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PubMed2003

ICA-based spatiotemporal approach for single-trial analysis of postmovement MEG beta synchronization.

The extraction of event-related oscillatory neuromagnetic activities from single-trial measurement is challenging due to the non-phase-locked nature and variability from trial to trial. The present study presents a method based on independent component analysis (ICA) and the use of a template-based correlation approach to extract Rolandic beta rhythm from magnetoencephalographic (MEG) measurements of right finger lifting. A single trial recording was decomposed into a set of coupled temporal independent components and corresponding spatial maps using ICA and the reactive beta frequency band for each trial identified using a two-spectrum comparison between the postmovement interval and a reference period. Task-related components survived dual criteria of high correlation with both the temporal and the spatial templates with an acceptance rate of about 80%. Phase and amplitude information for noise-free MEG beta activities were preserved not only for optimal calculation of beta rebound (event-related synchronization) but also for profound penetration into subtle dynamics across trials. Given the high signal-to-noise ratio (SNR) of this method, various methods of source estimation were used on reconstructed single-trial data and the source loci coherently anchored in the vicinity of the primary motor area. This method promises the possibility of a window into the intricate brain dynamics of motor control mechanisms and the cortical pathophysiology of movement disorder on a trial-by-trial basis.

Adult↗
PubMed2002

EEG synchronization upon reward in man.

OBJECTIVES: It was tested whether reward in humans is associated with EEG synchronization similar to that seen in animals. METHODS: In two experiments (I and II) the EEG was recorded from frontal, central, and parietal positions before, during, and after drinking or oral stimulation. In Experiment I, subjects (n=11) who had either been thirsty for 16h or had quenched thirst before recordings, drank 400ml of water. In Experiment II, thirsty subjects (n=11) either drank 400ml of water or sucked on a soother. The recording epochs included a 3min baseline, an interval of about 5min during which subjects drank or sucked on the soother, and a 7min post-drinking interval. RESULTS: During the drinking epoch, beta band-power (12-30Hz) was enhanced in both conditions of Experiment I and II, respectively. In Experiment I, after drinking, lower alpha power (8-10Hz) was higher when subjects were thirsty than when they were not. Lower alpha was also enhanced in the post-drinking interval of both conditions of Experiment II, and after sucking, lower alpha synchronization was in addition accompanied by increased theta activity (4-8Hz). CONCLUSIONS: Increased beta activity during drinking and sucking in thirsty subjects presumably reflects non-specific activation related to the motivational strength of sensorimotor regulation during consumatory behavior. The thirst dependent lower alpha synchronization after drinking, generated not only by water consumption but also by surrogate oral stimuli, can be considered a reflection of the drive reducing and rewarding qualities of oral stimulation and consumatory behavior.

Adult↗
PubMed2002

Self-organization of memory activity through spike-timing-dependent plasticity.

We studied the self-organization of memory-related activity through spike-timing-dependent plasticity (STDP). Relatively short time windows (approximately 10 ms) for the plasticity rule give rise to asynchronous persistent activity of low rates (20-30 Hz), which is typically observed in delay periods of working memory task. We demonstrate some network level effects on the activity regulation that cannot be addressed in single-neuron studies. For longer time windows (approximately 20 ms), the layered cell assemblies that propagate synchronized spikes (synfire chain) are self-organized. Synchronous spike propagation was suggested to underlie the precisely timed spikes in the monkey prefrontal cortex. The present results suggest that the two networks for sustained activity are different realizations of the same principle for synaptic wiring.

Action Potentials↗
PubMedDate not supplied

Nearest neighbor phase synchronization as a measure to detect seizure activity from scalp EEG recordings.

The author presents results from the application of a particular measure for synchronization between brain areas (i.e., phase synchronization) in its behavior to detect epileptic seizure activity from scalp EEG recordings. The primary motivation for the current study was to contribute to the development of physiologic measures that both transform the EEG to a visual domain that allows a more intuitive interpretation of the interictal and ictal EEG and allows automated analysis, both relevant for real-time monitoring. EEGs from 16 patients experiencing temporal lobe and generalized seizures were analyzed. Nearest neighbor phase synchronization (NNPS) values for several frequency bands were determined. Additional analysis of the NNPS in the delta band, using different thresholds, allows construction of receiver operating characteristics (ROC) curves for each EEG analyzed. The common value for the sensitivity and the specificity, Q*, was used as a measure for the test accuracy, with values of Q* near 1.0, indicating ROC curves with sensitivity and specificity both approaching 1.0. It was found that Q* = 0.48 to 0.87, depending on the EEG analyzed, indicating that the proposed method allows seizure detection in a significant portion of the EEGs studied. Nearest neighbor phase synchronization was typically increased during seizure activity and seems to be a promising method to detect seizure activity from scalp EEG recordings. The proposed visualization allows an intuitive interpretation of the EEG and may assist in real-time monitoring.

