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PubMed1989

Topographic mapping and habituation of event related EEG alpha band desynchronization.

Habituation of alpha wave suppression to an external auditory signal was studied using computer assisted EEG quantification procedures. Topographic maps of alpha amplitude were constructed from multiple electrode placements for seven healthy adults. The EEG preceding and following 10 standard or habituating stimuli, and 1 novel or sensitizing stimulus, was spectrally analyzed and stored as color amplitude maps. Individual and group composite maps were read-out and comparisons in alpha amplitude were made across stimulus conditions. The initial standard stimulus produced a sharp reduction in alpha amplitude whereas the 10th trial had no appreciable effect on spontaneous EEG activity. The novel stimulus immediately restored alpha desynchronization. The colormaps permitted easy visualization and quantification of the process of habituation and sensitization of the alpha rhythm.

Adult↗
PubMedDate not supplied

Prediction of outcome of prolonged coma caused by brain damage.

Thirty-one prolonged coma patients, who continued in a comatose state for at least 2 months, were classified electrophysiologically employing EEG, a compressed spectral array of continuous EEG frequency analysis, BSR, SEP and SSEP. The prognoses of long-term follow-up (at least 8 months) in these patients were compared with the results of such electrophysiological analysis and with the neurological gradings of the prolonged coma patients. In the continuous EEG frequency analysis, 22 cases were classified as having a changeable spectrogram, nine cases as having a slow monotonous spectrogram, and no cases as having a borderline spectrogram. We also classified the changeable spectrograms into the following three patterns: no desynchronization, slight desynchronization, and desynchronization. The nine cases with a slow monotonous spectrogram revealed severe damage of the brain stem and cerebral function with multimodality evoked potentials, and most of these cases could not survive without assisted respiration. The 22 cases with a changeable spectrogram had mild damage of the brain stem and cerebral function with multimodality evoked potentials, and these cases were identical with a persistent vegetative state. Three of the cases showed a changeable spectrogram that revealed a desynchronization pattern, normal BSR and normal N20 of SEP and SSEP, recovered spontaneously from the persistent vegetative state within 6 months after electrophysiological evaluation. We conclude that not only a neurological but also an electrophysiological classification is necessary to evaluate the brain function and prognosis of prolonged coma.

Adolescent↗
PubMed2000

Synchronised oscillations of the human sensorimotor cortex.

Oscillations are a prominent feature of macroscopic human sensorimotor cortical activity as recorded non-invasively with electroencephalography (EEG) and magnetoencephalography (MEG). The advent of whole-scalp MEG systems allowing rapid non-invasive recording from the entire cortex and accurate localisation of neural sources, and the development of refined signal analysis methods are important factors that led to an increasing interest in studies of sensorimotor oscillations during the last 10 years. Investigations on healthy subjects revealed frequency-specific localisation and modality-specific reactivity of 10 Hz and 20 Hz sensorimotor oscillations. Task-specific coherence between motor cortical and electromyographic oscillations, reflecting cortico-motoneuronal coupling, point towards a functional role of precentral oscillations in the cortical control of voluntary movements. Furthermore, abnormal cortico-motoneuronal coupling may underlie clinical symptoms of motor disorders, such as tremor. Thus, investigation of oscillatory sensorimotor activity proceeds from phenomenology to function and provides an interesting approach to address questions in human motor physiology and pathophysiology.

Cortical Synchronization↗
PubMed2001

Reduced degree of long-range phase synchrony in pathological human brain.

In this paper multivariate spontaneous EEG signals from three broad groups of human subjects--control, seizure, and mania--were studied with the aim of investigating the possible effect of these pathologies on the degree of phase synchronization between cortical areas. The degree of phase synchrony was measured by two recently developed measures which are more suitable than classical indices like correlation or coherence when dealing with nonlinear and non-stationary signals like the EEG. Signals were reduced to seven frequency bands (delta, theta, alpha-1, alpha-2, beta-1, beta-2 and gamma) which were statistically compared between the normal and the other two groups. It was found that the degree of long-range synchrony was significantly reduced for both pathological groups as compared with the control group. No clear differences were found in the degrees of short-range synchrony.

Bipolar Disorder↗
PubMed1976

Hippocampal theta activity in the acute pretrigeminal cat.

