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PubMed2004

Relationship between resting alpha activity and the ERPs obtained during a highly demanding selective attention task.

In spite of previous reports on the relationship between ongoing EEG and ERPs, there remains a lack of agreement on the nature of their nexuses. The aim of the present study was to evaluate the relationship between resting EEG and the ERP components in two groups of healthy subjects with different levels of performance in a highly demanding selective visual attention task. Young adults were classified according to the amount of their correct responses in the task, into high (HP; averaged hits (AH): 86%) and low performance groups (LP; AH: 59%). EEG was recorded during rest, prior to task performance and absolute (AP) and relative power (RP), as well as inter- (rTER) and intrahemispheric (rTRA) correlation were calculated. ERPs during task performance were also obtained and their amplitude and latency measures were assessed. Results showed that individuals with better behavioral performance had a higher synchronization between both hemispheres during rest as well as higher amplitude and shorter latencies of N2 and P3. Principal Component Analysis revealed that alpha2 AP and RP were inversely related to P2 and N2 latency. Higher values of alpha1 and alpha2 rTER were clustered with higher P3 amplitude and shorter reaction time. In conclusion, the differences in the cortical organization of HP and LP at rest (EEG) seem to be associated to the way the brain reacts during information processing (ERPs).

Adult↗
PubMed1982

[Paroxysmal EEG disorders in various forms of schizophrenia among children and adolescents].

A comparative study of the frequency of EEG paroxysmal disturbances in healthy and schizophrenic children and adolescents was carried out. The study has enabled the authors to reveal a greater occurrence of bilateral outbreaks of relatively high-amplitude slow waves in the picture of the cortical rhythms in patients with paroxysmal schizophrenia, as well as in a group of patients with psychopathy-like disorder taking the form of persistent pathological cravings. The intensification of the paroxysmal outbreaks on the EEGs of the patients with paroxysmal schizophrenia can be regarded as an indication of incidental rises of the excitability of the brain systems synchronizing the cortical rhythms, these rises creating conditions favouring the transition from one functional state of the patients to another. On the other hand, marked paroxysmal outbreaks in patients suffering from continuous schizophrenia with prevalence of psychopathic heboid-type disorders in the clinical picture can be associated with pronounced signs of retardation and distortion of the age regularities of the development.

Adolescent↗
PubMed2004

Scale-free dynamics of global functional connectivity in the human brain.

Higher brain functions depend upon the rapid creation and dissolution of ever changing synchronous cell assemblies. We examine the hypothesis that the dynamics of this process displays scale-free, self-similar properties. EEGs (19 channels, average reference, sample frequency 500 Hz) of 15 healthy subjects (10 men; mean age 22.5 years) were analyzed during eyes-closed and eyes-open no-task conditions. Mean level of synchronization as a function of time was estimated with the synchronization likelihood for five frequency bands (0.5-4, 4-8, 8-13, 13-30, and 30-48 Hz). Scaling in these time series was investigated with detrended fluctuation analysis (DFA). DFA analysis of global synchronization time series showed scale-free characteristics, suggesting neuronal dynamics do not necessarily have a characteristic time constant. The scaling exponent as determined with DFA differed significantly for different frequency bands and conditions. The exponent was close to 1.5 for low frequencies (delta, theta, and alpha) and close to 1 for beta and gamma bands. Eye opening decreased the exponent, in particular in alpha and beta bands. Fluctuations of EEG synchronization in delta, theta, alpha, beta, and gamma bands exhibit scale-free dynamics in eyes-closed as well as eyes-open no-task states. The decrease in the scaling exponent following eye opening reflects a relative preponderance of rapid fluctuations with respect to slow changes in the mean synchronization level. The existence of scaling suggests that the underlying dynamics may display self-organized criticality, possibly representing a near-optimal state for information processing.

Adolescent↗
PubMed2005

Synaptic transmission and synchronous activity is disrupted in hippocampal slices taken from aged TAS10 mice.

