG activity are digitally filtered in 7 frequency bands. Then the RMS values of these filtered signals are calculated along segments of 2.5 seconds. The resulting matrix of RMS values is representing information on the power of the signal localized in time and frequency and serves as input to an artificial neural network. A pooled set of EEG data together with the corresponding manual evaluation of the recordings was used in the training process. 3. Afterwards more than 90% of the time periods not belonging to the training set could be correctly labeled into REM and nonREM periods. In comparison to an older algorithm based on RMS values calculated along segments of 20 seconds, the error rate could be reduced by 20%.

Adult↗

PubMed1997

The influence of lorazepam upon pre- and poststimulus EEG during sleep in man.

Enhancement of beta power in the spontaneous EEG under the influence of benzodiazepine medication is a well known phenomenon under waking conditions as well as during sleep. On the other hand, in certain frequency bands EEG activity following external stimulation is also enhanced. Therefore, the question arises what relationship exists between pre- and poststimulus EEG under the influence of benzodiazepines. Is an augmentation of beta activity during benzodiazepine medication further enhanced when external stimulation is applied? In order to address this question we compared the spectral power of pre- and poststimulus EEG under 2.5 mg lorazepam during sleep with placebo conditions. The hypothesis tested was that of Basar (1980): if the beta power is high prior to the stimulation, no further enhancement following stimulation is observed. Our results confirm the hypothesis during sleep stages II and III. At the present time it is unclear whether this effect might be dose-dependent. In any case, the investigation presented here has furnished additional information on the mechanisms by which benzodiazepines alter the brain's electrical activity.

Acoustic Stimulation↗

PubMed1997

Different phase relationships between EEG frequency bands during NREM and REM sleep.

Phase relationships between distinct frequency bands of the sleep electroencephalogram (EEG) were studied in healthy subjects using cross-correlation coefficients, both over the entire night and separately for nonrapid eye movement (NREM) and rapid eye movement (REM) sleep. Over the entire night, a large positive correlation developed within high- and low-frequency bands, while a negative correlation emerged between low- and high-frequency bands, reflecting their reciprocal temporal course. More detailed analysis revealed different phase relationships during NREM and REM sleep. Findings during NREM were similar to the entire night. However, during REM, a large increase of the correlation between low- and high-frequency bands occurred compared to NREM, even with a change of sign. The results indicate the complexity of the interrelation of the different frequency bands depending on sleep state, with low- and high-frequency bands being out of phase during NREM and in phase during REM sleep.

Adult↗

PubMed1997

Spectral analysis of P300 generation in depression and schizophrenia.

In the past it was reported in several studies that both depressive and schizophrenic patients exhibit reduced P300 amplitudes compared to healthy controls. In order to elucidate the underlying mechanisms of spectral P300 generation, we analysed P300 responses in depression and schizophrenia by a frequency based approach. Herefore, the amplification (poststimulus/prestimulus) of spectral power in different frequency bands was evaluated for non-target and target epochs. Generally, we found that P300 responses are accompanied by a pronounced frequency amplification in the delta and theta range. For the depressive patients we detected only under target condition a statistically significant reduction of alpha and gamma amplification compared to controls. In contrast to this, we observed a highly significant reduction of delta amplification in schizophrenic patients, under both target and non-target conditions.

Adult↗

PubMed1997

No short-term effects of digital mobile radio telephone on the awake human electroencephalogram.

A recent study reported the results of an exploratory study of alterations of the quantitative sleep profile due to the effects of a digital mobile radio telephone. Rapid eye movement (REM) was suppressed, and the spectral power density in the 8-13 Hz frequency range during REM sleep was altered. The aim of the present study was to illuminate the influence of digital mobile radio telephone on the awake electroencephalogram (EEG) of healthy subjects. For this purpose, we investigated 34 male subjects in a single-blind cross-over design experiment by measuring spontaneous EEGs under closed-eyes condition from scalp positions C3 and C4 and comparing the effects of an active (0.05 mW/cm2) and an inactive digital mobile radio telephone (GSM) system. During exposure of nearly 3.5 min to the 900 MHz electromagnetic field pulsed at a frequency of 217 Hz and with a pulse width of 580 microseconds, we could not detect any difference in the awake EEGs in terms of spectral power density measures.

Adult↗

PubMed1996

Single trial analysis of event related potentials: a comparison between schizophrenics and depressives.

