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Results for “Cortical Synchronization”

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At least 1,297 records · Page 72Linked to original sources
PubMed1991

The role of the right parietal region in a movement time estimation task.

Thirteen right-handed male students performed a time estimation task by pressing a button with their left or right hand for an interval of either 0.5 or 1.3 s. Thirty channels of EEG were recorded, with the right ear as reference. After transforming the raw EEG data into local average reference data, the topography of event related desynchronization (ERD) of the rhythm within the 10-12 Hz frequency band was studied by computing ERD maps separately for accurate and inaccurate performance. Statistical comparison of ERD maps for accurate and inaccurate movement (Wilcoxon test) resulted in significant differences for the right parietal region prior to movement onset, with a larger ERD before accurate movement.

Adult↗
PubMed1996

Mu-rhythm changes in brisk and slow self-paced finger movements.

We analysed whether type of movement (brisk vs slow) and active muscle force are encoded in the time course of mu-rhythm desynchronization during self-paced finger movements. Ten subjects performed 100 brisk and slow extensions of the right index finger. The time course of mu-rhythm desynchronization in the contralateral sensorimotor area before movement was identical for both types of movements. Brisk movements accompanied by a stronger extensor muscle contraction were preceded by larger desynchronization. The onset of mu-rhythm recovery was related to the duration of the extensor EMG burst in both types of movement. The results suggest that both amplitude and duration of the extensor muscle contraction are encoded in the time course of murhythm desynchronization.

Analysis of Variance↗
PubMed1997

Autonomous cortical rhythms affect temporal modulation transfer functions.

A correlational study between the dominant frequencies in the spontaneous local field potential and the single unit's best modulation frequency (BMF) for periodic click train stimulation in the primary auditory cortex of the cat is presented. Data were obtained from 251 single units recording in 29 cats. The correlation between spindle frequency (mean 8.2 Hz) and BMF (mean 9.3 Hz) was significant (r2 = 0.58, p < 0.0001). The limiting click-following rate was negatively correlated with the strength of the spindle rhythm: the longer the oscillation the lower the limiting rate. This suggests that the click-following responses of the primary auditory cortex depends as much on ongoing autonomous activity as it does on stimulus-induced activity.

Acoustic Stimulation↗
PubMed1997

Firing rate and firing synchrony distinguish dynamic from steady state sound.

The role of firing-rate and firing synchrony within and between three auditory cortical areas in coding complex sounds was investigated. In cortex, steady-state sound rarely caused any difference in firing rate over the spontaneous rate, but induced greater neural synchrony within and between cortical areas than were present during silence. Dynamic changes, other than onsets, produced similar synchrony as steady-state stimulation, but the firing rates were significantly larger in each cortical area than for steady-state sound. This suggests that the firing rate signals the difference between dynamic and steady-state stimulation. Because firing rates are high for stimulus onsets, the combination of firing rate and intercortical synchrony may distinguish between dynamic and steady-state stimuli and silence.

Acoustic Stimulation↗
PubMed2000

Quantitative aspects of the state-dependent co-variation of cat lateral geniculate and perigeniculate visual activity.

The quantitative relationship between EEG-related changes in the visual activity of perigeniculate (PGN) and lateral geniculate (LGN) neurons with overlapping receptive fields was analyzed in the anesthetized and paralyzed cat. While transient response peaks were independent of the EEG state, we found opposite changes in spontaneous activity and tonic visual responses, with PGN cells increasing and LGN cells decreasing their spontaneous/tonic activity with increasing EEG delta activity in most cases. The tonic firing rates of PGN and LGN cell pairs were clearly correlated with a slope of about -0.5. Thus, LGN firing was low when PGN activity was high and vice versa. With a change from low to high EEG delta activity the difference between the tonic responses of PGN and LGN cells increased on average by 50 spikes/s, both for the whole population and at the single cell level, indicating that state-dependent changes in retino-geniculate transmission are regulated by a distinct ratio of PGN-LGN activity.

Action Potentials↗
PubMed2003

Alpha and beta oscillatory changes during stimulus-induced movement paradigms: effect of stimulus predictability.

