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Results for “Cortical Synchronization”

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At least 865 records · Page 48Linked to original sources
PubMed2000

Movement-related desynchronization of the cerebral cortex studied with spatially filtered magnetoencephalography.

Event-related desynchronization (ERD) within the alpha and beta bands on unilateral index finger extension and hand grasping was investigated on six normal volunteers with magnetoencephalography (MEG). A novel spatial filtering technique for imaging cortical source power, synthetic aperture magnetometry (SAM), was employed for the tomographic demonstration of ERD. SAM source image results were transformed into statistical parametric images. On the same hand grasping task, a functional MRI (fMRI) study was conducted on two subjects and compared with the ERD result. When the MEG data were analyzed with the fast Fourier transformation, power attenuation within the alpha and beta bands was evident on the contralateral sensorimotor area just prior to movement onset. The tomographic distribution of ERD was clearly obtained with SAM statistical imaging analysis. The equivalent current dipole (ECD) for the signal-averaged motor field was localized to the hemisphere contralateral to the hand movement, roughly at the center of the region displaying beta-band ERD. The signal increase on fMRI roughly colocalized with the ERD on the contralateral sensorimotor area. In conclusion, with the novel spatial filtering technique for the brain magnetic field, SAM, cortical regions contributing to ERD on finger movement were successfully demonstrated in a tomographic manner. The relative colocalization of the contralateral SAM ERD with ECD as well as the fMRI activation suggests that SAM is a practically useful technique to extract event-related signals from brain noise.

Adult↗
PubMed2002

A new method to identify multiple sources of oscillatory activity from magnetoencephalographic data.

Identifying the sources of oscillatory activity in the human brain is a challenging problem in current magnetoencephalography (MEG) and electroencephalography (EEG) research. The fluctuations in phase and amplitude of cortical oscillations preclude signal averaging over successive sections of the data without a priori assumptions. In addition, several sources at different locations often produce oscillatory activity at similar frequencies. For example, spontaneous oscillatory activity in the 8- to 13-Hz band is produced simultaneously at least in the posterior parts of the brain and bilaterally in the sensorimotor cortices. The previous approaches of identifying sources of oscillatory activity by dipole modeling of bandpass filtered data are quite laborious and require that multiple criteria are defined by an experienced user. In this work we introduce a convenient method for source localization using minimum current estimates in the frequency domain. Individual current estimates are calculated for the Fourier transforms of successive sections of continuous data. These current estimates are then averaged. The algorithm was tested on simulated and measured MEG data and compared with conventional dipole modeling. The main advantage of the proposed method is that it provides an efficient approach for simultaneous estimation of multiple sources of oscillatory activity in the same frequency band.

Algorithms↗
PubMed2002

Steady-state visually evoked potential topography during processing of emotional valence in healthy subjects.

The International Affective Picture System (IAPS) is increasingly used in brain imaging studies to examine emotional processes. This task allows valence and arousal content to be systematically investigated; however, previous studies have generally failed to select images that vary in one dimension as well as hold constant the variability on the other dimension. In addition, no studies have investigated the temporal structure associated with the conscious, ongoing processing of emotional stimuli following systematic selection of IAPS images. The aim of the present study was therefore to use steady-state probe topography (SSPT) to examine the steady-state visually evoked potentials (SSVEPs) associated with the processing of pleasant and unpleasant images low in arousal content. Seventy-five IAPS images, categorized as unpleasant, neutral, or pleasant, were presented to 16 healthy subjects while brain activity was recorded from 64 scalp sites. Analysis subtracted the activity associated with the presentation of neutral images from the activity associated with the presentation of pleasant as well as unpleasant images. Results demonstrate that both pleasant and unpleasant valence is associated with transient, widespread, and bilateral frontal SSVEP latency reductions. Unpleasant images were also associated with a transient bilateral anterior frontal amplitude decrease. Latency reductions are interpreted as increases in neural information processing speed, while amplitude reductions are interpreted in the current paper as analogous to an event-related desynchronisation commonly associated with the alpha bandwidth. These key findings support previous literature in terms of there being substantial overlap in frontal neural circuitry when the brain processes pleasant and unpleasant valence relative to neutral valence.

