Computing the center of mass for traveling alpha waves in the human brain.

The phenomenon of traveling waves of the brain is an intriguing area of research, and its mechanisms and neurobiological bases have been unknown since the 1950s. The present study offers a new method to compute traveling alpha waves using the center of mass algorithm. Electroencephalographic alpha waves are oscillations with a characteristic frequency range and reactivity to closed eyes. Several lines of evidence derived from qualitative observations suggest that the alpha waves represent a spreading wave process with specific trajectories in the human brain. We found that during a certain alpha wave peak recorded with 30 electrodes the trajectory starts and ends in distinct regions of the brain, mostly frontal-occipital, frontal-frontal, or occipital-frontal, but the position of the trajectory at the time in which the maximal positivity of the alpha wave occurs has a definite position near the central regions. Thus we observed that the trajectory always crossed around the central zones, traveling from one region to another region of the brain. A similar trajectory pattern was observed for different alpha wave peaks in one alpha burst, and in different subjects, with a mean velocity of 2.1+/-0.29 m/s. We found that all our results were clear and reproducible in all of the subjects. To our knowledge, the present method documents the first explicit description of a spreading wave process with a singular pattern in the human brain in terms of the center of mass algorithm.

[Cognitive processes and dynamic time structures. Introduction of a measuring instrument for studying the Micro-Vigilance-Shift-(MVS) hypothesis]. / Kognitive Prozesse und dynamische Zeitstrukturen. Vorstellung eines Messgerätes zur Untersuchung der Mikro-Vigilanz-Shift-(MVS-)Hypothese.

The psychophysiological measuring method for the determination of the auditory order threshold (OT) is steadily gaining in importance, both for the diagnosis and treatment of speech disorders. Observed intraindividual variability of (macro-) vigilance led to the hypothesis of discontinuous cognitive processing in the central nervous system. The base for the variability of microvigilance is hypothesized to be in the phase difference of the alpha rhythm. To test for this hypothesis, we developed an EEG-comparator, which allows for a phase-dependent triggering of external stimuli. In direct comparison with stochastic (i.e. non-phase-dependent) stimulus presentation, the threshold in phase-dependent OT-testing is distinctly lower. Optimal results occurred at phase angels of phi = 90 degrees and phi = 270 degrees. Our findings support the hypothesis of a correlation between alpha rhythm and vigilance processes. Furthermore, there seems to be evidence that memory processes go with changes in vigilance, and in this context the alpha phase correlation seems to be important.

[The dynamic localization of a dipole source of the alpha rhythm in the human brain]. / Dinamicheskaia lokalizatsiia dipol'nogo istochnika al'fa-ritma v mozge cheloveka.

In 11 subjects the dynamic localization (with 2-ms step) of the equivalent current dipole of alpha rhythm during travelling alpha waves was studied using one-dipole 3-layered spherical head model and MRI. The dipole was localized in the occipital cortex and during the development of a single alpha wave it shifted in one or another direction while dipole's moment revealed fan-like rotation mainly in sagittal and horizontal planes. The results obtained indicate changing localization of the alpha-rhythm source in the region corresponding to striate cortex. They seem to prove scanning hypothesis that is still under discussion.

[Generators of the rhythmic alpha activity in the human EEG]. / Generatory ritmicheskoi al'fa-aktivnosti EEG cheloveka.

An attempt to localize brain mechanisms of the rhythmic activity in the alpha-rhythm range was made using the equivalent dipole model. It is known that light flickering stimuli with the frequency close to that of the individual alpha rhythm induce an increase in its spectral power ("photic-driving" phenomenon). It was shown that the activity of the neuronal structures generating the alpha rhythm can be identified by specific frequency of the light stimulation and localized by means of construction of dipole models. Two sources of the alpha rhythm in the narrow-frequency bands with the maximal resonance responses in the frequencies of 10.1 and 10.5 Hz were localized in the thalamic structures.

[A search for the sources of pathological alpha activity in the human EEG in limbic structure lesions]. / Poisk istochnikov patologicheskoi al'fa-aktivnosti EEG cheloveka pri porazhenii limbicheskikh struktur.

Dependence of manifestations of EEG pathological activity on the electrode montage was studied in cases of brain lesions involving limbic structures by means of the topographic mapping and 3-d dipole source localization. The original program DIPVIS on the basis of BRAINLOC software allowed us to reveal the stable sources of lateralized pathologic alpha activity and demonstrate the discrepancy between its localization and the localization of the normal human alpha rhythm. The sources of pathological activity in question were predominantly localized in the mediobasal structures of the affected hemisphere in contrast to the occipital region of a healthy human. It was established that the topography of the cortical pathological activity may be determined by peculiarities of localization and, especially, orientation of its dipole generators. Afferent stimulation produced an enhancement of the pathological alpha-activity and increase in dipole source concentration in the mediobasal portion of the temporal lobe. The findings suggest that the discovered from of the alpha-rhythm reflects the reaction of activation of the hippocampal structures involved in the pathological process.

[Visual illusions evoked by rhythmic bursts and the "movement" through the cortex of waves of alpha activity]. / Zritel'nye illiuzii, vyzvannye ritmicheskimi vspyshkami, i "dvizhenie" po kore voln al'fa-aktivnosti.

