[Phase-locked alpha oscillations evoked by illusory contour perception in normal and autistic preschool boys].

We examined temporal dynamics of EEG phase-locked alpha oscillations during perception of illusory (Kanizsa square) and non-illusory images in boys with autism and age-matched typically developing boys. In typically developing boys the illusory contour (IC) as compared to the control stimulus provoked an increased alpha response at the parietal scalp areas. This IC effect demonstrated continuity within the time window of 133-267 ms after the stimulus onset. Although boys with autism did not display this effect at the group level, part of the sample showed an atypical two-stage pattern of illusory contour effect. The first early stage of IC effect (50-133 ms) was pronounced at the midline occipital electrode localized in the vicinity of the primary visual cortex. The localization and the early onset time suggest that this early IC effect is related to abnormally enhanced "low-level" locally-oriented processes of contour completion in autism. The second stage of IC effect (267-400 ms) was observed at the left parietal region only, and was delayed comparatively to that in healthy boys, suggesting the deficit of "intermediate" processes of perceptual grouping linked to the higher-order visual areas.

The nature of individual differences in EEG parameters during homogeneous visual field in 5- and 6-year-old twins: a pilot study.

OBJECTIVE: To assess the genetic and environmental influences on the inter-individual variability of spectral EEG parameters under two conditions of reduced visual input in preschoolers. METHODS: EEG was recorded in 21 monozygotic and 20 same-sex dizygotic twin pairs aged 5-6 years under the Closed eyes and Darkness conditions. The contributions of genetic and environmental influences to individual EEG parameters were estimated using structural equation modeling. RESULTS: The alpha rhythm parameters - both spectral amplitude and frequency - were influenced mainly by genetic factors. Theta spectral amplitude variance was presumably accounted for by both genetic and shared environmental factors. The difference in the nature of population variance between EEG alpha and theta band spectral amplitudes was reproduced for two identical functional loads: Closed eyes and Darkness. CONCLUSIONS: The majority of EEG spectral parameters in preschool children are determined by genetic factors. Tentative finding on systematic environmental influences on theta spectral amplitude under the condition of reduced visual input may point to the role of experience in the individual differences in the functioning of theta response system. SIGNIFICANCE: The findings contribute to the scanty knowledge about the heritability of EEG rhythms in preschool children.

[Alpha oscillations of human brain elicited by illusory contour perception].

We examined the changes in the phase-locked and total alpha oscillations of EEG during perception of illusory (Kanizsa square) and non-illusory images in 16 healthy adults. We applied a wavelet-based time-frequency analysis to compute alpha band power, statistical evaluation was performed using repeated-measures ANOVA and the non-parametric multi-way analysis. Results showed that both stimuli provoked an initial increase of total alpha power emerging not later than in 100 ms after the stimulus onset. The increase was caused by the phase-locked alpha response, and the illusory contour was systematically followed by a higher level of alpha power than the non-illusory one. Further suppression of total alpha power occurred within the time window of 200-500 ms after the stimulus onset and did not depend on the stimulus type. Both stages of the total alpha response were more prominent over the parieto-occipito-temporal scalp areas. We hypothesize that the first stage of alpha response is related to the modulation of the activity of neural circuits participating in processing of a coherent pattern whereas a later suppression of total alpha power links to the orienting processes.

EEG theta rhythm in infants and preschool children.

OBJECTIVE: To study behavioral correlates of theta oscillations in infants and preschool children. METHODS: EEG was recorded during baseline (visual attention) and two test conditions--exploration of toys and attention to 'social' stimulation. Age specific frequency boundaries of theta and mu rhythms were assessed using narrow bin analysis of EEG spectra. RESULTS: Theta spectral power increased whereas mu power decreased under test conditions in both age groups. In preschoolers theta rhythm increased predominantly over anterior regions during exploratory behavior and over posterior regions during attention to social stimulation. Theta frequency range changed with age from 3.6 to 5.6 Hz in infants to 4-8 Hz in children, and mu range from 6.4-8.4 Hz to 8.4-10.4 Hz. CONCLUSIONS: In early life, theta oscillations are strongly related to behavioral states with substantial attentional and emotional load. The scalp distribution of theta spectral power depends on age and behavioral condition and may reflect engagement of different brain networks in control of behavior. SIGNIFICANCE: The findings contribute to the scanty knowledge about the developmental course of theta rhythm. Data on behavioral correlates of theta rhythm in early life may improve our understanding of cognitive and mental processes in healthy and neuropsychiatrically diseased children.

