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PubMed2003

Epileptic seizures are preceded by a decrease in synchronization.

The exact mechanisms leading to the occurrence of epileptic seizures in humans are still poorly understood. It is widely accepted, however, that the process of seizure generation is closely associated with an abnormal synchronization of neurons. In order to investigate this process, we here measure phase synchronization between different regions of the brain using intracranial EEG recordings. Based on our preliminary finding of a preictal drop in synchronization, we investigate whether this phenomenon can be used as a sensitive and specific criterion to characterize a preseizure state and to distinguish this state from the interictal interval. Applying an automated technique for detecting decreased synchronization to EEG recordings from a group of 18 patients with focal epilepsy comprising a total of 117 h, we observe a characteristic decrease in synchronization prior to 26 out of 32 analyzed seizures at a very high specificity as tested on interictal recordings. The duration of this preictal state is found to range from several minutes up to a few hours. Investigation of the spatial distribution of preictal desynchronization indicates that the process of seizure generation in focal epilepsy is not necessarily confined to the focus itself but may instead involve more distant, even contralateral areas of the brain. Finally, we demonstrate an intrahemispheric asymmetry in the spatial dynamics of preictal desynchronization that is found in the majority of seizures and appears to be an immanent part of the mechanisms underlying the initiation of seizures in humans.

Adult↗
PubMed2002

Visualization of significant ERD/ERS patterns in multichannel EEG and ECoG data.

OBJECTIVES: Analysis of event-related desynchronization (ERD) and event-related synchronization (ERS) often requires the investigation of diverse frequency bands. Such analysis can be difficult, especially when using multichannel data. Therefore, an effective method for the visualization of event-related changes in oscillatory brain activity is required. METHODS: A bootstrap-based method is presented which gives time-frequency maps showing only significant changes of ERD or ERS in predetermined frequency bands. RESULTS: Examples from an electroencephalographic study and an electrocorticographic study are shown. The results demonstrate how easily reactive channels and their spatio-temporal and frequency-specific characteristics can be identified by means of this method. CONCLUSIONS: The proposed method is a simple but effective way to visualize significant ERD/ERS patterns.

Algorithms↗
PubMed2002

[Reflection of the emotion manifestation in effects of evoked EEG synchronization and desynchronization].

Event-related desynchronization (ERD) and synchronization (ERS) in response to neutral, positive and negative emotional IAPS stimuli were measured in narrow theta, alpha-1, alpha-2 and alpha-3 frequency bands in 22 healthy Ss. A high resolution 62-channel EEG was recorded while subjects viewed a sequence of pictures. The effects of valence discrimination related to hemispheric asymmetries are associated with increased theta and alpha-3 synchronization. Theta ERS revealed a significant valence by hemisphere interaction for anterior temporal leads in the time window of 100-700 ms after stimulus onset indicating a relatively greater right hemisphere ERS for negative and a left hemisphere ERS for positive stimuli in comparison to neutral those. In the alpha-3 band, negative stimuli induced a left hemisphere ERS increase (F7 site) in the time window of 800-1200 ms not observed for neutral and positive stimuli. The results obtained along with the earlier observations on EEG correlates of affective processing challenge the notion that effective anterior hemispheric asymmetries are reflected mainly in the wide alpha frequency band.

Adolescent↗
PubMedDate not supplied

[The effect of microwaves on the bioelectric brain activity].

The experiments on rats have shown that the effect of millimeter range electromagnetic radiation on the bioelectric brain activity is dependent on the initial functional state of central nervous system. Microwaves are able to cause a nonspecific electroencephalographic reaction of synchronization and probably the lower the bioelectric brain process dynamics of active rats. Enrichment of electrocorticograms with high-frequency rhythms and increase in degree of bioelectric brain dynamics can be observed in narcosis conditions. The appearance of biological resonance in the brain of narcotized rats preliminary injected aminazin by pulse-modulated microwaves is noted. This is expressed as epileptiform convulsive activity in electrocorticogram. It has been shown that the nonlinear dynamics method may provide a reliable characterization of changing bioelectric brain activity under of nonionized electromagnetic fields. It is possible to modulate the bioelectric brain activity by microwaves to change the functional state of central nervous system and probably of the whole organism.

Alpha Rhythm↗
PubMed2004

Spatial and temporal structure of phase synchronization of spontaneous alpha EEG activity.

Spatiotemporal characteristics of spontaneous alpha EEG activity patterns are analyzed in terms of large-scale phase synchronization. During periods with strong phase synchronization over the entire scalp, phase patterns take either of two forms; one is a gradual phase shift between frontal and occipital regions and the other is a stepwise pattern with a sudden phase shift in the central region. The former is regarded as a traveling wave of electrocortical activity, of which the direction of propagation is predominantly from anterior to posterior in three out of four subjects, and opposite in the remaining one. The other activity pattern observed may correspond to a standing wave composed of two traveling waves propagating in opposite directions. The duration distributions of these patterns have similar forms within a subject, which suggests that they share the same mechanism for their generation.

