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PubMed2001

Synchronous oscillatory activity in immature cortical network is driven by GABAergic preplate neurons.

Neurons dissociated from embryonic cerebral rat cortex form a differentiated network of synaptic connections and develop synchronous oscillatory network activity with the beginning of the second week in culture. During an initial phase lasting 3-4 d, synchronous calcium transients can be blocked completely by either CNQX or bicuculline, showing that both glutamatergic and GABAergic neurons are required for the generation of this form of activity. By manipulating dissociation and growth conditions, cultures containing different populations of GABAergic neurons were obtained. These cultures revealed that a distinct population of large GABAergic neurons is a key element in the generation of synchronous oscillatory network activity. A minimal number of two large GABAergic neurons per square millimeter are required for the occurrence of synchronous activity. Changes in the density of all other types of GABAergic or non-GABAergic neurons has no influence on the synchronous activity. Electron microscopic analysis shows that the large GABAergic neurons form an interconnected network. Exceptionally high somatodendritic innervation and extended axonal arborization enable these neurons to collect electric network activity and to distribute it effectively throughout the neuronal network. Additional experiments indicated that most neurons developing in culture to large GABAergic neurons are derived from the primordial plexiform layer and reside in the subplate at the time of birth. We suggest that they function as an integrating element that synchronizes neuronal activity during early cortical development by collecting incoming extrinsic and intrinsic signals and distributing them effectively throughout the developing cortical plate.

Animals↗
PubMedDate not supplied

[The subsystems of the spatial-temporal organization of cortical potentials and their role in EEG spatial synchronization].

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.

Adolescent↗
PubMed2002

EEG theta synchronization conjoined with alpha desynchronization indicate intentional encoding.

The involvement of different oscillating neuronal systems activated during intentional learning was investigated by measuring ongoing EEG activity. In 17 subjects, the EEG was recorded while learning pairs of words and faces. Subjective task difficulty was rated and a control condition of mental relaxation was also run. Spontaneous EEG activity during epochs which subsequently resulted in efficient encoding was associated with upper alpha desynchronization (10-12 Hz) and theta synchronization (4-8 Hz) when compared with spontaneous EEG activity during epochs of poor recall performance. The combined measure of theta synchronization plus upper alpha desynchronization was enhanced selectively over left frontotemporal cortical regions during efficient learning of words and over right parietal cortical regions during efficient learning of faces (P < 0.001). This striking topographical dissociation between learning materials for the combined measure of theta and upper alpha EEG activity suggests that the mode of intentional learning relies essentially on an interdependent regulation of two neuronal circuits: the thalamo-cortical circuit and the hippocampo-cortical circuit.

Action Potentials↗
PubMed2006

A comparison of stimulus synchronous activity in the primary motor cortices of athletes and non-athletes.

In this study, we measured primary motor cortex (MI) activity during a reaction time task to examine the appearance of MI activity that synchronized with the stimulus presentation (stimulus synchronous MI activity, SSMA). Because brain activity was expected to be enhanced by the repetitive/extensive activation, we hypothesized that the SSMA would be more clearly observable in athletes who were trained to perform reactive movements than in non-athletes. MI activity was measured in ten athletes and ten non-athletes by magnetoencephalography. The tasks were a simple reaction task and a Go/Nogo reaction task in which the subjects were asked to abduct their right index fingers in response to a visual stimulus. The Go/Nogo reaction time task was adopted to confirm the presence of the SSMA, because the MI activity in response to a Nogo stimulus did not overlap with the MI activity that was synchronous with the execution of the movement. The results show that the SSMA was clearly apparent in the athlete group (9/10). In the non-athlete group, however, only three subjects showed the SSMA (3/10). Moreover, the MI activity of the athletes tended to be larger than that of the non-athletes, even though the athletes did not specifically practice these index finger movements during their daily training. We concluded that long-term physical training promotes MI activity and the effects of reactive task repetition were more clearly apparent in the MI activity of the athletes.

Adult↗
PubMed2004

Spike synchronization in the cortex/basal-ganglia networks of Parkinsonian primates reflects global dynamics of the local field potentials.

Cortical local field potentials (LFPs) reflect synaptic potentials and accordingly correlate with neuronal discharge. Because LFPs are coherent across substantial cortical areas, we hypothesized that cortical spike correlations could be predicted from them. Because LFPs recorded in the basal ganglia (BG) are also correlated with neuronal discharge and are clinically accessible in Parkinson's disease patients, we were interested in testing this hypothesis in the BG, as well. We recorded LFPs and unit discharge from multiple electrodes, which were placed in primary motor cortex or in the basal ganglia (striatum and pallidum) of two monkeys before and after rendering them parkinsonian with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine. We used the method of partial spectra to construct LFP predictors of the spike cross-correlation functions (CCFs). The predicted CCF is an estimate of the correlation between two neurons under the assumption that their association is explained solely by the association of each with the LFP recorded on a third electrode. In the normal condition, the predictors account for cortical rate covariations but not for the association among the tonically active neurons of the striatum. In the parkinsonian condition, with the appearance of 10 Hz oscillations throughout the cortex-basal ganglia networks, the LFP predictors account remarkably better for the CCFs in both the cortex and the basal ganglia. We propose that, in the parkinsonian condition, the cortex-basal ganglia networks are more tightly related to global modes of brain dynamics that are echoed in the LFP.