Alpha activity as an index of cortical inhibition during sustained internally controlled attention in infants.

OBJECTIVES: The study examined the suggestion that infant ability to maintain attention in anticipatory task and to sustain interference is related to the active inhibitory processes in cortical neural networks. METHODS: The extent of selective EEG synchronization in the alpha range has been taken as a measure of cortical inhibition. EEG was registered in 60 infants aged 8-11 months during: (1) attention to an object in the visual field (externally controlled attention); (2) anticipation of the person in the peek-a-boo game (internally controlled attention). RESULTS: The infants who demonstrated longer periods of anticipatory attention had higher absolute spectral amplitude in the broad frequency range under both experimental conditions. It was suggested that the effect of 'overall' EEG synchronization is related to some stable individual differences in psychophysiological traits. To control for the effect of overall EEG synchronization the relation between relative alpha amplitudes in 6.4-10 Hz range and the duration of internally controlled attention was analyzed. The infants with longer compared to shorter anticipatory attention spans had relatively higher 6.8 Hz alpha synchronization at posterior parietal sites under this experimental condition. CONCLUSIONS: It was suggested that alpha synchronization over posterior parietal cortex reflects an active inhibition of certain parietal networks involved in maintaining attention to peripheral visual field rather than merely an 'idle' state of this cortical area. Such an inhibition appears to allow infants to avoid interference of concurrent visual stimulation at the periphery of the visual field.

EEG alpha rhythm in infants.

The 'functional topography' approach has been applied to study alpha rhythms in infant twins during the second half-year of life. The experimental sample included 154 normal infants 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: sustained visual attention and dark homogenous visual field. During darkness as compared with visual attention the sharp increase of spectral amplitudes within 5.2-9.6 Hz band was observed over the occipital-parietal 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. 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 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.

Theta synchronization during sustained anticipatory attention in infants over the second half of the first year of life.

The neurophysiological basis of attention control has been investigated in infants during the second half of the first year of life. The marked improvement of voluntary control of attention and action is known to occur during this age period. EEG was registered in 60 infants aged 8-11 months under three experimental conditions: (1) attention to an object in the visual field (externally controlled attention or the 'baseline'); (2) anticipation of the person in the peek-a-boo game (internally controlled attention); and (3) attention to the 'reappeared' person in the peek-a-boo game ('control' condition). Spectral analysis of the data revealed sharp increase of the EEG theta activity (3.6-6.0 Hz) during internally controlled attention as compared to the 'baseline' and the 'control' conditions. The theta1 (3.6-4.8 Hz) increase was maximal at frontal electrode sites. The reactivity of the frontal theta1 during internally controlled attention differentiated subjects with different ability to maintain this type of attention. The theta2 (5.2-6.0 Hz) reactivity was maximal at right temporal electrode site and did not depend on the ability to maintain anticipatory attention. The data point to different functional significance of theta1 and theta2 rhythms in infants. It was suggested that the frontal theta1 synchronization in infants reflects activity of the anterior attention system subserving executive control of attention. The ability to maintain anticipatory attention increased, whereas the frontal theta1 synchronization decreased during the studied age period. There was the direct relationship between frontal theta1 synchronization and persistence of internally controlled attention in 8-month-olds. On the contrary, at 9 and 10 months, these variables were inversely-related. There was no link between theta1 reactivity and persistence of anticipatory attention in 11-month-olds. It was suggested that the age-dependant dynamic of the relationship between frontal theta1 reactivity and attention behaviour reflects the maturational shift in the functioning of anterior attention system. The shift leads to more economic and more efficient functioning of this system.

Externally and internally controlled attention in infants: an EEG study.