Adolescent↗
PubMed2003

Changing excitation and inhibition in simulated neural networks: effects on induced bursting behavior.

The development of synchronous bursting in neuronal ensembles represents an important change in network behavior. To determine the influences on development of such synchronous bursting behavior we study the dynamics of small networks of sparsely connected excitatory and inhibitory neurons using numerical simulations. The synchronized bursting activities in networks evoked by background spikes are investigated. Specifically, patterns of bursting activity are examined when the balance between excitation and inhibition on neuronal inputs is varied and the fraction of inhibitory neurons in the network is changed. For quantitative comparison of bursting activities in networks, measures of the degree of synchrony are used. We demonstrate how changes in the strength of excitation on inputs of neurons can be compensated by changes in the strength of inhibition without changing the degree of synchrony in the network. The effects of changing several network parameters on the network activity are analyzed and discussed. These changes may underlie the transition of network activity from normal to potentially pathologic (e.g., epileptic) states.

Action Potentials↗
PubMed1992

Measurement of interhemispheric time differences in generalised spike-and-wave.

We have compared interhemispheric time differences (ITD) calculated by coherence/phase and linear and non-linear correlation analyses of generalised spike-wave episodes in 30 patients (15 with primary generalised epilepsy (PGE), 5 with secondary generalised epilepsy (SGE) and 10 with a lateralised epileptogenic area). Most cases were recorded during routine departmental EEGs. No significant difference was found between measures of interhemispheric synchrony (IS) (proportion of ITDs that are synchronous) calculated using the linear and the non-linear correlation techniques, although the latter gave slightly more (average 7%) valid ITD estimates. This suggests that the non-linear correlation technique does not provide significantly more time difference information than its linear counterpart. Similarly, no significant differences in IS values were identified between the coherence/phase and the correlation techniques. For all 3 techniques, IS values greater than 50% were derived for most patients with PGE and SGE; the proportion of patients with a lateralised epileptogenic area showing this was smaller. However, broad overlap in the distribution of IS values between the 3 groups suggests that individual patients cannot reliably be distinguished using these methods.

Action Potentials↗
PubMed1992

Simultaneous EEG 10 Hz desynchronization and 40 Hz synchronization during finger movements.

Nineteen-channel EEG was recorded with closely spaced electrodes overlaying the left sensorimotor cortex during self-paced, voluntary right finger movements. Three right-handed people served as subjects. The EEG was analysed in the 10 Hz band (10-12 Hz) and in four 40 Hz bands (34-36, 36-38, 38-40, 40-42) by calculation of ERD time courses and ERD maps, whereby a ERD is characterized by a movement-related band power decrease. In all three subjects a close to C3 localized 10 Hz ERD was found, starting about 2 s prior to movement onset and continuing during movement. Along with this 10 Hz ERD a localized and short-lasting (about 0.5 s) burst of 40 Hz oscillations was embedded around movement onset. This can be interpreted as indicating that planning of movement is accompanied by a desynchronization of central mu rhythm and a generation of 40 Hz oscillations.

Brain Mapping↗
PubMed2002

Novel object presentation affects sleep-wake behavior in rats.

Sleep is suggested to be crucial for the processing and storage of new information. Several learning tasks have been shown to increase the amount of rapid eye movement sleep (REMS) with its typical theta activity (6-8 Hz) relative to total sleep time. Vice versa, REMS deprivation is able to affect memory consolidation following some, but not all learning tasks. Furthermore, recent studies have shown an increase of spindle activity (12-15 Hz) within the electroencephalogram (EEG) of nonREMS as well. The enhancement of both spindle and theta activity is suggested to serve as background activity for the synchronization of those neuronal pathways that were involved in the registration and, later on, participate in the long-term storage of new information in defined brain regions. In the present study, the presentation of a novel object to rats enhanced the amount of preREMS, an intermediate sleep stage with high spindle activity, within the first 2 h of the subsequent sleeping phase. Four hours later, the amount of REMS was increased as well. However, there were no changes in the EEG power spectra of nonREMS, preREMS and REMS. We therefore hypothesize that the increase of preREMS and REMS amounts and the related spindle and theta activity stand for the processing and storage of new information about the presented novel objects.

Action Potentials↗
PubMed1998

[Dependence of human EEG spatial synchronization on the geomagnetic activity on the day of experiment].