In five cats with a pretrigeminal brainstem transection ocular behavior and cortical and hippocampal EEG activity were recorded. The ECoG desynchronization was usually accompanied by clear hippocampal theta activity. The episodes of ECoG desynchronization and hippocampal theta activity lasted in some cases for several hours. Visual stimuli evoked two types of hippocampal EEG response: (I) increase of regularity and frequency of theta activity (II) EEG desynchronization. The intensity of these responses was positively correlated with the intensity of ocular and ECoG components of the orienting reflex (the most conspicuous phenomenon being their habituation with stimulus repetition). Electrical stimulation of the midbrain reticular formation evoked theta activity of a frequency proportional to stimulus voltage; for maintaining it constant stimulus strength had to be elevated gradually. Depriving the brain of influences from the lower brainstem does not influence qualitatively the function of reticulo-septo-hippocampal system.

Animals↗
PubMed1976

[Comparative study of the electrocorticogram of several brain fields of dozing cats in a chronic experiment].

Peculatities of background electrical activity of some projection regions, the I somatosensory (field 53), and I and II auditory (fields 22 and 52, respectively), visual (field 17) and associative cortex (field 5), were studied in chronic experiments, performed on unanesthetized dozy cats. In transient periods, from vigil to sleep and vice versa, the maximal distinctions in slow-wave activity were detected between the regions under recording. They consisted in dissimilarities of spindle activity and low crosscorrelation coefficients (0.21 +/- 0.04). The synchrony of the potentials of different cortical regions increased and the crosscorrelation coefficients grew from 0.4 +/- 18 as sleep deepened. The functional reorganization of thalamic pacemaker mechanisms is supposed to take place with changes in the sleep depth. No distinctions in desynchronization were observed in different projective cortical fields because of the expressive orientation reflex. Only after the orientation reaction was suppressed and after application of the stimuli of adequate strength it was possible to reveal specific peculiarities of the projective field electrical reaction. Availability of definite conditions is emphasized for developing specific signs of the projective field electrical reaction.

Animals↗
PubMedDate not supplied

[The typological characteristics of higher nervous activity in dogs and the maxima of the cross-correlation function between the electrical activities of the frontal cortex and the brain limbic systems].

Electrical activity of the frontal cortex, dorsal hippocampus, basolateral amygdala and lateral hypothalamus was recorded in eight dogs with chronically implanted electrodes. Mean values of the maxima of crosscorrelation function (MCCF) between electrical potentials in the theta, alpha and beta-2 ranges were used as a basis for assessment of conditions for interaction between these structures. Typological features of the higher nervous activity were assessed by the animal performance under conditions of free choice of the reinforcement mode of a conditioned stimulus: either high probable but of low alimentary quality or with low probability but more valuable. The mean MCCF values in the theta range were higher than in the other ranges. The brain structure which had the high MCCF in the theta-range, at least, with two of the structures under study was considered as "dominant". It was shown that hippocampus was the dominant structure for melancholic dogs, the frontal cortex was in phlegmatics. The hypothalamus was shown to be the "dominant structure" in both sanguine and choleric animals, but, for the most part, its activity was correlated with different structures. Thus, conditions for interaction between the frontal cortex, hippocampus, amygdala and hypothalamus seem to be an important factor, which determines typological features of the higher nervous activity of dogs.

Acoustic Stimulation↗
PubMed1999

[The neurobiology of slow-wave sleep].

In the two last years my lectures were addressed to the biological bases of wakefulness and REM sleep. The present lecture is focused on slow wave sleep, which corresponds to stages 3 and 4 in humans. These two sleep stages both present high voltage slow waves in the EEG that belong to the delta band (less than 3 Hz). Slow wave sleep usually lasts between 70 and 90 minutes in normal individuals, and takes place during the first hours of the night, as though our organism was making sure we got this essential sleep. Slow wave sleep is: a) the first sleep stage to recuperate after sleep deprivation, b) the stage with the most constant length even in individuals who have very different sleep habits, and c) the sleep stage that remains constant during experiments of gradual sleep reduction for eight-hour sleepers. This sleep stage is the one in which growth hormone is released and it essential for physical and intellectual efficiency and normal behavior in young adult individuals. Slow wave sleep is remarkably reduced in old people. What brain structures are responsible for the bioelectric and behavioral events of the slow waves sleep? Both the cerebral cortex and thalamus are indispensable for the existence of the slow waves EEG characteristic to this stage. Other brain structures participate in slow wave sleep organization; these include the basal forebrain, the oral pontine reticular nucleus, the deep cerebellar nuclei and the solitary tract nucleus. In this presentation I consider the most relevant functions of these structures as well as their anatomical connections, mainly with the neuronal networks responsible for other stages of the sleep-wakefulness cycle.