We studied the effect of stimulus predictability on the alpha and beta changes observed in central regions during stimulus-induced movement paradigms. Six young volunteers were instructed to extend briskly their dominant wrist as soon as possible after hearing a 2000 Hz sound. Two sequences of stimuli were presented to each subject, the first rhythmic at 1/6 s and the second with random intervals between 5 and 13s. A time-frequency analysis of nonphase-locked activity in the 7-37 Hz range was performed on stimulus-centred EEG sweeps using wavelet filters and Gabor transforms. During the sequence of predictable rhythmic stimuli, stimulus-induced movements were accompanied by a decrease in beta activity that began contralaterally about 1 s prior to the stimulus and extended to both sides later on. This decrease was followed by a rebound after the end of the movement. In the alpha band, the decrease observed started just after the sound. During the sequence of non-predictable, random stimuli, stimulus-induced movements were accompanied by a shorter and smaller alpha and beta-ERD, that started after the stimulus. The presence of a pre-stimulus beta ERD only in the rhythmic predictable paradigm suggests that central pre-movement beta ERD may be an indicator of motor preparation, and could be used for objective evaluation of time estimation and motor timing. The minimal differences observed in the alpha changes in both paradigms suggest that alpha-ERD may not be linked to motor preparation.

Acoustic Stimulation↗
PubMed2005

Increased gamma-band synchrony precedes switching of conscious perceptual objects in binocular rivalry.

Gamma-band neural synchrony has been proposed as a correlate of consciousness and as a solution for the binding problem. Research on visual working memory and the perception of coherent images in ambiguous figures supports this view. To test the relationship between perceptual consciousness and gamma synchrony, we recorded electroencephalogram activity while participants were presented with rivalling visual images to each eye. Participants pressed buttons to indicate which image they were perceiving, and response-locked phase-locking values (6-60 Hz) were calculated from the electroencephalogram time series. Results revealed transient bursts of increased global phase synchrony in the gamma-band peaking approximately 425 and approximately 260 ms preresponse. This suggests that global gamma synchrony is associated with the emergence of a coherent conscious percept.

Adolescent↗
PubMed1998

Reduced interhemispheric EEG coherence in Alzheimer disease: analysis during rest and photic stimulation.

The present study was conducted to examine interhemispheric electroencephalogram (EEG) coherence at rest and during photic stimulation (5, 10, and 15 Hz) in 10 patients with presenile dementia of the Alzheimer type (AD; mean age at onset, 56 years) and 10 sex- and age-matched control subjects. Compared with the control subjects, the AD patients had significantly lower interhemispheric coherence in the resting EEG for the delta, theta-2, alpha, and beta-1 frequency bands. EEG analysis during photic stimulation also showed that the patients had significantly lower coherence, irrespective of the stimulus frequency. In addition, when we examined the changes in coherence from the resting state to the stimulus condition (i.e., coherence reactivity), significant group differences were found at the brain region primarily involved in visual functioning; the patients had significantly smaller coherence reactivity to photic stimulation at 5 and 15 Hz over the posterior regions. These findings suggest that AD patients have an impairment of interhemispheric functional connectivity in both nonstimulus and stimulus conditions. The findings also suggest a failure of normal stimulation-related brain activation in AD.

Aged↗
PubMed1989

Functional topography during sensorimotor activation studied with event-related desynchronization mapping.

Event-related desynchronization (ERD) of alpha components was studied in four subjects during self-paced voluntary movements and somatosensory stimulation. EEG was recorded from 29 electrodes with a common right ear reference; local average reference derivations were calculated and used for computing ERD maps at 250-ms intervals. It was found that upper alpha components were desynchronized close to electrodes C3 and C4 overlying the primary sensorimotor cortex during voluntary movements and somatosensory stimulation. ERD started contralaterally more than 2 s before the movement and some hundreds of milliseconds before the stimulation. During the performance of unilateral movement and unilateral stimulation, ERD was bilaterally symmetric. Desynchronization of lower alpha components was found over the superior parietal cortex, clearly starting some hundreds of milliseconds after the desynchronization of upper frequency components. Therefore, the desynchronization of lower and upper alpha components reflects activation of different neuronal structures.

Arousal↗
PubMed1989

Neonatal electroencephalography and neuropathology.

