B. Grözinger

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.

Musicians versus Nonmusicians

Abstract: The ability to perceive sounds and correctly categorize them within a scale is the result of the interaction between inherited capabilities and acquired rules. If a subject listens to a melody, occasional and unexpected endings of the melody typically evoke characteristic auditory evoked responses in the latency range of 300‐400 ms (P300). Also, earlier stages of auditory information processing have been exhaustively investigated by means of mismatch negativity (MMN), a deflection that occurs in the auditory evoked response at a latency of about 200 ms, whenever a deviance is randomly inserted in a series of otherwise equal stimuli. Conceivably, perceptual deviations could also be detected against expectancies that are based on abstract rules; introspective experience suggests that such deviations may also elicit fast intuitive responses that typically initiate processes of analytical reasoning for confirmation. In music, the physical features of the stimulus are, in fact, always changing, because the melodic contour consists of a series of notes with different pitch characteristics. In such a condition, a typical mismatch negativity would not be evoked on the basis of physical deviance, but rather of criteria involving the musical contour of the stimulus. In this study, 20 healthy subjects (10 nonmusicians and 10 musicians) underwent auditory stimulation (tone, chord, chord sequence, Mozart and Bach melodies) and both electrical and magnetic recordings. Clear N1 was recorded for all paradigms, in all subjects; MMN and P300 were also recorded, and their amplitudes and latencies were significantly correlated with the musicality score and with the paradigms difficulty.

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.

The Bereitschaftspotential Preceding the Act of Speaking. Also an Analysis of Artifacts

Publisher Summary This chapter discusses the Bereitschaftspotential (BP) preceding the act of speaking. The BP and R-wave are widely but not uniformly distributed over the cranium. Responses are most prominent over the speech areas and also on the contralateral homologous frontal area. Less activity is present when electrodes are located over cortex between the speech areas of the dominant hemisphere, and also over left parieto-temporal regions. In general the R-wave seemed to be more pronounced over the right hemisphere, especially over electrode position A. Only A showed clear side-differences consisting of a prominent short-latency BP over the left hemisphere. In leads C and D no such side-differences of the BP could be seen. There is no clear BP over the electrode position H, while in I, probably over the region of Wernicke, a small BP is present, which is slightly more prominent over the dominant hemisphere. The symmetrical positive going BP over K may reflect less activity from these brain areas.

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.

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 fields 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.

Evidence for the Cerebral Origin of the R-Wave in the Pig

Publisher Summary This chapter discusses the evidence for the cerebral origin of the R-wave in the pig. The maximal absolute amplitude of the cross-correlation is a function of the signal-to-noise ratio. The signal is the R-wave, and all other Electroencephalography (EEG) components except those in the range of the R-wave may be considered noise. The EEG signals are filtered excluding frequencies above 5 Hz. This leads to a relatively good signal-to-noise ratio for the hypercapnia conditions. It might be argued that the increasing absolute amplitude of the cross-correlation functions (CCF) depends on the increasing signal-to-noise ratio. This cannot account for the results during hypoxia, however, while on the one hand it decreases the signal-to-noise ratio, while concomitantly the absolute amplitude of the CCF is increased. It appears unlikely that the change of the noise (in the raw EEG) in the various conditions can produce the increasing absolute amplitude of cross-correlation. It should be mentioned that anaesthesia depresses the respiratory centers. It is highly likely that the absolute values of cross-correlation would have been even higher in the unanaesthetized animal.

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

Summary15 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 informationtheoretical 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.

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.