Adult↗
PubMed2000

Movement-related electroencephalographic desynchronization in patients with hand cramps: evidence for motor cortical involvement in focal dystonia.

We studied the dynamic changes in the amplitude of scalp electroencephalographic (EEG) oscillations to self-paced simple index finger abduction movements in patients with writer's cramp and compared them with those of normal aged-matched controls. The changes in EEG oscillations were measured in predefined frequency bands (8-10, 10-12, 12-20, and 20-30 Hz) by using the event-related desynchronization technique. Movements of the affected and unaffected hand in patients with writer's cramp showed significantly less reduction in 20- to 30-Hz power compared with controls. The differences in movement-related EEG power decline were apparent over the contralateral central and midline regions before and after electromyographic onset. Because EEG beta rhythm in the sensorimotor region likely emanates from the motor cortex and is related to ongoing muscle activity, this abnormality could be a manifestation of the abnormal motor command at the cortical level.

Adult↗
PubMed2000

Amplitude envelope correlation detects coupling among incoherent brain signals.

Cognitive processing involves gamma-activation over broad cortical regions. Phase coupling of these activities has rarely been reported for areas far apart. Other forms of coupling are generally not detected by conventional measures. Here, we use amplitude envelope correlation (AEC), which can detect signal coupling without phase coherence, even among different frequencies. We apply it to subdural recordings from humans performing a visual delayed match-to-sample task and systematically compare it with spectral amplitude and coherence. The different measures often show divergent results. In particular, AEC reveals y-coupling completely missed by coherence. We argue that coherence and AEC are adapted to different cortical mechanisms of short- and long-range interactions, respectively.

Adult↗
PubMed2000

Reduction of pentylenetetrazole-induced seizure activity in awake rats by seizure-triggered trigeminal nerve stimulation.

Stimulation of the vagus nerve has become an effective method for desynchronizing the highly coherent neural activity typically associated with epileptic seizures. This technique has been used in several animal models of seizures as well as in humans suffering from epilepsy. However, application of this technique has been limited to unilateral stimulation of the vagus nerve, typically delivered according to a fixed duty cycle, independently of whether ongoing seizure activity is present. Here, we report that stimulation of another cranial nerve, the trigeminal nerve, can also cause cortical and thalamic desynchronization, resulting in a reduction of seizure activity in awake rats. Furthermore, we demonstrate that providing this stimulation only when seizure activity begins results in more effective and safer seizure reduction per second of stimulation than with previous methods. Seizure activity induced by intraperitoneal injection of pentylenetetrazole was recorded from microwire electrodes in the thalamus and cortex of awake rats while the infraorbital branch of the trigeminal nerve was stimulated via a chronically implanted nerve cuff electrode. Continuous unilateral stimulation of the trigeminal nerve reduced electrographic seizure activity by up to 78%, and bilateral trigeminal stimulation was even more effective. Using a device that automatically detects seizure activity in real time on the basis of multichannel field potential signals, we demonstrated that seizure-triggered stimulation was more effective than the stimulation protocol involving a fixed duty cycle, in terms of the percent seizure reduction per second of stimulation. In contrast to vagus nerve stimulation studies, no substantial cardiovascular side effects were observed by unilateral or bilateral stimulation of the trigeminal nerve. These findings suggest that trigeminal nerve stimulation is safe in awake rats and should be evaluated as a therapy for human seizures. Furthermore, the results demonstrate that seizure-triggered trigeminal nerve stimulation is technically feasible and could be further developed, in conjunction with real-time seizure-predicting paradigms, to prevent seizures and reduce exposure to nerve stimulation.

Animals↗
PubMedDate not supplied

[Hemispheric organization of verbal memory functions in seasonal winter depression: electrophysiological analysis].

