Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Cortical Synchronization”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,693 records · Page 94Linked to original sources
PubMed1997

Intracellular and computational characterization of the intracortical inhibitory control of synchronized thalamic inputs in vivo.

We investigated the presence and role of local inhibitory cortical control over synchronized thalamic inputs during spindle oscillations (7-14 Hz) by combining intracellular recordings of pyramidal cells in barbiturate-anesthetized cats and computational models. The recordings showed that 1) similar excitatory postsynaptic potential (EPSP)/inhibitory postsynaptic potential (IPSP) sequences occurred either during spindles or following thalamic stimulation; 2) reversed IPSPs with chloride-filled pipettes transformed spindle-related EPSP/IPSP sequences into robust bursts with spike inactivation, resembling paroxysmal depolarizing shifts during seizures; and 3) dual simultaneous impalements showed that inhibition associated with synchronized thalamic inputs is local. Computational models were based on reconstructed pyramidal cells constrained by recordings from the same cells. These models showed that the transformation of EPSP/IPSP sequences into fully developed spike bursts critically needs a relatively high density of inhibitory currents in the soma and proximal dendrites. In addition, models predict significant Ca2+ transients in dendrites due to synchronized thalamic inputs. We conclude that synchronized thalamic inputs are subject to strong inhibitory control within the cortex and propose that 1) local impairment of inhibition contributes to the transformation of spindles into spike-wave-type discharges, and 2) spindle-related inputs trigger Ca2+ events in cortical dendrites that may subserve plasticity phenomena during sleep.

Animals↗
PubMed1990

Correlation of instantaneous heart rate and EEG suppression during enflurane anaesthesia: synchronous inhibition of heart rate and cortical electrical activity?

EEG burst suppression and instantaneous heart rate were studied during enflurane anaesthesia in 15 patients. Heart rate increased at EEG burst onset and decreased at suppression onset. Short epileptic discharges accompanied by an increase in heart rate were seen in 2 patients. We suggest that suppressions in EEG may be caused by active inhibition, with synchronous decrease of heart rate.

Adolescent↗
PubMed2000

Oscillatory cortical activity and movement-related potentials in proximal and distal movements.

OBJECTIVES: Event-related desynchronization (ERD) of alpha- and beta-rhythms, the post-movement beta-synchronization and the cortical movement-related potentials were analyzed in distal (finger) and proximal (shoulder) movements. METHODS: EEG was recorded in 7 healthy right-handed men using a 59-channel whole-head EEG system while subjects performed self-paced movements. RESULTS: The amplitude of the Bereitschaftspotential (BP) was greater over the central midline area and smaller over the contralateral sensorimotor hand area in shoulder than in finger movements. The maximal alpha- and beta-ERD was localized at parietal electrodes in shoulder movements and over the left and right sensorimotor hand area in finger movements. The post-movement beta-ERS was greater in shoulder than in finger movements, especially at the electrode located 3.5 cm left of the central midline electrode. A significant correlation between the slope of the terminal portion of the BP (negative slope) and amplitude of the post-movement beta-synchronization was observed in shoulder but not in finger movements. CONCLUSIONS: Enhancement of BP over the central midline electrode suggests increased activation of the supplementary motor area in proximal movements. The spatial distribution of the alpha- and beta-ERD and of the post-movement beta-ERS shows topographic differences which may refer to the somatotopic organization of the primary sensorimotor cortex with shoulder representation medial to hand and fingers. The correlation between the negative slope and the post-movement beta-ERS in proximal movements supports the view that the brief post-movement inhibition over the motor cortical area is related to the pre-movement activation of that area.

Adult↗
PubMedDate not supplied

[Effect of serotonin on the electrical activity of the cerebral cortex in the rabbit].