The aim of the present paper was to perform a single trial analysis of event-related potentials in order to elucidate the mechanisms behind a reduced P300 amplitude occurring in unmedicated depressives (n = 11) and schizophrenics (n = 18). For this purpose, tools from linear system theory were applied to single trials in an oddball paradigm. This analysis provides estimates of the magnitude of the positive deflection occurring around the latency of P300 following target and nontarget simuli. According to the density functions of these amplitude distributions, we operationally defined "false-negative" (P300 amplitude lower than an individual threshold under target conditions) as well as "false-positive" responses (P300 amplitude higher than the threshold following nontarget stimuli). Our investigations revealed a reduction of the single-trial P300 amplitude in depression and a combination of amplitude reduction along with fewer elicited single-trial P300 waves in schizophrenics.

Adult↗

PubMed1996

Amplitude frequency characteristics of evoked potentials during sleep: an analysis of the brain's transfer properties in depression.

Classical analysis of the spontaneous sleep EEG in depressive disorder commonly reveals alterations of sleep continuity, number of awakenings, slow-wave sleep, and REM sleep compared to healthy controls; however, conventional analysis can not help understand dynamic differences of the sleep EEG during different sleep stages. In order to elicit qualitative alterations of information processing between depressives and healthy controls, we measured late components of auditory and visual evoked potentials (AEPs and VEPs) during different sleep stages of 15 depressive inpatients and in a sex- and age-matched control group from scalp positions Fz, Cz and Pz. According to linear system theory, we then computed the amplitude frequency characteristic (AFC) from averaged AEPs and VEPs in different sleep stages. These AFCs describe the input/output relation of the system under study leading to a characterization of the transfer properties of the brain during sleep in depression. Our investigations showed that information processing appears characteristically altered in depression during non-REM sleep for both auditory and visual stimulation compared to healthy controls. The transfer properties for processing auditory as well as visual information during REM sleep do not appear dynamically impaired in depressive disorder.

Adult↗

PubMed1996

Surrogate data analysis of sleep electroencephalograms reveals evidence for nonlinearity.

We tested the hypothesis of whether sleep electroencephalographic (EEG) signals of different time windows (164 s, 82 s, 41 s and 20.5 s) are in accordance with linear stochastic models. For this purpose we analyzed the all-night sleep electroencephalogram of a healthy subject and corresponding Gaussian-rescaled phase randomized surrogates with a battery of five non-linear measures. The following nonlinear measures were implemented: largest Lyapunov exponent L1, correlation dimension D2, and the Green-Savit measures delta 2, delta 4 and delta 6. The hypothesis of linear stochastic data was rejected with high statistical significance. L1 and D2 yielded the most pronounced effects, while the Green-Savit measures were only partially successful in differentiating EEG epochs from the phase randomized surrogates. For L1 and D2 the efficiency of distinguishing EEG signals from linear stochastic data decreased with shortening of the time window. Altogether, our results indicate that EEG signals exhibit nonlinear elements and cannot completely be described by linear stochastic models.

Adult↗

PubMed1996

Effects of yohimbine on sexual experiences and nocturnal penile tumescence and rigidity in erectile dysfunction.

The therapeutic effect of the alpha 2-antagonist yohimbine in erectile dysfunction was studied in a double-blind placebo-controlled design. Thirty-one male patients underwent extensive clinical, urological, and psychiatric diagnosis and were dichotomically classified into an organic and a nonorganic subgroup. Following a 1-week placebo run-in period, patients were randomly assigned to a placebo or a verum group (yohimbine 15 mg daily) for a treatment period of 7 weeks. The Clinical Global Impression (CGI) scale was used as the primary efficacy parameter. Additionally, nocturnal penile tumescence and rigidity (NPTR) were measured. Global assessment of erectile function applying the CGI scale revealed, beyond a placebo effect in both organic and nonorganic patients, a therapeutic effect in the subgroup of nonorganic patients, with a significantly greater improvement in the yohimbine group compared to the placebo group. No superiority of yohimbine compared to placebo was found in the organic patients. These findings on the subjective level had no correlate in the NPTR recordings. The NPTR parameters were unchanged under yohimbine treatment in both the nonorganic and organic subgroup. No interrelation was found between subjective improvement and NPTR alterations. Polysomnographic control of the NPTR registrations ensured that the duration of REM sleep under treatment was not influenced.

Adult↗