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Biomedical subjects

G Pfurtscheller

Publications and source records attributed to G Pfurtscheller.

At least 19 recordsLinked to original sources
PubMed1992

[Model of electromyographic study of small intestinal transplants in the rat].

Adequate motility of a small bowel transplant is a prerequisite for its resorptive function as well as its self-purging capacity. The literature contains some reports on changes in motility following denervation or transplantation, but none on the impact of acute rejection on motility of small bowel grafts. Therefore an experimental model was established to meet the following criteria: orthotopic position of graft, adequate nutritional status even when graft is functionally impaired, chronically implantable electrodes attached to graft and corresponding segment of native bowel, isogeneic or allogeneic set-up. 10 cm of proximal jejunum were transplanted from Lewis donors to five Lewis recipients in an orthotopic position just distal of the ligament of Treitz without resection of native small bowel. Three bipolar electrodes were sutured to the graft and the same number to the subsequent recipient bowel. Serial myoelectric measurements were taken until the end of week 3. From day 5 on, migratory myoelectric complexes independent of myoelectric activities of native bowel were recorded. Pacemaker frequency of the graft was found to be the same as that of the transsected native small bowel. This early reappearance of myoelectric activities makes this model suitable for comparative studies of small bowel transplant motility and in particular its changes during rejection, since even in strongly allogeneic combinations Lewis small bowel does not show histological signs of rejection before day 6.

Animals↗
PubMed1992

Brain death: timing of apnea testing in primary brain stem lesion.

In a 73-year-old patient complete areflexia of the cerebral and peripheral nerves following the rupture of an aneurysm of the basilar artery was diagnosed. During apnea testing the spectral analysis of electroencephalography (EEG) revealed an irreversible shift of peak from 6 to 3 Hz within the low-frequency bands. These findings suggest that apnea testing in patients with primary lesion of the brain stem should be carried out only after an isoelectric EEG.

Aged↗
PubMed1992

Prediction of the side of hand movements from single-trial multi-channel EEG data using neural networks.

Thirty channels of EEG data were recorded prior to voluntary right or left hand movements. Event-related desynchronization (ERD) was quantified in the 8-10 Hz and 10-12 Hz bands in single-trial data and used as training input for a neural network comprised of a learning vector quantizer (LVQ). After a training period, the network was able to predict the side of hand movement from single-trial EEG data recorded prior to movement onset.

Brain↗
PubMed1992

Event-related synchronization (ERS): an electrophysiological correlate of cortical areas at rest.

Oscillations in the alpha and beta bands can display either an event-related blocking response or an event-related amplitude enhancement. The former is named event-related desynchronization (ERD) and the latter event-related synchronization (ERS). Examples of ERS are localized alpha enhancements in the awake state as well as sigma spindles in sleep and alpha or beta bursts in the comatose state. It was found that alpha band activity can be enhanced over the visual region during a motor task, or during a visual task over the sensorimotor region. This means ERD and ERS can be observed at nearly the same time; both form a spatiotemporal pattern, in which the localization of ERD characterizes cortical areas involved in task-relevant processing, and ERS marks cortical areas at rest or in an idling state.

Adult↗
PubMed1992

Simultaneous EEG 10 Hz desynchronization and 40 Hz synchronization during finger movements.

Nineteen-channel EEG was recorded with closely spaced electrodes overlaying the left sensorimotor cortex during self-paced, voluntary right finger movements. Three right-handed people served as subjects. The EEG was analysed in the 10 Hz band (10-12 Hz) and in four 40 Hz bands (34-36, 36-38, 38-40, 40-42) by calculation of ERD time courses and ERD maps, whereby a ERD is characterized by a movement-related band power decrease. In all three subjects a close to C3 localized 10 Hz ERD was found, starting about 2 s prior to movement onset and continuing during movement. Along with this 10 Hz ERD a localized and short-lasting (about 0.5 s) burst of 40 Hz oscillations was embedded around movement onset. This can be interpreted as indicating that planning of movement is accompanied by a desynchronization of central mu rhythm and a generation of 40 Hz oscillations.

Brain Mapping↗
PubMed1992

Functional topography during a visuoverbal judgment task studied with event-related desynchronization mapping.

Event-related desynchronization (ERD) of alpha components was studied in 10 subjects in a visuoverbal judgment task. EEG was recorded from 29 electrodes; ERD, measured by percentage of alpha power decrease, was calculated in 125-ms intervals and displayed in a time course over 7-s intervals and in the form of topographical ERD maps. ERD, interpreted as a measure of activated cortical areas, was studied in the upper and lower alpha bands. It was found that upper alpha band ERD was short-lasting (less than 1 s), localized to the posterior region and not found before stimulation; in contrast to this, lower alpha band ERD was longer-lasting (greater than 1 s), more widespread, with a left hemisphere dominance, and was already present before stimulation. ANOVA revealed significant interactions among alpha frequency bands, scalp location, and pre-/poststimulus intervals. The self-organizing topological Kohonen network was used to analyze the stability of consecutive ERD maps. There is evidence that topographical ERD patterns can be stable for about 300-400 ms.

