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In the present work, a commonly used index for evaluating the Event-Related Synchronization and Desynchronization (ERS/ERD) in the EEG was expressed as a function of the Spectral F-Test (SFT), which is a statistical test for assessing if two sample spectra are from populations with identical theoretical spectra. The sampling distribution of SFT has been derived, allowing hence ERS/ERD to be evaluated under a statistical basis. An example of the technique was also provided in the EEG signals from 10 normal subjects during intermittent photic stimulation.

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INTRODUCTION: Increased neuronal activity in the internal pallidum (GPi) and the subthalamic nucleus (STN) has been clearly demonstrated in Parkinsonian models, and the two structures have thus been selected as therapeutic targets for functional neurosurgery. High-frequency electrical stimulation of the GPi or the STN improves the parkinsonian symptoms but also dyskinesias directly by GPi stimulation or indirectly by reduction of L-Dopa associated with STN stimulation. According to Alexander's model of the organisation of the basal ganglia, electrical stimulation of GPi or STN should have led to uncontrolled hyperkinesia. This apparent paradox could be explained on one hand by the involvement of different anatomo-functional areas within these structures and on the other by spatial and temporal changes in neuronal discharge patterns in the basal ganglia which in turn produce variations in synchronisation. RESULTS: Event-related (de)synchronisation (ERD) has enabled us to study variations in subcortico-cortical oscillatory activity: it has been shown that high-frequency electrical stimulation of the GPi/STN increases desynchronisation of low frequency rhythms (mu and beta,<30 Hz) during movement preparation and execution and augments post-movement synchronisation. Stimulation also decreases the abnormal frontocentral spreading of desynchronisation during movement preparation. CONCLUSIONS: In accordance with previous coherence analyses, electrical stimulation of STN is likely to restore the activity of high-frequency and low-frequency systems, as evidenced by a decrease in the hypersynchronisation of low-frequency rhythms at rest and restoral of a high-frequency rhythm during movement. Stimulation may improve spatial selectivity by activating the selected programs in conjunction with the primary sensorimotor cortex, whilst inhibiting competitive programs represented by abnormal spreading outside the primary sensorimotor cortex.

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This study investigates the acoustic reflex threshold (ART) dependency on stimulus phase utilizing low-level reflex audiometry [Neumann et al., Audiol. Neuro-Otol. 1, 359-369 (1996)]. The goal is to obtain optimal broadband stimuli for elicitation of the acoustic reflex and to obtain objective determinations of cochlear hearing loss. Three types of tone complexes with different phase characteristics were investigated: A stimulus that compensates for basilar-membrane dispersion, thus causing a large overall neural synchrony (basilar-membrane tone complex-BMTC), the temporally inversed stimulus (iBMTC), and random-phase tone complexes (rTC). The ARTs were measured in eight normal-hearing and six hearing-impaired subjects. Five different conditions of peak amplitude and stimulus repetition rate were used for each stimulus type. The results of the present study suggest that the ART is influenced by at least two different factors: (a) the degree of synchrony of neural activity across frequency, and (b) the fast-acting compression mechanism in the cochlea that is reduced in the case of a sensorineural hearing loss. The results allow a clear distinction of the two subjects groups based on the different ART for the utilized types and conditions of the stimuli. These differences might be useful for objective recruitment detection in clinical diagnostics.

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Recent findings are reviewed indicating that upper alpha oscillations - when analyzed with appropriate time/ frequency resolution - show a similar physiological reactivity as theta in working memory tasks. Comparable to theta, a load dependent increase in power can be observed during retention and increased evoked activity during retrieval. During retrieval attempts theta behaves like a traveling wave spreading from anterior to posterior sites. During actual retrieval, however, evoked upper alpha becomes transiently nested in theta. We suggest that theta reflects working memory functions whereas upper alpha may be important for the reactivation of long-term memory codes in short-term memory.

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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.