Spontaneous EEG was registered under different activity conditions in 26 volunteers. The EEG synchronisation parameters were compared with the geomagnetic and solar activity on the day of experiment. A positive correlation of the EEG data with the geomagnetic activity was revealed, being most obvious in the frontal and central areas. A negative correlation between some local EEG synchronisation parameters and different indices of the solar activity, was also revealed. The degree of synchronisation of the spontaneous EEG seems to reflect sensitivity of the human nervous system to the Earth's magnetic field. A stressor response to strong short-term disturbances in the geomagnetic field reveals itself in the form of enhancement of the EEG global synchronisation. A sedative effect of slow magnetic oscillations is locally revealed in the parameters of the EEG synchronisation within the left hemisphere as well as the interhemisphere synchronisation.

Adolescent↗
PubMedDate not supplied

Abnormal action-potential bursts and synchronized, GABA-mediated inhibitory potentials in an in vitro model of focal epilepsy.

Focal, freeze-induced lesions were made in isolated hemispheres of turtle cerebral cortex in vitro, permitting the investigation of epileptiform discharges in a preparation with preserved intracortical circuitry. Freeze lesions resulted in interictal discharges and occasional ictal-like events. The interictal discharges were dependent upon activation of non-NMDA excitatory amino acid receptors and were affected by but did not require NMDA receptor activation. Voltage clamp and current clamp recordings revealed abnormal bursts of low-amplitude action potentials in 36% of recorded neurons, while large, repetitive inhibitory potentials, mediated by GABAA receptors, were recorded in 90% of the neurons. Thus, prominent findings in this model include abnormalities of both excitatory and inhibitory activity. Since these changes in neuronal excitability resulted from a localized physical injury, they may resemble the changes that occur in acute posttraumatic epilepsy.

Action Potentials↗
PubMed2005

Phase synchronization measurements using electroencephalographic recordings: what can we really say about neuronal synchrony?

Phase synchrony analysis is a relatively new concept that is being increasingly used on neurophysiological data obtained through different methodologies. It is currently believed that phase synchrony is an important signature of information binding between distant sites of the brain, especially during cognitive tasks. Electroencephalographic (EEG) recordings are the most widely used recording technique for recording brain signals and assessing phase synchrony patterns. In this study, we address the suitability of phase synchrony analysis in EEG recordings. Using geometrical arguments and numerical examples, employing EEG and magnetoencephalographic data, we show that the presence of a common reference signal in the case of EEG recordings results in a distortion of the synchrony values observed, in that the amplitudes of the signals influence the synchrony measured, and in general destroys the intended physical interpretation of phase synchrony.

Action Potentials↗
PubMed2005

Genetic components of functional connectivity in the brain: the heritability of synchronization likelihood.

Cognitive functions require the integrated activity of multiple specialized, distributed brain areas. Such functional coupling depends on the existence of anatomical connections between the various brain areas as well as physiological processes whereby the activity in one area influences the activity in another area. Recently, the Synchronization Likelihood (SL) method was developed as a general method to study both linear and nonlinear aspects of coupling. In the present study the genetic architecture of the SL in different frequency bands was investigated. Using a large genetically informative sample of 569 subjects from 282 extended twin families we found that the SL is moderately to highly heritable (41-67%) especially in the alpha frequency (8-13 Hz) range. This index of functional connectivity of the brain has been associated with a number of pathological states of the brain. The significant heritability found here suggests that SL can be used to examine the genetic susceptibility to these conditions.

Alpha Rhythm↗
PubMed1992

Primary and secondary bilateral synchrony in epilepsy: differentiation by estimation of interhemispheric small time differences during short spike-wave activity.

Estimation of interhemispheric small time differences (TDs) during spike-wave bursts in the EEG by coherence and phase analysis is useful for differentiation between primary bilateral synchrony (PBS) and secondary bilateral synchrony (SBS) in epilepsy. Because the previous method via Fast Fourier Transform needed long bursts for reliable analysis, a method using a 2-dimensional autoregressive model was newly developed to enable estimation of TDs even in 1.2 sec bursts, and applied to 19 epileptic patients with apparently bilaterally synchronous spike-wave bursts. At the onsets of bursts, estimated maximal TDs were 5.8 msec or less and inconsistent in leading hemispheres in 10 patients with a clinical diagnosis of idiopathic, cryptogenic or symptomatic generalized epilepsy indicating PBS, while the maximal TDs were 9.3-41.5 msec and consistent in leading in 7 patients with clinically symptomatic partial epilepsy and also in two with idiopathic and symptomatic generalized epilepsy suggesting SBS. Among 8 patients with bursts which suggested SBS and long enough for evaluation of intra-burst TD variation, TDs tended to disappear in the middle to end parts of the bursts in 5 cases, but not in the other 3, suggesting 2 different pathophysiological mechanisms in SBS.

