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Results for “Cortical Synchronization”

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PubMedDate not supplied

Synchronous adrenal cortical carcinoma in a patient with lung cancer.

Workup of a patient with lung cancer involves adrenal imaging for evaluation of metastatic disease. When nodules are detected, biopsy is often attempted to differentiate a primary neoplasm from metastatic carcinoma or other lesions, such as granuloma. CT-guided biopsy of the deep seated adrenal glands is technically difficult and material is often scanty. We present a case and review histologic features enabling the diagnosis of adrenal cortical carcinoma.

Adrenal Cortex Neoplasms↗
PubMedDate not supplied

[Effect of stimulation of the mediodorsal nucleus of the thalamus on the synchronous flow of cortical electrical processes].

It was shown in chronic experiments on rabbits that stimulation of the mediodorsal thalamic nucleus brings about, as a rule, en enhancement of amplitudes of the spatially-synchronous cortical theta-rhythm and a decreased frequency of its oscillations. Analysis of the phenomenon by means of a simple mathematical models shows that such a connection between amplitude and frequency EEG parameters may be accounted for by the existence of two-way cyclic interactions between the cortex and the thalamus, forming a closed contour of a feedback connection. The capacity of the mediodorsal thalamic nucleus to influence the synchroneity of cortical electrical processes is compared with published data on its role in conditioned activity.

Animals↗
PubMed2004

Visual assessment of selected high amplitude frontopolar slow waves of sleep: differences between healthy subjects and apnea patients.

Slow wave sequences with individually defined amplitude criterion were selected manually from frontopolar sleep EEG of eight healthy control subjects and eight patients with sleep apnea syndrome. Healthy subjects had clearly more time occupied by slow wave sequences in all night sleep. Closer examination revealed that the difference in the amount of slow wave sequence time between the groups was statistically significant only in the first NREM sleep episode. In other words, healthy subjects had more time with slow wave sequences in the first NREM sleep episode, where sleep pressure is supposed to be highest. The lower amount of slow wave sequences in the apnea patients might reflect the fragmented sleep of the patients, inhibiting cortical synchronization.

Adult↗
PubMed2000

Lateral spike conduction velocity in the visual cortex affects spatial range of synchronization and receptive field size without visual experience: a learning model with spiking neurons.

Classical receptive fields (cRF) increase in size from the retina to higher visual centers. The present work shows how temporal properties, in particular lateral spike velocity and spike input correlation, can affect cRF size and position without visual experience. We demonstrate how these properties are related to the spatial range of cortical synchronization if Hebbian learning dominates early development. For this, a largely reduced model of two successive levels of the visual cortex is developed (e.g., areas V1 and V2). It consists of retinotopic networks of spiking neurons with constant spike velocity in lateral connections. Feedforward connections between level 1 and 2 are additive and determine cRF size and shape, while lateral connections within level 1 are modulatory and affect the cortical range of synchronization. Input during development is mimicked by spike trains with spatially homogeneous properties and a confined temporal correlation width. During learning, the homogeneous lateral coupling shrinks to limited coupling structures defining synchronization and related association fields (AF). The size of level-1 synchronization fields determines the lateral coupling range of developing level-1-to-2 connections and, thus, the size of level-2 cRFs, even if the feedforward connections have distance-independent delays. AFs and cRFs increase with spike velocity in the lateral network and temporal correlation width of the input. Our results suggest that AF size of V1 and cRF size of V2 neurons are confined during learning by the temporal width of input correlations and the spike velocity in lateral connections without the need of visual experience. During learning from visual experience, a similar influence of AF size on the cRF size may be operative at successive levels of processing, including other parts of the visual system.

Action Potentials↗
PubMed1979

The effect of high mesencephalic transection (cerveau isolé) and pentobarbital on basal forebrain mechanisms of EEG synchronization.