Synaptic transmission was studied in hippocampal slices from aged (12-14 months of age) TAS10 mice overexpressing the human form of the amyloid precursor protein harboring the Swedish mutation. A significant deficit in the input-output relationship of glutamatergic synapses in the CA3-CA1 Schaffer collateral pathway was observed, while synaptic transmission in the medial perforant pathway of the dentate gyrus was comparatively preserved. Despite this deficit, relative levels of short- and long-term synaptic plasticity in the CA1 region were similar to those observed in wildtype slices. Specifically, paired pulse facilitation, frequency facilitation (at frequencies of 1, 5, and 10 Hz), and long-term potentiation induced by a theta burst stimulation paradigm were all normal in the CA3-CA1 synapses of TAS10 hippocampal slices. However, synchronized network activity induced by bath application of 4-aminopyridine (4-AP) was compromised. Thus, the frequency of synchronous events induced by 100 microM 4-AP was significantly lower in TAS10 hippocampal slices (inter-event interval: WT, 2.4+/-0.6 s; TAS10, 6.9+/-1.7 s). To study gamma-aminobutyric acid (GABA)ergic synaptic transmission NBQX (20 microM) and D-AP5 (50 microM) were added in order to isolate bicuculline-sensitive GABA-mediated synchronous network activity. The GABAergic network activity was not significantly different from wildtype in terms of frequency. This study suggests that the deficit in glutamatergic synaptic transmission observed in the TAS10 hippocampal slices, may be coupled with alterations in synchronous network activity, which in turn would lead to deficient information processing.

4-Aminopyridine↗
PubMed2004

EEG synchronization likelihood in mild cognitive impairment and Alzheimer's disease during a working memory task.

OBJECTIVE: Synchronization likelihood analysis of resting state EEG has shown that cognitive dysfunction in Alzheimer's disease (AD) and its precursor mild cognitive impairment (MCI) are associated with a loss of functional connectivity in high (upper alpha and beta) frequency bands. Working memory tasks are known to change functional connectivity, but it is unknown whether this increases the differences between AD, MCI and healthy controls. Our objective was to investigate the behavior of synchronization likelihood of multichannel EEG in AD, MCI and cognitively healthy controls, both at rest and during a working memory task. METHODS: EEGs (200 Hz sample frequency, 21 channels, average reference) were recorded at rest as well as during a visual working memory task in 14 patients with AD according to the NINCDS-ADRDA criteria (mean age 76.4; SD 13.6), 11 patients with MCI according to the criteria of Petersen (mean age 78.4; SD 6.4) and 14 with subjective memory complaints but no demonstrable memory disturbance (mean age 61.6; SD 26.6). The synchronization likelihood was computed over 19 channels, comparing each channel with all the other channels for the 0.5-4, 4-8, 8-10, 10-12, 12-30, 30-50 Hz frequency bands. RESULTS: The synchronization likelihood was significantly decreased in the upper alpha (10-12) and beta (12-30) bands in AD compared to persons with subjective memory complaints. The working memory task scores strongly correlated with Mini-Mental State Examination scores. During the working memory task the synchronization likelihood was significantly higher in MCI compared to the control subjects in the lower alpha band (8-10 Hz). CONCLUSIONS: Decrease of beta band synchronization occurs in mild AD, both in a resting condition and during a working memory task. SIGNIFICANCE: Decrease of beta band synchronization in mild AD is a robust finding. The present study confirms our findings in a different cohort of patients, using alternative frequency bands. The diagnostic value of the synchronization likelihood in AD and MCI needs to be further established.

Aged↗
PubMed2005

Brain electrical activity changes in treatment refractory schizophrenics after olanzapine treatment.

The aim of the present study was to identify brain electrical activity changes generated by olanzapine (OLZ) in treatment refractory schizophrenics (TRS). 14 paranoid TRS (31.5+/-8.39 years old) were evaluated before and after 8 weeks of OLZ treatment. Psychopathology was evaluated by means of total BPRS and PANSS scores. Resting EEG was recorded in the pre (under typical neuroleptics) and post (under OLZ) sessions. A good response to OLZ was observed in 57% of TRS. A significant reduction in positive and negative symptoms scales of PANSS was found. Absolute power of theta1, theta2, alpha1 bands increased after treatment, while beta2 power showed a decrease. Intrahemispheric correlation increased between different zones of the frontal areas and between frontal and posterior areas, while interhemispheric correlation decreased in theta2. EEG changes were more evident in those patients who had a better response to OLZ. OLZ showed to be effective in TRS, improving psychiatric symptoms and increasing activity synchronization between different areas within each hemisphere that may indicate a functional reorganization, particularly in good responders.