Action Potentials↗
PubMed2005

Sensory recoding via neural synchronization: integrating hue and luminance into chromatic brightness and saturation.

If neural spike trains carry information in the frequency and timing of the spikes, then neural interactions--such as oscillatory synchronization--that alter spike frequency and timing can alter the encoded information. Using coupled oscillator theory, we show that synchronization-based processing can be used to integrate sensory information, resulting in new second-order sensory percepts signaled by the compromise frequency of the coupled system. If the signals to be coupled are nonlinearly compressed, the coupled system behaves as if it signals the product or ratio of the uncoupled signals, e.g., chromatic brightness can be signaled by the compromise frequency of coupled neurons responding to hue and luminance, and chromatic saturation can be signaled by the coupled frequency of neurons responding to hue and brightness, with a power- (Stevens's) law scaling like that observed psychophysically. These emergent properties of coupled sensory systems are intriguing because multiplicative processing and power-law scaling are fundamental aspects of sensory processing.

Action Potentials↗
PubMed2001

Event-related synchronization and desynchronization during affective processing: emergence of valence-related time-dependent hemispheric asymmetries in theta and upper alpha band.

Event-related desynchronization (ERD) and synchronization (ERS) in the individually defined theta, alpha-1, alpha-2, and alpha-3 frequency bands were measured in 22 healthy subjects (Ss) in response to neutral (Neut), emotionally positive (Pos), and negative (Neg) IAPS stimuli. The 62-channel EEG, facial EMG and ECG were simultaneously recorded while subjects viewed sequentially presented pictures and subjectively rated them after each presentation. The obtained findings indicate that differences induced by pictures varying in emotional valence are associated mainly with increased theta and alpha-3 synchronization activity and anterior hemispheric asymmetries. In the anterior temporal leads theta ERS revealed a significant valence by hemisphere interaction showing relatively greater right hemisphere theta ERS for Neg and left hemisphere ERS for Pos stimuli in the time window of 100-700 ms post-stimulus, whereas in the alpha-3 band Neg stimuli induced lateralized time-dependent left hemisphere ERS increased in the time window of 800-1200 ms, were not observed for Neut and Pos stimuli. The obtained results along with earlier observations on EEG correlates of affective processing challenge the notion that affective anterior hemispheric asymmetries are mainly sensitive to wide alpha frequency band. Frequency and time dependence of anterior hemispheric asymmetries in emotional valence discrimination is emphasized.

Adult↗
PubMed2006

Simultaneous rate-synchrony codes in populations of spiking neurons.

Firing rates and synchronous firing are often simultaneously relevant signals, and they independently or cooperatively represent external sensory inputs, cognitive events, and environmental situations such as body position. However, how rates and synchrony comodulate and which aspects of inputs are effectively encoded, particularly in the presence of dynamical inputs, are unanswered questions. We examine theoretically how mixed information in dynamic mean input and noise input is represented by dynamic population firing rates and synchrony. In a subthreshold regime, amplitudes of spatially uncorrelated noise are encoded up to a fairly high input frequency, but this requires both rate and synchrony output channels. In a suprathreshold regime, means and common noise amplitudes can be simultaneously and separately encoded by rates and synchrony, respectively, but the input frequency for which this is possible has a lower limit.

Action Potentials↗
PubMed2006

Oscillatory neuronal dynamics during language comprehension.

Language comprehension involves two basic operations: the retrieval of lexical information (such as phonologic, syntactic, and semantic information) from long-term memory, and the unification of this information into a coherent representation of the overall utterance. Neuroimaging studies using hemodynamic measures such as PET and fMRI have provided detailed information on which areas of the brain are involved in these language-related memory and unification operations. However, much less is known about the dynamics of the brain's language network. This chapter presents a literature review of the oscillatory neuronal dynamics of EEG and MEG data that can be observed during language comprehension tasks. From a detailed review of this (rapidly growing) literature the following picture emerges: memory retrieval operations are mostly accompanied by increased neuronal synchronization in the theta frequency range (4-7 Hz). Unification operations, in contrast, induce high-frequency neuronal synchronization in the beta (12-30 Hz) and gamma (above 30 Hz) frequency bands. A desynchronization in the (upper) alpha frequency band is found for those studies that use secondary tasks, and seems to correspond with attentional processes, and with the behavioral consequences of the language comprehension process. We conclude that it is possible to capture the dynamics of the brain's language network by a careful analysis of the event-related changes in power and coherence of EEG and MEG data in a wide range of frequencies, in combination with subtle experimental manipulations in a range of language comprehension tasks. It appears then that neuronal synchrony is a mechanism by which the brain integrates the different types of information about language (such as phonological, orthographic, semantic, and syntactic information) represented in different brain areas.

Brain↗