An adaptive and learning system for feedback-controlled evoked response studies.
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Electroencephalography↗
Biomedical subjects
G Pfurtscheller
Publications and source records attributed to G Pfurtscheller.
Changes in central EEG activity in relation to voluntary movement. I. Normal subjects.
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Cerebral Cortex↗
Changes in central EEG activity in relation to voluntary movement. II. Hemiplegic patients.
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Cerebral Cortex↗
[Asymmetries in the central alpha activity (my-rhythm) at rest and during activation in patients with cerebrovascular lesions (author's transl)].
Eleven patients with a history of ischemic lesion and weak hemiparesis were used in this study. Bipolar EEG recordings were made from the central region at rest and during voluntary infrequent first-clenching. After computer analysis, percentage alpha power, alpha power decrease during movement (ERD: event-related desynchronization) and alpha-peak frequency were calculated and compared for symmetry in homologeous derivations. As reference a collectiv of 33 normals was used. In 8 out of 11 patients a significant (p < 0.05) alpha-asymmetry was found and in 2 out of 11 a significant (p < 0.05) asymmetry in the ERD. Summarizing all results, 9 out of 11 patients showed significant asymmetry within the central alpha activity. Computer EEG was done on average 18 days after onset of infarction. In clinical EEG, recorded within one week after infarction, 3 out of 11 patients were reported with pathological findings.
Adult↗
Amplitude of evoked potentials and degree of event-related desynchronization (ERD) during photic stimulation.
The variations in amplitude of visual evoked potentials (VEPs) and parallel changes in amount of event-related desynchronization (ERD) of the rhythmic activity within the alpha band were studied in central derivations of scalp EEG, in 10 normal subjects. Two methods were used to estimate the amplitude of VEPs in small groups of 10 responses: (1) inverse and matched filtering techniques; (2) two-way rank analysis of variance by the Friedman test. The two methods gave similar results and two groups, statistically different, emerged. The first, with large VEP amplitude, having at the same time large ERD, and the second, with small VEP amplitude and small ERD.
Adult↗
Evaluation of event-related desynchronization (ERD) preceding and following voluntary self-paced movement.
A method of accurate storage and on-line preprocessing of an EEG signal, preceding and following a trigger signal, elicited by button pressing, is described. The method was used to study the changes occurring in the power of the rhythmic activity within the alpha band in central areas, during voluntary, self-paced movement in 10 normal humans. A short-lasting decrease or phasic event-related desynchronization (ERD) of alpha power, representing mu activity, was observed in all 10 subjects. During the 2 sec period preceding movement the phasic ERD was mostly bilateral, but larger prior to right than to left thumb movement. At onset and during the first second of execution of movement, the phasic ERD was mostly bilateral but predominant in ipsilateral areas. Preceding or during movement, maximum ERD was observed in most cases in central-vertex regions.
Adult↗
Occipital rhythmic activity within the alpha band during conditioned externally paced movement.
The time-dependent behaviour of the power within the alpha band during conditioned movement was studied from the scalp EEG of 9 normal humans. Two tasks were used: (1) button pressing at imperative signal S1 and release at signal S2; (2) button pressing at imperative signal S2, preceded by warning signal S1. Together with a complex correlate of the CNV and EPs, the components of power decrease related to initiation of movement were not clearly identifiable in the central areas. They were sharply isolated in the occipital areas, using tone as the imperative signal. During initiation of movement a significant short-lasting decrease in power of the occipital alpha activities was observed in all 9 subjects. However, 'mu activity', tested in the classical manner and with help of power spectra, was not present in some of these subjects.
Acoustic Stimulation↗
A new approach to spike detection using a combination of inverse and matched filter techniques.
For the detection of spikes and other types of transient signal, a combination of inverse and matched filter techniques can be used. The inverse filter improves the signal to noise (spike to EEG) ratio; the matched filter makes it possible to classify different types of spikes. When compared, the combined inverse matched filter techniques gave a higher detection rate than the inverse filter technique alone, for the same error probability. Both simulated and patient data were used for testing the methods.
Electroencephalography↗
On and off effects in the background EEG activity during one-second photic stimulation.
The changes in alpha band power of the background EEG activity during 1-sec light stimulation were investigated in 10 normal human subjects. The EEG data were band-pass filtered, centering on the alpha range, and the time-dependent power changes were evaluated for their significance. The most significant finding was a light-on power decrease (on-effect) occurring in occipital areas 250--500 msec after onset of the stimulus, observed in all subjects, and reaching values of 72.2 +/- 13.2% decrease, with reference to power in the pre-stimulus interval. In 8 subjects there was also a significant light-off power decrease occuring 250--500 msec after offset of the photic stimulus (average across subjects: 41.8 +/- 24.4%) also in the occipital region. Similar on- and off-effects were observed in central regions, with lesser statistical significance. This pattern of light-on and -off power decreases was consistent and reproducible, with small inter- and intraindividual variability.
Alpha Rhythm↗
[Reactions in the brainactivity during increased carbondioxyde concentration (author's transl)].
A comparative study of two kinds of respiration (normal air and mixed with 4% CO2) was carried out in 8 healthy students. During the three experiments, each one lasting over 120 min, CO2 or air was inhaled using a mask. Blood samples were taken from the fingers, an average increase of pCO2 of 1.9 mm (p less than 0.01) and pO2 of 7.3 mm (p less than 0.01) was found during CO2-inhalation. The ECG and EEG were recorded and reaction times to tone stimuli in a foreperiod reaction time experiment were measured. During CO2-inhalation a clear reduction of the power in the alpha-band was found in frontal, central and occipital region in the order of 23% (p less than 0.05) and 12% (p less than 0.05) and 22% (p less than 0.01). The heart rate interval decreased significantly by 2.3% (p less than 0.05). No significant changes were found in CNV, reaction time and percentage event-related alpha-desynchronization.