Cortical Synchronization↗
PubMed1996

Neuronal synchronization of tonically active neurons in the striatum of normal and parkinsonian primates.

1. Previous studies indicate that tonically active neurons (TANs) are the cholinergic interneurons of the striatum and predict that their activity is synchronized. To test whether TANs do fire synchronously, and whether dopamine depletion affects their synchronization, we recorded the simultaneous activity of several TANs in the putamens of two vervet monkeys before and after 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) treatment. 2. Cross-correlation analysis revealed that most pairs of TANS (33 of 54; 61.1%) fire synchronously at +/- 60-ms delay. Correlated activity was more common between neurons with characteristic response to reward (17 of 19 pairs; 89.5%). 3. Cross-correlation study of 24 triplets of TANS showed synchronization of spiking activity of all 3 TANS in only 29.2% of cases (7 of 24 triplets). Correlated activity of two of three possible pairs was found in 25% of the cases. 4. After MPTP treatment and the development of parkinsonian symptoms, most TANS' auto- and cross-correlograms (22 of 28 units; 78.6%; and 23 of 28 pairs; 82.1%) became oscillatory. The number of correlated pairs was slightly increased (24 of 28; 85.7%). The strength of the synchronization was not significantly different from the normal values. 5. These findings support the notion that TANs function as distributed, partially overlapping synchronized networks. However, a normal dopaminergic system is not essential for synchronization of TANs; on the contrary, dopaminergic activity may even have a desynchronizing effect on the basal ganglia's system.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗
PubMed2002

Synchronized neuronal discharge in the basal ganglia of parkinsonian patients is limited to oscillatory activity.

It has been proposed that an increase in synchronization between neurons in the basal ganglia contributes to the clinical features of Parkinson's disease (PD). To examine this hypothesis, we looked for correlations in the discharge activity of pairs of neurons in the globus pallidus internus (GPi), globus pallidus externus (GPe), and the substantia nigra pars reticulata (SNr). Recordings were performed in PD patients undergoing functional stereotactic mapping for pallidotomy (eight patients) or subthalamic nucleus deep brain stimulation (four patients). A double-microelectrode setup was used to simultaneously record from neurons separated by distances as small as 250 microm. In the five pallidotomy patients without limb tremor during the procedure, none of the 73 GPi pairs and 15 GPe pairs displayed synchronous activity. In the three pallidotomy patients with limb tremor, 6 of 21 GPi pairs and 5 of 29 GPe pairs displayed oscillatory synchronization in the frequency range of the ongoing limb tremor (3-6 Hz) or at higher frequencies (15-30 Hz). Synchronized activity was not observed in the SNr (10 pairs). The findings indicate that oscillatory synchronization between pairs of GPi or GPe neurons is found in patients with limb tremor. These results also suggest that overt neuronal synchronization, which may be attributable to an increase in direct synaptic connections or common collateral afferent inputs, is not present in the basal ganglia of patients with PD.

Action Potentials↗
PubMed1999

Sympathetic neuronal oscillators are capable of dynamic synchronization.

In this paper we show that the discharges of sympathetic neurons innervating an identified peripheral target are driven by multiple oscillators that undergo dynamic synchronization when an entraining force, central respiratory drive (CRD), is increased. Activity was recorded from postganglionic sympathetic neurons (PGNs) innervating the caudal ventral artery of the rat tail: (1) at the population level from the ventral collector nerve (VCN); and (2) from pairs of single PGNs recorded simultaneously using a focal recording technique. Autospectral analysis of VCN activity revealed a more prominent rhythmical component in the presence of CRD than in its absence, suggesting that (1) multiple oscillators drive the discharges of PGNs and (2) these oscillators can be entrained and therefore synchronized by CRD. This interpretation was supported by analysis of the firing behavior of PGN pairs. Autocorrelation and cross-correlation analysis showed that pairs were not synchronized in the absence of CRD but showed significant synchronization when CRD was enhanced. Time-evolving spectral analysis and raster plots demonstrated that the temporal stability of PGN-to-PGN and CRD-to-PGN interactions at a given level of CRD were also dynamic in nature, with stable constant phase relationships predominating as CRD was increased. This is the first reported example of dynamic synchronization in populations of single postganglionic sympathetic neurons, and we suggest that, as in sensory processing and motor control, temporal pattern coding may also be an important feature of neuronal discharges in sympathetic pathways.

