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At least 973 records · Page 54Linked to original sources
PubMed1981

The prognostic value of the electroencephalogram in premature infants.

A retrospective analysis of 184 EEGs performed during the neonatal period was accomplished on 81 premature infants (gestational age less than or equal to 36 weeks). The neurological outcome of the 64 surviving infants, considered as normal or abnormal with minor or major sequelae, was compared with the neonatal EEGs which were graded as normal, moderately or markedly abnormal. Infants whose serial EEGs were normal during the neonatal period were usually normal at follow up or suffered minor sequelae. All the children who had at least one markedly abnormal EEG suffered some type of neurological sequela or died. EEGs were classified as markedly abnormal if they contained at least one of the following patterns: isoelectric or paroxysmal backgrounds, positive rolandic sharp waves, electrographic seizures, marked interhemispheric voltage asymmetry or asynchrony or excessively slow background with a reduction or absence of the patterns expected at the particular conceptional age. A moderately abnormal EEG was of no significant prognostic value. This study also revealed the value of recording serial EEGs in the neonatal period. In many cases, markedly abnormal EEG patterns were transient and normal records were often obtained prior to the child's release from the nursery.

Brain Stem↗
PubMed1981

Central beta rhythm during sensorimotor activities in man.

Blocking or desynchronization of the central beta rhythm prior to and parallel to voluntary movement was found in 31 of 33 normal subjects investigated. The beta blocking was short lasting (1-3 sec), very often accompanied by blocking of the mu rhythm and localized in the central region. Phasic beta desynchronization was also observed after somatosensory stimulation. The beta rhythm showed a bilateral symmetrical blocking pattern with unilateral movement or stimulation. Patients with unilateral cerebral ischaemia showed an asymmetric blocking response and therefore demonstrated a high degree of hemispheric independence of the rhythmic generating systems. Central beta desynchronization is, therefore, a normal physiological phenomenon caused by activation processes of the sensorimotor cortex and detectable on the scalp very easily with closely spaced electrodes.

Beta Rhythm↗
PubMed1984

Computer assisted analysis of relations between single-unit activity and spontaneous EEG.

Two mutually complementary computer methods are described which can be used for the study of unit-EEG relationships during spontaneous EEG waves. The first one consists of using the unit activity to trigger the averaging of sections of EEG preceding and following each unit; the same unit activity is used for building a histogram of unit firing from another cell. Sections of data subjected to this analysis need not be continuous; they may be chosen interactively on the computer terminal, thus allowing to analyze intermittent phenomena. The second method consists of using a particular point of an EEG wave to trigger EEG averages from other channels as well as unit histograms. Here again the waves are chosen interactively. The unit-triggered EEG averages are more objective and less time consuming. However, they do not describe accurately the characteristics of the individual wave to which a unit firing is associated and also they give no information about inhibitory phenomena. Both these drawbacks are corrected by the wave-triggered unit histograms where the experimenter interactively selects and stores for analysis EEG waves with the appropriate characteristics. Several examples are given from the utilization of these programs in neurophysiological and neuropharmacological experiments, with special emphasis on generalized epilepsy.

Animals↗
PubMed1985

Mechanisms of epileptogenesis in photosensitive epilepsy implied by the effects of moving patterns.

The triggering of epileptiform EEG discharges by pattern is thought to depend on the intensity of excitation within the visual cortex. The present study investigates the role of the synchronisation of neuronal activity by the stimulus. In 10 pattern-sensitive subjects the effects of the following patterns have been compared: (1) static gratings, (2) gratings oscillating in a direction orthogonal to the lines (which should synchronise activity in direction-sensitive cortical units), and (3) gratings drifting at the same angular velocity (which should produce little or no synchronisation, because the contours enter and leave the overlapping receptive fields of individual neurones asynchronously). The oscillating gratings were most, and the drifting least, epileptogenic. In 2 further subjects oscillating and phase-reversing patterns were more epileptogenic than drifting gratings. Although open to alternative explanations, the findings conform with predictions from the hypothesis that synchronisation of individual cortical neurones by the stimulus contributes to epileptogenesis in photosensitive subjects.

Adolescent↗
PubMed1989

Electrocorticographic (ECoG) correlates of language. I. Desynchronization in temporal language cortex during object naming.

