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PubMedDate not supplied

Cortical coding.

Physiological photic and sound stimulation generated almost synchronous summated cortical evoked peak interval patterns over all regions of the head studied in man. Although the peak interval synchrony in all regions was obvious, it was observed that the peak amplitudes, and even phase relations varied over the different brain regions. The almost invariant peak time interval patterns for the input modalities studied, suggested a simple, generalized direct cortical coding that signaled immediate environmental change to the entire brain.

Acoustic Stimulation↗
PubMed2001

Does post-movement beta synchronization reflect an idling motor cortex?

After the completion of a voluntary movement, a synchronization of cortical beta rhythms is recorded over the contralateral central region, which is assumed to reflect the termination of the motor command. In order to test this hypothesis, we compared in eight healthy subjects the synchronization of EEG beta rhythms following active and passive index extension. The passive movement was also performed after deafferentation by ischaemic nerve block in three subjects. Beta synchronization was present in all subjects after both active and passive movements, and disappeared under ischaemia in all three subjects. Post-movement beta synchronization can not solely be explained by an idling motor cortex. It may also, at least in part, reflect a movement-related somatosensory processing.

Adult↗
PubMed1985

Alterations in preoptic unit activity on stimulation of caudal brain stem EEG-synchronizing structures.

Effects of stimulation of EEG-synchronizing structures of the caudal brain stem reticular formation with low (6 Hz) and high (100 Hz) frequencies were studied on 42 neurons of the preoptic area, in encéphale isolé cats. Though low-frequency stimulation produced excitation and inhibition, the majority of the influenced neurons of the preoptic area had effects of the former type. Cortical EEG synchronization was also induced by low-frequency stimulation of the caudal brain stem. High-frequency stimulation, on the other hand, produced inhibition in a majority of the influenced neurons and induced, mostly, desynchronization of the cortical EEG. A majority of the neurons that were inhibited on high-frequency stimulation, remained unaffected during low-frequency stimulation. The influence induced on the preoptic area neurons by low-frequency stimulation could be obtained even in the absence of cortical EEG synchronization. Changes induced on preoptic neurons by high-frequency stimulation may be partially related to induced cortical EEG desynchronization.

Animals↗
PubMed1996

Reorganization in the auditory cortex of the rat induced by intracortical microstimulation: a multiple single-unit study.

Many manipulations are able to change or perturb various aspects of single neuron properties and interneuronal relationships. Changes of cerebral cortex organization have been observed in different cortical areas and at different time scales in relation to peripheral stimulation, peripheral damage, associative learning, and electrical stimulation. Here we describe studies on separable multineuron recordings in the rat's auditory cortex under two different anesthetics. Acoustic stimuli were used as a normal, physiological input, and weak electrical intracortical microstimulation (ICMS) as a perturbation that forces a rapid cortical reorganization. ICMS induced fast changes in the cortical map and in the receptive field properties of cells at the electrically stimulated and adjacent electrodes. In effect there was an enlargement of the cortical domain tuned to the acoustic frequency that had been represented at the stimulating electrode. ICMS also incremented afterdischarge responses; these consisted of an initial response to the auditory stimulus followed by less intense repetitive activity that was stimulus-time locked and had a period of 8-12 Hz, similar to that of the spontaneous synchronous activity. Cortical activity under ketamine differed from that under pentobarbital sodium, although in both situations we observed that cortical neurons were highly synchronous.

Acoustic Stimulation↗
PubMed2006

Efficient localization of synchronous EEG source activities using a modified RAP-MUSIC algorithm.