Animals↗
PubMed2003

Influence of membrane properties on spike synchronization in neurons: theory and experiments.

In the brain spike synchronization in neurons is involved in information transfer and certain forms of dysfunction. The theory of random point processes was used to relate the statistical properties of input point processes to synchronization between firing in neurons viewed as threshold devices. Derived analytical relations describe normalized synchronization in the case of shared input with balanced excitation and inhibition. For neuronal models with unbalanced shared input and spike generating Hodgkin-Huxley type conductances, the theory satisfactorily describes the temporal dependence of spike synchronization on the delay between spikes. Computer generated stochastic stimulus current was used to stimulate motoneurons in turtle spinal cord slices. Theory was able to approximate the temporal dependence of spike synchronization on the delay between spikes when the membrane time constant and the relative spike threshold measured were used in calculations. In agreement with the theoretical prediction, normalized spike synchrony was reduced when the threshold for spike generation was lowered by injection of steady depolarizing bias current. In spinal motoneurons the relative spike threshold can be lowered by a persistent inward current facilitated by activation of certain metabotropic transmitter receptors. After induction of this inward current spike synchronization was reduced several times. It is suggested that downregulation of the persistent inward current in motoneurons by disruption of brainstem modulatory systems, as in Parkinson disease, can facilitate tremor due to the increased synchrony between motoneurons.

Action Potentials↗
PubMed2002

Spatial eigenmodes and synchronous oscillation: co-incidence detection in simulated cerebral cortex.

Zero-lag synchronisation arises between points on the cerebral cortex receiving concurrent independent inputs; an observation generally ascribed to nonlinear mechanisms. Using simulations of cerebral cortex and Principal Component Analysis (PCA) we show patterns of zero-lag synchronisation (associated with empirically realistic spectral content) can arise from both linear and nonlinear mechanisms. For low levels of activation, we show the synchronous field is described by the eigenmodes of the resultant damped wave activity. The first and second spatial eigenmodes (which capture most of the signal variance) arise from the even and odd components of the independent input signals. The pattern of zero-lag synchronisation can be accounted for by the relative dominance of the first mode over the second, in the near-field of the inputs. The simulated cortical surface can act as a few millisecond response coincidence detector for concurrent, but uncorrelated, inputs. As cortical activation levels are increased, local damped oscillations in the gamma band undergo a transition to highly nonlinear undamped activity with 40 Hz dominant frequency. This is associated with "locking" between active sites and spatially segregated phase patterns. The damped wave synchronisation and the locked nonlinear oscillations may combine to permit fast representation of multiple patterns of activity within the same field of neurons.

Cerebral Cortex↗
PubMed1995

Event-related potentials and alpha synchronization in preadolescent boys at risk for psychoactive substance use.

Numerous studies have evaluated event-related potentials (ERPs) as biological indicators of the liability for alcoholism. This study extends that approach by investigating ERPs in boys at risk for other substance use disorders. Prepubertal (10-12 years) sons of fathers diagnosed with psychoactive substance dependence (n = 28) were compared to matched sons of nonaffected fathers (n = 26) on an auditory ERP oddball task. Multivariate analyses of variance applied to peak amplitude and latency measures indicated small to moderate between-groups differences at midline or parietal sites: N2 and P3 amplitude; P2, N2, P3, and Nc latency. This replicated P3 amplitude findings in alcoholism-risk studies, though the effect size was moderate. Analysis of event-related alpha power indicated significantly longer latency of alpha synchronization and oscillations of desynchronization in boys at risk. The alpha power findings were statistically the more robust of the measures applied. The role of neurocognitive factors in determining liability for substance use disorders is discussed.

Alpha Rhythm↗
PubMed1975

Influence of increasing doses of pentobarbital on the mesencephalic reticular formation in rats. Spontaneous firing of neuronal pairs and activity evoked by polarization.

In rats immobilized by D-tubocurarine the spontaneous activity in pairs of mesencephalic reticular neurons was recorded by means of one microelectrode and differentiated by amplitude discriminators. Spontaneous activity of neuronal pairs and activity evoked by electrical polarization of cells (5-235 nA) through the recording microelectrode was evaluated in the curarized state and after cumulative doses of 15 mg/kg pentobarbital. No correlation between mean interspike interval duration in pairs of adjacent neurons was found in the unanesthetized state. After pentobarbital a slight dependence was observed between the values. Furthermore, it is probable that adjacent neurons will both cease firing at the same dose of pentobarbital. Cross-correlation of the spike trains of two adjacent neurons was found in the range of minus 10 msec to plus 10 msec (which is probably an expression of direct interaction or of a common input) in 6 of 50 pairs analyzed in the unanesthetized state. This dependence fully disappeared after 15-30 mg/kg of pentobarbital. After 15 mg/kg of pentobarbital in 17 recorded pairs (out of 50 analyzed) peaks in the cross-correlograms appeared in a range of about 100 msec and at a distance of 150-300 msec. Such a relationship was already present in 4 pairs of neurons in the unanesthetized state. The similarity of autocorrelation and cross-correlation histograms in this case favors the hypothesis that spontaneous activity of many mesencephalic reticular neurons is synchronized after pentobarbital administration. In many reticular neurons the firing may be evoked by direct cell polarization through the recording microelectrode even at cumulative doses of pentobarbital much higher than those sufficient to block spontaneous activity.

