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At least 145 records · Page 8Linked to original sources
PubMed1997

[Use of artificial neural networks in recognition of types of thinking by EEG].

Reflection in EEG parameters of the process of solving two types of mental tasks, i.e. spatial-imaginary and verbal-logical, was investigated in nine test-subjects. Mental efforts were found to specify EEG spatiofrequency patterns depending on the task type and subject's identity. These patterns were unique and reproducible enough to enable identification of this or the other type of mental task within several seconds of EEG record. Recognition was executed with the use of an artificial neural network algorithm in order to simultaneously weigh a wealth of signs of a specific EEG pattern. Recognition precision was 85% on the average.

Adult↗
PubMed1995

Extensive macrogyri or no visible gyri: distinct clinical, electroencephalographic, and genetic features according to different imaging patterns.

We studied 43 children with extensive brain gyral anomalies diagnosed radiologically and defined by (a) the absence or paucity of sulci over cortical areas affecting at least two lobes in each hemisphere, and (b) the absence or reduction of interdigitation between gray and white matter. We correlated the clinical, EEG, and genetic findings with the imaging features. A seemingly homogeneous group of patients (group A, n = 30) presented a common imaging pattern characterized by four features: (1) a thickened neocortex, (2) widened lateral ventricles, (3) apparent verticalization and widening of sylvian fissures, and (4) bilateral and symmetric distribution of the abnormalities. Another group of patients (group B, n = 13) exhibited heterogeneous imaging anomalies, termed "nonlissencephalic brain malformation," differing in at least one of the following four ways from the radiologic criteria defining group A: absence of verticalization of sylvian fissures (n = 12), thin neocortex (n = 2), normal-size lateral ventricles (n = 2), and asymmetric brain defects (n = 3). In group A, some clinical features had a significantly lower frequency (p < or = 0.01) than in group B: microcephaly, a complete lack of postural development, and intractable epilepsy. There was a significant relationship, but only in group A, between the degree of gyral anomalies and the extent of neurodevelopmental delay. Some EEG patterns (rapid rhythms and delta-theta rhythms) were highly specific for the group A patients. There was lower risk of familial recurrence in group A (recurrence of convolutional anomalies was 3.5% of sibship in group A versus 44% of sibship in group B, p = 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Cerebral Cortex↗
PubMed1994

Diurnal rhythm of plasma delta-sleep-inducing peptide in humans: evidence for positive correlation with body temperature and negative correlation with rapid eye movement and slow wave sleep.

Since delta-sleep-inducing peptide (DSIP) was isolated in 1977, numerous reports have suggested that this nonapeptide stimulates delta-sleep [slow wave sleep (SWS)]. Although DSIP-like immunoreactivity (DSIP-LI) has been found in the serum of many animals and man, its diurnal rhythm and relation to sleep stages have not been well defined. We hypothesized that circulating levels of this putative sleep hormone would be highest at night and would probably be elevated before or during episodes of SWS. We, therefore, measured plasma DSIP-LI levels every 30 min for 24 h in 12 normal volunteers in whom we obtained simultaneous polygraphic recordings. We found a distinct diurnal rhythm for plasma DSIP-LI levels, with the maximum at 1500 h and the minimum at 0100 h. DSIP-LI levels were substantially lower in rapid eye movement sleep (P < 0.005) and somewhat lower in SWS (P < 0.05) compared to awake values. DSIP-LI levels did not rise before, during, or after a significant percentage of episodes of SWS. We found, however, that the diurnal rhythm of DSIP-LI closely followed that of body temperature with a high degree of correlation (r2 = 0.66; P < 0.0001). We conclude that endogenous elevations of circulating DSIP may be associated with suppression of slow wave and rapid eye movement sleep, and that the circadian rhythm of this peptide is coupled directly or indirectly to that of body temperature.

Adrenocorticotropic Hormone↗
PubMed1983

Circadian acrophases of powers and frequencies in the waking EEG.

Circadian changes in frequencies and powers of the close-eyed EEG were measured over six days in 12 healthy volunteers living in a regular rest-activity cycle. EEGs were recorded every two hours and the probands were awakened for the recordings during the period of rest. Circadian rhythms occurred in powers and frequencies with diurnal amplitudes differing between individuals and locally on the scalp. Acrophases of peak frequencies and beta-power coincide with those of body temperature between 5 and 7 p.m., however, the crests of the diurnal rhythms in delta-, theta- and alpha-power varied more between individuals and covered systematically different times of the day. Acrophases of delta- and theta-powers occurred during the second half of the rest period and during the first half of the waking period. Only powers in the alpha-band showed locally different acrophases on the scalp. This could be observed in single individuals, too. In the central and parietal leads, acrophases of alpha-power were found during rest, whereas in the occipital leads of some probands acrophases occurred in the second half of the waking period.

Adolescent↗
PubMed1984

Delta-sleep-inducing peptide (DSIP): a review.