Application of serotonin on the rabbit cerebral cortex produced prolonged (minutes) periodical oscillations of the activation level and the level of spatial synchronization of neocortical biopotentials. Periodical changes of biopotentials correlation were due above all to a significant reorganization of phasic correlation of the EEG theta-components of remote neocortex points. The changes may be explained by the appearance, due to serotonin, of slow oscillations of the excitation level of the cortical neurones, as a systemic transitional reaction to the change in the balance of excitatory and inhibitory processes. The ability of serotonin to influence phasic relationships of the distantly-synchronous cortical theta-rhythm is of considerable significance for conditioned activity.

Animals↗
PubMedDate not supplied

Fast synchronization of perceptual grouping in laminar visual cortical circuits.

Perceptual grouping is well known to be a fundamental process during visual perception, notably grouping across scenic regions that do not receive contrastive visual inputs. Illusory contours are a classical example of such groupings. Recent psychophysical and neurophysiological evidence have shown that the grouping process can facilitate rapid synchronization of the cells that are bound together by a grouping, even when the grouping must be completed across regions that receive no contrastive inputs. Synchronous grouping can hereby bind together different object parts that may have become desynchronized due to a variety of factors, and can enhance the efficiency of cortical transmission. Neural models of perceptual grouping have clarified how such fast synchronization may occur by using bipole grouping cells, whose predicted properties have been supported by psychophysical, anatomical, and neurophysiological experiments. These models have not, however, incorporated some of the realistic constraints in which groupings in the brain are conditioned, notably the measured spatial extent of long-range interactions in layer 2/3 of a grouping network, and realistic synaptic and axonal signaling delays within and across cells in different cortical layers. This work addresses the question: Can long-range interactions that obey the bipole constraint achieve fast synchronization under realistic anatomical and neurophysiological constraints that initially desynchronize grouping signals? Can the cells that synchronize retain their analog sensitivity to changing input amplitudes? Can the grouping process complete and synchronize illusory contours across gaps in bottom-up inputs? Our simulations show that the answer to these questions is Yes.

Animals↗
PubMed2005

Functional relationship between human rolandic oscillations and motor cortical excitability: an MEG study.

Synchronization and desynchronization of the neural rhythm in the brain play an important role in the orchestration of perception, motor action and conscious experience. Based on the results of electrocorticographic and magnetoencephalographic (MEG) recordings, it has been considered that human rolandic oscillations originate in the anterior bank of the central sulcus (20-Hz rhythm) and the postcentral cortex (10-Hz rhythm): the 20-Hz oscillation is closely related to motor function, while the 10-Hz rhythm is attributed mainly to sensory function. To test whether the rolandic oscillations are functionally relevant to the motor cortical excitability, we examined effects of 1-Hz repetitive transcranial magnetic stimulation (rTMS) of the left primary motor cortex (M1) on movement-related changes of the rolandic oscillations in 12 normal subjects. MEG data recorded during brisk extension of the right index finger in two different sessions (with and without rTMS conditioning) were compared. Motor-evoked potential (MEP) of the right hand muscle was also measured before and after rTMS to assess the motor cortical excitability. We found that 1-Hz rTMS over M1 significantly reduced the movement-related rebound of the 20-Hz oscillation in association with decreased motor cortical excitability. In particular, movement-related rebound of the 20-Hz rhythm was closely tied with motor cortical excitability. These findings further strengthen the notion of functional relevance of 20-Hz cortical oscillation to motor cortical excitability. In the framework of previous studies, the decrease in movement-related rebound may be regarded as a compensatory reaction to the inhibited cortical activity.

Adult↗
PubMedDate not supplied

Neural dynamics in a model of the thalamocortical system. II. The role of neural synchrony tested through perturbations of spike timing.