Adult↗
PubMed1980

Evoked responses by physiological sensory inputs in human central motor structures.

In human with chronic implanted electrodes physiological evoked responses could be detected from those structures they were thought to be parts mainly of central motor system. Investigating the functional changes of evoked responses to motor states and attention the results have suggested the responses do not sign the centres to treat as directly the sensory inputs i.e. auditory, visual, somatosensory stimuli as motor stimuli.

Attention↗
PubMed1979

The effect of sleep upon the transmission of afferent activity in the somatic afferent system.

Macaque monkeys were trained to fall asleep while sitting in a primate chair with their heads restrained. A gentle vibratory stimulus was delivered to the glabrous skin of the hand; it did not provoke awakening or change the sleep cycle of the macaque. Postcentral neuronal response to the amplitude of a sine wave mechanical stimulus and neuronal spontaneous activity were observed repetitively during all the phases of normal night sleep cycles. One hundred six neurons which could be entrained by a cutaneous mechanical stimulus were studied during both waking and sleep. At threshold, cyclic entrainment of the discharges of postcentral neurons decreased to 81 +/- 0.25% during light sleep (S1 + S2), to 64 +/- 0.26% during deep sleep (S3 + S4), and to 9 +/- 0.98% during desynchronized sleep with rapid eye movements (REMs).

Afferent Pathways↗
PubMed1975

Effect of chlorpromazine on the interaction between phasic and tonic electrocortical arousal mechanisms.

The effect of chlorpromazine on the rate of habituation of phasic arousal responses has been studied in cats carrying permanently implanted cortical recording electrodes. In the sleeping animal repeated presentation of an auditory stimulus (1 sec duration, 3000 Hz) at intensities which only produced a localised, phasic electrocortical change in the auditory cortex, resulted in the rapid habituation of this latter response. Once habituation had occurred the intensity of the stimulus was increased until a similar change in electrocortical activity once again appeared in the auditory cortex. The habituation procedure was then repeated. In this way it was possible to habituate the animal gradually to successively higher intensities of auditory stimulation without ever inducing behavioural arousal or tonic, generalised changes in electrocortical activity. Indeed, it was possible to reach a level of stimulation which previously would have induced overt behavioural effects and tonic arousal. It may be concluded that alterations in the activity of the mechanisms responsible for phasic electrocortical responses leads to changes in the responsiveness of the animal even during sleep. Following chlorpromazine phasic electrocortical responses were still elicited but their rate of habituation was significantly increased. Thus the overall effect of chlorpromazine was a marked shortening in the time taken to "train" the animal while still asleep, not to respond behaviourally or with tonic electrocortical changes to a particular auditory stimulus.

Acoustic Stimulation↗
PubMed1976

The effects of alcohol and atropine on EEG and behavior in the rabbit.

Electroencephalographic (EEG) activity was recorded from hippocampus and neocortex of rabbits. It was found that movement, movement-related 6-12 Hz rhythmical slow activity (RSA), and movement-related neocortical desynchronization were unaffected by intravenous atropine sulfate but depressed by ethyl alcohol (ethanol). Slower 4-8 Hz immobility-relate- RSA and immobility-related neocortical desynchronization produced by sensory stimulation (visual, auditory, tactile, vestibular) were relatively unaffected by ethanol even at high (0.1-0.2 g-%) blood alcohol levels, but were abolished by atropine sulfate. The results provide evidence for the idea of two pharmacologically separable cortical activating systems and suggest that ethanol has a greater effect on non-cholinergic than cholinergic systems.

Animals↗
PubMed1975

Electroencephalographic studies on the development of tolerance and cross tolerance to mescaline in the rat.