Action Potentials↗
PubMed1996

Post-movement synchronization of beta rhythms in the EEG over the cortical foot area in man.

Post-movement synchronization of the electroencephalogram (EEG) was studied in nine right-handed subjects who performed voluntary self-paced dorsal flexions with the right and left foot. The findings revealed that foot movement results in enhanced beta oscillations after movement. These beta bursts showed subject-specific resonance frequencies in the range between 12 and 32 Hz and were localized to electrode Cz and to one electrode 2.5 cm more anterior. Comparison of left and right foot movement revealed a larger post-movement beta synchronization (PMBS) with left foot movement, but no differences concerning the topographical distribution of the PMBS.

Adult↗
PubMed1998

Modification of parallel activity elicited by propagating bursts in developing networks of rat cortical neurones.

Networks of cultured cortical neurones exhibit regular, synchronized, propagating bursts which are synaptically mediated, and which are hypothesized to play a part in activity-dependent formation of connections during development in vivo. The relationship between the strength of synaptic connections and the characteristics of synchronized propagating bursting, however, is unclear. Modification of synchronized activity in cortical cultures in response to electrical stimulation was examined using multisite electrode array recording. By measuring the response of the network to weak, localized, test stimulation (TS), we observed a potentiation of activity following a relatively stronger inducing stimulation (IS). This potentiation was evident as an increased probability of eliciting bursts by TS, an increased frequency of spontaneous bursts and number of spikes per burst, and increased speed of burst propagation, and it lasted for at least 20 min. Changing the parameters of IS revealed that high frequency tetanic stimulation is not necessary to induce potentiation, while it is essential for IS to produce a regeneratively propagating burst. The results provide a direct demonstration of modification of both the spatial and temporal characteristics of synchronized network activity, and suggest an important physiological role for propagating synchronized bursting, as a mechanism for inducing plastic modifications in the developing cortex.

Animals↗
PubMed2003

A model of desynchronizing deep brain stimulation with a demand-controlled coordinated reset of neural subpopulations.

The coordinated reset of neural subpopulations is introduced as an effectively desynchronizing stimulation technique. For this, short sequences of high-frequency pulse trains are administered at different sites in a coordinated way. Desynchronization is easily maintained by performing a coordinated reset with demand-controlled timing or by periodically administering resetting high-frequency pulse trains of demand-controlled length. Unlike previously developed methods, this novel approach is robust against variations of model parameters and does not require time-consuming calibration. The novel technique is suggested to be used for demand-controlled deep brain stimulation in patients suffering from Parkinson's disease or essential tremor. It might even be applicable to diseases with intermittently emerging synchronized neural oscillations like epilepsy.

Cortical Synchronization↗
PubMed1999

Coherent cortical and muscle discharge in cortical myoclonus.

There is increasing evidence in man that the cortical drive to motor neurons is rhythmic. This oscillatory drive may be exaggerated in patients with cortical myoclonus. Spectral analysis of surface bipolar EEG and EMG activity was performed in eight such patients. Only three cases had evidence of giant cortical evoked potentials or a cortical correlate on back-averaging at the time of study. In six subjects, significant coherence between contralateral and vertex EEG and EMG was observed in ranges similar to that previously reported for normal subjects (15-30 and 30-60 Hz). Three out of these six subjects also had significant coherence at higher frequencies (up to 175 Hz). All eight patients had a correlate in the cumulant density estimate between EEG and contralateral EMG. EMG lagged EEG by about 14, 25 and 35 ms for the muscles of the forearm, hand and foot, respectively. These delays were estimated from the slope of the phase curves and the timing of the peaks in the cumulant density estimates, and are appropriate for conduction in fast pyramidal pathways. The results provide clear evidence of a cortical drive synchronizing muscle discharge over a broad range of frequencies in patients with cortical myoclonus. Fourier analysis is a promising technique in the diagnosis and investigation of such patients.

Adolescent↗
PubMed2002

Movement-related changes in synchronization in the human basal ganglia.

