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Results for “Cortical Synchronization”

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At least 1,459 records · Page 81Linked to original sources
PubMed1992

[Event-related negativity and alpha band desynchronization in motor reactions].

The foreperiod of a motor reaction to an impending stimulus is accompanied by a slow negative wave of the event-related potential, the "contingent negative variation" (CNV), when the imperative stimulus follows at a fixed interval to a warning stimulus. Using similar experimental paradigms, an event-related desynchronization (ERD) in the alpha range occurs indicating cortical activation before and during motor acts. Both EEG-parameters were quantified for four subjects using the following experimental design: One second after a non-informative warning signal (WS) a cue was presented that indicated by which hand the subject had to respond quickly after presentation of a reaction stimulus (RS); subjects were requested to respond by pressing a button with their left or right thumb. EEG-signals were recorded unipolarly from 17 electrodes. Average ERPs and ERD were computed for all electrode sites for trials with left and right hand movements, respectively, and topographically displayed in simultaneous amplitude and ERD-maps. CNV and ERD could be observed simultaneously over similar brain regions, namely central over the motor cortex, frontal with possible location over the supplementary motor area (SMA) and also covering the parietal region. While the CNV had a interindividually different and wide distribution, the ERD calculated for the upper alpha band mapped focally over the electrode sites C3 and C4 overlaying primary sensorimotor structures, with a contralateral dominance. In contrast to the negativity which is terminated following delivery of the response stimulus, the ERD persisted during the motor reaction showing a similar pattern some hundreds of milliseconds before and after movement onset.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMedDate not supplied

[Attention and memory model based on the principle of dominant and comparative function of the hippocampus].

Six basic problems of attention are described in terms of the dominant focus by Ukhtomsky, which is simulated as a system of phase transitions in the brain. Theoretical and experimental arguments in favor of the existence of metastable states in the brain with the life time of about a second or more are deduced. This forms an approach to resolution of all the problems of interaction between attention and memory, binding, and central control. A neurobiological model of attention and memory is advanced, which integrates the system properties of dominanta by A.A. Ukhtomsky and comparator function of the hippocampus by O.S. Vinogradova. New literature evidence is given for the existence of the brain system of information processing with the hippocampus as a central executive.

Attention↗
PubMedDate not supplied

[Some features of spatiotemporal organization of brain biopotentials in persons with different levels of anxiety and other personality traits].

Anxiety and other personality traits were scored in 55 practically healthy subjects with the aid of 16-PF Cattell questionnaire. EEG was analysed by the mapping method after N.E. Sviderskaya. It was shown that two groups with equally high anxiety scores had different spatiotemporal organizations of brain biopotentials. The most "unfavorable" EEG characteristics were found in the group of "anxious conformists": poorly pronounced alpha rhythm with a low level of coherence in the alpha band was concomitant with the theta and beta rhythms with high levels of coherence and power density.

Adolescent↗
PubMed2004

[Discrimination between left and right hand movement imagery event-releated EEG pattern].

Left and right hand movement imagery can modifty the neural activity in the primary sensorimotor areas in a very similar way as observable with a real executed movement, leading to the special changes of EEG components such as event-related desynchronization/synchronization (ERD/ERS). Quick and correct classification of these event-related EEG pattern can be used to help patients with severe paralysis to move a cursor or orthosis to replace impaired motor function and provide a new communicatoion channel to environment. In this paper left and right hand movement imagery experiment method was introduced, some kinds of classification methods for event-related EEG pattern during motor imagery were reviewed and the prospect of classification methods was also put forward.

Communication Devices for People with Disabilities↗
PubMedDate not supplied

[The effect of a high-intensity radiation exposure on the brain function of monkeys. The postradiation changes in the EEG response to rhythmic photostimulation].

