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Results for “Cortical Synchronization”

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PubMed1982

Synchronization of double asymmetrical epileptogenic foci in the cerebral cortex of the rat.

Discharges of two asymmetrical penicillin foci progressively synchronized during 25 min after creation of these foci. Section of the corpus callosum seriously impaired but did not completely block this synchronization. Thalamic spreading depression did not significantly change the synchronization in rats with intact corpus callosum. Noncallosal component of synchronization is probably realized through brain stem structures.

Animals↗
PubMed2002

Spontaneous development of synchronous oscillatory activity during maturation of cortical networks in vitro.

Recent studies have focused attention on mechanisms of spontaneous large-scale wavelike activity during early development of the neocortex. In this study, we describe and characterize synchronous neuronal activity that occurs in cultured cortical networks naturally without pharmacological intervention. The synchronous activity that can be detected by means of Fluo-3 fluorescence imaging starts to develop at the beginning of the second week in culture and eventually includes the entire neuronal population about 1 wk later. A synchronous increase of [Ca(2+)](i) in the neuronal population is associated with a burst of action potentials riding on a long-lasting depolarization recorded in a single cell. It is suggested that this depolarization results directly from synaptic current, which was comprised of at least three different components mediated by AMPA, N-methyl-D-aspartate (NMDA), and GABA(A) receptors. We never observed a gradually depolarizing pacemaker potential and found no evidence for a change of excitability during inter-burst periods. However, we found evidence for a period of synaptic depression after bursts. Network excitability recovers gradually over seconds from this depression that can explain the episodic nature of spontaneous network activity. Using pharmacological manipulation to investigate the propagation of activity in the network, we show that synchronous network activity depends on both glutamatergic and GABA(A)ergic neurotransmission during a brief period. Reversal potential of GABA(A) receptor-mediated current was found to be significantly more positive than resting membrane potential both at 1 and 2 wk in culture, suggesting depolarizing action of GABA. However, in cultures older than 2 wk, inhibition of GABA(A) receptors does not result in block of synchronous network activity but in modulation of burst width and frequency.

Action Potentials↗
PubMed2005

Language disorder in schizophrenia as a developmental learning disorder.

Receptive language disorder in schizophrenia is hypothesized to represent a learning disorder that involves a neurodevelopmental etiology. It is argued that a preexisting developmental language disorder may characterize a subset of schizophrenia patients. A primary deficit in the temporal dynamics of brain function is assumed to cause receptive language disorder in schizophrenia. This hypothesized core deficit includes both disturbance in the processing of rapid, sequential information and disruptions to patterns of brain activation and synchronization. These timing deficits may alter the way associative connections are formed and/or accessed in semantic memory. It is suggested that abnormalities in second-messenger pathways of subcortical-cortical circuitry offer an etiological nexus for language dysfunction in schizophrenia and developmental dyslexia.

Brain↗
PubMed2004

Neonatal seizure monitoring using non-linear EEG analysis.

Birth asphyxia is a major concern in neonatal care. Epileptic seizures are associated with subsequent neurodevelopmental deficits. Eighty-five percent of these seizures remain subclinical and therefore an on-line monitoring device is needed. In an earlier study we showed that the synchronization likelihood was able to distinguish between neonatal EEG epochs with and without epileptic seizures. In this study we investigated whether the synchronization likelihood can be used in complete EEGs, without artifact removal. Twenty complete EEGs from 20 neonatal patients were studied. The synchronization likelihood was calculated and correlated with the visual scoring done by 3 experts. In addition, we determined the influence of seizure length on the likelihood of detection. Using the raw unfiltered EEG data we found a sensitivity of 65.9 % and a specificity of 89.8 % for the detection of seizure activity in each epoch. In addition, the seizure detection rate was 100 % when the seizures lasted for 100 seconds or more. The synchronization likelihood seems to be a useful tool in the automatic monitoring of epileptic seizures in infants on the neonatal ward. Due to the retrospective nature of our study, the consequences for clinical intervention cannot yet be determined and prospective studies are needed. Therefore, we will conduct a prospective study on the neonatal intensive care unit with a recently developed on-line version of the synchronization likelihood analysis.

Cortical Synchronization↗
PubMed1998

Three methods compared for detecting the onset of alpha wave synchronization following eye closure.