Synchronization across different brain regions is suggested to be a possible mechanism for functional integration. Noninvasive analysis of the synchronization among cortical areas is possible if the electrical sources can be estimated by solving the electroencephalography inverse problem. Among various inverse algorithms, spatio-temporal dipole fitting methods such as RAP-MUSIC and R-MUSIC have demonstrated superior ability in the localization of a restricted number of independent sources, and also have the ability to reliably reproduce temporal waveforms. However, these algorithms experience difficulty in reconstructing multiple correlated sources. Accurate reconstruction of correlated brain activities is critical in synchronization analysis. In this study, we modified the well-known inverse algorithm RAP-MUSIC to a multistage process which analyzes the correlation of candidate sources and searches for independent topographies (ITs) among precorrelated groups. Comparative studies were carried out on both simulated data and clinical seizure data. The results demonstrated superior performance with the modified algorithm compared to the original RAP-MUSIC in recovering synchronous sources and localizing the epileptiform activity. The modified RAP-MUSIC algorithm, thus, has potential in neurological applications involving significant synchronous brain activities.

Algorithms↗
PubMed1980

Synchronous development of motor cortical output to different muscles in the kitten.

Previous observations indicate that the output linkages from motor cortex (area 4) to triceps brachii motoneurons develop relatively late in the postnatal kitten. Responses in multiple, simultaneously-recorded EMG's from facial, forelimb and proximal hindlimb musculature to intracortical microstimulation appear over gestational days 107-111 (about 41 days postnatally). Thus, output from the motor cortex to alpha motoneurons develops in a synchronous, rather than a sequential manner across the area 4 homunculi.

Aging↗
PubMed2002

Conditional cross-correlation analysis of thalamocortical neurotransmission.

We developed a method to quantify the probability of a target neuron discharge following synchronous or asynchronous discharges among a pair of reference neurons. To illustrate this method, we simultaneously recorded three neurons having overlapping receptive fields in the somatosensory system: two reference neurons in the thalamic ventrobasal complex and one target neuron in the secondary somatosensory (SII) cortex. Our results show that focal cutaneous stimulation elicits synchronized discharges among thalamic neurons having similar place and submodality properties. Conditional cross-correlation analysis of the reference and target spike trains indicates that thalamic synchronization increases cortical responsiveness. This result suggests that neuronal synchronization plays a critical role in transmitting sensory information from thalamus to the cerebral cortex.

Algorithms↗
PubMed1983

[Paroxysmal nocturnal activity in partial epilepsy in the adult].

Thirty-four adults with partial epilepsy underwent polysomnographic sessions. Three sub-groups of patients were determined by timing their EEG paroxysmal activities (PA) according to the possible increase in PA related to their sleeping or awake state. Twenty-seven had an increase in PA when sleeping, 5 when awake and no significant difference was found in two other patients. Patients who suffered from nocturnal or partial elementary epileptic seizures were those who showed a PA increase when in a sleep state. These patients had a lower PA density during a waking state than the patients with a PA increase when awake. The more synchronized (stages 3 + 4) and desynchronized (waking) cortical states influence the PA densities in such a way that there is a significant difference between both sub-groups. The PA density modulation found with the slow-wave sleep stages adds to that induced by sleep and waking states.

Adolescent↗
PubMed2006

The self-regulating nature of spontaneous synchronized activity in developing mouse cortical neurones.

Waves of spontaneous electrical activity that are highly synchronized across large populations of neurones occur throughout the developing mammalian central nervous system. The stages at which this activity occurs are tightly regulated to allow activity-dependent developmental programmes to be initiated correctly. What determines the onset and cessation of spontaneous synchronous activity (SSA) in a particular region of the nervous system, however, remains unclear. We have tested the hypothesis that activity itself triggers developmental changes in intrinsic and circuit properties that determine the stages at which SSA occurs. To do this we exposed cultured slices of mouse neocortex to tetrodotoxin (TTX) to block SSA, which normally occurs between embryonic day 17 (E17) and postnatal day 3 (P3). In control cultured slices, SSA rarely occurs after P3. In TTX-treated slices, however, SSA was generated from P3 (the day of TTX removal) until at least P10. This indicates that in the absence of spontaneous activity, the mechanisms that normally determine the timing of SSA are not initiated, and that a compensatory response occurs that shifts the time of SSA occurrence to later developmental stages.