Adolescent↗
PubMed2000

Propagation of synchronous burst discharges from entorhinal cortex to morphologically and electrophysiologically identified neurons of rat lateral amygdala.

Intracellular and field potential recordings were taken from the lateral nucleus of the amygdala in a rat horizontal brain slice preparation that included hippocampal formation. Pyramidal cells comprised the majority of labeled cells (77%). Electrophysiological classification based on hyperpolarizing or depolarizing afterpotentials subdivided both the pyramidal and non-pyramidal cell classes, although pyramidal cells tended to have hyperpolarizing afterpotentials (70%) and non-pyramidal cells tended to have depolarizing afterpotentials (63%). Synchronous population bursts were triggered with single extracellular stimuli in the deep layers of entorhinal cortex. These events propagated from deep layers of entorhinal cortex into the lateral nucleus of the amygdala. Latencies were consistent with a direct entorhinal to amygdala projection. Individual lateral nucleus neurons exhibited responses ranging from a long burst response that included an initial period of 200 Hz firing and a tail of gamma frequency firing lasting over 100 ms (grade 1) to an epsp with no firing (grade 4). Half of pyramidal cells responding to events initiated in entorhinal cortex were found to receive epsps strong enough to trigger firing. Only one stellate neuron fired in response to entorhinal stimulation. Excitatory postsynaptic responses included NMDA and non-NMDA receptor mediated components. We demonstrate that synchronous population events can propagate from entorhinal cortex to the lateral nucleus of the amygdala and that pyramidal neurons of the lateral nucleus are more common targets than stellate neurons. We conclude that other synchronous events such as sharp waves and interictal spikes can spread from entorhinal cortex to amygdala in the same manner.

6-Cyano-7-nitroquinoxaline-2,3-dione↗
PubMed2004

Neural synchronization deficits to auditory stimulation in bipolar disorder.

Patients with bipolar disorder show cognitive deficits and disorganized behavior, which may reflect a disturbance in neural synchronization. We tested whether EEG measures of auditory neural synchronization were abnormal in bipolar disorder. Nineteen symptomatic patients with bipolar disorder and 32 non-psychiatric control subjects were evaluated. Click trains (500 ms duration) presented at 20, 30, 40 and 50 Hz were used to evoke EEG synchronization. Patients with bipolar disorder showed reduced power across the frequencies of stimulation. Phase-locking across trials was also disturbed in bipolar disorder, consistent with poor phase synchronization between the stimulus and EEG. Abnormal high frequency neural synchronization may contribute to cognitive deficits in bipolar disorder.

Acoustic Stimulation↗
PubMed1995

Dentate EEG spikes and associated interneuronal population bursts in the hippocampal hilar region of the rat.

1. This paper describes two novel population patterns in the dentate gyrus of the awake rat, termed type 1 and type 2 dentate spikes (DS1, DS2). Their cellular generation and spatial distribution were examined by simultaneous recording of field potentials and unit activity using multiple-site silicon probes and wire electrode arrays. 2. Dentate spikes were large amplitude (2-4 mV), short duration (< 30 ms) field potentials that occurred sparsely during behavioral immobility and slow-wave sleep. Current-source density analysis revealed large sinks in the outer (DS1) and middle (DS2) thirds of the dentate molecular layer, respectively. DS1 and DS2 had similar longitudinal, lateral, and interhemispheric synchrony. 3. Dentate spikes invariably were coupled to synchronous population bursts of putative hilar interneurons. CA3 pyramidal cells, on the other hand were suppressed during dentate spikes. 4. After bilateral removal of the entorhinal cortex, dentate spikes disappeared, whereas sharp wave-associated bursts, reflecting synchronous discharge of the CA3-CA1 network, increased several fold. 5. These physiological characteristics of the dentate spikes suggest that they are triggered by a population burst of layer II stellate cells of the lateral (DS1) and medial (DS2) entorhinal cortex. 6. We suggest that dentate spike-associated synchronized bursts of hilar-region interneurons provide a suppressive effect on the excitability of the CA3-CA1 network in the intact brain.

Animals↗
PubMed2005

[Psychophysiologic and clinical aspects of EEG synchronization related to cognitive processes].