Adult↗
PubMed1992

EEG classification by learning vector quantization.

EEG classification using Learning Vector Quantization (LVQ) is introduced on the basis of a Brain-Computer Interface (BCI) built in Graz, where a subject controlled a cursor in one dimension on a monitor using potentials recorded from the intact scalp. The method of classification with LVQ is described in detail along with first results on a subject who participated in four on-line cursor control sessions. Using this data, extensive off-line experiments were performed to show the influence of the various parameters of the classifier and the extracted features of the EEG on the classification results.

Algorithms↗
PubMed1992

Sleep classification in infants based on artificial neural networks.

The study reports on the possibility of classifying sleep stages in infants using an artificial neural network. The polygraphic data from 4 babies aged 6 weeks, 6 months and 1 year recorded over 8 hours were available for classification. From each baby 22 signals were recorded, digitized and stored on an optical disc. Subsets of these signals and additional calculated parameters were used to obtain data vectors, each of which represents an interval of 30 sec. For classification, two types of neural networks were used, a Multilayer Perceptron and a Learning Vector Quantizer. The teaching input for both networks was provided by a human expert. For the 6 sleep classes in babies aged 6 months, a 65% to 80% rate of correct classification (4 babies) was obtained for the testing data not previously seen.

Cerebral Cortex↗
PubMed1992

[Event-related negativity and alpha band desynchronization in motor reactions].

The foreperiod of a motor reaction to an impending stimulus is accompanied by a slow negative wave of the event-related potential, the "contingent negative variation" (CNV), when the imperative stimulus follows at a fixed interval to a warning stimulus. Using similar experimental paradigms, an event-related desynchronization (ERD) in the alpha range occurs indicating cortical activation before and during motor acts. Both EEG-parameters were quantified for four subjects using the following experimental design: One second after a non-informative warning signal (WS) a cue was presented that indicated by which hand the subject had to respond quickly after presentation of a reaction stimulus (RS); subjects were requested to respond by pressing a button with their left or right thumb. EEG-signals were recorded unipolarly from 17 electrodes. Average ERPs and ERD were computed for all electrode sites for trials with left and right hand movements, respectively, and topographically displayed in simultaneous amplitude and ERD-maps. CNV and ERD could be observed simultaneously over similar brain regions, namely central over the motor cortex, frontal with possible location over the supplementary motor area (SMA) and also covering the parietal region. While the CNV had a interindividually different and wide distribution, the ERD calculated for the upper alpha band mapped focally over the electrode sites C3 and C4 overlaying primary sensorimotor structures, with a contralateral dominance. In contrast to the negativity which is terminated following delivery of the response stimulus, the ERD persisted during the motor reaction showing a similar pattern some hundreds of milliseconds before and after movement onset.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

[Acoustic evoked brainstem potentials--patterns of stimulus artefacts in irreversible coma].

Brainstem auditory evoked potentials (BAEP) were performed in a total of 20 subjects (mean age 33.2 +/- 15.1 years; severe head injury in most cases) with the diagnosis of coma dépassé. The control group consisted of 33 healthy volunteers (mean age 26.9 +/- 5.3 years). The presence, latency and amplitude of the single BAEP-components and the variations of the stimulus artifact were evaluated. The mean amplitudes of the stimulus artifact of the brain dead subjects were calculated (means +/- SD) to be 0.26 +/- 0.12 microV (control group: 0.11 +/- 0.03 microV). Pathological alterations of the mechanics of the inner ear as well as extracerebral changes in conductivity or stimulus related depolarization processes in extracerebral parts of the auditory system were taken into consideration to be possible reasons for this significant (p less than 0.001; t-test) difference.

Adolescent↗
PubMed1991

Continuous multivariable monitoring in neurological intensive care patients--preliminary reports on four cases.

Evoked potential monitoring is a standard examination method in neurological intensive therapy units. Previously, multimodality observation was only possible in follow-up examinations. First experience with a new bed-side system continuously monitoring 12 neurophysiological and clinical parameters is reported. It consists of a personal computer and various stimulation units. EEG activity, median nerve somatosensory evoked potentials (SEPs) and brainstem auditory evoked potential (BAEPs) are recorded. Additionally, EEG spectral band power, heart rate, heart rate variability, intracranial pressure, body temperature, expiratory PCO2, blood pressure and transcutaneously measured oxygenation can be monitored. This paper reports on 4 exemplary cases of the 33 patients we have monitored to date, illustrating the principles and main advantages of the system. The system was developed to support the observation of ICU patients as well as to aid therapeutic decisions. It supports the clinical determination of brain death by specifying the deterioration of various neurological systems.

Aged↗
PubMed1991

The role of the right parietal region in a movement time estimation task.

