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Biomedical subjects

B Grözinger

Publications and source records attributed to B Grözinger.

At least 19 recordsLinked to original sources
PubMed1998

Localisation of epileptic foci with electric, magnetic and combined electromagnetic models.

We compare the localisation of epileptic foci by means of (1) EEG, (2) magnetoencephalography (MEG) and (3) combined EEG/MEG data in a group of patients suffering from pharmaco-resistant focal epilepsy. Individual epileptic events were localised by means of a moving dipole model in a 4-shell spherical head approximation. A patient's epileptic activity was summarised by calculating the spatial density distribution (DD) of all localised events, and the centre of gravity of DD was considered the most likely locus of seizure generation. To verify these loci a subgroup of 6 patients was selected, in which seizures could be related to a clearly identifiable lesion in MRI. On average, the combined EEG/MEG approach resulted in the smallest error (1.8 cm distance between calculated locus and the nearest lesion border); using only MEG yielded the largest error (2.4 cm), while EEG resulted in an intermediate value (2.2 cm). In the individual patients, EEG/MEG would also rank intermediate, but never worst. In summary, combining EEG/MEG appears to be a more robust approach to localisation than using only EEG or only MEG. Finally, we also report on the use of the barbiturate methohexital as a safe method of increasing the number of spike events during an EEG/MEG recording session.

Algorithms↗
PubMed1998

Bereitschaftspotential in amyotrophic lateral sclerosis (ALS): lower amplitudes in patients with hyperreflexia (spasticity).

In a pilot study the Bereitschaftspotential (BP) was investigated in 16 patients suffering from amyotrophic lateral sclerosis (mean age 58.6, mean severity of the illness according to Norris ALS score 76.4 points). Comparing the total ALS group (n=16) with matched controls no significant differences in the BP amplitude parameters were found. However, a subgroup of 7 ALS patients with signs of pronounced spasticity (hyperreflexia) differed significantly at the central midline from matched controls and significantly in addition from patients with a lower degree of spasticity. Controls as well as patients with a lower degree of spasticity had significantly higher BP amplitudes at the midline (electrode positions Cz and Pz, P<0.05, H-test). The correlation coefficient between the hyperreflexia Norris score and the various BP parameters for the total ALS sample (n=16) revealed a significant correlation especially over the midline. Stronger signs of spasticity (hyperreflexia) are associated with lower amplitudes of the BP.

Adolescent↗
PubMed1997

Electrophysiological analysis of expectancy: P3 in informed guessing.

18 healthy subjects had to guess, which of two nonequiprobable events would occur next. Each trial was preceded by a cue which increased the probability of the corresponding event as compared to its global probability. Event-related potentials (ERPs) were recorded and then classified according to global probability of events, their relation to the preceeding cue (valid versus invalid cues) and to subject's prediction (predicted versus nonpredicted). Two late positive waves (P350 and P550) with parietal maxima were distinguished. Both waves had larger amplitudes in response to improbable events than to highly-probably events. Similarly, both had larger amplitudes following invalid cues than following valid cues, and this difference was larger in those subjects who tended to follow the cue than in those who tended to reject it. No difference in terms of ERP component amplitudes was found between predicted and unpredicted events; however, the latency of the P350 peak was longer following unpredicted events. Taken together with data of the literature, the present results indicate that ERP allow us to distinguish between two meanings of the word "expectancy": (1) the rule-related expectancy as cognitive estimation of the likelihood or "representativeness" of an event (based on grasping event contingencies), and (2) the goal-related expectancy manifested in the subject's overt behavior. Only the former "expectancy" affects the amplitude of the late positive wave ("P3"), while the latter does not.

Adolescent↗
PubMed1996

Changes in EEG order in neuroleptically treated normal volunteers during a voluntary movement task.

15 normal volunteers were treated over three weeks with haloperidol (HAL) and in the third week additionally with biperidene (BIP). The order of the EEG spectra at different topographical locations and in different frequency bands during a movement task was analyzed using uncertainty analysis (UA), a multivariate analysis technique based on information-theoretical methods. Different patterns of drug-induced changes were found. HAL decreases the theta and alpha band order at the fronto-central lateral areas but increases it at the fronto-central midline in the theta band and at the parietal areas in the alpha band. With the exception of the fronto-central midline locations, BIP more or less counterbalances the effect of HAL. Volunteers felt unwell and had motor disturbances during HAL and felt well again during HAL + BIP. Reaction time values were increased during HAL and normalized during HAL + BIP.

Adult↗
PubMed1996

Event-related brain potentials in a varied-set memory search task: a reconsideration.

Event-related potentials (ERPs) were recorded in 19 healthy subjects as they completed two Sternberg (1969, American Scientist, 57, 421-457) memory tests. In separate sessions, either single digits (i.e., 0-9) or 10 abstract figures were used as stimuli. In both sessions, memory set sizes were 1 (M1), 2 (M2), or 4 (M4). The amplitude and latency of the parietal P400 and the frontocentral negativity preceding P400 varied significantly with set size, but only between M1 and M2, whereas reaction time increased dramatically from M1 to M2 and from M2 to M4. These findings challenge previous assertions that the ERPs reflect aspects of the exhaustive serial search proposed by Sternberg. A late parietal positivity (P620), which failed to vary with set size, was larger in response to figures than to digits and may represent the search for, or utilization of, semantic traces of the stimuli.