Activity in the mammalian thalamocortical system is often accompanied by a synchronous discharge of cortical and thalamic neurons. Although many functions have been attributed to such synchronous firing, it is not known whether or how synchrony of firing per se affects thalamocortical operations. Direct experimental tests of the consequences of neuronal synchronization in vivo are hard to carry out, whereas theoretical studies based on single-neuron models cannot reveal the effects of synchrony at the system level. To overcome these limitations, we have used a perturbational approach to test the causal efficacy of synchrony per se in large-scale simulations of the thalamocortical system. The test consists of selectively disrupting firing synchrony by 'jittering' the timing of action potentials in the simulations and determining whether firing rates are modified by this perturbation. The simulations are based in detail on the known anatomy and physiology of the thalamocortical-visual system of the cat, and have been shown in a companion paper to produce episodes of fast synchronous activity at multiple levels. By carrying out the perturbation analysis, we established that neurons can have long membrane time constants (8-16 ms) and balanced synaptic activations, and yet function collectively in such a way that synchrony within a time window of 4 ms significantly affects the rates and selectivity of the responses to visual stimuli. The simulations also revealed a complex interplay, at the network level, between synchrony of firing and rate of firing. The dynamic consequences of firing synchrony were most evident when spike jittering was applied to specific polysynaptic loops involving corticocortical and corticothalamic connections. These results support the view that firing synchrony within thalamocortical and corticocortical loops plays a causal role in the cooperative and competitive neural interactions that produce pattern-selective responses in the cortex.

Action Potentials↗
PubMed1998

Strengthening of synchronized activity by tetanic stimulation in cortical cultures: application of planar electrode arrays.

Rat cortical neurons were cultured on planar electrode arrays with 64 embedded electrodes. Whole-cell recording from single neurons and multisite extracellular recording were carried out simultaneously in the cultured cortical networks, and the effects of focal tetanic stimulation of the culture were studied. Both the number of action potentials and the propagation velocity of stimulated bursts were increased after tetanic stimulation. These changes were associated with a marked increase in the number of late components in the synaptic current, but with little or no increase in the early peak synaptic current. The effects of tetanic stimulation were consistent with a widespread increase in the reliability of monosynaptic transmission.

Action Potentials↗
PubMed1995

Short- and long-range neuronal synchronization of the slow (< 1 Hz) cortical oscillation.

1. Multisite, extra- and intracellular recordings were carried out in cats under ketamine and xylazine anesthesia to assess the degree of synchrony and time relations among cellular activities in various neocortical fields during a slow (< 1 Hz) oscillation consisting of long-lasting depolarizing and hyperpolarizing phases. 2. Recordings were performed from visual areas 17, 18, 19, and 21, association suprasylvian areas 5 and 7, motor pericruciate areas 4 and 6, as well as some related thalamic territories, such as the lateral geniculate (LG), perigeniculate (PG), and rostral intralaminar nuclei. We used spike analyses (auto- and cross-correlograms) to reveal rhythmicities, time relations and coherence properties, analyses of field potentials recorded through the same microelectrodes as used for unit discharges (auto-and cross-correlation functions and their spectral equivalents), and spike-triggered averages. The results are based on 194 groups of neurons with a total of 591 neurons. Seventeen groups included intracellular recordings of cortical neurons with membrane potentials more negative than -60 mV and overshooting action potentials. 3. The most obvious and frequent signs of neuronal synchrony were found within and between association areas 5 and 7 and 18/19 and 21. Closely located cells or neuronal pools were also "closer" in time. The shortest mean time lag was found between cells within adjacent foci (1-2 mm) of areas 5 and 7 and was 12 +/- 11.2 (SE) ms, with more caudal neurons preceding the rostral ones in 70% of cases. In visual cortical fields, the time lag between areas 18/19 and 21 neurons was 27.6 +/- 36 ms, between areas 17 and 21 was 36.2 +/- 47.8 ms, and between areas 18/19 and 17 was 40 +/- 73 ms. In the majority of cases, neuronal firing in area 21 preceded that in areas 18/19. The longest time lags were found in distant recordings from visual and motor areas, with a mean of 124 +/- 86.8 ms, although in some cell groups the time intervals between neuronal firing in areas 18/19 or 21 and areas 4 or 6 were as short as approximately 20 ms. 4. Similar time relations were found in those instances in which the unit firing of the same cortical neuron was used as reference in spike triggered averages and was related to the field potential recorded from an adjacent area before impaling a neuron and, thereafter, to membrane potential fluctuations after impaling the cell. 5. The PG reticular thalamic neurons reflected the slow cortical oscillation in 75% of multisite recordings.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed2003

Propagating wave and irregular dynamics: spatiotemporal patterns of cholinergic theta oscillations in neocortex in vitro.

