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Biomedical subjects

D Lehmann

Publications and source records attributed to D Lehmann.

At least 181 records · Page 10Linked to original sources
PubMed1983

Spectral analysis of all-night sleep EEG in healthy adults.

Power and coherence spectra were computed from all-night sleep EEG records in 6 healthy adult subjects. Derivations were from F3, F4, P3, P4, O1, O2, T3, and T4 to the vertex (Cz). Records were conventionally scored into sleep stages. Average power per sleep stage was maximal at frequencies 0.4-6 c/s in stage 4, at 6-10 c/s in either stage 3 or stage 4, at 12-14 c/s in stage 2 and at 14-30 c/s in stage 1. The average power range from highest values in the lowest frequency band to lowest values in the highest frequency band showed marked differences between sleep stages: It was lowest (12-14 dB) in stage 1, followed by stage 2 (20-22 dB), and stage 3 (16-28 dB), and largest in stage 4 (29-32 dB). REM sleep (15-16 sB) was between stage 1 and 2. The waking state showed an average power range of 11-15 dB. Alpha power at 8-10 c/s in occipital and parietal leads was remarkably constant during sleep, i.e. independent of sleep stage. Coherence showed maximal values at 2-8 c/s in REM sleep, at 8-12 c/s in stage 4, at 12-17 c/s in either stage 3 or 4, and at 17-30 c/s again in stage REM. There was significant coherence increase at 2-8 and 17-30 c/s from NREM to REM sleep, most pronounced between parietal to vertex derivations. Overall coherence between both occipital-to-vertex, or between occipital and parietal-to-vertex derivations, was essentially higher than in the other derivations. The results, essentially, give a comprehensive phenomenology of the dynamic spectral structure of all-night sleep EEG. They suggest that the different brain states during sleep (e.g. stage 1 NREM vs. REM) which are associated with different functions (e.g. hypnagogic hallucinations vs. dreams) differ in EEG spectral parameters if coherence is considered. Likewise, they suggest that studies of automatic sleep staging based exclusively on EEG spectral parameters appear promising.

Adult↗
PubMed1983

Dreaming: The functional state-shift hypothesis. A neuropsychophysiological model.

The different brain functional states during sleep and wakefulness are associated with differences in processing strategies, memory stores, and EEG patterns. Shifts of functional state occur spontaneously or as orienting reactions to processed information, and cause the formal characteristics of dreams. Forgetting of dreams is a function of the magnitude of the difference between states during storage and recall. Based on EEG similarities between sleep stages and developmental stages, brain states during sleep in adults are proposed to correspond functionally with waking states during childhood. Repeated functional regressions occur during sleep, with access to earlier memory material and cognitive strategies unavailable during waking life, so that earlier experiences can be used for current problems. This dream work constitutes the biological significance of sleep.

Adolescent↗
PubMed1983

Fuzzy clustering of EEG signal and vigilance performance.

An automatic method for classification of EEG data, based upon segmentation of the signal using the autoregressive model and decision making in fuzzy environment, is described. The classification is applied to explore the relations between EEG states during waking, and vigilance performance studied through auditory choice reaction time. The average auditory choice reaction time measured during occurrences of "alpha" segments was significantly shorter than that measured during occurrences of "nonalpha" signal segments. A significant negative correlation was also found between the segments auditory choice reaction time and the segments spectral power in the alpha or beta frequency band.

Adult↗
PubMed1982

Spatial principal components of multichannel maps evoked by lateral visual half-field stimuli.

Multichannel records of responses to large and small hemiretinal stimuli were obtained from 6 healthy subjects. Scalp distribution maps were constructed for all conditions at all post-stimulus times and component latencies were objectively determined by computing a reference-independent measure of field power. This procedure identified 2 components (at 100 and 140 msec). The scalp distribution data at these latencies were entered into a spatial principal components analysis which further reduced the data set to three underlying spatial principal components. These components may be regarded as reflecting underlying processes and were related to experimental conditions. A component reflecting lateralized brain activity displayed a significant interaction between size and retinal location of the stimulus with large stimuli showing a more pronounced lateralization over the hemisphere contralateral to the stimulated hemiretina, and the scores on this component were low for upper hemiretinal stimuli. These findings are in agreement with intracranially recorded evoked potential data and theoretical dipole source computations, and confirm a model of cortical neuronal generator processes whose locations and orientations in the hemisphere ipsilateral to the hemiretina stimulated are influenced not only by retinal stimulus location but also by stimulus size.