Adult↗
[Changes in the spontaneous EEG-activity before and during voluntary self-paced movement. New ways of investigation of the central mu-activity (author's transl)].
Movement-related desynchronization was investigated in the EEG from central region in human subjects, during voluntary self-paced movement of the thumb. The average dynamic time-behaviour of the power in the alpha band was calculated from 4 sec before to 2 sec after voluntary movement. In all investigated subjects (9 students and 7 patients with several forms of hemiplegia) a significant power reduction before voluntary movement of the thumb was found. This power decrease can be interpreted as desynchronization of the central mu activity. Therefore, it appears that in all subjects a mu activity can be demonstrated. In most cases, a short-lasting desynchronization of central mu activity occurred about 2 sec before movement onset and was followed by a second one, about 1 sec before movement onset which reached a maximum during initiation of movement. Frequently the first desynchronization occurred in parallel but often also before the Bereitschaftspotential.
Alpha Rhythm↗
Graphical display and statistical evaluation of event-related desynchronization (ERD).
A new method which enables quantification of event-related desynchronization (ERD) by measuring changes in the power of rhythmic activity within the alpha band during sensory stimulation and during the interstimulus interval of a CNV paradigm is described. For the processing, EEG trials recorded under the same stimulus conditions and with eyes closed are used. For the power changes, the statistical significance is tested with a non-parametric test. With the proposed method it is possible to measure very brief power changes of the order of 21 percent (corresponding to amplitude changes of 11%). An ERD may thus be observed in a restricted cortical region.
Cortical Synchronization↗
Inter- and intrahemispheric differences in the peak frequency of rhythmic activity within the alpha band.
EEG was recorded simultaneously from several scalp regions in 5 normal subjects and analysed, using a PDP 11/45 computer by means of an autoregressive model. Significant intra- and interhemispheric differences in the peak frequencies within the alpha band were observed, up to 0.8 c/sec. Local modality -dependent increases in the peak frequency were also observed, which were predominant in occipital areas during visual stimulation and in central regions during acoustic stimulation. In most cases an increase in the peak frequency occurred together with a marked decrease in power, which could be interpreted as a desynchronization of slow components within the alpha band. These peak frequency differences found in the scalp EEG lead to the assumption that there might also be different alpha rhythms at the level of the cortex.
Adult↗
Event-related cortical desynchronization detected by power measurements of scalp EEG.
Changes in the background EEG activity occurring at the same time as visual and auditory evoked potentials, as well as during the interstimulus interval in a CNV paradigm were analysed in human subjects, using serial power measurements of overlapping EEG segments. The analysis was focused on the power of the rhythmic activity within the alpha band (RAAB power). A decrease in RAAB power occurring during these event-related phenomena was indicative of desynchronization. Phasic, i.e. short lasting, localised desynchronization was present during sensory stimulation, and also preceding the imperative signal and motor response (motor preactivation) in the CNV paradigm.
Auditory Perception↗
[Spontaneous and evoked EEG-activity during one-second light-stimulation (author's transl)].
EEG data were recorded in 13 students during one-second light-stimulation with eyes closed and sometimes eyes opened, from central and occipital regions. The background EEG was computer-analyzed in the alpha-band using the power time course where a short decrease in power was indicative of a phasic desynchronization of the rhythmic activity within the alpha-band. The maximal desynchronization was observed in the occipital region independent of eyes-opened or eyes-closed conditions. With eyes closed a reinforced power decrease was found 0.25-0.5 sec after the on- and offset of light-stimulation, which was interpreted as "on"- and "off"- effect of the background EEG activity. Parallel with the on- and off-effect a slow potential change occurred in the evoked responses. The behaviour of the background activity during 1 sec light-stimulation was intramodality specific in contrast to the evoked response which showed an intramodality unspecific behaviour with maximal amplitude in the central region.
Computers↗
[Ultra-slow changes in the rhythmic activity within the alpha band and their probable origin (author's transl)].
The time variation of spectral parameters of EEG data, from occipital and central regions, were analysed in normal subjects. Three-second segments, overlapping at 1-s intervals, were studied as to their peakfrequency, bandwidth and power within the alpha band using an autoregressive model of 7th order. In addition, the EKG and respiration were also analysed. Beat-to-beat intervals from the EKG were measured to quantify underlying slow rhythms. Individual EEG parameters were found to change synchronously with respiration and also with the 6/min rhythms underlying the heart rate variation. These changes occurred most frequently only for a short time and they seldom appeared in several cortical regions simultaneously. In addition, the EEG parameters also changed synchronously with the repetition of a specific task (e.g., CNV paradigm) showing dependence from stimulus modality and from task complexity. Basically a decrease in power within the alpha band, sometimes together with a small increase or decrease of peak frequency, was shown to occur predominantly in that cortical area involved with processing of task-relevant information. Ultra-slow changes of the EEG parameters can be interpreted as changes in cortical excitability and responsiveness.
Adult↗
Variability of cortical evoked responses in man related to slow wave activity.
Acoustically evoked responses were recorded from subdural and intracerebral electrodes chronically implanted in man. It was found that during slow wave activity especially the negative component at about 100 ms latency varies in form and amplitude. If the stimuli were presented during increasing cortical negativity, the amplitude of the 100 ms component of the evoked responses was generally larger than in the case of stimuli presented during decreasing negativity.
Cerebral Cortex↗
Changes of the e.e.g. during a c.n.v. paradigm.
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Attention↗