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V Diekmann

Publications and source records attributed to V Diekmann.

14 recordsLinked to original sources
PubMed1992

Spectral analysis of EEG during self-paced movements: differences between untreated schizophrenics and normal controls.

Thirteen untreated schizophrenic patients, among them nine who had never been treated, were compared with a corresponding number of matched normal controls with regard to changes of the spectral composition of the electroencephalogram (EEG) accompanying voluntary movements. Triggered by self-paced movements of the right fingers (fast fist closure), the spectral composition of three epochs was analyzed: (1) rest (2,5-1,5 sec before movement), (2) movement preparation (last sec before movement onset), and (3) movement execution (1st sec following movement onset). For frequencies above 6 Hz, marked differences between schizophrenics and controls were evident, in particular over the parietal electrodes. Whereas patients exhibited a clear decrease of power density during movement as compared to rest, controls showed only a small decrease (left and mid parietal) or virtually none (only right parietal). Consequently there were significant differences over the right parietal area (P4) between patients and controls in the theta, alpha- and beta-bands with regard to the mean power density and center frequencies of these bands. Also at parietal positions, schizophrenics lacked the enhancement of theta-power during the preparatory epoch that was characteristic for normal controls at all parietal positions. The results are discussed with regard to the well-known disturbances of voluntary motor behavior in schizophrenia.

Adolescent↗
PubMed1992

Anticholinergic influences of biperidene on the EEG effects of haloperidol.

15 normal volunteers demonstrated after 14 days of haloperidol (HA) medication (3 mg/day) a higher mean power density (mpd) in all frequency bands of the EEG power spectra combined with a higher theta and a lower alpha center frequency (cf). After further 7 days of HA medication together with the additionally applied anticholinergic biperidene (BI) (6 mg/day) the HA effects were antagonized especially in the theta cf and the alpha mpd. The higher delta and theta mpd were not antagonized. The EEG spectra of the pre- and posttreatment condition did not differ. There was a significant effect of HA on the "Adjective Mood Scale" and on the "Complaint List", which disappeared during the additional BI medication. The reaction times were prolonged with HA and decreased with BI. Blocked dopaminergic impulses on the cholinergic EEG mechanisms possibly produce higher amplitudes during HA medication. Schizophrenic patients treated with neuroleptic drugs showed similar EEG spectra in previous studies during rest but not during motor activation.

Adult↗
PubMed1991

A comparison of normal and tangential magnetic field component measurements in biomagnetic investigations.

Because of the way most available hardware gradiometers are designed and in view of the prediction, by theory, that the normal magnetic field component provides all available information on the intrinsic current source, MEG and MCG measurements generally consider only the field vector normal to the head or truck surface. However, when looking for single events, the information contained in the normal component often cannot be fully sampled, because the sensor array has limited dimensions and therefore covers only a fraction of the field's spatial extension. Simulation of a current dipole in a sphere using realistic parameters shows that there is a considerable area where the amplitude of the tangential field components is larger than that of the normal one. Measurements using a 28-channel magnetometer system with normal and tangential pick-up coils and a current dipole in a phantom model confirm this prediction; depending on dipole orientation, the signal-to-noise ratio (SNR) could improve by a factor of up to 20 if the total field was considered instead of only the normal component. MCG recordings with the same instrument demonstrated a broad area above the heart where the tangential SNR was clearly better than the normal one. Preliminary measurements indicate that tangential components can also be recorded in the MEG; it is suggested that they may help source localisation.

Brain↗
PubMed1990

Slower theta activity over the midfrontal cortex in schizophrenic patients.

Disturbances of the topographical distribution of theta activity in the EEG spectra before and during voluntary movements were investigated in 31 neuroleptic-treated and in 13 untreated schizophrenics and matched controls as well as in 15 normals medicated with haloperidol. All 4 groups demonstrated similar topographical distribution of theta mean power density, with highest values over the midfrontal region. In the center frequency of the theta band, however, treated and untreated schizophrenics had lower values over the midfrontal region than at parietal electrodes. In controls and normals medicated with haloperidol, this frontoparietal "gradient" demonstrated the inverse picture, with highest values at the frontal midline electrode. Patients and controls differed significantly in this gradient. The slower theta activity over the midfrontal cortex in the schizophrenic patients is related to the hypofrontality hypothesis.