Recent work indicates that the variation in the occipital alpha wave component of the EEG spectrum, controlled through eye closure, can be used by an untrained person to effect reliable activation of electrical devices. Here we describe and compare three real-time strategies, based on analogue and digital signal processing methods, of detecting the onset of alpha wave synchronization during eye closure. The goal of this work is to establish a method which satisfies the condition of rapid detection of alpha wave enhancement, thereby allowing for the efficient activation of devices, while simultaneously registering few or no false positives due to the natural variation in the alpha signal with eyes open. This work, based on measurements on 15 subjects in the age range 12 to 40 years, indicates that renal-time analysis of the EEG power spectrum provides for rapid detection of the onset of alpha wave synchronization while maintaining low counts of false positives.

Alpha Rhythm↗
PubMed2004

Optimal synchrony state for maximal information transmission.

This work investigated the roles of spontaneous synchronized rhythmic oscillations in information processing in a globally coupled neural network. We found that in the encoding of input aperiodic signals, there exists a range of optimal synchronous states in the network, where the information transmission rate and coding efficiency of the network are maximized. Our results indicate that it is not the weaker or stronger but an appropriate synchronous state may be of more functional significance in sensory encoding.

Cortical Synchronization↗
PubMed2004

Synchronization phenomena in pulse-coupled networks driven by spike-train inputs.

We present a pulse-coupled network (PCN) of spiking oscillators (SOCs) which can be implemented as a simple electrical circuit. The SOC has a periodic reset level that can realize rich dynamics represented by chaotic spike-trains. Applying a spike-train input, the PCN can exhibit the following interesting phenomena. 1) Each SOC synchronizes with a part of the input without overlapping, i.e., the input is decomposed. 2) Some SOCs synchronize with a part of the input with overlapping, i.e., the input is decomposed and the SOCs are clustered. The PCN has multiple synchronization phenomena and exhibits one of them depending on the initial state. We clarify the numbers of the synchronization phenomena and the parameter regions in which these phenomena can be observed. Also stability of the synchronization phenomena is clarified. Presenting a simple test circuit, typical phenomena are confirmed experimentally.

Action Potentials↗
PubMed1992

Oscillatory Neuronal Responses in the Visual Cortex of the Awake Macaque Monkey.

An important step in early visual processing is the segmentation of scenes. Features constituting individual objects have to be grouped together and segregated from those of other figures or the background. It has been proposed that this grouping could be achieved by synchronizing the fine temporal structure of responses from neurons excited by an individual figure. In the cat visual cortex evidence has been obtained that responses of feature-selective neurons have a distinctive oscillatory structure and can synchronize both within and across cortical areas, the synchronization depending on stimulus configuration. Here we investigate the generality of oscillatory responses and their synchronization and specifically whether these phenomena occur in extrastriate areas of the visual cortex of the awake behaving primate. We find in the caudal superior temporal sulcus of the macaque monkey (Macaca fascicularis) that adjacent neurons can synchronize their responses, in which case their discharges exhibit an oscillatory temporal structure. During such periods of local synchrony spatially separated cell groups can also synchronize their responses if activated with a single stimulus. These findings resemble those described previously for the cat visual cortex, except that in the awake monkey the oscillatory episodes tend to be of shorter duration and exhibit more variability of oscillation frequency.

Journal Article↗
PubMed2004

Gamma oscillation maintains stimulus structure-dependent synchronization in cat visual cortex.

Visual cortical cells demonstrate both oscillation and synchronization, although the underlying causes and functional significance of these behaviors remain uncertain. We simultaneously recorded single-unit activity with microelectrode arrays in supragranular layers of area 17 of cats paralyzed and anesthetized with propofol and N(2)O. Rate-normalized autocorrelograms of 24 cells reveal bursting (100%) and gamma oscillation (63%). Renewal density analysis, used to explore the source of oscillation, suggests a contribution from extrinsic influences such as feedback. However, a bursting refractory period, presumably membrane-based, could also encourage oscillatory firing. When we investigated the source of synchronization for 60 cell pairs we found only moderate correlation of synchrony with bursts and oscillation. We did, nonetheless, discover a possible functional role for oscillation. In all cases of cross-correlograms that exhibited oscillation, the strength of the synchrony was maintained throughout the stimulation period. When no oscillation was apparent, 75% of the cell pairs showed decay in their synchronization. The synchrony between cells is strongly dependent on similar response onset latencies. We therefore propose that structured input, which yields tight organization of latency, is a more likely candidate for the source of synchronization than oscillation. The reliable synchrony at response onset could be driven by spatial and temporal correlation of the stimulus that is preserved through the earlier stages of the visual system. Oscillation then contributes to maintenance of the synchrony to enhance reliable transmission of the information for higher cognitive processing.