In computer-controlled experiments the visual illusions were studied which appeared in human subjects under conditions of diffuse rhythmic photostimulation through the closed eyes with the individual dominant alpha-rhythm frequency. A significant correlation was demonstrated between the type of experienced illusion (or its absence) and the trajectory of the alpha-wave travelling in the prestimulation and stimulation periods.

[The characteristics of the alpha-rhythm electroencephalogram in patients with liver cirrhosis]. / Osoblyvosti al'fa-rytmu elektroentsefalohramy u khvorykh na tsyroz pechinky.

The brain functional state in patients with liver cirrhosis was investigated, the correlational dependence between the intrinsically present alpha-rhythm of electroencephalogram pattern of examined patients and the brain reactions signs while the functional tests conduction was studied up. The data obtained are compared with the results of such investigations, conducted in healthy persons. The results of investigations witness the brain functional possibilities lowering in patients with liver cirrhosis. The test with photostimulation is pathognomonic for this disease.

[Differences in the the EEG frequency characteristics during the perception of positive-emotional, negative-emotional and neutral words]. / Razlichiia chastotnykh kharakteristik EEG pri vospriiatii polozhitel'no-émotsional'nykh, otritsatel'no-émotsional'nykh i neitral'nykh slov.

Power spectral analysis of the theta- and alpha-rhythms was performed in narrow frequency bands (1 Hz) for EEGs recorded from F3, F4, C3, C4, T3, T4, P3, P4, O1, and O2 derivations in 9 healthy adults viewing emotionally positive, negative, and neutral words displayed on the screen. The relative spectral power in the 7-8 Hz band was higher during presentation of the emotionally significant words than the neutral ones. The EEG reaction to emotional words within this frequency range depended on the word valency. The relative power increase was revealed in the range of 7-7.5 Hz during presentation of emotionally positive stimuli. This reaction was most expressed in the frontal, central, and temporal cortical areas. During presentation of the negative words similar EEG reactions were observed within 7.5-8 Hz. In this case the frequency changes dominated in symmetrical frontal, right central, temporal, and parietal cortical areas.

[The nature of the variability in the individual differences of the frequency characteristics of the alpha-rhythm EEG in 6- to 8-year-old children]. / Priroda izmenchivosti individual'nykh razlichii chastotnykh kharakteristik al'fa-diapazona EEG detei 6--8 let.

Behavioural genetic technique (model fitting) was used to study the genetic and environmental contributions to individual variability of power of the alpha-frequency band and its components (alpha 1 = 7.5-9.0 Hz; alpha 2 = 9.5-11.0 Hz; alpha 3 = 11.5-13.0 Hz) in different brain areas. 26 pairs of monozygotic and 22 pairs of dizygotic twins aged 6-8 years participated in EEG study. EEG was recorded from the frontal (F3, F4), central (C3, C4), temporal (T3, T4), parietal (P3, P4), and occipital (O1, O2) areas. Our study revealed that the nature of different alpha-components was different. It was found that the later in the ontogenesis a component of the alpha-frequency band became dominant in the EEG the less genetic factors contribute into the family resemblance.

Validity of electrode placement at Fpz to detect alpha wave.

The possibility on placing electrodes at Fpz-A2 instead of C3-A2 was investigated to obtain a more stable configuration avoiding obstruction by the hair. Our original system of alpha wave detection by a microcomputer was used, and a total of 22 all-night hypnograms of five healthy young students was recorded. Pearson's moment correlation coefficients of alpha wave % between the two positions were 0.780-0.948. Except for one subject, alpha wave % taken at Fpz-A2 tended to be 3-5% lower than that at C3-A2. The above analysis indicates that using EEG electrode position of Fpz-A2 is valid and useful as a stable electrode configuration for a long-time monitoring.

[The spatial structure of the alpha rhythm in the healthy human being studied by EEG mapping]. / Issledovanie prostranstvennoi struktury al'fa-ritma zdorovogo cheloveka metodom kartirovaniia EEG.

EEG study was conducted in the state of relative rest in 15 healthy subjects with predominance of the alpha rhythm. Data processing was performed on neuromapper ("Neuroscience", Great Britain). Principal attention was paid to the dynamics of spatial-temporal relations of the alpha rhythm. Cyclic changes were shown of the alpha-rhythm amplitude, proceeding with change of high and low amplitudes during seconds, varying in time in various individuals. Three types of spatial distribution of the alpha rhythm over the cortex at the relative rest were obtained: 1) generalized distribution over the cortex with the wavy shift of the frequency fields; 2) formation of delimited local zones of the alpha rhythm, differing by the frequency from the rhythm in other cortical areas; 3) local zone of the low-frequency alpha rhythm in the visual projection zone (18 and 19 fields). Change of the distribution types of the alpha rhythm in the state of rest takes place in the seconds of time intervals, corresponding, according to the literature data, to the proceeding of elementary mental processes.

Biofeedback instruments for the management of anxiety and for relaxation training.

An EEG alpha biofeedback system and a portable GSR monitor/feedback box are described. The rationale for the use of these instruments in the management of anxiety and for relaxation training, respectively, is also described, as well as the training techniques presently in use at St. Bartholomew's Hospital.