Adult↗
PubMed1990

EEG-spectra parameters distinguish pathophysiological and pharmacological influences on the EEG in treated schizophrenics.

Movement related EEG segments of one second duration were analyzed by Fast Fourier Transformation in the Bereitschaftspotential paradigm in 31 neuroleptic treated schizophrenics compared to 21 matched controls. Schizophrenics demonstrated a higher theta mean power density and center frequency together with a lower radius of gyration, skewness and kurtosis in the theta band than controls. The higher theta power in the faster frequency range of the theta band is probably due to neuroleptic medication, but the higher theta power in the lower frequency range may be related to the disease. In the alpha band the schizophrenic group differed from controls by a lower center frequency, higher radius of gyration and skewness. Both groups did not differ in the alpha mean power density. The lower center frequency reflects the fact that alpha activity is distributed towards the lower frequency range which seems to be a consequence of the neuroleptic treatment. The more widespread alpha activity (higher radius of gyration) in schizophrenics indicates less frequency stability, i.e., more desynchronized alpha rhythm which corresponds to a highly activated functional state. By means of the applied spectral parameters more detailed quantitative descriptions of the power distributions in each frequency band are available, allowing to test hypothesis in relation to underlying physiological processes.

Adolescent↗
PubMed1988

Event-related EEG-spectra in a concept formation task.

Event-related spectra of short EEG epochs were investigated in a concept formation paradigm. In this task, subjects had to learn to transform letters into Morse codes. Related to a resting state, cognitive performance in this learning task was characterized (i) by an increased mean power density (MPD) within the Theta frequency band (theta) in recordings over the frontal lobes and (ii) by a reduced Alpha (alpha) MPD in all recording sites. The performance-related increase of the theta-MPD, as obtained in left frontolateral and frontomedial recordings, separated (i) the learning task from an appropriate control and (ii) a group of successful learners from a group which performed less efficiently. MPDs of the alpha- and the delta-(Delta) frequency band did not differ between tasks and groups. A consistent finding in the learning tasks was a temporal dissociation of performance-related alpha-attenuation between parietal and frontal recordings: in the period preceding the presentation of the informative stimuli, the alpha-rhythm is attenuated especially at parietal recordings, whereas in frontal recordings, alpha-attenuation accompanied information processing and response selection.

Adult↗
PubMed1987

Uncertainty analysis of human EEG spectra: a multivariate information theoretical method for the analysis of brain activity.

Short time Fourier power spectra yield activity related data of the EEG. The mean power densities of frequency bands have proved a reliable descriptive parameter of that activity. Due to their distributional properties of these data their analysis by conventional statistics is restricted to nonparametric univariate or at most bivariate tests. In order to account for the many-relational characteristics of EEG data, uncertainty analysis was employed and specific data transformations were developed. This technique was applied to some of our experimental records. The results confirm prior knowledge of the functional diversity of brain areas and demonstrate the general applicability of uncertainty analysis to this problem. In addition, the spatio-temporal coordination of these activities suggests a systems interpretation: These neuronal processes follow the self-organizing principle.

Analysis of Variance↗
PubMed1986

The influence of concentration and relaxation on the EEG power spectra during a CNV paradigm.

EEG segments of 1 sec duration, beginning 1 sec before the imperative stimulus were analysed by Fast Fourier Transformation in a CNV paradigm with interstimulus intervals (ISI) of different durations (1, 3, 5 sec) and with constant (K1, K3, K5) and randomized (R1, R3, R5) ISI presentation. In the alpha band, there were found differences in the power spectra between the constant and the longer randomized (R3, R5) ISI conditions, the latter having a slower center frequency, a smaller radius of gyration and a higher kurtosis. This describes a sharper alpha line of slower frequency in the R3 and the R5 ISI condition, due to pronounced synchronisation of alpha activity. It is discussed as an expression of increased relaxation and reduced concentration. In the theta band, differences appeared between the short ISI conditions (K1, R1) and the longer ones.

Adult↗