634 EEG topography of visual reactivity in school-age children

Abstracts

/International

Journal

Our group consisted of 72 normal children, 10 normal adult controls, 20 dyslexics, 20 children with minor brain dysfunction, 10 psychotics, and 8 persons after a cerebrovascular accident. All persons had EEG curve frequency analysis (= BEAM, brain electrical activity mapping) and psychological investigation. Cognitive tests were generally marked by a decline in basic alpha activity (8-13 Hz) with the degree of attenuation inversely proportional to the alpha rhythm. Cognitive tests further elicited increasing delta activity (0.5-3.5 Hz) in line with the rule: the more difficult the test, the more delta activity. Dyslexic showed a relatively greater delta activity while reading than during pseudoRaven’s tests, unlike normal children, whose reading was already a fairly automatic process; they had more delta during pseudoRaven’s test, and less of it while reading. In some subjects, two degrees of mentation difficulty could be distinguished. Simple tests such as the addition of one-digit numbers were marked by increasing or accelerating alpha whereas more complex tests such as the addition of two-digit numbers elicited also more delta activity. To a certain degree, this implies that simple mentation is produced by the thalamocortical system which gives rise mainly to alpha activity. More complex mental activity would then be produced by subcortical association and commisural connections which generate delta activity.

634 EEG TOPOGRAPHY OF VISUAL SCHOOLAGE CHILDREN

REACTIVITY

IN

Z.J. Martinovic*, D. Ristanovic, V: Jovanovic, V. Radivojevic Institute for Mental Health, Palmoticeva 37, 11 000 Belgrade, FR Yugoslavia In order to quantify normal visual reactivity during EEG recording, the topography of power spectra for a sample of 72 healthy subjects of age ranging from 7-15 years was investigated. According to age, the whole group was further divided into three subgroups (youngest 7-9, middle 10-12, and eldest 13-15 years). The EEGs were recorded from 16 scalp sites under the eyes open (EOP) and eyes closed (ECL) conditions. Absolute EEG power acquired under two conditions was tested with students’ paired t test for differences between the power means in the whole group and in three age subgroups. In the whole group, the mean absolute powers in total and alpha band were signilicantly higher in all derivations under the ECL, as compared with EOP condition. Mean absolute power in theta band under the ECL condition was significantly higher than that under the EOP condition, except for frontal derivations. Changes in delta and beta mean powers were seldom significant. For the youngest subjects, the ECL/EOP ratio of alpha powers was significantly higher than that in the elder subgroups in posterior derivations. This is mostly due to lower values of alpha power recorded from the youngest subjects under the EOP condition. Under that condition, mean beta power in anterior regions was significantly higher

of Psychophysiology

30 (1998)

241

95-271

for the subjects within an age range of 13-15 years than that for two younger subgroups. The differences between the hemispheres were found mainly in the prefrontal and laterofrontal areas in all frequency bands and under both conditions. The results showed that the visual blocking of EEG was mostly due to a higher degree of EEG desynchronization for the subjects aged lo-15 years.

635 THE RHYTHMS

DEVELOPMENT DURING INFANCY

OF

EEG

SENSORY

E.V. Orekhova* , T.A. Stroganova* , I.N. Posikera* *Psychological Institute RAE, Mokhovaya str., 9V, Moscow, Russia * * Brain Research Institute RAMS, Moscow The “functional topography” approach (Kuhlman, 1980) was applied to study alpha rhythm in infant twins during the second half-year of life. The experimental sample included 154 normal infant born at 32-41 weeks of gestational age. Their chronological age varied from 7.4 to 12.4 months. EEG was registered during wakefulness under two experimental conditions: 11 sustained visual attention; 2) dark homogenous visual field. During darkness as compared to visual attention the sharp increase of spectral amplitudes within 5.2-9.6 Hz band was observed over the occipitoparietal cortex. The properties of the 5.2-9.6 Hz occipital rhythmic activity comply with the classical properties of alpha rhythm. The distinct spectral peak in 6.0-8.8 Hz band at precentral recording sites was observed during sustained visual attention. This rhythmic component was suppressed under the condition of total darkness. The arguments in favour of homology between the infant central rhythm and adult sensorimotor mu rhythm are advanced. The group mean of alpha peak frequency increased from 6.24 + 0.45 Hz at 8 months to 6.78 * 0.38 Hz at 11 months of chronological age. The frequency of infant alpha rhythm depended only on the period of extrauterine experience, regardless of gestational age at birth. This result points to the critical role of the early visual experience in alpha rhythm development. The group mean of the peak frequency of mu rhythm also increased during the second half-year of life, from 7.03 * 0.47 Hz at 8 months to 7.42 + 0.46 Hz at 11 months. Unlike alpha rhythm, the peak frequency of mu rhythm depended on duration of both intra- and extrauterine development. We speculate that the development of sensorimotor mu rhythm is influenced by somatosensory stimulation, which, in sharp contrast to the visual input, is present in the uterus.

636 EVENT-RELATED POTENTIALS VERBAL AND NONVERBAL STIMULI WITH COGNITIVE DISORDERS L.A. Rozhkova*

TO VISUAL, IN CHILDREN