Brain↗
PubMed1982

Day-time residual effects and motor activity after three benzodiazepine hypnotics.

The benzodiazepine hypnotics triazolam (T) (0.25, 0.5 and 1.0 mg), nitrazepam (N) (10 mg) and flunitrazepam (F) (2.0 mg) were investigated with respect to night-time effects and day-time residual effects, in healthy, young subjects. Drug or placebo was taken orally at home before bed-time. Tests for residual drug effects were administered in the laboratory throughout the following day. They included multiple sleep latency tests, the digit cancellation test, questionnaires, self-ratings and experimenter ratings. In addition, motor activity was recorded with a wrist-worn activity monitor during the drug-night, the day following drug intake, and the two subsequent nights. Residual effects consisted of reduced day-time motor activity (T 0.5, F 2.0), enhanced self-rated day-time sleepiness (T 1.0, F 2.0), increased experimenter-rated tiredness (T 0.5, F 2.0), and impaired performance in the digit cancellation test (F 2.0). Grogginess was a common symptom in the morning after flunitrazepam. All drugs reduced motor activity during sleep, and increased subjective depth and quietness of sleep. Increased motor activity in the second post-drug night was observed after triazolam 0.5 mg. The results indicate that a small dose of a short-acting benzodiazepine may be appropriate for promoting sleep without subsequent day-time residual sequelae.

Adult↗
PubMed1982

[Visual evoked potentials and click-evoked brainstem potentials in early diagnosis of multiple sclerosis: statistics (author's transl)].

95 sequential unselected patients which had been referred to our lab as certain (31), probable (32) and possible (32) MS cases were examined using checkerboard (VEP) and click-brainstem (BAEP) average potentials. In VEPs, latency of the positive wave around 100 msec, and in BAEPs, latency differences between waves III-V, I-V and latency wave V was measured. Pathology was defined as values of more than 3 SD above mean of controls. VEPs were pathological in 68%/50%/41% and BAEPs were pathological in 32%/28%/9% of the certain/probable/possible cases. Eleven of the probable cases had spinal symptomatology only; 9 of these had pathological VEPs, 4 in addition pathological BAEPs. Ten of the possible cases had spinal symptomatology only; 5 of these had pathological VEPs, 2 in additional pathological BAEPs. - Improved diagnostic certainty was reached in 11 of the 32 probable cases because of pathological VEPs (4 of these in addition had pathological BAEPs). - 10 of the 32 possible cases could be classified as probable, 8 of these because of pathological VEPs and 2 because of pathological BAEPs (the latter 2 had normal VEPs). - Monaural stimulation was not significantly more effective than binaural stimulation. In general, VEPs were clearly more useful than BAEPs in the early diagnostics of MS, and for clarification of spinal symptomatology; however in occasional cases, BAEPs might contribute to the early diagnosis.

Acoustic Stimulation↗
PubMed1982

Analysis and restitution of visual function in a case of cerebral amblyopia.

In a patient suffering from a severe bilateral dysfunction in both occipital and parietal areas we have found: (1) A loss of contrast-sensitivity, being strongest in the range of spatial frequencies where the normal eye is most sensitive; (2) Virtually normal grating resolution, a severe loss in letter acuity (about 15-fold), and a very strong loss in vernier acuity (about 100-fold); (3) Rapid partial recovery of contrast sensitivity due to stimulation; (4) Slow partial recovery of letter acuity due to CAM rotating grating treatment; (5) No improvement of a 10-fold temporal retardation in the speed of reading. Evidence is presented that the residual impairment of vision depends upon improper synthesis of spatial frequency components originating from a heavy loss in processing speed and abnormally long store duration for high spatial frequency information.