One-hundred-eight EEGs from 47 newborn infants were compared with the postmortem neuropathological findings. The degree of EEG background abnormality had good correlation with the severity of the brain lesion; the more severe the EEG background abnormality, the more extensive and intensive the morphological change. Widespread encephalomalacia was demonstrated in six infants who manifested isoelectric tracings. In particular, cerebral cortex, corpus striatum, thalamus, midbrain, and pons were affected in all patients with this abnormal EEG pattern. Burst-suppression patterns, which were seen in seven infants, also correlated with multifocal severe brain damage, but there was no common structure that was consistently affected for all patients with this pattern. Positive rolandic sharp-wave transients (PRS) appeared highly specific for white matter lesions. All eight infants with PRS had white matter lesions. However, the sensitivity of PRS for white matter lesions was not high (32%), and the white matter lesions of PRS-positive patients were not necessarily composed of periventricular leukomalacia. The sensitivity of EEG asymmetry was also low (40%) for the focality of morphological change, although the specificity was relatively high (85%). The origin of seizure discharges, on the other hand, had poor correlation with the site of the brain lesion.

Brain↗
PubMed1992

Functional topography during a visuoverbal judgment task studied with event-related desynchronization mapping.

Event-related desynchronization (ERD) of alpha components was studied in 10 subjects in a visuoverbal judgment task. EEG was recorded from 29 electrodes; ERD, measured by percentage of alpha power decrease, was calculated in 125-ms intervals and displayed in a time course over 7-s intervals and in the form of topographical ERD maps. ERD, interpreted as a measure of activated cortical areas, was studied in the upper and lower alpha bands. It was found that upper alpha band ERD was short-lasting (less than 1 s), localized to the posterior region and not found before stimulation; in contrast to this, lower alpha band ERD was longer-lasting (greater than 1 s), more widespread, with a left hemisphere dominance, and was already present before stimulation. ANOVA revealed significant interactions among alpha frequency bands, scalp location, and pre-/poststimulus intervals. The self-organizing topological Kohonen network was used to analyze the stability of consecutive ERD maps. There is evidence that topographical ERD patterns can be stable for about 300-400 ms.

Adult↗
PubMed1997

Comparison between the alpha pattern in normal subjects and in alpha pattern coma.

Alpha pattern coma (APC) is an uncommon clinical EEG pattern in comatose patients, most commonly in association with anoxic-ischemic encephalopathy after cardiac arrest. Despite the pattern's striking similarity to that of the normal awake EEG, there are theoretical and experimental reasons for believing that the two rhythms result from different processes. The analysis of quantitative differences in APC from normal rhythms requires computer analysis. Because most cases of this rare entity have been collected over the years on paper traces, computer analysis appears implausible. In a companion article, we describe a method to quantify sections of paper EEGs. We applied this method to EEGs of five APC patients and five normal controls and noted a significant difference in the coherence between the two hemispheres in the alpha range. This finding is in keeping with theoretical, experimental, and clinical observations suggesting that APC may result from significant thalamo-cortical disruption.

Alpha Rhythm↗
PubMed2001

Characterizing neurodynamic changes before seizures.

The study of dynamic changes in neural activity preceding epileptic seizure allows the characterization of a preictal state several minutes before seizure onset. This opens up new perspectives for studying the mechanisms of epileptogenesis as well as for possible therapeutic interventions, which represent a major breakthrough. In this review the authors present and discuss the results from their group in this domain using nonlinear analysis of brain signals, as well as the limitations of this topic and current questions.

Animals↗
PubMed2001

Early seizure detection.

For patients with medically intractable epilepsy, there have been few effective alternatives to resective surgery, a destructive, irreversible treatment. A strategy receiving increased attention is using interictal spike patterns and continuous EEG measurements from epileptic patients to predict and ultimately control seizure activity via chemical or electrical control systems. This work compares results of seven linear and nonlinear methods (analysis of power spectra, cross-correlation, principal components, phase, wavelets, correlation integral, and mutual prediction) in detecting the earliest dynamical changes preceding 12 intracranially-recorded seizures from 4 patients. A method of counting standard deviations was used to compare across methods, and the earliest departures from thresholds determined from non-seizure EEG were compared to a neurologist's judgement. For these data, the nonlinear methods offered no predictive advantage over the linear methods. All the methods described here were successful in detecting changes leading to a seizure between one and two minutes before the first changes noted by the neurologist, although analysis of phase correlation proved the most robust. The success of phase analysis may be due in part to its complete insensitivity to amplitude, which may provide a significant source of error.