There is a wealth of data suggesting that behavioural events are reflected in the basal ganglia through phasic changes in the discharge of individual neurones. Here we investigate whether events are also reflected in momentary changes in the degree of synchronization between neuronal elements. We simultaneously recorded local potentials (LPs) from the subthalamic nucleus (STN) and/or ipsilateral globus pallidus interna (GPi) or scalp EEG during voluntary movements of a hand-held joystick in six awake patients following neurosurgery for Parkinson's disease. Without medication the power within the STN and the coherence between the STN and the GPi were dominated by activity with a frequency of <30 Hz. This coupling was attenuated by movement. In the presence of exogenous dopaminergic stimulation, power within the STN and coherence between the STN and the GPi was dominated by activity at 70-85 Hz, which increased with movement. The movement-related changes in coherence between the STN and EEG showed a similar pattern of pharmacological dependence, as seen subcortically. Movement-related frequency-specific changes in synchronization occur in the basal ganglia and extend to involve subcortico-cortical motor loops. The dynamic organization of activities in the frequency domain might provide a means for temporal co-ordination within and across different processing streams in the basal ganglia. This organization is critically dependent on the level of dopaminergic activity.

Adult↗
PubMed1994

Brain wave synchronizers: Part 1--Review of the literature and the first dental anxiety study.

Using specific frequencies, photostimulation was developed into units known as brain wave synchronizers. Medical literature has shown the results of brain wave synchronizer use in obstetrics during labor and delivery, as an aid in anesthesiology, and for hypertension control. Dental studies have been conducted using brain wave synchronizers to relax patients during anxiety-inducing endodontic treatment. The first part of this article will review the medical and dental literature on brain wave synchronizers and the first brain wave synchronizer study on dental patients.

Cortical Synchronization↗
PubMed1996

Synchronization of fast (30-40 Hz) spontaneous cortical rhythms during brain activation.

We investigated the synchronization of fast spontaneous oscillations (mainly 30-40 Hz) in anesthetized and behaving cats by means of simultaneous extra- and intracellular recordings from multiple neocortical areas. Fast Fourier transforms, auto- and cross-correlations, and spike- or wave-triggered averages were used to determine the frequency and temporal coherence of fast oscillations that outlasted the stimulation of ascending activating systems or that occurred naturally during behavioral states of waking and rapid eye movement (REM) sleep but also appeared during the depolarizing phases of slow sleep oscillations. In 90% of microelectrode tracks, the fast oscillations did not show field reversal at any depth of the cortex and were not observable in the underlying white matter. The negative field potentials of the fast oscillations were associated at all depths with neuronal firing. This field potential property of fast oscillations was in sharp contrast to the reversal of slow sleep oscillation or evoked potentials at depths of 0.25-0.5 mm. The coherence of fast spontaneous rhythms was spatially limited, being confined within a cortical column and among closely located neocortical sites, in contrast to the long-range synchronization of slow sleep rhythms. Depolarizing current pulses elicited spike-bursts (200-400 Hz) recurring at a frequency of 30-40 Hz. Our experiments demonstrate that the conventional notion of a totally desynchronized cortical activity upon arousal should be revised as fast rhythms are enhanced and synchronized within intracortical networks during brain activation. Spontaneously occurring, subthreshold membrane potential depolarizing oscillations may bias cortical and thalamic neurons to respond synchronously, at fast frequencies, to relevant stimuli in the wake state or to internally generated drives in REM sleep.

Animals↗
PubMed1992

Event-related synchronization (ERS): an electrophysiological correlate of cortical areas at rest.

Oscillations in the alpha and beta bands can display either an event-related blocking response or an event-related amplitude enhancement. The former is named event-related desynchronization (ERD) and the latter event-related synchronization (ERS). Examples of ERS are localized alpha enhancements in the awake state as well as sigma spindles in sleep and alpha or beta bursts in the comatose state. It was found that alpha band activity can be enhanced over the visual region during a motor task, or during a visual task over the sensorimotor region. This means ERD and ERS can be observed at nearly the same time; both form a spatiotemporal pattern, in which the localization of ERD characterizes cortical areas involved in task-relevant processing, and ERS marks cortical areas at rest or in an idling state.

Adult↗
PubMedDate not supplied

[Spectral characteristics of neocortical and dorsal hippocampal activity following coagulation of the septum].

Spectral characteristics of the activity of the visual and motor neocortical zones and of the dorsal hippocampus were examined in chronic experiments in intact alert rabbits and in rabbits subjected to an electrolytic ablation of the septum. Following septum coagulation, the spectrograms of these formations were characterized by a considerable reduction of power spectra within the theta-range; a discordance of theta-frequencies in the spectrograms of the simultaneously recorded activity of the studied formations; an enhancement of power spectra within the higher frequencies range. The results obtained allow to suggest the presence in the above brain regions of facultative generators of the theta-activity which function under a synchronizing influence of the septum.

Animals↗