In experiments with monkeys (Macaca fascicularis) it has been shown that whole-body irradiation with a dose of 45 Gy (6.5 Gy/s) causes considerable changes in the EEG response to rhythmic photostimulation (PS). These changes are: reduction of the desynchronizing effect of PS with regard to a background rhythmicity; decrease in the reception rate of the rhythms of light flashes (RLF); narrowing of the RLF frequency range; and increase in the reaction momentum. The postirradiation changes in the EEG response to PS are considered as a manifestation of inhibition of the cortex functional activity and impairment of sensory information processing in the brain.

Animals↗
PubMed2005

A model of attention and memory based on the principle of the dominant and the comparator function of the hippocampus.

The six major questions of attention are described in terms of the dominant, as defined by Ukhtomskii. The dominant was in turn simulated as a systems manifestation of phase transitions in the brain. The theoretical and experimental bases for the existence of metastable states in the brain are reviewed, these states having lifetimes of 1 sec and more. This approach simultaneously provides solutions for all the major questions of attention and the "central controller." A neurobiological model of attention and memory is proposed, based on the systems properties of Ukhtomskii's dominant and the comparator function of the hippocampus as described by Vinogradova. New published data are presented to support the existence of an information processing system in the brain in which the hippocampus plays the central role.

Animals↗
PubMed1992

[Absence attacks with secondary bilateral synchrony].

Three cases with petit mal absence attacks with secondary bilateral synchrony were presented. The interictal EEG showed unilateral focal epileptic discharges in the frontal area with normal background activity. The ictal EEG disclosed 3-Hz generalized symmetrical spike-wave patterns preceded by unilateral focal discharges, which were elicited by hyperventilation. None of the three cases had abnormal neurological findings or abnormal CT findings. All three cases had normal psychomotor development. One case had a history of febrile convulsions. The ictal manifestations were as follows; impairement of consciousness without any other signs in one case, with decreased posture tone in the second, and automatism in the third. The authors suggest that there can be petit mal absence with 3-Hz generalized spike-wave discharges induced by secondary bilateral synchrony.

Child↗
PubMedDate not supplied

[The structure of the background EEG of the rabbit in the high-frequency portion of the spectrum].

With the purpose of studying the character and structure of high frequency bioelectric activity of rabbits cerebral cortex in the state of calm alertness, the EEG ensembles of different areas of the cortex (sensorimotor, visual, acoustic) and dorsal hippocampus were studied with FFT method. A supposition was made about the presence of systemic organization of the background EEG in rabbits cerebral cortex, reflected, in particular, in the presence of determined components both of chaotic and rhythmic character having different degrees of manifestation. Heterogeneity was revealed in distribution of energies of spectral EEG components in the studied frequency ranges from 14.7 to 100 Hz with predominance of total specific energy value in the band of 14.7-60 Hz. In coherence functions of all the studied pairs of EEG leads rhythmic component, stable in time, was absent. Functions of the mean EEG coherence in the band of 61-100 Hz had significantly greater values in comparison with the values in the band of 14.7-40 Hz.

Animals↗
PubMedDate not supplied

[The cross-correlation relations of the electrical activity of the cortical structures at different levels of the activation of the midbrain reticular formation in the rabbit].

Changes of correlation coefficients and coherence of the delta-, theta- and alpha-rhythms were studied between the somatosensory, motor and visual neocortex areas, dorsal hippocampus and dentate fascia at stimulation frequencies of the midbrain reticular formation from 60 to 1000 imp/s. It was shown that correlation coefficient between the structures studied increased at 60-200 imp/s and decreased at the further increase of stimulation frequency. In pairs with the visual area the correlation coefficient changed but little. The delta-rhythms coherence tended to decrease with the increase of stimulation frequency. Coherence of the theta-rhythms between the neocortical areas and the hippocampus increased with the increase of stimulation frequency up to 200 imp/s and decreased at higher frequency stimulation while in pairs of these areas with the dentate fascia it continued to rise with the increase of stimulation frequency up to 1000 imp/s. The coherence of the alpha-rhythms was almost unchanged at 60-200 imp/s and mostly had an increase at higher frequency stimulation.