Spatial organization of EEG power and coherence during memorization of dichotically presented lists of words were studied in patients with winter depression (N = 17) and control subjects (N = 22). In contrast to the control subjects, the depressed patients were characterized by the higher theta power in the right parietal and posterior temporal regions and the dominance of the alpha 2 in the left midfrontal area. The patients also differed in the lower theta 2 coherence in the left hemisphere and lower alpha 1 coherence in the right hemisphere. These effects showed different intrahemispheric distribution. The interhemispheric EEG coherence in the theta 2 range between the frontal areas and alpha 1 coherence between the left frontal and right posterior areas was lower in the patients than in the control subjects. Verbal-emotional interaction in depressions are discussed.

Adult↗
PubMed2001

P300 and alpha event-related desynchronization (ERD).

In the present study we evaluated the relationships between the P300 event-related potential and event-related desynchronization (ERD) of electroencephalographic alpha activity by simultaneously analyzing P300 as well as 7-10- and 10-14-Hz alpha ERD responses from auditory passive and active oddball conditions. We compared the effects of task (target vs. nontarget) and electrode (Fz, Cz, Pz) on P300 and ERD, and correlated P300 amplitude/latency with ERD maximal amplitude/latency across individuals. The major findings were that P300 as well as slow and fast alpha ERD manifested similar task and electrode effects. P300 preceded ERD and predicted individual variance of both slow and fast alpha ERD. The relationships of P300 with alpha ERD were different for the slow and fast alpha frequencies. These findings indicate that P300 and ERD are related such that slow and fast alpha ERDs are specifically guided or modified by the internal event(s) indexed by P300.

Adolescent↗
PubMed1998

Differential responses of brain stem neurons during spontaneous and stimulation-induced desynchronization of the cortical eeg in freely moving cats.

The EEG is desynchronized during wakefulness and REM sleep. There are awake and REM sleep-related neurons in the brain stem. This study was carried out to investigate if the same neuron in the brain stem reticular formation may be responsible for EEG desynchronization during wakefulness and REM sleep. Single neuronal activity was recorded in chronically prepared freely moving normal cats and their activities were correlated with EEG desynchronization during spontaneous wakefulness, REM sleep, and during wakefulness induced by stimulation of the brain stem reticular formation. A majority of the neurons showed an increased firing associated with spontaneous EEG desynchronization during wakefulness and REM sleep, however, about 55% of them showed a similar behavior during stimulation-induced desynchronization. It was found that responses of a majority of the neurons during stimulation-induced desynchronization were similar to that of their firing rate during EEG desynchronization associated with spontaneous wakefulness irrespective of their behavior during REM sleep; the REM-ON neurons were not affected by the stimulation-induced desynchronization. A majority of the neurons which showed an increased firing during spontaneous and stimulation-induced EEG desynchronization received an excitatory input from the brain stem reticular formation. The results of this study suggest that although some neurons may be common, there is a strong possibility that the same neuron in the brain stem reticular formation is not involved in EEG desynchronization during wakefulness and REM sleep.

Analysis of Variance↗
PubMed2001

[Biphasic response of the human nervous system to geomagnetic storms studied by EEG].

In two subjects: a male phlegmatic, 56, and a female melancholic, 22, the EEG was recorded at resting. The EEG patterns were juxtaposed with the geomagnetic activity index Ar and the solar activity index SF, as well as between themselves. The results revealed qualitatively similar biphasic responses: a generalised diminishing of the EEG spatial synchronisation and, on the next day, a generalised augmentation of the phenomenon, as compared with a prolonged quiet period. A general unspecific stress response is supposed to underlie the aforementioned dynamics, whereas a reduced cortical tone during a magnetic storm and an enhanced one after its cessation correspond to the two phases observed. Specifics of responses in both subjects corresponded to their individual profiles of interhemisphere asymmetry.

Adult↗
PubMed1975

[Participation of the posterior hypothalamus in the activity of the ascending activating system].

In chronic experiments on cats with premezencaphalic section of the brain stem electrica stimulation of the posterior hypothalamus caused desynchronization of the electrical activity of the neocortex. After the isolated injury of the posterior hypothalamus a moderate electrical stimulation of the medical part of the midbrain reticular formation failed to cause any pronounced activation of the neocortex. The results obtained indicated an important role of the posterior hypothalamus in the function of the ascending activating system.

Animals↗