The authors review the various forms of EEG-synchronization with special emphasis on the characteristics of the induced and enhanced rhythms. The suggested role of the various EEG frequency bands in the cognitive processes is demonstrated by examples from the literature. The relationship between linear and nonlinear electrophysiological complexity and EEG synchronization is analyzed, with a touch on the use of Omega-complexity and synchronization likelihood methods. In the present study the EEG recorded during adding and subtracting tasks was analyzed with the above methods. It was found that during the adding task the theta band increased in the frontal area, which may be related to activation of working memory processes. Mapping the scalp-distribution of synchronization likelihood also confirmed increased synchronization in the frontal area in addition to which increased values were found in the left temporo-parietal area. The analysis of linear and nonlinear EEG synchronization associated with cognitive processing is suitable to explore the task-related and region specific features of these events.

Alpha Rhythm↗
PubMedDate not supplied

[Spatio-temporal organization of ECoG spindles during sleep onset].

Spatio-temporal organization of spindle activity in the cerebral cortex during deepening of slow-wave sleep (SWS) was studied in experiments on cats and rabbits. Patterns of both "sleep" and recruiting reaction spindles were analyzed. In the process of sleep development spindle activity was transformed from local to a diffuse one, organized in a sort of packages. The rate of synchroneity in spindle packages depended on the sleep depth. At the deepest SWS stages a sharp desynchronization of spindles in the packages was observed and then--complete disappearance of spindle activity. Interaction of thalamic spindle pacemakers seems to play an important role in the mechanism of SWS development; changes in it result in reorganization of spindle activity on the cortical surface. A considerable part in this interaction is reserved to the processes of emergence and spread of delta-activity.

Animals↗
PubMed2005

Purkinje cell rhythmicity and synchronicity during modulation of fast cerebellar oscillation.

Fast (approximately 160 Hz) cerebellar oscillation has been recently described in different models of ataxic mice, such as mice lacking calcium-binding proteins and in a mouse model of Angelman syndrome. Among them, calretinin-calbindin double knockout mice constitute the best model for evaluating fast oscillations in vivo. The cerebellum of these mice may present long-lasting episodes of very strong and stable local field potential oscillation alternating with the normal non-oscillating state. Spontaneous firing of the Purkinje cells in wild type and double knockout mice largely differs. Indeed, the Purkinje cell firing of the oscillating mutant is characterized by an increased rate and rhythmicity and by the emergence of synchronicity along the parallel fiber axis. To better understand the driving role played by these different parameters on fast cerebellar oscillation, we simultaneously recorded Purkinje cells and local field potential during the induction of general anesthesia by ketamine or pentobarbitone. Both drugs significantly increased Purkinje cell rhythmicity in the absence of oscillation, but they did not lead to Purkinje cell synchronization or to the emergence of fast oscillation. During fast oscillation episodes, ketamine abolished Purkinje cell synchronicity and inhibited fast oscillation. In contrast, pentobarbitone facilitated fast oscillation, induced and increased Purkinje cell synchronicity. We propose that fast cerebellar oscillation is due to the synchronous rhythmic firing of Purkinje cell populations and is facilitated by positive feedback whereby the oscillating field further phase-locks recruited Purkinje cells onto the same rhythmic firing pattern.

Anesthetics, Dissociative↗
PubMed2001

Musicians and the gamma band: a secret affair?

While listening to music, a significant high degree of phase synchrony in the gamma frequency range globally distributed over the brain was found in subjects with musical training (musicians) compared with subjects with no such training (non-musicians). No significant differences were found in other EEG frequency bands. Listening to neutral text did not produce any significant differences in the degree of synchronization between these two groups. For musicians, left-hemispheric dominance was found during listening to music. The right hemisphere was found to be dominant for non-musicians in text listening. The high degree of synchronization in musicians could be due to their high ability to retrieve musical patterns from their acoustic memory, which is a cogent condition for both listening to and anticipating musical sounds.

Adult↗
PubMed1984

[An electroencephalographical study on timiperone, a new antipsychotic drug].