Adult↗
PubMed1995

Evoked brain potentials and memory: more positivity in response to forgotten items.

Brain evoked potentials (EPs) were recorded in human subjects participating in a free recall memory task involving retroactive interference. A learning list was presented five times. The fifth repetition was followed by an interference list. Both lists were composed of either words or abstract figures, and each subject experienced each of four possible combinations. Analysis of items recalled during the learning phase revealed larger N400 and P600 amplitudes for those items that were later forgotten vs remembered following the interference. This contradicts the usual finding that more positivity is associated with better memory. However, both the present as well as the extant findings can be explained in terms of cognitive resource allocation. Specifically, items receiving greater allocations are more likely to be immediately recalled. However, as the number of items in working memory increases, the allocation required to add new items also increases. Thus, items learned on later trials would receive larger allocations (i.e., larger positivities) than items learned earlier, yet would be more likely forgotten following the interference because their presence in memory would not be reinforced during later trials, as is the case with items learned earlier.

Adult↗
PubMed1995

Individual differences in slow brain potentials in a guessing task.

18 healthy right-handed subjects had to predict one of two random non-equiprobable events by pressing one of two buttons with the right index finger. Each trial was preceded by a cue that increased the probability of the corresponding event in comparison to its overall probability. The Bereitschaftspotential (BP) before an action and the stimulus-preceding negativity (SPN) between the action and the event presentation were recorded. The subjects were subdivided into groups according to their tendency to follow the cue or to reject it. Cue rejection provided in the present situation a larger final gain than cue acceptance. Those subjects who used the former strategy were characterized by a local BP increase over the right parietal cortex, when a low-probable cue was presented. Their SPN amplitude was relatively small, but it increased substantially after a low-probable cue. Subjects who tended to follow the cue had a very large BP amplitude over the projection area and at vertex. Their SPN was overall large, regardless of condition. Peculiarities of the potentials recorded in these subjects are thought to relate to their desire to minimize errors.

Adolescent↗
PubMed1994

Changes in functionally determined order processes of the EEG in a motor task due to various dosages of biperidene.

Animal experiments have demonstrated that the cholinergic system plays an important role in the activation of the cerebral cortex in conjunction with motor activities. In order to study the significance of the cholinergic system in the generation of voluntary movements in man, the effects of the anticholinergic drug biperidene on EEG states were analyzed. The effects depend strongly on the dosage and are shown in various frequency bands, topographic loci and time periods. Different functional significances of various frequency bands were found. In the alpha band motoric control processes are seen as an expression of mechanisms which substitute the cholinergic system. A shift of functions from the theta to the delta band with the increase of the medication seems to parallel an enhancement of motivational or volitional effort. The emergence of highly ordered EEG states is seen to be meaningful in view of the underlying processes of voluntary movements.

Adult↗
PubMed1993

EEG-blocking before and during voluntary movements: differences between the eyes-closed and the eyes-open condition.

Movement-related EEG periods of 1 s duration were analyzed by fast Fourier transformation in the Bereitschaftspotential (BP) paradigm in 21 healthy, right-handed normals. Spectra of the rest period and the BP period before the onset of the voluntary movement, and of the rest period and the movement period, were compared in order to describe blocking effects before and during movement execution (fast fist closure of the right hand). When comparing the rest period and the movement period with the eyes closed as well as with the eyes open, blocking was pronounced in both conditions within the total frequency range of the alpha-band, especially at positions contralateral to the movement over the motor cortex (C3') and the parietal cortex (P3) as well as at the parietal midline electrode (Pz). Moreover, when comparing the spectra of the rest and the BP periods in the eyes-closed condition, significant differences were again seen, with lower values during the BP period at C3' and P3. We were, however, able to observe over the parietal cortex an increase of alpha power in the 10 Hz range during the BP period with the eyes opened and fixated. This increase during the BP period in the eyes-open condition was not found when the eyes were closed. This paradoxical phenomenon of an increase of power with the eyes opened instead of blocking during the BP period, as observed in the eyes closed, may be due to an additional activation effect on the already activated (blocked) EEG in the eyes-open condition during fixation.

Adult↗
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↗
PubMed1987

Do event-related potentials (ERPs) reflect right hemisphere's processing of semantics?

To test the right hemisphere's functional difference in relation to semantically related vs. semantically unrelated linguistic tasks we investigated 25 young right-handed healthy adults. A S1-S2 design was used. At S1 one word was presented binaurally, at S2 two words dichotically. S1-S2 was composed of sentence-like (syntagmatic) and nonsentence-like (paradigmatic) word sequences with and without semantic relations. As control trials we used pure tones and modulated noise. The EEG was recorded over frontal, central and temporoparietal areas of both hemispheres. Referring to semantics it could be shown only that semantic relations between words increased the amount of recalled words. Additionally, ERPs reflected: modes of presentation (binaural vs. dichotic) processing of different linguistic categories (e.g., syntagmatic vs. paradigmatic) and frontocentrally focused neuronal processes of both hemispheres before language production.

Adult↗
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↗