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Biomedical subjects

E Rahn

Publications and source records attributed to E Rahn.

12 recordsLinked to original sources
PubMed1998

Spontaneous EEG theta activity controls frontal visual evoked potential amplitudes.

Frontal visual evoked potentials (VEPs) were studied in order to extend the application of a recently introduced algorithm for selective averaging of evoked potentials. This algorithm is based on the inverse relationship between amplitudes of alpha or theta components of the spontaneous EEG activity and evoked potential (EP) amplitudes. Stimuli were only applied if the root mean square (RMS) value of the ongoing EEG at the lead F4 was below an individual threshold level ('selective stimulation'). For this comparison, the EEG was filtered in one of the frequency ranges 'alpha', 'theta' and 'alpha and theta', respectively. 'Alpha' and 'alpha-and-theta-dependent' selective stimulation conditions resulted in significant amplitude increases (P < 0.05) at the input reference channel F4 and partly at ipsihemispherical temporal and parietal leads and at Cz. The largest increase of 35% at F4 (P < 0.01) was obtained with visual stimulation during low prestimulus theta activity. We conclude that spontaneous theta activity of the frontal cortex may be a factor influencing the amplitudes of frontal VEPs. A sophisticated analysis of frontal EPs, mainly in the framework of cognitive studies, should consider the theta activity prior to stimulation.

Adult↗
PubMed1996

Scombroid poisoning.

Scombroid poisoning is described in the literature as a toxic poisoning caused by ingestion of certain dark meat fish undergoing bacterial decomposition. Poisoning results from the ingestion of a heat-stable toxin. We describe the case of a man who presented to the emergency department several hours after eating tuna steak with evidence of scombroid poisoning that was associated with loss of vision and atrial tachycardia with block. All signs and symptoms resolved after treatment for scombroid poisoning.

Acute Disease↗
PubMed1996

[Hospital depression units judged by patients].

The ward atmosphere is an imposant aspect of the clinical treatment. This survey shows the difference in the assessment of the ward atmosphere by patients with major depressive disorders between specialized and non-specialized organisation of the clinical treatment. Measured with a ward atmosphere scale the judgement differs significant in the points involvement and organization between the two groups.

Adult↗
PubMed1995

Auditory event-related magnetic fields in a tone-duration discrimination task. Source localization for the mismatch field and for a new component M2".

Auditory event related magnetic fields were measured using an odd-ball paradigm in which the rare event was a tone of short duration, D2, and the frequent one a tone of longer duration, D1. The subjects were required to attend to and count the number of rare stimuli. In the average across target stimuli a mismatch field (MMF) occurs and the dependence of the MMF, especially its latency, on the tone duration D2 is examined in detail. The location of an equivalent current dipole for the MMF-source is found and turns out to be at variance with earlier results. In addition to the MMF we propose a new component, here called M2", which in time overlaps the magnetic equivalent of the P200 signal and which has a source location (equivalent current dipole) lying rather close to the MMF-source. The two sources are, however, active at latencies differing by a time equal to D2. We speculate that M2" indicates the onset of the process: "evaluation of tone-duration" while the MMF indicates the end of this process.

Acoustic Stimulation↗
PubMed1994

Event-related theta rhythms in cat hippocampus and prefrontal cortex during an omitted stimulus paradigm.

In a recent study on human subjects which performed a time prediction task in an omitted stimulus paradigm we found an increase in the amplitudes of evoked potentials (EPs) for the stimulus preceding the omitted stimuli, probably due to expectancy and focused attention. The amplitude increases were dominant over frontal and parietal association areas and were mainly reflected in enhancements of the theta (3-6 Hz) components. In the present study we analyse the responses of the auditory cortex (GEA, gyrus ectosylvianus anterior), different parts of hippocampus (CA1, CA3), reticular formation (RF), and motor cortex (MC) of the cat brain using a similar paradigm. Similar theta component increases of the EPs were obtained in various parts of the hippocampus, which were dominant in pyramidal cell layers (CA3, CA4), and in motor cortex. The results are interpreted as signs of a diffuse theta response system in the brain including mainly the hippocampus and frontal and parietal association areas. The diffuse theta system is probably involved in general attention and expectancy processes.

