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Results for “Cortical Synchronization”

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PubMedDate not supplied

[Influence of the mesencephalic reticular formation on the synchronization of cortical evoked potentials].

It has been shown in experiments on alert rabbits that evoked potentials (EP) of the visual and motor cortex to a millisecond stimulation of the midbrain reticular formation (RF) have a greater similarity (due to increased amplitude and coherence of the theta-rhythmic components) as compared with preceding background activity and evoked potentials to a photic flash. The EPs of these neocortical areas to a photic flash had a more similar form after preliminary RF stimulation. The similarity of evoked responses to stimulation of RF increased after its repeated presentations. The summate poststimulus histogram in which the responses of individual units (24 neurones) of the visual cortex to a single RF stimulation were summed up, proved to be similar in form to EP recorded on the surface of the visual cortex after a similar RF stimulation.

Animals↗
PubMed2000

Different frequencies for different scales of cortical integration: from local gamma to long range alpha/theta synchronization.

Cortical activity and perception are not driven by the external stimulus alone; rather sensory information has to be integrated with various other internal constraints such as expectations, recent memories, planned actions, etc. The question is how large scale integration over many remote and size-varying processes might be performed by the brain. We have conducted a series of EEG recordings during processes thought to involve neuronal assemblies of varying complexity. While local synchronization during visual processing evolved in the gamma frequency range, synchronization between neighboring temporal and parietal cortex during multimodal semantic processing evolved in a lower, the beta1 (12-18 Hz) frequency range, and long range fronto-parietal interactions during working memory retention and mental imagery evolved in the theta and alpha (4-8 Hz, 8-12 Hz) frequency range. Thus, a relationship seems to exist between the extent of functional integration and the synchronization-frequency. In particular, long-range interactions in the alpha and theta ranges seem specifically involved in processing of internal mental context, i.e. for top-down processing. We propose that large scale integration is performed by synchronization among neurons and neuronal assemblies evolving in different frequency ranges.

Alpha Rhythm↗
PubMed1985

Mapping of regions in the caudal brain stem that produce stimulus-bound synchronization in the cortical EEG.

This study was aimed at filling the lacunae in our knowledge regarding the localization of the regions in the caudal brain stem that bring about cortical EEG synchronization on electrical stimulation and characteristic features of synchronized waves elicited from those regions. Studies were conducted on 40 encéphale isolé cats. Stimulation of ventromedial regions of the caudal brain stem, with low frequency, elicited stimulus-bound synchronized waves in the cortex which were more prominent ispsilaterally. On the other hand, low-frequency stimulation of dorsal and lateral areas produced synchronized waves which were either equally prominent on both sides, or more prominent on the contralateral side. The loci in the brain stem that produce synchronization were very specific. The induced synchronized waves showed amplitude modulation and did not outlast the train of stimuli. The results are further confirmation of the role of caudal brain stem structures in cortical EEG synchronization. They also provide information regarding the nature of cortical synchronization elicited from these brain stem structures.

Animals↗
PubMedDate not supplied

[Effect of anodal polarization of several subcortical structures on the spatial synchronization of cortical potentials during elaboration of a defensive conditioned reflex in rabbits].

The effect of the functional state of some thalamic and hypothalamic nuclei, modified by anode polarization, on spatial synchroneity of cortical potentials (SSCP) and the speed of elaboration of a conditioned defensive reflex (CDR) were studied in chronic experiments on 15 rabbits. Reversible blockade of the studied subcortical structures considerably affected the local SSCP form and the reflex execution. In intrasignal periods the global SSCP practically did not change. A comparative analysis of the results permits an assumption that the mammillary bodies play an important role in the formation of local SSCP at the beginning of defensive conditioning and that in the stabilized reflex, this SSCP form requires the activity of non-specific thalamic nuclei.

Animals↗
PubMed1993

[The spatial synchronization of cortical bioelectrical activity in different degrees of severity of alcohol dependence].

Stage-II alcoholics were examined 1-2 weeks after drinking periods, as were alcoholics during remissions lasting for 0.5 to 6 years. EEG was recorded by 10 symmetrical leads: prefrontal, central, motor, sincipital, and temporal. Analysis of EEG correlations revealed reliable differences between the two groups in the total level of synchronism of cortical biopotentials, in activities of different regions, and in time course of relationships of various areas during hyperventilation and without it. The data may be used as objective criteria in assessment of the degree of a pathologic process in the CNS and for differentiating the patients by this sign for further differentiated therapy.