Since the turn of the century, it has been postulated that humoral factors induce sleep. Many compounds were proposed as sleep-factors, but only two of the sleep-peptides have been purified to homogeneity and characterized, so far. One of them, DSIP, was shown to be a nonapeptide of MW 849 and to induce mainly delta-sleep in rabbits, rats, mice, and humans, whereas in cats, the effect on REM sleep was more pronounced. A U-shaped activity curve was determined for the dose as well as for the time of infusion. DSIP-like material was found by RIA and immunohistochemistry in brain and by RIA in peripheral organs of the rat as well as in plasma of several mammals. In addition to sleep, the peptide also has been observed to affect electrophysiological activity, neurotransmitter levels in the brain, circadian and locomotor patterns, hormonal levels, psychological performance, and the activity of neuropharmacological drugs including their withdrawal.

Animals↗
PubMed1991

A statistical approach to computerized EEG: preliminary data on control subjects and epileptic patients.

Factor Analysis represents an important method of extracting salient features from EEG data condensing functional as well as spatial informations in a few factors and so reducing redundancy of multi-channels computerized EEG data. A 16-channel computerized frequency analysis of background brain electrical activity during 3 functional conditions (eyes closed, eyes open and hyperventilation) were performed in 2 groups, 50 healthy subjects and 14 epileptic patients with generalized seizures. The differences in each frequency band between the 2 groups have been assessed by means of factor scores. Factor scores differences between control and epileptic patients have been found in theta and alpha frequency bands. These interictal EEG abnormalities were more evident in epileptic patients. This preliminary study shows the confirmatory capability of Factor Analysis and its usefulness in managing and comparing computerized EEG data.

Adult↗
PubMed1983

EEG and sleep in aged hospitalized patients with senile dementia: 24-h recordings.

Polygraphic recordings of wake and sleep were performed on 10 partly bed-ridden, severely deteriorated patients with senile dementia. Compared with healthy elderly persons these subjects showed less SWS (slow wave sleep, characterized by high amplitude, slow EEG waves), less REM sleep (rapid eye movement sleep, usually accompanied by dream activity) and poorly organized stage 2 sleep (no sleep spindles, i.e. phasic EEG activity with a frequency of 12-14 Hz). Six of the 10 patients had no dominant alpha rhythm during wakefulness; this seemed to be related to their more deteriorated clinical state, to still less SWS and REM sleep and more time spent in stage 2. The basic NREM-REM cycle of sleep, i.e. the regular alternation between non-REM- and REM-periods, could still be distinguished, however, and showed similar average temporal characteristics as in healthy old and younger people. Similarly, although sleep was severely fragmented in most patients and many sleep episodes occurred during the day, the day-night alternation of wakefulness and sleep was maintained in the sample as a whole.

Aged↗
PubMed1993

Fluoxetine, amitriptyline and the electroencephalogram.

Electroencephalograms recorded before and after 4 weeks treatment of depressed patients with fluoxetine or amitriptyline were assessed visually and by power spectrum analysis blind to patient, treatment and whether the recordings were carried out before or after treatment. No significant between-group differences in alpha, beta or theta activity were found on visual assessment. Power spectrum analysis revealed a significant decrease in the amount of beta activity at week 4. There was no EEG evidence of drowsiness or epileptiform activity in either of the treatment groups.

Adult↗
PubMed2006

Classic electroencephalographic parameters: median frequency, spectral edge frequency etc.

Even today many anaesthesiologists rely on parameters of the autonomic nervous system, such as blood pressure and heart rate to decide if a patient is adequately anaesthetized. It is thought that the electroencephalogram (EEG) may provide more information on the state of anaesthesia. Because full EEG analysis is not possible in the operating room, processed EEG parameters have been developed comprising complex information into a single value. Time and frequency domain parameters are calculated. The power spectrum results from a Fourier analysis and can be described by parameters such as median frequency, spectral edge frequency and others. It was noted, however, that anaesthetics at low doses increase frequency of the EEG, whereas at high doses the EEG is depressed. This biphasic response makes it difficult to clearly distinguish the exact anaesthetic state of a patient. Median frequency and spectral edge frequency have been studied in numerous studies. However, no sole indicator has been derived from the EEG that could serve as a descriptor of anaesthetic depth.

Alpha Rhythm↗
PubMed1996

Electrophysiological analysis of the registration, storage and retrieval of information in delayed matching from samples.