The electrocorticogram (ECoG) was recorded during a language task, silent naming, from sites identified as essential for naming by electrical stimulation mapping and from surrounding cortex of left dominant temporal cortex at craniotomies under local anesthesia. The ECoG was analyzed quantitatively for a reduction in spectral density in 7-12 Hz frequencies indicating 'desynchronization.' These measurements were made on the averaged ECoG in 3 subjects and on individual ECoG segments in 4. Statistically significant increases in desynchronization were identified during silent naming at most sites essential for language, most often in the epoch from 700 to 1200 msec after presentation of the item to be named. During silent naming, there was a greater degree of desynchronization at those sites than in surrounding cortex. At several sites essential for language in several subjects, significantly less desynchronization was evident during a spatial task using physically identical stimuli. Thus, localized desynchronization in temporal cortex is an ECoG change with temporal, anatomic, and sometimes behavioral specificity to a language task. This finding provides insights into cortical physiologic mechanisms active during human language.

Adult↗
PubMed1989

Patterns of cortical activation during planning of voluntary movement.

The influence of planning of self-paced voluntary finger movements on alpha band components was studied in 6 volunteers. Brain potentials from 29 electrodes, referred to the right ear, were recorded 4 sec before and 2 sec after movement onset. These data were transformed to obtain the laplacian operator, which was done by computing the local average reference. The event-related desynchronization (ERD) of upper alpha components was then calculated in each record at intervals of 250 msec and topographically displayed in the form of serial ERD maps. A first significant ERD (P less than 0.01, sign test) was found 1.75 sec +/- 0.61 before the movement, most prominent over the contralateral sensorimotor area and over midfrontal areas (the latter can probably be interpreted as an activation of the supplementary motor area). From these data we can conclude that the side of movement is predetermined more than 1 sec before movement onset.

Adult↗
PubMed1991

Tonic changes in alpha power during immersion of the hand in cold water.

Phasic event-related desynchronization (ERD) of alpha activity briefly follows many types of stimulation. In order to define EEG changes resulting from longer stimulation. EEG records were made before and during hand immersion into cool and painfully cold water (cold pressor). Five minutes of 13-lead EEG records were obtained from 14 subjects for each condition. EEG frequency analysis was performed on artifact-free epochs from 60 to 240 sec following immersion. Following an initial phasic decrease in alpha power during cold water immersion, there was an augmentation of alpha power (8-12 Hz) in bilateral frontal and posterior electrodes. This augmentation was largely the result of an increase in the low alpha band (8-10 Hz). Alpha power at both central electrodes C3 and C4 changed little during cold water immersion. Cool water immersion produced less alpha power augmentation than cold water immersion. These observed changes were primarily in the high alpha band (10-12 Hz) and were larger in electrodes ipsilateral rather than contralateral to the stimulation. There was also an increase of beta bilaterally in frontal and posterior regions with cold water immersion. Our data demonstrate sustained topographic EEG responses during tonic stimulation from hand immersion in painfully cold water. These changes differ from those produced by stimulation with cool water immersion.

Adolescent↗
PubMed1991

Quantification of EEG irregularity by use of the entropy of the power spectrum.

A new method for quantifying irregularity of EEGs is proposed in this study. The entropy, an information measure, determines the uniformity of proportion distribution. The peakedness or flatness of the distribution of the EEG power spectrum, representing EEG rhythmicity, can be measured by the entropy, because the power spectrum consists of proportions of power at each frequency. The irregularity of the EEG was measured by the entropy of the power spectrum, called an irregularity index (II). The II was obtained from the power spectrum at F3, F4, C3, C4, P3, P4, O1 and O2 during rest and mental arithmetic in 10 normal subjects. Relative band powers of delta, theta, alpha and beta bands and alpha peak frequency were also obtained. EEGs during rest were significantly more irregular anteriorly than in the occipital areas. Alpha activity was also more irregular in the anterior region. A greater degree of EEG desynchronization during mental arithmetic was found over the left hemisphere and the right occipital area. The II was more sensitive to such desynchronization than alpha band power and alpha peak frequency. The differences in spectral structures between rest and mental arithmetic conditions, mainly over the left hemisphere, were also confirmed by the Kullback-Leibler information.

Adolescent↗
PubMed1991

Lesions of nucleus basalis alter ChAT activity and EEG in rat frontal neocortex.