Alpha Rhythm↗
PubMed2006

[Off-line experiments and analysis of independent brain--computer interface].

In order to study event-related desynchronization (ERD) related to voluntary movement, we designed two experiments. In the first experiment, untrained subjects were required to imagine the action of typing with left or right index finger for about 1 second before real action, whereas they were required to type instantly after instruction in the second experiment. By analyzing spontaneous EEG signals between the instruction and the action, we predicted which finger was used. The prediction accuracy in the first experiment fell from 85% to 71% with the progress of experiment, the average accuracy being 78%, whereas the prediction result was almost random guess in the second experiment. The results demonstrate that (1) ERD patterns are significantly affected by the effective duration of motion imagination, (2) unconscious reduction of this duration can decrease the prediction accuracy. Therefore, when designing subsequent BCI experiments, we should devote our attention to the question of how to keep the effective duration of motion imagination.

Brain↗
PubMed2006

[The role of micro-arousals in the regulation of sleep].

This work give a short account about a three decades research of the sleep microstructure. The studies, executed by the Strassbourg, Budapest and Parma schools, paved the way of exploring the participation of micro-arousals in the sleep regulation. It was shown that micro-arousals, not leading to instant arousal but influencing the later course of sleep are weaved into the network of sleep. A certain class of micro-arousals differs from the traditional desyncronisation-type and in a paradox way result a rebound like mobilisation of sleep-like activity with deltas and K-complexes. The desynchronisation- and synchronisation-type micro-arousals show different distribution along the sleep cyclicity and may play different role in sleep regulation. On the basis of the studies dealing with micro-arousals we can assume that beside the traditional long time constant, brain stem driven tonic chemical regulation, an other phasic regulation, with shorter time constant, associated with the micro-arousals, also exists. This kind of phasic regulation makes sleep flexible and possible to adapt the actual sleep course to the inner and outer demands. An other important role of micro-arousals in pathological sleeps is to provide a gate for the different pathological events, pinpointing the key-points where these events could be expected in the sleep process.

Arousal↗
PubMed2006

[Quantitative EEG analysis in Alzheimer's disease: spectral, coherence and complexity parameters].

In our study we examined the linear and non-linear characteristics of EEG signals derived from patients with Alzheimer's disease (AD) with the future aim of developing a widely available method for monitoring therapy and the progression of the disease or to be used even for the purposes of differential diagnosis. EEG was recorded with eyes closed and eyes open conditions ("resting") in a group of patients with early-stage AD and in healthy control subjects matched by age. In addition to the conventional methods of analysis (frequency spectrum, coherence), the so-called complexity measures developed in recent years (Omega-complexity, synchronised probability) have also been determined. By means of frequency spectrum analysis, we managed to detect the slowdown of EEG in the early stage of dementia, a feature that so far has been associated with the later stages of AD. Coherence was reduced in the majority of frequency bands in the patient group; however, this difference could be observed only in some of the leads. Thus, resting EEG coherence is less suitable for separating various stages than the other methods. Complexity features have shown the most robust changes in Alzheimer's disease in our investigation. Besides the reduction in synchronised probability, significantly higher values of Omega-complexity were obtained in the patient group. This may be associated with the impairment of cortical afferentation (cholinergic and monoaminergic) and with the reduction in the number of neurons and synapses. Our methods have proved to be very sensitive to quantify these changes.

Aged↗
PubMed1991

[The effect of vibration on the electrocorticographic shifts during the switching off of specific and nonspecific afferent systems of the brain].

Electrocorticograms of vibration induced effects were studied in intact and labyrinthectomized rabbits under midbrain reticular formation and renoreactive structures blockade. There was involvement of the specific (vestibular) and non-specific brain structures in the mechanisms underlying the cortex' electric activity. The article contains a review of the vibration-related shifts in the cortex, both specific and nonspecific--and in other afferent modalities (proprioceptive, somatic, visceral).

Afferent Pathways↗