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STUDY OBJECTIVES: To determine the frequency of classical markers of non-rapid eye movement (NREM) parasomnias--hypersynchronous delta sleep (HSD) electroencephalogram waves and sudden arousals from slow-wave sleep (SWS)--in patients without histories of somnambulism or other NREM parasomnias. DESIGN: Retrospective review. SETTING: Sleep disorders center laboratory. PATIENTS: 82 consecutive patients without a history of parasomnias who underwent diagnostic polysomnograms; 57 men and 25 women, mean age 48+/-13.3 years, were included without regard to diagnosis or findings. All patients had at least 30 seconds of stage 3 or 4 sleep during the polysomnogram. MEASUREMENTS AND RESULTS: The primary diagnosis of all but 4 patients was obstructive sleep apnea (mean respiratory disturbance index, 30 +/- 23.6 [range, 2.7-117] per hour of sleep). Polysomnograms were then reviewed for the presence of HSD and SWS arousals. A total of 235 arousals (mean, 2.9 +/- 2.7; range, 0-14) from stage 3 or 4 sleep were noted. Eight-five percent of all patients had at least 1 SWS arousal and 45% had 3 or more SWS arousals; 85.1% of all arousals from SWS were secondary to sleep-disordered breathing, and 5.9% were secondary to leg movements. At least 1 episode of HSD (mean, 1.4 +/- 1.6; range, 0-9) was noted in 65.8% of patients. CONCLUSIONS: HSD and SWS arousals were a common finding in patients without clinical histories of sleepwalking or other parasomnias but who were found to have frequent respiratory-related arousals during sleep. HSD and SWS arousals thus have a low specificity for NREM parasomnias and, without further research, are not useful for the objective confirmation of parasomnias in clinical evaluations and in the forensic evaluation of sleepwalking as a legal defense.

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Thirteen high intelligent (H-IQ) and 13 low intelligent (L-IQ) individuals solved two figural working-memory (WM) tasks and two figural learning tasks while their EEG was recorded. For the WM tasks, only in the theta band group related differences in induced event-related desynchronization/synchronization (ERD/ERS) were observed. L-IQ individuals displayed greater theta synchronization in the later phases of task completion (1000-2000 ms) as compared to H-IQ individuals. For the learning tasks group related differences in the three alpha bands were observed. In the upper alpha band L-IQ individuals showed greater ERD in the frontal brain areas, whereas H-IQ individuals displayed greater ERD in the parieto-occipital brain areas.

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Event-related synchronization (ERS) and desynchronization (ERD) in delta, theta1, theta2, alpha1, alpha2, beta1, beta2, beta3, and gamma were measured in 20 healthy right-handed subjects in response to IAPS stimuli with low, moderate, and high arousal reactions. The 62-channel EEG was simultaneously recorded while subjects viewed sequentially presented pictures and subjectively rated them after each presentation. The results show that emotionally loaded stimuli induced higher ERS in the delta, theta1, theta2, beta1, beta3, and gamma bands along with combined ERD and ERS effects in alpha2 band. As to hemispheric asymmetries, the effects of emotional arousal were restricted not only to right parietal (theta1 and theta2 ERS, alpha2 ERD) but also to left frontal (theta2 ERS) regions. In terms of affective chronometry, lower theta was the first to catch the affective salience of incoming stimuli (time window 0-600 ms after the stimulus input). For theta2, alpha2, and gamma bands this process was delayed to 600-1000 ms.

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Information from different sensory modalities is processed in different cortical regions. However, our daily perception is based on the overall impression resulting from the integration of information from multiple sensory modalities. At present it is not known how the human brain integrates information from different modalities into a unified percept. Using a robust phenomenon known as the McGurk effect it was shown in the present study that audio-visual synthesis takes place within a distributed and dynamic cortical networks with emergent properties. Various cortical sites within these networks interact with each other by means of so-called operational synchrony (Kaplan, Fingelkurts, Fingelkurts, & Darkhovsky, 1997). The temporal synchronization of cortical operations processing unimodal stimuli at different cortical sites reveals the importance of the temporal features of auditory and visual stimuli for audio-visual speech integration.

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A temporal delay (parameter of synchronization) between the incidence of epileptiform discharges in cortical sited located at a distance of 4 mm from each other was studied in rat intact cortex and neuronally isolated cortical slab using the cross-correlation function. Experiments were carried out at different stages of axonal sprouting. By 30 days of isolation, a significant increase in the number of boutons in the V cortical layer coincided with a significant decrease in the delay, whereas a reduction of the number of boutons by 90 days corresponded to its increase. These findings convincingly testify that the newly formed boutons form a basis for increase in synchronization and thus affect the epileptogenesis. The results obtained in this work and literature data suggest that under pathological conditions large pyramids of the V layer form a neuronal network which provides exclusively cortical synchronization of epileptiform field potentials.