Neocortical "theta" oscillation (5-12 Hz) has been observed in animals and human subjects but little is known about how the oscillation is organized in the cortical intrinsic networks. Here we use voltage-sensitive dye and optical imaging to study a carbachol/bicuculline induced theta ( approximately 8 Hz) oscillation in rat neocortical slices. The imaging has large signal-to-noise ratio, allowing us to map the phase distribution over the neocortical tissue during the oscillation. The oscillation was organized as spontaneous epochs and each epoch was composed of a "first spike," a "regular" period (with relatively stable frequency and amplitude), and an "irregular" period (with variable frequency and amplitude) of oscillations. During each cycle of the regular oscillation, one wave of activation propagated horizontally (parallel to the cortical lamina) across the cortical section at a velocity of approximately 50 mm/s. Vertically the activity was synchronized through all cortical layers. This pattern of one propagating wave associated with one oscillation cycle was seen during all the regular cycles. The oscillation frequency varied noticeably at two neighboring horizontal locations (330 microm apart), suggesting that the oscillation is locally organized and each local oscillator is about </=300 microm wide horizontally. During irregular oscillations, the spatiotemporal patterns were complex and sometimes the vertical synchronization decomposed, suggesting a de-coupling among local oscillators. Our data suggested that neocortical theta oscillation is sustained by multiple local oscillators. The coupling regime among the oscillators may determine the spatiotemporal pattern and switching between propagating waves and irregular patterns.

Animals↗
PubMed2006

Analysis of synchrony demonstrates 'pain networks' defined by rapidly switching, task-specific, functional connectivity between pain-related cortical structures.

Imaging studies indicate that experimental pain is processed in multiple cortical areas which are often characterized as a network. However, the functional connectivity within the network and the other properties of the network is poorly understood. Substantial evidence demonstrates that synchronous oscillations between two cortical areas may indicate functional connectivity between those areas. We test the hypothesis that cortical areas with pain-related activity are functionally connected during attention to a painful stimulus. We stimulated with a painful, cutaneous, laser stimulus and recorded the response directly from the cortical surface (electrocorticography--ECoG) over primary somatosensory (SI), parasylvian (PS), and medial frontal (MF) cortex through subdural electrodes implanted for treatment of epilepsy. The results demonstrate synchrony of ECoGs between cortical structures receiving input from nociceptors, as indicated by the occurrence of laser-evoked potentials (LEPs) and/or event-related desynchronization (ERD). Prior to the stimulus, directed attention to the painful stimulus consistently increased the degree of synchrony between SI and PS regions, as the subject anticipated the stimulus. After the laser stimulus, directed attention to the painful stimulus consistently increased the degree of synchrony between SI and MF cortex, as the subject responded by counting the stimulus. Therefore, attention to painful stimuli always enhanced synchrony between cortical pain-related structures. The pattern of this synchrony changed as the patient switched tasks from anticipation of the stimulus to counting the stimulus. These results are the first compelling evidence of pain networks characterized by rapidly switching, task-specific functional connectivity.

Adult↗
PubMed1982

[Intracranial pressure pulse waveform: considerations about its origin and methods of estimating intracranial pressure dynamics].