Action Potentials↗
PubMed1977

The dipole layer as a model for scalp potentials.

Estimates are made of the potential field at the scalp and cortical surfaces due to large numbers of synchronously active cortical current sources. The basic model is a dipole layer in an infinite, homogeneous conducting medium. Estimates are made of the effects of various inhomogeneities on the attenuation of potentials. It is shown that these approximate methods seem to illuminate the following questions which are of interest in EEG research: (1) The interpretation of reference recordings in terms of local source currents; (2) The differences in amplitude between scalp and cortical recordings; (3) The differences in frequency spectra between scalp and cortical recordings; (4) The observation that alpha rhythm can be recorded deep in the brain; and (5) The effects of simple inhomogeneities on the attenuation of potentials.

Cerebral Cortex↗
PubMed2006

The role of corticothalamic coupling in human temporal lobe epilepsy.

The EEG activity of the thalamus and temporal lobe structures (hippocampus, entorhinal cortex and neocortex) was obtained using intracerebral recordings (stereoelectroencephalography, SEEG) performed in patients with TLE seizures undergoing pre-surgical evaluation. Synchrony was studied using a statistical measure of SEEG signal interdependencies (non-linear correlation). The results demonstrated an overall increase of synchrony between the thalamus and temporal lobe structures during seizures. Moreover, although there was great inter-individual variability, we found that values from seizure onset period were significantly higher than values from the background period (P = 0.001). Values at the end of seizure were significantly higher than values from the seizure onset (P < 0.0001). Several indices were also defined in order to correlate some clinical features to the degree of coupling between cortical structures and the thalamus. In patients with mesial TLE seizures, a correlation was found between the degree of thalamocortical synchrony and the presence of an early loss of consciousness but not with other clinical parameters. In addition, surgical prognosis seemed better in patients with low values of thalamocortical couplings at the seizure onset. This report demonstrates that the thalamus and remote cortical structures synchronize their activity during TLE seizures and suggest that the extension of the epileptogenic network to the thalamus is a potential important factor determining surgical prognosis.

Adolescent↗
PubMed1997

The role of axonal delay in the synchronization of networks of coupled cortical oscillators.

Coupled oscillator models use a single phase variable to approximate the voltage oscillation of each neuron during repetitive firing where the behavior of the model depends on the connectivity and the interaction function chosen to describe the coupling. We introduce a network model consisting of a continuum of these oscillators that includes the effects of spatially decaying coupling and axonal delay. We derive equations for determining the stability of solutions and analyze the network behavior for two different interaction functions. The first is a sine function, and the second is derived from a compartmental model of a pyramidal cell. In both cases, the system of coupled neural oscillators can undergo a bifurcation from synchronous oscillations to waves. The change in qualitative behavior is due to the axonal delay, which causes distant connections to encourage a phase shift between cells. We suggest that this mechanism could contribute to the behavior observed in several neurobiological systems.

Axons↗
PubMed1995

[Synchronization processes in the mechanisms of short-term memory in monkeys: the participation of cholinergic and glutaminergic cortical structures].

Administration of amysil blocking M-cholinoreceptors, and APV the duration of short-term storing of information was decreased whereas the motor response time increased. This was followed by a considerable desynchronisation of the unit activity. The NMDA and APB improved the characteristics of the short-term memory. The role of synchronisation of the information processes in the short-term memory mechanisms and participation of cholinergic and glutamatergic systems in them, are discussed.

Acoustic Stimulation↗
PubMed1998

[Effect of high frequency cortical microstimulation on the interhemisphere synchronization in the rat motor cortex].

Long-term posttetanic changes of callosal neurons' synchronisation was studied in the rat motor cortex. Following tetanisation, the synchronisation of previously active cells decreased whereas the cells that became active were mostly synchronised. Ultra "narrow" peaks appeared in callosal interactions and correlated with "intermediate" (30-80 ms) those.