This work was designed to investigate EEG indices of Internally and Externally Controlled Attention in infancy. EEG was recorded in 15 infants aged 7-8 months under three experimental conditions: (1) visual attention to a new stimulation (Externally Controlled Attention or baseline condition); (2) attention guided by internal cognitive schemata during 'anticipatory' phase of the peek-a-boo game (Internally Controlled Attention); and (3) 'reappearance' phase of the peek-a-boo game when the experimenter talked and smiled to an infant (reappearance). The relative power (RP) in 4-5 single-Hz theta sub-band increased under both phases of the peek-a-boo game. The reactive changes of 4-5 single-Hz RP at prefrontal and frontal leads under the Internally Controlled Attention condition positively correlated with the total time during which an infant was able to maintain ICA. The RP in 5-6 single-Hz theta sub-band significantly increased only under the Internally Controlled Attention condition and did not correlate with the total time of this type of attention. The results support the concept of 'Diffuse Theta-Response System' that is active during expectancy and effortfully focused attention. In contrast to theta, the RP in 6-7, 7-8, and 8-9 single-Hz bands decreased during both phases of the game. The decrease was maximal at precentral leads and most probably reflected blockage of the sensorimotor (mu) rhythm due to higher motility and muscular tension in the game situation. It is concluded that EEG is an adequate vehicle for investigation of brain mechanisms of attention and voluntary control in infants.

[The theta rhythm of the infant EEG and the development of the mechanisms of voluntary control of attention in the 2nd half of the first year of life]. / Teta-ritm EEG mladentsev i razvitie mekhanizmov proizvol'nogo kontrolia vmimaniia na vtorom polugodii pervogo goda zhizni.

The neurophysiological basis of attention control was studied in infants at the second half-year of life, i.e. in the period when the capability for voluntary control over behavior fundamentally improves. EEG was recorded in 60 infants aed 8-11 months in three experimental conditions: 1) attention to an object in the visual field (externally controlled attention, or the baseline state), 2) anticipation of a person in the peek-a-boo game (internally controlled attention), 3) attention to the reappeared person in the peek-a-boo game (control condition). The spectral analysis of the EEG data revealed a sharp increase in the EEG theta (3.6-6.0 Hz) during internally controlled attention as compared to the baseline and control conditions. The theta1 (3.6-4.8 Hz) increase was maximal in the frontal derivations. The reactivity of the frontal theta1 during internally controlled attention discriminated infants with different abilities to maintain this type of attention. The reactivity of the theta2 (5.2-6.0 Hz) was maximal in the right temporal derivation (T6) and did not depend on stability of the anticipatory attention. The findings point to different functional significance of the theta1 and theta2 rhythms in infants. It is suggested that synchronization of the frontal theta1 rhythm in infants reflects the activity of the anterior attention system which realizes the executive attention control. The ability to maintain anticipatory attention increased with age, whereas the frontal theta1 synchronization decreased and totally disappeared at the age of 11 months. At the age of 8 months there was a positive correlation between the frontal theta1 synchronization and behavioral index of stability of the internally controlled attention. On the contrary, this correlation was negative at the age of 9 and 10 months. It is suggested that the age-dependent dynamics of the relationship between the frontal theta1 reactivity and attention reflects a leap in maturation of the anterior attention system resulting in its more economic and efficient functioning.

[The effect of early visual deprivation on the formation of a control system for brain states in early human ontogeny]. / Vliianie rannei zritel'noi deprivatsii na formirovanie sistemy kontrolia sostoianii mozga v rannem ontogeneze cheloveka.

Late effects of early visual deprivation on state control in sleep were studied in 23 infants with bilateral congenital cataract before and after surgery (usually, on the 6th month of life). In the course of three years 67 observations were performed. Laboratory assessments included videotaping infant sleep behaviour, recording EEG, EOG, ECG, galvanic skin response. It was shown that the early visual deprivation led to general changes in the basic mechanisms underlying state control in infancy. The sleep stages (active and quiet sleep), their duration and physiological autonomic and central characteristics were modified as compared to the age norm over a protracted period after surgery, when the visual experience became available for the infant. This type of sleep cycle can be identified as "partially perinatal sleep pattern". Revealed peculiarities of sleep cycle organization were suggested to reflect the higher level of activation in the neural arousal systems owing to the deficit of environmental stimulation during the critical stage (2-4 months) of brain development.