Action Potentials↗
PubMed1995

Aberrant expression of neuropeptide Y in hippocampal mossy fibers in the absence of local cell injury following the onset of spike-wave synchronization.

Stargazer mutant mice inherit a recessive neuronal excitability phenotype featuring frequent non-convulsive spike-wave seizures that arise from synchronous bursting in neocortical, thalamic and hippocampal networks. Immunocytochemistry reveals that granule cells in the mutant dentate gyrus aberrantly express neuropeptide Y (NPY) at multiple ages following the developmental onset of seizures. The ectopic NPY is selectively concentrated in the mossy fibers, co-localizing with the releasable dense core vesicle pool. The NPY content of native NPY+local circuit neurons is also elevated in the mutant CNS. There is no concurrent elevation of hippocampal 72 kDa heat shock protein (HSP72), glial fibrillary acidic protein (GFAP) or NADPH-diaphorase, three markers that are induced during cellular injury, and no evidence of granule cell loss. Since mossy fiber NPY expression appears after the developmental onset of spike-wave discharges and can be induced in wild type granule cells by electrical stimulation, the altered peptide phenotype is likely to reflect transynaptic gene induction triggered by synchronous bursting. These results link a specific pattern of repetitive synaptic input with selective molecular plasticity in dentate granule cells that may contribute to dynamic modifications in hippocampal network excitability.

Action Potentials↗
PubMedDate not supplied

Is autism due to brain desynchronization?

The hypothesis is presented that a disruption in brain synchronization contributes to autism by destroying the coherence of brain rhythms and slowing overall cognitive processing speed. Particular focus is on the inferior olive, a precerebellar structure that is reliably disrupted in autism and which normally generates a coherent 5-13 Hz rhythmic output. New electrophysiological data reveal that the continuity of the rhythmical oscillation in membrane potential generated by inferior olive neurons requires the formation of neuronal assemblies by the connexin36 protein that mediates electrical synapses and promotes neuronal synchrony. An experiment with classical eyeblink conditioning is presented to demonstrate that the inferior olive is necessary to learn about sequences of stimuli presented at intervals in the range of 250-500 ms, but not at 700 ms, revealing that a disruption of the inferior olive slows stimulus processing speed on the time scale that is lost in autistic children. A model is presented in which the voltage oscillation generated by populations of electrically synchronized inferior olivary neurons permits the utilization of sequences of stimuli given at, or faster than, 2 per second. It is expected that the disturbance in inferior olive structure in autism disrupts the ability of inferior olive neurons to become electrically synchronized and to generate coherent rhythmic output, thereby impairing the ability to use rapid sequences of cues for the development of normal language skill. Future directions to test the hypothesis are presented.

Animals↗
PubMed2004

Neuronal synchrony mediated by astrocytic glutamate through activation of extrasynaptic NMDA receptors.

Fast excitatory neurotransmission is mediated by activation of synaptic ionotropic glutamate receptors. In hippocampal slices, we report that stimulation of Schaffer collaterals evokes in CA1 neurons delayed inward currents with slow kinetics, in addition to fast excitatory postsynaptic currents. Similar slow events also occur spontaneously, can still be observed when neuronal activity and synaptic glutamate release are blocked, and are found to be mediated by glutamate released from astrocytes acting preferentially on extrasynaptic NMDA receptors. The slow currents can be triggered by stimuli that evoke Ca2+ oscillations in astrocytes, including photolysis of caged Ca2+ in single astrocytes. As revealed by paired recording and Ca2+ imaging, a striking feature of this NMDA receptor response is that it occurs synchronously in multiple CA1 neurons. Our results reveal a distinct mechanism for neuronal excitation and synchrony and highlight a functional link between astrocytic glutamate and extrasynaptic NMDA receptors.

Animals↗
PubMed1988

[Quantitative characteristics of the electrocorticographic sleep stages in bottle-nosed dolphins].