Adult↗
PubMed1981

Sleep deprivation: effect on sleep stages and EEG power density in man.

Sleep was analysed in 8 young adults subjects during two baseline nights and two recovery nights following 40.5 h sleep deprivation. Sleep stages were scored from the polygraph records according to conventional criteria. In addition, the EEG records of the entire nights were subjected to spectral analysis to compute the frequency distribution of the power density in the 0.25-25 Hz range for 0.5 Hz or 1.0 Hz bins. In the first recovery night, the power density in the delta band was significantly higher than baseline for total sleep time as well as for sleep stages 2, 3 and 4, 4 and REM. These changes were not restricted to the delta band, but extended to higher frequency bands. Minor, but significant, effects of sleep deprivation were seen in the power density distribution of the second recovery night. In the baseline nights, a progressive reduction of power density in the delta/theta range was present for successive non-REM-REM sleep cycles for total sleep time and stages 2, 3 and 4, and 4. The results show that effects of sleep deprivation as well as trends within the sleep periods are readily apparent from spectral analysis, but are inadequately reflected by conventional sleep scoring. When the power density values were integrated over the entire frequency range (0.75-25 Hz) for each non-REM-REM sleep cycle, an exponential decline from cycle 1 to cycle 3 was suggested. The present findings support the hypothesis that the EEG power density in the low frequency range is an indicator of a progressively declining process during sleep whose initial value is determined by the duration of prior waking.

Adult↗
PubMed1981

EEG power and coherence during non-REM and REM phases in humans in all-night sleep analyses.

All-night spectral power and coherence analysis of six channels of EEG data from 6 healthy volunteers was performed. Integrated power and integrated coherence for the frequency bands of 0.1-7 and 7-12 Hz in 20 s epochs was plotted over the entire nights. Power and coherence increased with deepening slow wave sleep. With the onset of REM periods, power expectedly decreased, whereas coherence showed a further increase or maintained levels. With post-REM phase awakenings, power showed further reductions, and coherence decreased. The REM coherence results were most pronounced in interhemispheric right to left parietal comparisons (recorded vs. a Cz reference) in the 0.1-7 Hz band. It is hypothesized that the high interhemispheric coherence facilitates or reflects right-left transfer of information.

Electroencephalography↗
PubMed1980

Reference-free identification of components of checkerboard-evoked multichannel potential fields.

A method is proposed to determine components of evoked scalp potentials, in terms of times of occurrence (latency) and location on the scalp (topography). The scalp field distributions were evoked by checkerboard reversal and were recorded simultaneously in 47 channels. Component latencies are defined as times of maximal values of the electrical power of the evoked field (a measure of the amount of field relief); this measurement is independent of the choice of the reference electrode. In 10 subjects, two evoked components were found consistently: at 100 and at 140 msec. Plots of scalp locations of the extreme field values (i.e., reference-free data) at the occurrence times of the components showed occipitally positive and anteriorly negative extreme values at 100 msec, and vice versa at 140 msec. The occipital extreme values were surrounded by steep field gradients suggesting occipital generator processes. The polarity reversal of the evoked field distributions between 100 and 140 msec was a quick, jump-like location change of the extreme values in the field. The locations of the extreme field values were stable for long periods around peak times of the power curve. During these periods, the shape of the field remained constant (assessed by the average standard deviation of voltages per electrode between successive field distributions), suggesting also a stable localization of the generating process in depth. The field distributions tended to be concentric around the extreme field values. The major characteristics of the observed scalp fields showed no wave fronts, and no continuous 'traveling' of extreme values over larger distances.

Adult↗
PubMed1980

[On the synthesis of compounds with beta-adrenergic activity (author's transl)].

It is reported of the synthesis of 1-phenoxy-2-hydroxy-3-aminopropane derivatives with different substituents in the phenoxy residue as well as in the amino group. The potency and the efficacy of these derivatives depend on the substituents. By the introduction of the arylamino-ethyl residue into the nitrogen atom, beta-adrenergic locking agents with marked agonistic activity are obtained.

Adrenergic beta-Agonists↗