Alcoholism↗
PubMed1976

Changes in multiunit activity and EEG induced by the administration of natural progestins to flaxedil immobilized cats.

The effects of progesterone (P) and 7 of its metabolites on the EEG and multiunit activity (MUA) of various limbic structures were studied in flaxedil immobilized cats. Most progestins inhibited the MUA of the mesencephalic reticular formation, hippocampus and hypothalamus and induced cortical EEG synchronization. MUA changes in the mesencephalic reticular formation frequently preceded EEG synchronization. Progestins reduced in the 5 beta postition (pregnanolone, epipregnanolone and pregnanedion) inhibited neuronal discharge and synchronized EEG activity with shorter latencies and in lower doses than those reduced in the 5 alpha position (allopregnanolone and allopregnanedion). Progestins having the delta 4,3-keto structure (P, 20 alpha-hydroxy pregnenone, 20 beta-hydroxy pregnenone) induced electrophysiological changes with prolonged latencies and in doses significantly higher than ring A reduced progestins. Administration of epipregnanolone to "cerveau isole" preparations depressed neuronal firing in those structures located rostral to the level of the brain stem transection (hypothalamus, hippocampus), but failed to increase the already synchronized cortical activity. These results suggest that: a, ring A reduction increases the capacity of P and other delta 4,3-keto progestins to inhibit neuronal discharge in certain brain areas and b, changes in neuronal firing induced by progestins are not necessarily mediated through the cat brain stem reticular formation.

Animals↗
PubMed2005

Local coherence oscillations in the EEG during development in the fetal baboon.

OBJECTIVE: To test the hypothesis that local coherence in extra-dural EEG recordings, a direct measure of synchronous cortical network activity, oscillates with the same periodicity as EEG power cycling and follows a similar developmental trajectory. METHODS: Local coherence was derived from continuous EEG recordings from closely spaced (1 cm) chronically implanted extra-dural electrodes over the right hemisphere in five fetal baboons (Papio sp.). A ratio of high to low frequency EEG band power (14-18 Hz to 4-7 Hz), was used to characterize EEG power cycling. RESULTS: Data were obtained within a developmental window (137-151 days; term approximately 175 days) during which fetal EEG power cycling becomes increasingly well-organized. During this period ultradian oscillations in local coherence with periods of approximately 1h developed in parallel with EEG power cycling of approximately the same periods. However, the cross-correlation and phase relationship between local coherence and power oscillations were variable. CONCLUSIONS: These findings suggest that cycles in cortical synchrony develop in parallel with fetal power cycles, but are not tightly coupled to them. SIGNIFICANCE: Coherence provides a direct measure of cortical network dynamics not possible with univariate EEG measures such as spectral power. Reported here are the first measurements of local coherence in the developing fetal brain. Local coherence is studied with the long-term goal of monitoring the development of cortical network activity.

Activity Cycles↗
PubMed2006

Distinct cognitive neurophysiologic profiles for lamotrigine and topiramate.

PURPOSE: To contrast the effects of lamotrigine (LTG) and topiramate (TPM) on cognitive task-related and resting-state EEG and evoked potential (EP) measures. METHODS: We used a double-blind, randomized, crossover design. Healthy adults (N = 29) had two 8-week periods of dose escalation, 4 weeks of drug maintenance (300 mg daily), and 4 weeks of washout. EEG was recorded during working memory (WM) tasks and resting conditions at baseline, at the end of each maintenance phase, and after final washout. RESULTS. LTG did not affect overt performance on the tasks, although it reduced EEG power in both resting and WM task conditions, most prominently in the 6- to 12-Hz frequency range, and attenuated P300 evoked-potential amplitude equally in both WM task loads. TPM slowed responses and increased errors. It also increased EEG power below 6 Hz in all conditions, and reduced the amplitude of a slow wave observed in a difficult version of the WM task. CONCLUSIONS: The drugs produced both task-independent and task-related alterations in neurophysiologic measures. The EEG and EP changes produced by TPM are consistent with an impairment of WM, as evidenced by overt performance deficits on the behavioral tasks. By contrast, the reduction in synchronous cortical activity produced by LTG was not accompanied by cognitive impairment. It is unknown whether such effects would also be observed at lower doses, such as those that often are used in monotherapy for newly diagnosed patients.