Quantitative analysis of the ECoG stages in four bottle-nosed dolphins has demonstrated that unihemispheric slow-wave sleep is the dominant type of their natural sleep. All the variants of the bilateral and unilateral ECoG synchronization comprise 33.4% of the total recording time, with unilateral slow-wave sleep accounting for 28.8%. A single brain hemisphere is in a state of ECoG synchronization for 19% of the total recording time. The maximal amount of sleep is registered during a night and the second half of the day. Unihemispheric sleep episodes tend to appear alternatively in both hemispheres.

Animals↗
PubMed2002

Cortical origin of mini-asterixis in hepatic encephalopathy.

The authors investigated 12 patients with cirrhosis who had hepatic encephalopathy (HE): six with continuous mini-asterixis and six with subclinical HE without asterixis. They studied the coupling between hand-muscle electromyography (EMG) recordings and brain activity recorded by magnetoencephalography. On forearm elevation, patients with tremor developed excessive coupling between activity in the motor cortex (M1) and contralateral hand-muscle EMG recordings at the frequency of mini-asterixis, which was not found in controls. The corticomuscular coupling demonstrates the involvement of M1 in asterixis and may reflect a pathologically slowed and synchronized motor cortical drive.

Adult↗
PubMed2004

Alpha power dependent light stimulation: dynamics of event-related (de)synchronization in human electroencephalogram.

The desynchronization and resynchronization of alpha oscillations was studied in 10 normal subjects after visual stimulation of both eyes under two experimental conditions, "eyes opened" and "eyes closed". The electroencephalogram (EEG) was recorded bipolarly over the occipital area and sampled at 200 Hz. The data was processed in real time and evaluated online. In accordance with the alpha power in the 7 to 13 Hz band, short red light flashes of 10 ms duration were presented at intervals of at least 2 s. This stimulation resulted in an event-related desynchronization (ERD) followed by resynchronization. Trials were controlled for artifacts, averaged offline, and the amount of event-related (de)synchronization was calculated. The event-related desynchronization was significantly larger in the eyes open paradigm. In addition, the latencies of event-related desynchronization and resynchronization maxima were larger in the eyes open paradigm compared to the eyes closed one.

Alpha Rhythm↗
PubMed1994

Synchronization properties of spindle oscillations in a thalamic reticular nucleus model.

1. We address the hypothesis of Steriade and colleagues that the thalamic reticular nucleus (RE) is a pacemaker for thalamocortical spindle oscillations by developing and analyzing a model of a large population of all-to-all coupled inhibitory RE neurons. 2. Each RE neuron has three ionic currents: a low-threshold T-type Ca2+ current (ICa-T), a calcium-activated potassium current (IAHP) and a leakage current (IL). ICa-T underlies a cell's postinhibitory rebound properties, whereas IAHP hyperpolarizes the neuron after a burst. Each neuron, which is a conditional oscillator, is coupled to all other RE neurons via fast gamma-aminobutyric acid-A (GABAA) and slow GABAB synapses. 3. For generating network oscillations IAHP may not be necessary. Synaptic inhibition can provide the hyperpolarization for deinactivating ICa-T that causes bursting if the reversal potentials for GABAA and GABAB synapses are sufficiently negative. 4. If model neurons display sufficiently powerful rebound excitability, an isolated RE network of such neurons oscillates with partial but typically not full synchrony. The neurons spontaneously segregate themselves into several macroscopic clusters. The neurons within a cluster follow the same time course, but the clusters oscillate differently from one another. In addition to activity patterns in which clusters burst sequentially (e.g., 2 or 3 clusters bursting alternately), a two-cluster state may occur with one cluster active and one quiescent. Because the neurons are all-to-all coupled, the cluster states do not have any spatial structure. 5. We have explored the sensitivity of such partially synchronized patterns to heterogeneity in cells' intrinsic properties and to simulated neuroelectric noise. Although either precludes precise clustering, modest levels of heterogeneity or noise lead to approximate clustering of active cells. The population-averaged voltage may oscillate almost regularly but individual cells burst at nearly every second cycle or less frequently. The active-quiescent state is not robust at all to heterogeneity or noise. Total asynchrony is observed when heterogeneity or noise is too large, e.g., even at 25% heterogeneity for our reference set of parameter values. 6. The fast GABAA inhibition (with a reversal potential more negative than, say, -65 mV) favors the cluster states and prevents full synchrony. Our simulation results suggest two mechanisms that can fully synchronize the isolated RE network model. With GABAA removed or almost totally blocked, GABAB inhibition (because it is slow) can lead to full synchrony, which is partially robust to heterogeneity and noise.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