Brain processes of registration, storage in working memory and retrieval of different kinds of information were studied by analysis of EEG and ERP activity recorded during two delayed matches from sample tasks: (1) matching the digits in two series of six numbers, and (2) matching the sums of the same two series of six numbers. each trial was composed of six intervals continuing six equally spaced visual stimuli: (1) control--observing a series of six fixation points, P1, on a computer monitor; (2) priming--viewing a series, S1, of six numbers; (3) delay--observing a second series of six fixation points, P2; (4) matching--viewing a second series, S2, of six numbers; (5) response selection--selecting the left button to press if S1 contained all the items in S2 or the right button if any item appeared only in S2, while observing six fixation points; (6) feedback--six color coded fixation points indicate correct or error. Each interval was 4 s in duration and 20 trials were presented in each task. During each interval the visual field flickered at a tracer frequency of 1.5/s, whether numbers or fixation points were on the monitor screen. Very narrow band power spectra (VNB), ERPs elicited by presentation of S1 or S2 information items, and non-contingent probes (NCP) elicited by presentation of fixation points were used to trace the processing of information by neural populations activated by the visual stimulation. Global field power maxima identified latencies at which functional landscapes were analyzed. VNB, ERP, NCP and landscape differences were found between digits and sums. However, though these differences were highly significant within each subject (p < 0.001), no consistency was found across individuals for the electrophysiological changes during the tasks. This suggests that utilization of brain resources in cognition varies greatly with individual cognitive styles and strategies.

Alpha Rhythm↗
PubMed2003

Body posture affects electroencephalographic activity and psychomotor vigilance task performance in sleep-deprived subjects.

OBJECTIVE: This study examined the effects of posture on electroencephalographic (EEG) activity and psychomotor vigilance task (PVT) performance in 16 sleep-deprived volunteers. METHODS: EEG data were collected while participants completed 10 min PVTs under two counterbalanced sitting/standing conditions during 28 h of continuous wakefulness. RESULTS: In both the sitting and standing conditions, theta activity progressively increased as a function of sleep loss, but standing upright significantly attenuated this effect, suggesting that alertness was improved by the more upright posture. The PVT results showed that cognitive psychomotor performance was maintained at nearly well-rested levels by standing upright, whereas reaction time and attention noticeably deteriorated when participants were seated. CONCLUSIONS: These results suggest that an upright posture increases EEG arousal and sustained attention, indicating that postural manipulations can be useful for counteracting fatigue in sleep-deprived individuals.

Adult↗
PubMed1999

Long-term intra-individual variability of the background EEG in normals.

OBJECTIVES: Forty-five healthy adult volunteers underwent repeated qEEG examinations with retest intervals 25-62 months in order to investigate the long-term intra-individual variability of several qEEG features such as, absolute and relative power, power asymmetry, coherence, mean and peak frequency and entropy. Prior to any computations all parameters were transformed to Z-scores on the basis of a normal database. METHODS: Correlation coefficients were used to test the effect of the time on the test-retest differences. Correlation coefficients were also computed between baseline and retest values, as a measure of intra-individual stability, to make our results comparable to most literature data. By computing the standard deviations for test-retest differences, the intra-individual variabilities of the examined parameters were obtained in the unit of inter-individual variability of normal population. The same calculations were carried out with values obtained from the odd and even numbered epochs of the same EEG sections. This way, that portion of the intra-individual variability was estimated that might be introduced even by chance only when the epochs were selected randomly from the same section of EEG conforming to selection criteria. RESULTS: As for our results, further increase of test-retest differences with time after 25 months might be so insignificant that it could not be demonstrated in our test material. The long-term intra-individual variability for most parameters, especially for total absolute power and alpha mean frequency, was less than the inter-individual variability in the normal population. The moment-to-moment variability was least in the case of the absolute power. CONCLUSIONS: Estimates for intra-individual variability expressed this way in Z-scores might easily be used in the follow-up of patients even for a few years.

Adult↗
PubMed1991

A comparison of median frequency, spectral edge frequency, a frequency band power ratio, total power, and dominance shift in the determination of depth of anesthesia.

Five numerical descriptors were derived from the electroencephalogram (EEG), recorded, and processed (Tracor Nomad) during emergence from isoflurane-nitrous oxide anesthesia. The five descriptors (median frequency, spectral edge frequency-90%, total power, a frequency band power ratio, and the ratio of frontal to occipital power) were compared for their ability to predict imminent arousal. Arousal was defined as spontaneous movement, coughing or eye opening. All of the descriptors except the frontal-occipital power ratio underwent significant (P less than 0.05) changes between the initial recordings made intraoperatively during surgical stimulus under anesthesia and later recordings in the 40 s preceding arousal. A post hoc analysis was performed to identify the threshold value for each parameter that best served to predict imminent arousal. For median frequency, spectral edge frequency-90%, total power, and the frequency band power ratio, thresholds that predicted imminent arousal with sensitivities of 90% and specificities of 82-90% could be identified. The data indicate that, even in the favorable circumstances of the present study (uniform anesthetic technique, post hoC identification of thresholds), none of several previously popularized EEG descriptors (median frequency, spectral edge frequency-90%, total power, a frequency band power ratio) can serve as a completely reliable sole predictor of imminent arousal. As presently derived, these EEG descriptors at best provide trend information to be used in concert with other clinical signs of depth of anesthesia.

Adult↗