Recordings of the electroencephalogram (EEG) and the electromyogram (EMG) were collected continuously from rats equipped with permanent cortical and temporalis muscle electrodes. Automatic injections of mescaline were administered through indwelling i.p. cannulas at an initial dose of 30 mg/kg every 6 hrs for the first 2 days. This dose was then increased to 60 mg/kg 6 hr which was given for the duration of the study. The initial injections of the mescaline induced an immediate desynchronization of the EEG and behavioral arousal of the rat, which endured for 2-3 hrs. After this time, slow wave (SW) sleep and rapid eye movement (REM) sleep episodes reappeared, with the return of regular alternations of the sleep-wakefulness cycle. Upon continued administration of the drug, partial tolerance to the arousal effects of mescaline developed, which was reflected by a gradual reduction in the latencies to onset of SW sleep and REM sleep. Rats rendered tolerant to mescaline in this manner were found to be cross tolerant to lysergic acid diethylamide (LSD) and N,N-diethyl-tryptamine (DET). In contrast, cross tolerance did not occur to amphetamine, which exerts similar arousal and EEG desynchronizing effects. These results agree with physiological and behavioral studies of tolerance and cross tolerance among hallucinogens and support the usefulness of the EEG as a quantitative indicator of central nervous system function.

Amphetamine↗
PubMed1976

Sleep: effects of d- and l-amphetamine in man and in rat.

Almost identical results are reported in man and in rat for the effects of the amphetamine isomers on polygraphically recorded sleep. In both species, dextro-amphetamine produces a significantly greater increase in waking time. In both species, the two isomers have equal effects in reducing desynchronized sleep time. These findings combined with other recent data suggest that dopamine plays a direct rolw in wakefulness while norepinephrine is related inversely to amolnts of desynchronized sleep.

Adult↗
PubMed1979

Perfusion of the fourth cerebral ventricle with fentanyl induces naloxone-reversible bradycardia, hypotension, and EEG synchronisation in conscious dogs.

Injection of fentanyl into the cisterna magna of the brain leads to hypotension and bradycardia in anesthetised dogs. To determine if this effect is related to the recently discovered opiate receptors fentanyl was perfused in increasing concentrations (2.5-20 microgram/ml) through the cerebro-ventricular system in conscious dogs. Blood pressure was recorded continuously from a punctured exteriorised carotid artery; heart rate was derived from the ECG. Baroreflex activity was tested repeatedly by clamping of both common carotid arteries. Cerebral activity was evaluated from the EEG. Perfusion of the fourth cerebral ventricle resulted in a concentration-related fall in heart rate by 43% and in an inhibition of the reflex response of heart rate to carotid clamping. In contrast, blood pressure fell only moderately by 14% and its reflex response was well maintained. The EEG pattern changed from frequencies in the beta-band (awake control) to gradual synchronisation with delta-activity corresponding to behavioural signs of tranquilisation and sleep-like states. All these effects were reversed by naloxone. No effects were seen when fentanyl was perfused through the lateral ventricles and third ventricle although this yielded similar serum concentration as after perfusion of the fourth ventricle. It is concluded that opiate receptors bordering the fourth cerebral ventricle mediate the cardiovascular and hypnotic action of fentanyl.

Animals↗
PubMed1990

Topographical display and interpretation of event-related desynchronization during a visual-verbal task.

Multichannel EEG recordings were performed during a visual-verbal judgement task with a verbal response using an event-related paradigm. EEG trials of 7 sec were first digitally band pass filtered (10-12 Hz, 10-11 Hz, 11-12 Hz), and the amplitudes were then squared and averaged over all trials. This processing method results in a time course of alpha power and allows us to quantify the event-related desynchronization (ERD) in each EEG channel and to compute series of ERD maps in intervals of 125 msec. Analyzing the 10-11 Hz band, it was possible to study the time course and topographical pattern of cortical activation during visual encoding and cognition. Analysis of the 11-12 Hz band has enabled us, for the first time, to study the time course, spatial localization and extent of activation of speech, premotor and motor areas. We found that the speech centers were activated maximally 250 to 375 msec before speech onset and the SMA about 250 msec before speech onset. The results are preliminary, but demonstrate how much information can be extracted from the scalp EEG.

Acoustic Stimulation↗