Brain Mapping↗
PubMed2001

Mechanical stimulation of the fingertip can induce bursts of beta oscillations in sensorimotor areas.

Short mechanical stimulation of the fingertip was studied in 10 subjects using 34 closely spaced EEG electrodes overlying sensorimotor areas. The tactile skin stimulation device consisted of a dot matrix printer head. Each stimulus lasted 10 msec with an interstimulus interval of 4 seconds. Tactile stimulation induced beta oscillations, which were largest in the 16 to 20-Hz band, with a maximum centered within 1 second after stimulation. These beta oscillations were found over both hemispheres with a clear dominance over the contralateral hand representation area.

Adult↗
PubMed2004

Advances in pediatric electrophysiology.

PURPOSE OF REVIEW: The pediatric electrophysiology literature during the past year has addressed several topics that are particularly relevant for children and other patients with congenital heart disease. This paper reviews selected studies germane to physicians and health care personnel who treat pediatric and adult congenital heart patients with arrhythmias and electrophysiologic disorders. RECENT FINDINGS: Advances in arrhythmia diagnostics have been reported in pediatrics using loop monitoring, both external and implanted. Diagnostic criteria and risk stratification strategies have been refined for the congenital and inherited rhythm disorders such as cardiomyopathies and long QT syndrome. The use of therapeutic procedures such as catheter ablation for complex arrhythmias in congenital heart disease is discussed. Finally, a summary of articles on implanted devices in pediatrics and congenital heart disease is reviewed, including implantable defibrillators, atrial antitachycardia pacemakers, and cardiac resynchronization therapy in pediatrics. SUMMARY: Pediatric electrophysiology is a rapidly changing field, with advances seen in diagnostic evaluation of arrhythmia, refinement of risk-stratification testing, and therapeutic options such as catheter ablation and cardiac rhythm management devices. The evolution of pediatric electrophysiology from a diagnostic specialty into a therapeutic and interventional subspecialty has advanced the treatment options for children with cardiac arrhythmias and conduction disorders.

Arrhythmias, Cardiac↗
PubMed2006

An fMRI study of semantic priming: modulation of brain activity by varying semantic distances.

OBJECTIVE: Our purpose was to study the effect of semantic priming at varying semantic distances on brain activation during a lexical decision experiment, using functional magnetic resonance imaging (fMRI). BACKGROUND: Neuroimaging studies have demonstrated decreased brain activation for primed versus unprimed stimuli in language areas due to semantic priming, suggesting facilitated semantic retrieval. However, the effect of varying semantic distances on brain activation has not been studied. Therefore we examined direct and indirect priming effects on cerebral activation to provide information regarding spread of activation in the semantic network. METHODS: Participants were presented with closely, distantly, and unrelated word pairs during fMRI, and asked to make a lexical decision on the second word. RESULTS: Behavioral measurements demonstrated significant priming effects for all semantic distances. Imaging results showed modulation of brain activation due to different semantic relationships in the left inferior frontal gyrus, bilateral middle frontal gyrus and anterior temporal lobe, and consisted of decreased magnitude of activation when primed stimuli were processed compared with unprimed stimuli, with the greatest effect observed for closely related words. CONCLUSIONS: This study demonstrates graduated effects of semantic priming on fMRI in semantic but not attentional brain regions, contributing to explain how semantic knowledge is organized and retrieved. These findings support the network model for organization of the semantic lexicon.

Adult↗
PubMed2006

A multielectrode study of the inferotemporal cortex in the monkey: effects of grouping on spike rates and synchrony.

We measured spiking activity from 175 pairs of visually selective neurons while a monkey performed a visual classification task in which the same image pairs appeared in informative and uninformative contexts. Spike counts and synchrony counts were higher during fixations of informative configurations. Spike field coherence showed low frequency (approximately 5-15 Hz) desynchronization when viewing informative stimulus configurations. Jitter statistics, which quantify synchrony and control for spike rates, showed less probable, more surprising patterns of synchronies when the monkey made the correct response than when he erred. Our results suggest that changes in spike counts parallel changes in raw synchrony counts and that both track aspects of stimulus context. Synchrony unexplained by rates changes, however, also occurs and correlates with performance.

Action Potentials↗