Epidural pulse waveform is important as an indicator of intracranial pressure (ICP) dynamics. In this study, the origin of epidural pulse and the clinical implication of its waveform were investigated, using anesthetized artificially ventilated dogs. For this purpose, a cortical artery and a vein were cannulated, and the pressures were recorded simultaneously with epidural pressure (EDP), epidural pulse waveform (EDP-WF), systemic arterial pressure measured in a carotid artery (SAP), central venous pressure (CVP) and electrocardiogram. EDP-WF is composed of several initial peaks and a small delayed peak on the descending limb. The former peaks were slightly delayed from the SAP pulse and were synchronous with the cortical arterial pulse. The latter peak was synchronous with the atrial "a" wave on CVP, but not with the cortical venous pulse. Moreover, the cortical venous pulse was quite similar to EDP-WF. These findings indicate that the pulsation of the brain may be generated by the pulsatile arterial blood flow into the brain, which also affected the pulsation of the cortical vein. The latter peak which was considered to be of venous origin may reflect the dynamics of venules in the brain, not of the cortical vein. Increase of ICP by constant inflation of the epidural balloon or inhalation of CO2 cause EDP-WF monotonous. It is possible that the transmission of arterial pulse into the brain was augmented because of the tightness of the brain or decrease of cerebral vascular tone, although the cortical arterial pressure was not significantly changed or was even slightly decreased. Using a bolus injection technique, the change of EDP-WF in cats was compared with volume-pressure response (VPR) and pulse pressure (PP) which are reported to be good indicators for ICP dynamics. At about 30mmHg, EDP-WF became monotonous while VPR or PP showed only linear relationships with EDP up to 50 to 60 mmHg. Therefore EDP-WF may provide useful information about ICP dynamics in a relatively lower pressure range which could not be detected by VPR or PP study.

Animals↗
PubMed2002

Medium-range oscillatory network and the 20-Hz sensorimotor induced potential.

Although synchronously oscillating neuronal assemblies have been the subject of many studies, a clear identification of the spatiotemporal characteristics of a medium-range oscillatory network is still lacking. Herein, we present a method for the extraction of a new waveform, namely the mean induced potential (IP), which allows the identification of the spatiotemporal characteristics of induced EEG responses. The IP calculation was applied to the 20-Hz component of the sensorimotor rhythm in order to obtain a 20-Hz sensorimotor induced potential (20-Hz SIP). The spatiotemporal characteristics of the 20-Hz bursts seen after median nerve stimulation and self-paced finger movements were extracted by means of current source density reconstruction and synchronization analysis. A cortical network including the controlateral primary motor cortex, the supplementary motor area, and the controlateral supramarginalis gyrus was found to generate the 20-Hz bursts, and the various activated areas were found to be highly synchronized. Our results demonstrate for the first time the existence of a medium-range cortical network in the human sensorimotor region whose constituents oscillate synchronously.

Adult↗
PubMed1995

Large-scale cortical networks and cognition.

The well-known parcellation of the mammalian cerebral cortex into a large number of functionally distinct cytoarchitectonic areas presents a problem for understanding the complex cortical integrative functions that underlie cognition. How do cortical areas having unique individual functional properties cooperate to accomplish these complex operations? Do neurons distributed throughout the cerebral cortex act together in large-scale functional assemblages? This review examines the substantial body of evidence supporting the view that complex integrative functions are carried out by large-scale networks of cortical areas. Pathway tracing studies in non-human primates have revealed widely distributed networks of interconnected cortical areas, providing an anatomical substrate for large-scale parallel processing of information in the cerebral cortex. Functional coactivation of multiple cortical areas has been demonstrated by neurophysiological studies in non-human primates and several different cognitive functions have been shown to depend on multiple distributed areas by human neuropsychological studies. Electrophysiological studies on interareal synchronization have provided evidence that active neurons in different cortical areas may become not only coactive, but also functionally interdependent. The computational advantages of synchronization between cortical areas in large-scale networks have been elucidated by studies using artificial neural network models. Recent observations of time-varying multi-areal cortical synchronization suggest that the functional topology of a large-scale cortical network is dynamically reorganized during visuomotor behavior.