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The electroencephalogram (EEG) is modified by motor imagery and can be used by patients with severe motor impairments (e.g., late stage of amyotrophic lateral sclerosis) to communicate with their environment. Such a direct connection between the brain and the computer is known as an EEG-based brain-computer interface (BCI). This paper describes a new type of BCI system that uses rapid prototyping to enable a fast transition of various types of parameter estimation and classification algorithms to real-time implementation and testing. Rapid prototyping is possible by using Matlab, Simulink, and the Real-Time Workshop. It is shown how to automate real-time experiments and perform the interplay between on-line experiments and offline analysis. The system is able to process multiple EEG channels on-line and operates under Windows 95 in real-time on a standard PC without an additional digital signal processor (DSP) board. The BCI can be controlled over the Internet, LAN or modem. This BCI was tested on 3 subjects whose task it was to imagine either left or right hand movement. A classification accuracy between 70% and 95% could be achieved with two EEG channels after some sessions with feedback using an adaptive autoregressive (AAR) model and linear discriminant analysis (LDA).

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Electrical activity of the frontal cortex, dorsal hippocampus, basolateral amygdala and lateral hypothalamus was recorded in eight dogs with chronically implanted electrodes. Mean values of the maxima of crosscorrelation function (MCCF) between electrical potentials in the theta, alpha and beta-2 ranges were used as a basis for assessment of conditions for interaction between these structures. Typological features of the higher nervous activity were assessed by the animal performance under conditions of free choice of the reinforcement mode of a conditioned stimulus: either high probable but of low alimentary quality or with low probability but more valuable. The mean MCCF values in the theta range were higher than in the other ranges. The brain structure which had the high MCCF in the theta-range, at least, with two of the structures under study was considered as "dominant". It was shown that hippocampus was the dominant structure for melancholic dogs, the frontal cortex was in phlegmatics. The hypothalamus was shown to be the "dominant structure" in both sanguine and choleric animals, but, for the most part, its activity was correlated with different structures. Thus, conditions for interaction between the frontal cortex, hippocampus, amygdala and hypothalamus seem to be an important factor, which determines typological features of the higher nervous activity of dogs.

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Poststimulus spectral EEG changes and their correlation with evoked potential (EP) were analyzed. The non-stationary components of the brain evoked activity were revealed in 32 volunteers during simple motor reaction and choice reaction to visual stimuli. This nonstationary activity was manifested in poststimulus changes in the mean wave half-period duration (MWHPD) and mean wave half-period power of the delta- and beta-frequency oscillations computed in the EEG realizations after the EP subtraction. The latencies of high-frequency EP components fell into the intervals of the MWHPD decrease and increase in the power of beta-oscillations, and the latencies of low-frequency EP components coincided with the intervals of the MWHPD increase and decrease in the power of delta and beta-oscillations, which pointed to correlation of these changes with the EP.

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Studying successive topograms of potentials made it possible to reveal different types (subsystems) of the spatio-temporal organization of human and animal cortical electrical activity, which covered significant cortical surface. The dominance of the inversion of the sagittal potential gradient in the topograms of the resting state or complicated relief forms in the active states co-existed with oscillations of the mean level of topogram potentials, the contribution of which to the spatial EEG synchronization changed depending on the functional state of the brain. The role of the ratio between these subsystems was shown and the influence of this ratio was demonstrated on the spatial synchronization of cortical potentials in experiments with 11 rabbits (in the course of their adaptation to the environment and learning) and examination of 50 healthy adult subjects (during motor task performance and elaboration of verbal set). The spatial synchronization of cortical potentials was found to have a complex structure, which was determined by the ratio between the effects of subsystems of the spatio-temporal organization of cortical potentials.

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The EEG phenomenon was studied of high-frequency bursts (60-70 Hz, 70-80 mcV) in electrical activity of dog's neocortex (EA, 1-200 Hz) in the process of instrumental conditioning. These bursts of high-frequency oscillations appeared at the generalization state of the conditioned reflex during interstimulus intervals at the background of dominant EA of the lower frequency and voltage (10-40 mcV). Application of the developed by us novel strategy of the primary analysis of EA realizations (in particular, inhomogeneity coefficient) enabled estimation of the amplitude-frequency EA inhomogeneity, namely, high-frequency bursts. The regional peculiarities of the high-frequency bursts were revealed by means of the original technique based on the expansion of EA oscillation into a system of half-waves and construction of distribution maps on the basis of their parameters. The presented data verified our earlier findings obtained using other techniques (FFT analysis and factor analysis). These data testify to differential participation of cortical areas (even those which are close to each other within a distance of 3-5 mm) in the spatio-temporal organization of potentials characteristic for a given learning paradigm.

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