Thirteen right-handed male students performed a time estimation task by pressing a button with their left or right hand for an interval of either 0.5 or 1.3 s. Thirty channels of EEG were recorded, with the right ear as reference. After transforming the raw EEG data into local average reference data, the topography of event related desynchronization (ERD) of the rhythm within the 10-12 Hz frequency band was studied by computing ERD maps separately for accurate and inaccurate performance. Statistical comparison of ERD maps for accurate and inaccurate movement (Wilcoxon test) resulted in significant differences for the right parietal region prior to movement onset, with a larger ERD before accurate movement.

Adult↗
PubMed1990

Topographical display and interpretation of event-related desynchronization during a visual-verbal task.

Multichannel EEG recordings were performed during a visual-verbal judgement task with a verbal response using an event-related paradigm. EEG trials of 7 sec were first digitally band pass filtered (10-12 Hz, 10-11 Hz, 11-12 Hz), and the amplitudes were then squared and averaged over all trials. This processing method results in a time course of alpha power and allows us to quantify the event-related desynchronization (ERD) in each EEG channel and to compute series of ERD maps in intervals of 125 msec. Analyzing the 10-11 Hz band, it was possible to study the time course and topographical pattern of cortical activation during visual encoding and cognition. Analysis of the 11-12 Hz band has enabled us, for the first time, to study the time course, spatial localization and extent of activation of speech, premotor and motor areas. We found that the speech centers were activated maximally 250 to 375 msec before speech onset and the SMA about 250 msec before speech onset. The results are preliminary, but demonstrate how much information can be extracted from the scalp EEG.

Acoustic Stimulation↗
PubMed1990

Electroencephalographic and evoked potential monitoring in the hyperbaric environment.

The purpose of this study was to investigate brain bioelectrical activity during hyperbaric oxygenation by continuous and simultaneous monitoring of electroencephalographic and bimodal (auditory, somatosensory) evoked potentials. Multivariable recordings (electroencephalogram, brainstem auditory evoked potentials, early somatosensory evoked potentials, heart rate, heart rate variability, and transcutaneous partial pressure of oxygen) were measured with a new technique in 12 healthy male volunteers 26 to 52 years old (mean +/- SD, 35.9 +/- 9.5 years). Recordings were obtained while the subjects breathed (1) air at normal atmospheric pressure, (2) 100% oxygen at normal atmospheric pressure, (3) air at 2 atm (10 meters sea water [msw]), and (4) 100% oxygen at 2 atm (10 msw). Spontaneous brain electrical activity, somatosensory evoked potentials, and heart rate variability were not significantly affected during hyperbaric oxygenation, whereas the heart rate showed a significant decrease (paired t test, P less than 0.05). Alterations in brainstem auditory evoked potentials were seen under hyperbaric conditions and did not reach statistical significance (increase of the I-V interpeak latency by paired t test; P less than 0.2). All subjects showed insignificant increases in dominant alpha frequency and decreases in delta frequency under hyperbaric situations.

Adult↗
PubMed1990

Ear dominance and laterality of cortical activation identified by event-related desynchronization mapping.

Lateralized cortical functioning was assumed to be involved in ear dominance for pitch information. Left ear dominant (LED), right ear dominant (RED) subjects and individuals with no distinct ear preference (NED) were examined by means of the event-related desynchronization-mapping method during stimulation with a dichotic listening test. Contrary to expectations ED-groups did not systematically show greater involvement of the hemisphere contralateral to the dominant ear. RED were characterized by a response-dependent cortical activation pattern, LED exhibited a marked ipsilateral desynchronization focus if they showed preference for the dominant ear. In the NED group an early asymmetrical activation distribution was observed during the perception interval, which was concentrated ipsilaterally to the preferred ear.

Acoustic Stimulation↗
PubMed1990

Event-related desynchronization, ERD-mapping and hemispheric differences for words and numbers.

Event-related desynchronization (ERD) is the amount of event-related decrease in alpha band power. In applying ERD as an index of cortical activation, the way in which attention and expectancy affect hemispheric differences for words and numbers was investigated. Subjects, 12 right-handed males, had to perform a semantic and a numerical classification task under two different counterbalanced expectancy conditions. Whereas under the high expectancy condition words and numbers were presented blockwise, they were presented randomly under the low expectancy condition. In the semantic task subjects had to indicate the category to which a word belonged; in the numerical task they had to judge whether a number was odd or even. Because 48 words and numbers were used in both expectancy conditions, each subject had to perform a total of 192 trials, practice trials not included. During each of the 192 trials, EEG-signals were recorded from 29 electrodes and analyzed in two frequency bands (6-10 Hz and 9-13 Hz). The data, which were also presented in the form of maps, were subjected to a 6-factorial ANOVA. The results reveal a complex pattern of interactions between the two frequency bands, expectancy conditions, stimulus types and the recording sites. The most important results concern the influence of expectancy. A consistent left hemispheric advantage could be observed under the high expectancy condition and in the lower alpha band only. This and other results seem to indicate that the lower alpha band is more sensitive to reflect expectancy and attentional processes.

Analysis of Variance↗