A study was made of the effects of high mesencephalic transection (cerveau isolé) and low doses of pentobarbital on the cortical synchronizations elicited in acute immobilized cats by (a) low frequency stimulation of the lateral hypothalamus (HL) and nucleus ventralis anterior thalami (VA) and (b) by low and high frequency stimulation of the laterobasal preoptic region (RPO) and olfactory tubercle (TbOf). The results obtained were as follows: (1) The synchronizations induced by basal forebrain stimulations were found to survive in acute cerveau isolé cats, moreover, even a facilitation of the synchronizing effect were observed. (2) A gradual facilitation was observed upon TbOf and RPO stimulation, while in the case of VA and HL stimulations, the facilitation appeared immediately after the transection. (3) Low doses of pentobarbital depressed the cortical effects of TbOf stimulation, while an increase of the synchronizing effect of low frequency VA and HL stimulation was found. The observations suggested that (i) the synchronizing mechanism in the ventral part of the basal forebrain (RPO and TbOf) differs from that of the thalamus and HL; (ii) the basal forebrain synchronizing mechanism is effective without the contribution of the brain stem; (iii) the mechanism responsible for the synchronizing effect of low frequency HL stimulation is similar as that described for the thalamus.

Animals↗
PubMed2003

Association of EEG coherence and an exonic GABA(B)R1 gene polymorphism.

The GABA(B) receptor 1 gene is mapped to chromosome 6p21.3 within the HLA class I region close to the HLA-F gene. Susceptibility loci for epilepsy and schizophrenia have been mapped in this region. Based on pharmacological evidence, it has been suggested that GABA(B) receptors may play a crucial role in the synchronization of EEG oscillations, which in turn can be abnormal in neuropsychiatric disorders. In the present study, the hypothesis was tested, whether three exonic variants of the gene encoding the human GABA(B) receptor (GABA(B)R1) modify cortical synchronization measured as scalp-recorded EEG-coherence. Two principal components of EEG coherence (frontal coherence, parietotemporal coherence) were investigated in 104 healthy subjects during three conditions: resting EEG, activated EEG, and event-related EEG. No significant associations were found between the frontal coherence component and any polymorphism or between the parietotemporal coherence component and the exon 1a1 polymorphism. However, parietotemporal coherence showed statistically highly significant associations across all three experimental conditions with exon 7 and trend associations with exon 11. The results provide evidence that the translated polymorphism of exon 7 may be functionally meaningful and impact cortical EEG oscillations. Since variations of EEG coherence have been described for several neuropsychiatric disorders, the present association should be tested in clinical samples using EEG coherence as an intermediate phenotype.

Adult↗
PubMed1993

Eegraphic and behavioural effects of ondansetron, a 5HT3 antagonist, in rabbits.

1. EEGraphic and behavioural effects of ondansetron, a 5HT3 antagonist, have been studied in the rabbit. Subsequently we tested the neurophysiological and behavioural interactions between ondansetron and L-5-HTP induced serotonergic syndrome. 2. The drug produced a dose-dependent (0.001, 0.01, 0.1 mg/kg i.v.) increase in the cortical power density spectrum, particularly in the range of the lowest frequencies bands. This effect is expression of cortical synchronization. 3. The lowest and mild dose, but not the highest, failed to produce behavioural sedation and to inhibit the arousal induced by vibroacustical stimulation. 4. L-5-HTP (10 mg/kg i.v.) administration generated a typical EEGraphic-behavioural pattern characterized by a decrease of cortical power spectrum density and stereotyped movements. The EEGraphic effects were significantly suppressed by administration of mild and higher doses of ondansetron, while the behavioural effects were inhibited by all doses tested. 5. It is concluded that ondansetron acts with considerably efficacy on central nervous system. The administration of low and mild doses shows a singular dissociation between EEGraphic and behavioural actions. The inhibition of the L-5-HTP behavioural syndrome by ondansetron suggests that this drug acts on behaviour only when there is an altered physiological pattern.

5-Hydroxytryptophan↗
PubMed1975

The effects of serotonin injections into the locus coeruleus on ponto geniculo occipital (PGO) waves and cortical EEG pattern in cats.

Reserpine injected iv at 0-8--1-0 mg/kg doses induced continuous ponto-geniculo-occipital (PGO-like) waves in immobilized cats. Both 5-HT and quipazine injected into the locus coeruleus decreased the frequency of reserpine-induced PGO waves and increased cortical synchronization. Suppression of PGO activity persisted for 15--30 min whilst synchronizing effects lasted much longer. Methysergide increased the frequency of PGO activity but caused no clear changes in the EEG pattern.

Animals↗
PubMed2004

Perception-related modulations of local field potential power and coherence in primary visual cortex of awake monkey during binocular rivalry.