Adult↗
PubMed1999

Cortico-subcortical synchronization in the chloralose-anesthetized cat.

The spontaneous and paroxysmal cerebral cortical synchronized activity was used as reference to study the cortical impact exerted on subcortical neurons. The sensorimotor cortical synchronized activity spread down to subcortical structures receiving direct cortical input, including neuronal populations that originate descending rubrospinal, tectospinal and reticulospinal motor axons, and to a somatosensory relay station, the cuneate nucleus. Lesion of the pyramidal tract abolished the cortically induced synchronization of the activity of contralateral cuneate nucleus neurons.

Anesthesia, Intravenous↗
PubMed1982

[Study of the associative activity of schizophrenic patients by the technic of remote synchronization of cortical biopotentials].

To reveal physiological correlates of the schizophrenic thinking peculiarities associated with impaired mechanisms of information selection, spatial synchronization of the cortical biopotentials was studied in 10 healthy probands and 9 patients with continuously progressing schizophrenia. Both the healthy probands and the patients were asked to solve problems of comparing notions in situations where standard or non-standard criteria for the solution could be chosen. The bioelectrical activity was recorded at 48 cortical sites with subsequent estimation of the cross-correlation interconnections between the EEGs. It was found that in the solution of problems with the use of standard criteria the spatial-temporary organization of the biopotentials differed but little in the healthy probands and the patients, whereas in the solution of problems for which secondary, latent features of the subjects were required, these differences were rather marked in a number of characteristics, such as the general level of the synchronism, the character of interhemispheral asymmetries, the topographic distribution of the biopotential synchronization. The data obtained are discussed in the light of the present-day concepts on the functional specialization of the hemispheres.

Adolescent↗
PubMed2001

A statistical technique for measuring synchronism between cortical regions in the EEG during rhythmic stimulation.

The coherence function has been widely applied in quantifying the degree of synchronism between electroencephalogram (EEG) signals obtained from different brain regions. However, when applied to investigating synchronization resulting from rhythmic stimulation, misleading results can arise from the high correlation of background EEG activity. We, thus propose a modified measure, which emphasizes the synchronized stimulus responses and reduces the influence of the spontaneous EEG activity. Critical values for this estimator are derived and tested in Monte Carlo simulations. The effectiveness of the method is illustrated on data recorded from 12 young normal subjects during rhythmic photic stimulation.

Adolescent↗
PubMed2006

Divergent thinking training is related to frontal electroencephalogram alpha synchronization.

Cortical activity in the human electroencephalogram alpha band was measured (by means of an event-related approach) in a pre- and a post-test (with intermediate training) while participants (n = 30) were confronted with divergent thinking tasks. Half of the participants received a divergent thinking training (over a time period of 2 weeks) which was composed of exercises structurally similar to those used in the pre- and post-test. Analyses revealed that the training group displayed higher task-related synchronization of frontal alpha activity (i.e. increases in alpha power from the pre-stimulus reference to the activation interval) than the control group. These findings are in line with the view of frontal alpha synchronization as a selective top-down inhibition process that prevents internal or top-down information processing being disturbed by incoming external input.

Adult↗
PubMed2005

Neural synchrony and gray matter variation in human males and females: integration of 40 Hz gamma synchrony and MRI measures.

Coherent cognition requires activity to be brought together across diverse brain networks. Synchronous, in-phase oscillations in the high-frequency (40 Hz) Gamma range are thought to be one mechanism underlying the functional integration of brain networks. While sex differences have been observed across a range of cognitive functions, their role in normal cortical synchronization has not been elucidated. We recorded Gamma phase synchrony in 500 male and 500 female subjects during an auditory oddball task, which taps discrimination of task-relevant signals. Results revealed a marked sex-linked dissociation in the spatio-temporal pattern of cortical synchronization. Females showed increased Gamma synchrony in the frontal brain, while males showed enhanced synchrony in the parieto-occipital region. These differences were not accounted for by sex differences in whole brain MRI volume. However, there were positive associations between Gamma synchrony and gray matter for females, while these relationships were negative for males. Sex differences in the profile of cortical synchronization may reflect distinct aspects of evolutionary advantage.

Adult↗