This investigation was undertaken to analyze the EEG synchronizing effects of timiperone in cats. The effects of timiperone on the brain-stem reticular and hypothalamic activating system, diffuse and specific thalamic projection system, and caudate spindle were investigated by the electroencephalographic method. Timiperone produced a weak inhibition of EEG arousal response induced by electrical stimulation of the sciatic nerve almost without affecting that which was induced by stimulation of the mesencephalic reticular formation. Furthermore, timiperone suppressed the activation of neocortical EEG in response to stimulation of the posterior hypothalamus more selectively than that of limbic EEG. Neither the recruiting response to stimulation of the centro-median nucleus of the thalamus nor the augmenting response to stimulation of the ventro-postero-lateral nucleus of the thalamus was modified by timiperone. In addition, timiperone significantly potentiated the caudate spindle. The EEG effects of haloperidol were qualitatively similar to those of timiperone. These results indicate that the synchronizing effect of timiperone may be mediated by a suppression of an ascending reticular activating system and may influence the conscious levels and sleep-wakefulness cycle in cats.

Animals↗
PubMedDate not supplied

[Rol' of the frontal lobe in synchronizing biopotentials in different regions of the dog brain].

The role of the frontal cortex in formation of neocortical systemic processes has been studied by the method of sign correlation of the summate electrical activity. A distant EEG synchronization in the temporal and occipital zones sets in following strychninization of F2 zones (but not of Prc2 zones) in anaesthetized dogs or in cerveau isolé preparations. In dogs with elaborated conditioned reflexes a statistically significant distant synchronization of the neocortical EEG sets in during the delay period only in case of well expressed motivation (of hunger in case of food reinforcement, and of thirst in case of water reinforcement). No distant conditioned EEG synchronization was revealed in lobectomised dogs. The role of the frontal cortex in the intracerebral integration is discussed which is necessary for achievement of the forthcoming signal activity.

Animals↗
PubMed2005

Multivariate linear discrimination of seizures.

OBJECTIVE: To discriminate seizures from interictal dynamics based on multivariate synchrony measures, and to identify dynamics of a pre-seizure state. METHODS: A linear discriminator was constructed from two different measures of synchronization: cross-correlation and phase synchronization. We applied this discriminator to a sequence of seizures recorded from the intracranial EEG of a patient monitored over 6 days. RESULTS: Surprisingly, we found that this bivariate measure of synchronization was not a reliable seizure discriminator for 7 of 9 seizures. Furthermore, the method did not appear to reliably detect a pre-seizure state. An association between anti-convulsant dosage, frequency of clinical seizures, and discriminator performance was noted. CONCLUSIONS: Using a bivariate measure of synchronization failed to reliably differentiate seizures from non-seizure periods in these data, nor did such methods show reliable detection of a synchronous pre-seizure state. The non-stationary variables of decreasing antiepileptic medication (without available serum concentration measurements), and concomitant increasing seizure frequency contributed to the difficulties in validating a seizure prediction tool on such data. SIGNIFICANCE: The finding that these seizures were not a simple reflection of increasing synchronization in the EEG has important implications. The non-stationary characteristics of human post-implantation intracranial EEG is an inherent limitation of pre-resection data sets.

Anticonvulsants↗
PubMed2006

Neuronal activity in globus pallidus interna can be synchronized to local field potential activity over 3-12 Hz in patients with dystonia.

Pallidal recordings of local field potentials (LFPs) in patients with dystonia have demonstrated semi-oscillatory activity over 3-12 Hz. Although this activity has been hypothesized to contribute to dystonia, it is unclear to what extent these LFP oscillations arise in the globus pallidus interna (GPi) and are synchronous with local neuronal discharge. We therefore recorded LFPs and neuronal activity from microelectrodes inserted into the pallidum on nine sides in six awake patients with primary dystonia during functional neurosurgery. Mean normalized LFP power over 3-12 Hz was higher in GPi than globus pallidus externa. Spike triggered averages were computed, and 11 exhibited significant features in the 3-12 Hz band, indicating that the discharges of local neurons were locked to 3-12 Hz oscillations in the LFP. All but two of these STAs were in GPi. We conclude that pallidal oscillations at 3-12 Hz are maximal in GPi, the surgical target, in patients with dystonia and that they can be synchronized to activity in local neurons. This lends support to a pathophysiological relationship between LFP activity at 3-12 Hz and dystonia.

Adult↗