Acoustic Stimulation↗
PubMed1993

Enhancement of visual evoked potentials by stimulation during low prestimulus EEG stages.

A new algorithm for averaging of visual evoked potentials (VEPs) is introduced and compared with the conventional method. The root mean square (RMS) values of the alpha and theta band EEG activities at the vertex 1-s preceding stimulus presentation were computed: stimuli were blocked during phases of high prestimulus activity. Stimulation was applied selectively during periods of low activity. Light stimuli of 1-s duration were given to twelve healthy, voluntary subjects. The main results were: (1) The averaged VEPs at the vertex showed an increase in the N1-P2 amplitude of about 35% in comparison to experiments with conventional stimulation. This increase was in the range of 25-30% when an ISI correction was taken into account. Frontal, temporal and parietal locations showed also increases of the N1-P2 amplitude in evoked potentials. (2) VEPs were also affected qualitatively depending on the frequency content of the prestimulus activity.

Adult↗
PubMed1991

Sensory and cognitive components of brain resonance responses. An analysis of responsiveness in human and cat brain upon visual and auditory stimulation.

We performed an analysis of topographic and modality-dependent responsiveness of auditory and visual cortex in 5 cats and of vertex and occipital derivations in 12 human subjects. The evoked potentials were studied in the frequency domain by means of the Fourier transform. Furthermore, digital filtering was applied to confirm and extend the analysis. Preliminary results indicate that resonances were observed mainly in the 5, 10, 20 and 40 Hz frequency bands. The frequency of resonance maxima depended on the sites of measurement electrodes and stimulus modality. It is concluded that the analysis of resonance phenomena in the brain is a useful approach to understanding the relation between evoked potentials, evoked magnetic fields and single-cell recordings.

Acoustic Stimulation↗
PubMed1990

Iritis and papillitis as a primary presentation of Lyme disease.

A 9-year-old boy had iridocyclitis and papillitis. Laboratory evaluation revealed a positive Lyme titer. Institution of therapy with intravenous ceftriaxone resulted in regression of the ocular inflammation. Ophthalmologists should consider Lyme disease in the differential diagnosis of iridocyclitis in conjunction with papillitis.

Ceftriaxone↗
PubMed1985

[Omphalocele and laparoschisis--a clinical analysis].

As yet, it has not been sufficiently investigated whether the pathogenesis of omphalocele and gastroschisis can be attributed to the same cause or to different processes. Therapeutical principles, however, are the same in omphalocele and gastroschisis: the very soon closure of the abdominal wall defect. Our own procedure strives for primary fascial closure. If this is not possible, we prefer skin closure above the silastic cylinder according to Schuster, 72 patients with omphalocele and 62 patients with gastroschisis were Schuster, 72 patients with omphalocele and 62 patients with gastroschisis were analysed. Lethality was 32% in omphalocele and 22% in gastroschisis during the last 6 years. The predominant cause of death was postoperative infection. It is therefore necessary to improve infection therapy in order to reduce lethality.

Abdominal Muscles↗
PubMedDate not supplied

Prestimulus EEG-activity strongly influences the auditory evoked vertex response: a new method for selective averaging.

A new algorithm for averaging of evoked potentials (EPs) is introduced and compared with the conventional method. The root mean square (rms) values of the alpha and theta band EEG activities 1-s preceding stimulus presentation were computed: stimuli were blocked during phases of high prestimulus activity, thus evoking auditory responses selectively during periods of low activity. Ten volunteers were stimulated with tone bursts of 2000 Hz, 80 dB and 1-s duration. The main results were: (1) The averaged EPs showed an increase in amplitude of nearly 40% in comparison to experiments with conventional stimulation. This increase was in the range of 30% when an ISI correction was taken into account. (2) Single trials tended to form patterns of damped oscillations of e.g., 7-8 Hz, thus revealing a high correlation to the averaged EP. In alpha or theta band contingent experiments, correlation coefficients between single trials and averaged EPs were significantly higher (p < .01; p < .05).

Adult↗