Cortical synchronization at gamma-frequencies (35-90 Hz) has been proposed to define the connectedness among the local parts of a perceived visual object. This hypothesis is still under debate. We tested it under conditions of binocular rivalry (BR), where a monkey perceived alternations among conflicting gratings presented singly to each eye at orthogonal orientations. We made multi-channel microelectrode recordings of multi-unit activity (MUA) and local field potentials (LFP) from striate cortex (V1) during BR while the monkey indicated his perception by pushing a lever. We analyzed spectral power and coherence of MUA and LFP over 4-90 Hz. As in previous work, coherence of gamma-signals in most pairs of recording locations strongly depended on grating orientation when stimuli were presented congruently in both eyes. With incongruent (rivalrous) stimulation LFP power was often consistently modulated in consonance with the perceptual state. This was not visible in MUA. These perception-related modulations of LFP occurred at low and medium frequencies (< 30 Hz), but not at gamma-frequencies. Perception-related modulations of LFP coherence were also restricted to the low-medium range. In conclusion, our results do not support the expectation that gamma-synchronization in V1 is related to the perceptual state during BR, but instead suggest a perception-related role of synchrony at low and medium frequencies.

Algorithms↗
PubMed2004

Respiratory chemoreflexes and effects of cortical activation state in urethane anesthetized rats.

Urethane anesthetized (< 1 .3 g/kg), Sprague-Dawley (SD) rats spontaneously cycled between a cortically desynchronized state (State I) and a cortically synchronized state (State III), which were very similar to awake and slow wave sleep (SWS) states in unanesthetized animals, based on EEG criteria. These low levels of urethane anaesthesia did not cause significant respiratory depression or reductions in sensitivity to hypoxia (10% O2 in nitrogen) or hypercapnia (5% CO2 in air) in rats in either State I or State III. Thus, breathing frequency (fR), tidal volume (VT) and total ventilation (VTOT) all increased on cortical activation in urethane-anaesthetized rats whether breathing air, the hypoxic or the hypercapnic gas mixture, in a manner that was very similar to that observed in unanaesthetized animals. The relative sensitivity to hypoxia was greater in State III than State I, the relative sensitivity to CO2, overall, was equal in both states, State III occurred less often during hypoxia and hypercapnia, and hypoxic, urethane-anaesthetized rats sighed frequently, particularly in State I. This is also similar to the situation seen in unanesthetized rats. Given the similarities seen between urethane anesthetized rats in the present study and literature values for unanesthetized rats, the data suggest that urethane-anaesthetized rats provide a good model system for studying respiratory patterns and chemoreflexes as a function of cortical activation state.

Analysis of Variance↗
PubMed1982

Phasic loss of constraints in timing of neuronal spikes in the feline centrum medianum during EEG alpha-like activity.

In unrestrained cats, temporal patterns of single neuronal firing in the centrum medianum-parafascicular complex (CM-Pf) of thalamus were studied during a state of motionless quiet wakefulness. The spike trains from each neuron were electronically divided into episodes that occurred during desynchronized EEG and those that occurred during bursts of 6-14 Hz EEG spindles or alpha-like activity over the parieto-occipital cortex and in the CM-Pf. Contrary to expectations based on the theory of inhibitory phasing of neuronal activity, the episodes of synchronized quiet wakefulness (S-QW) were associated with independent and random distribution of spike intervals, although they tended to occur in clusters. During episodes of desynchronized quiet wakefulness (D-QW), significant temporal patterns were emitted by most neurons studied. The results suggest that: (a) during D-QW and increased levels of vigilance, temporal patterns are generated by cognitive processes and enhanced specific connectivities between CM-Pf neurons and other systems; (b) if connectivity is defined as increased certainty of synaptic transmission and iterative activation of the same pathways, then the assumption that the gross EEG thalamo-cortical synchronization represents increased connectivities between the CM-Pf neurons and other systems, may be erroneous; and (c) since temporal patterns of single neuronal discharges are determined by specific spatio-temporal distribution of synaptic drive, therefore during EEG spindles, most EPSP-IPSP sequences impinging upon CM-Pf neurons are conveyed by randomly varying polysynaptic pathways and have random spatio-temporal distribution on the soma and dendrites. In light of other observations, such a process is equivalent to an active introduction of uncertainty or 'entropy' into the information processing system, a state which may be important in preserving plasticity of operational modes of CM-Pf neurons and those with which they directly and/or indirectly interact.

Action Potentials↗