The EEG was recorded from frontal, parietal and visual cortices of sham-operated control rats and rats having ibotenic acid lesions of the nucleus basalis. Recordings were made during a period of rest and during stimulus-evoked desynchronization. Spectral power was determined using a Fast Fourier Transform routine; 3 artifact-free 4 sec epochs of resting activity and two 4 sec epochs of activated EEG were analyzed. Choline acetyltransferase activity (ChAT) was measured in each cortical area and was reduced in lesioned animals an average of 25% in frontal cortex, 19% in the parietal region and 10% in visual cortex. The percent of low frequency activity (1-12 Hz) in the frontal EEG was significantly greater in lesioned animals than in the control group during quiet rest; a significant correlation was found between ChAT activity and power in this band. Desynchronized activity was largely unaffected except for a reduction in 25-31 Hz activity in the frontal cortex of lesioned animals. EEG activity in both the parietal and visual areas was unchanged from control values.

Animals↗
PubMed1992

Event-related desynchronization: the effects of energetic and computational demands.

The effects of a subject's activation state on cognitive processing were studied, while subjects performed verbal and non-verbal tasks under a speed and accuracy instruction. It was found that stressing speed influenced the level of prestimulus alpha power and consequently the amount of relative event-related desynchronization (ERD). Increasing task complexity led to an increase in the amount and duration of relative ERD. Both prestimulus level of alpha power and relative ERD were asymmetrically distributed over the left and right hemispheres. No verbal/non-verbal task-dependent asymmetries in phasic ERD were found. The data suggest that the level of prestimulus alpha power is mainly influenced by the subject's activation state, whereas relative ERD mainly reflects phasic changes in cognitive processing.

Adult↗
PubMed1992

Prediction of the side of hand movements from single-trial multi-channel EEG data using neural networks.

Thirty channels of EEG data were recorded prior to voluntary right or left hand movements. Event-related desynchronization (ERD) was quantified in the 8-10 Hz and 10-12 Hz bands in single-trial data and used as training input for a neural network comprised of a learning vector quantizer (LVQ). After a training period, the network was able to predict the side of hand movement from single-trial EEG data recorded prior to movement onset.

Brain↗
PubMed1993

Evaluation of event-related desynchronization (ERD) during a recognition task: effect of attention.

Event-related desynchronization (ERD) was studied in 10 subjects during a verbal recognition task. The attentional load of the task varied according to the difficulty to discriminate targets and distractors. The EEG recorded from 29 electrodes was used to compute ERD from 14 source derivations in 125 msec intervals and displayed as spatio-temporal maps. The results show that large brain areas of both hemispheres are significantly activated when the attentional load is high. This cerebral activation pattern is less pronounced when the load is low. ANOVA reveals main effects of attention and time and a significant interaction between attention and time.

Adolescent↗
PubMed1996

The effects of handedness and type of movement on the contralateral preponderance of mu-rhythm desynchronisation.

Event-related desynchronisation (ERD) of mu-rhythm was studied in 12 right-handed and 11 left-handed subjects during brisk and slow self-paced index finger movements of dominant and nondominant hand. Electroencephalogram (EEG) was recorded from the sensorimotor hand area of both hemispheres. The contralateral preponderance of mu-rhythm ERD in the pre-movement period showed the following changes: (i) the contrasts between left- and right-finger movements were larger and earlier in the dominant than nondominant hemisphere in both handedness groups; (ii) right-handed subjects showed larger lateralisation of mu-rhythm ERD prior to right-finger as compared to left-finger movements, whereas about equal contralateral preponderance for both sides was found in the left-handed; (iii) the lateralisation of mu-rhythm ERD was lower prior to brisk as compared to slow movements, especially in the left-handed subjects. The results demonstrate that hand dominance, handedness and type of movement influence the proportion of pre-movement mu-rhythm desynchronisation in the left and right peri-rolandic area.

Adult↗
PubMed1976

Behavioural, electrocortical and body temperature effects of cholera toxin.

In young chicks intrahypothalamic infusion of cholera toxin produced a dramatic and dose-dependent increase in motor activity. Similar effects were also obtained in adult fowls after injection of cholera toxin into the third cerebral ventricle, the hypothalamus or the paleostriatum augmentatum. Electrocortical changes consisted of a slight desynchronization during the hypermotor activity and were preceded, when the highest intraventricular doses were used, by a short period of slower frequency and higher amplitude potentials. Intraventricular and intrahypothalamic but not intrastriatal injection of cholera toxin produced a typical biphasic hyperthermic response.

Animals↗