Action Potentials↗
PubMed2005

Effectively desynchronizing deep brain stimulation based on a coordinated delayed feedback stimulation via several sites: a computational study.

In detailed simulations we present a coordinated delayed feedback stimulation as a particularly robust and mild technique for desynchronization. We feed back the measured and band-pass filtered local filed potential via several or multiple sites with different delays, respectively. This yields a resounding desynchronization in a naturally demand-controlled way. Our novel approach is superior to previously developed techniques: It is robust against variations of system parameters, e.g., the mean firing rate. It does not require time-consuming calibration. It also prevents intermittent resynchronization typically caused by all methods employing repetitive administration of shocks. We suggest our novel technique to be used for deep brain stimulation in patients suffering from neurological diseases with pathological synchronization, such as Parkinsonian tremor, essential tremor or epilepsy.

Brain↗
PubMed1982

Effects of a new benzodiazepine hypnotic (quazepam--SCH 16134) on EEG synchronization and sleep-inducing mechanisms in cats.

The sleep-inducing properties of a new benzodiazepine hypnotic (quazepam--SCH 16134) were evaluated in cats with transection at different levels of the brain stem structure. Effects observed after administration of doses ranging from 0.12 and 1 mg/kg given intravenously were compared with those of pentobarbital. In the encéphale isolé small doses of quazepam induced or increased the synchronized periods. The desynchronized electroencephalogram (EEG) pattern of midpontine pretrigeminal preparations was not modified by these small doses. Only larger doses induced a fast neocortical activity of high amplitude. In midpontine pretrigeminal hemisection the synchronization occurred exclusively or predominantly in the hemisphere contralateral to the lesion. In the cerveau isolé, quazepam did not influence the typical synchronized EEG pattern. The arousal threshold after mesencephalic and physiological stimulation was raised only in encéphale isolé animals. Pentobarbital provoked sustained synchronization in all preparations with a pattern quite different from that of the benzodiazepine. These results suggest that quazepam may act through facilitation of the EEG-synchronizing mechanisms localized in the lower brain stem which are involved in physiological EEG-synchronizing and sleep-inducing processes.

Acoustic Stimulation↗
PubMed1998

Prefrontal involvement in "temporal bridging" and timing movement.

Brain activity exclusively related to a temporal delay has rarely been investigated using modern brain imaging. In this study we exploited the temporal resolution of functional magnetic resonance imaging (fMRI) to characterise, by sinusoidal regression analysis, differential neuroactivation patterns induced in healthy subjects by two sensorimotor synchronization tasks different in their premovement delay of either 0.6 s or 5 s. The short event rate condition required rhythmic tapping, while the long event rate condition required timing of intermittent movements. Left rostral prefrontal cortex, medial frontal cortex, SMA and supramarginal gyrus demonstrated increased MR signal intensity during low frequency synchronization, suggesting that these brain regions form a distributed neural network for cognitive time management processes, such as time estimation and motor output timing. Medial frontal cortex showed a biphasic pattern of response during both synchronization conditions, presumably reflecting frequency-independent motor output related attention. As predicted, sensorimotor and visual association areas demonstrated increased MR signal intensity during high frequency synchronization.

Adult↗
PubMed2000

When pyramidal neurons lock, when they respond chaotically, and when they like to synchronize.

We give an overview on the locking properties of perturbed regularly firing pyramidal neurons, as a function of perturbation strength, self-spiking frequency and perturbation frequency. For inhibitory perturbations, instead of locking chaotic response emerges for a whole range of parameters. This suggests that global synchronization on the set of inhibitory connections may easily be achieved.

Action Potentials↗