Animals↗
PubMed2000

Neural mechanisms of visual feature grouping.

The present work relates compositions of visual scenes to signals in visual cortex and to cortical circuit models in order to understand neural mechanisms of perceptual feature grouping. It starts from the hypothesis that synchronization and decoupling of cortical gamma-activities (35-90 Hz) define the relations among visual objects. Here we concentrate on synchronization related to two basic visual situations, (1.) static retinal stimulation during ocular fixation, and (2.) transient stimulation during sudden luminance modulations or shifts in object position. For testing the synchronization hypothesis we investigated signal correlations of multiple micro-electrode recordings in visual cortex areas V1 and V2 of behaving monkeys. Static retinal stimuli induce gamma-activities that are loosely phase-coupled among neighboring neural populations of an object's cortical representation. This can explain why synchronization, measured by spectral coherence, is restricted to few millimeters cortex. Such patches of gamma-synchronization become de-coupled across the representation of an object's contour, and thereby can code figure-ground segregation. Transient stimuli evoke synchronized volleys of stimulus-locked activities that are typically non-rhythmic and include low frequency components in addition to those in the gamma-range. It is argued why stimulus-induced and stimulus-locked phase-coupled activations are both appropriate for supporting perceptual feature grouping. Clues for basic neural mechanisms participating in feature grouping are provided by our biologically motivated simulations of synchronization in cortical structures. (1.) Local populations generate gamma-oscillations via feedback inhibition during states of static retinal stimulation. (2.) Bidirectional facilitatory connections serve for phase-coupling among neighboring neural populations. (3.) Spike transmission delays, increasing with cortical distance, can explain the restriction of gamma-coherence to patches of few millimeters cortex. (4.) The size of synchronization patches in one visual area (e.g., V1) can define the size of classical receptive fields at the consecutive level of visual processing (V2) if Hebbian learning is operative. This may explain the increase in receptive field size at consecutive levels of visual processing. In conclusion, our results and those of others are supportive for the hypothesis that phase-coupled gamma-signals can code feature grouping and object continuity. However, convincing experimental proofs showing directly the dependence of perceptual grouping on cortical phase-coupling are still lacking.

Animals↗
PubMed1998

'Non-synaptic' mechanisms in seizures and epileptogenesis.

The role of 'non-synaptic' mechanisms (i.e. those mechanisms that are independent of active chemical synpases) in the synchronization of neuronal activity during seizures and their possible contribution to chronic epileptogenesis are summarized. These 'non-synaptic' mechanisms include electrotonic coupling through gap junctions, electrical field effects (i.e. ephaptic transmission), and ionic interactions (e.g. increases in the extracellular concentration of K(+)). Several lines of evidence indicate that granule cells and pyramidal cells of the hippocampus, and probably other cortical neurons, can generate synchronized electrical activity after active chemical synaptic transmission has been blocked. This synchronized activity is sensitive to alterations in the size of the extracellular space, thus suggesting that electrical field effects and ionic mechanisms contribute to this synchronized activity. Recent studies also indicate that 'non-synaptic' synchronization is quite prominent early in development. Electrophysiological data from hippocampal and neocortical slices have led to a re-interpretation of the fast prepotentials (i.e. partial spikes) recorded in cortical pyramidal cells, suggesting that they may not be due to dendritic spike generation. Improvement in freeze-fracture ultrastructural techniques have led to a re-assessment of previous data on gap junctions in the nervous system and opened new approaches to the quantitative analysis and characterization of gap junctions on glia and neurons. Finally, new methods of dye/tracer coupling have the potential to provide a more rigorous basis for evaluating gap junctions and electrotonic communication between neurons in the mammalian central nervous system. Therefore, recent data continue to suggest that gap junctions and electrotonic coupling play an important role in neural integration, although additional studies using new techniques will be needed to address some of the controversial issues that have arisen over the last several decades.

Animals↗