Action Potentials↗
PubMed2004

Contextual modulation of synchronization to random dots in the cat visual cortex.

Synchronization of neuronal activity has been proposed as a binding mechanism for integration of image properties into one coherent percept. In the present study, we investigated the contextual modulation of synchronization to random dot patterns. Coherent motion of random dots evoked well synchronized responses in area 17 of anaesthetized cats when the stimulus was presented in the compound receptive field of recorded sites. Gradually changing the directional coherence of random dots in the surround while maintaining fully coherent motion of the stimulus in the receptive field significantly suppressed synchronization of neuronal activity for some stimulus conditions. However, usually one or two peaks of increased synchronization were found in the surround coherence tuning curves with low (8-12%) and/or moderate (25-50%) coherence in the surround. At the population level, synchronization was significantly depressed with incoherent motion in the receptive field and when both the surround and the receptive field were jointly stimulated with 0% coherence. The intriguing finding was the discovery of two distinct groups of cells with opposite synchronization changes dependent on the presence or absence of significant synchronization in their spontaneous activity. The latter group of neurons showed peaks of increased synchronization with lower surround coherence, thus probably being more sensitive to the direction of the surround motion. Overall, our findings support the notion that binding of stimulus properties can be achieved by synchronized activity of cortical cells. However, our findings go further than the original hypothesis of feature binding by synchrony to show that synchronization of cortical activity may be directly related to the decision making processes, which in turn are related to the threshold of perception of coherent motion.

Animals↗
PubMed1986

Spinal neuronal inhibition and EEG synchrony by electrical stimulation in subcortical forebrain regions of the cat.

In cats anaesthetized with sodium pentobarbital and 70% N2O, single lumbar dorsal horn neurons were excited by controlled noxious radiant heating of glabrous hindpaw skin. The EEG was recorded from the pericruciate cortex and posterior lateral gyrus. Subcortical forebrain sites where electrical stimulation inhibited dorsal horn neuronal heat-evoked responses contralaterally were identified by mapping the caudate nucleus, internal capsule, septum, nucleus accumbens and basal forebrain regions. Inhibitory sites were mainly located in the ventral forebrain (ventral septum, diagonal band, basal forebrain). The caudate nucleus and internal capsule had a low incidence and effectiveness of inhibitory sites. In the basal forebrain, the incidence and effectiveness of inhibitory sites decreased from caudal to rostral regions. There was a rostral limit of inhibitory sites, both medially and laterally. The magnitude of inhibition increased with graded increases in brain stimulation intensity. The mean incremental increase in inhibition was greater for caudal than for rostral basal forebrain sites. Mean stimulus currents for threshold of inhibition and for inhibition to 50% of control heat responses were lower for caudal than for rostral sites. Responses of the dorsal horn neurons to increasing temperatures of noxious skin heating were monotonic linear functions over the temperature range studied (48-53 degrees C). Stimulation in both rostral and caudal basal forebrain decreased the slope of this stimulus-response function, with a greater decrease for caudal sites. Cortical EEG synchronization was evoked by stimulation in the caudate nucleus and rostral basal forebrain. For both regions, most synchronogenic sites did not produce descending inhibition of dorsal horn neurons. The significance of these findings in relation to descending inhibition from other brain regions and stimulation-produced analgesia is discussed.

Action Potentials↗
PubMed1978

EEG synchronization in seizures: facts and models.

In topographic studies of seizure patterns in the rabbit, the phenomenon of synchronization has turned out to be characterized by regular propagation of the potential fields underlying the raphoelements observed in the EEG: in most cases these potential fields describe circular paths within the cortex. Moreover, a multielectrode was developed to explore the different layers of the cortex simultaneously. Both approaches brought enough material to put forward a hypothesis on the origin and the maintenance of so-called synchronized activities.

Animals↗