ABSTRACT
Auditory sensory modulation difficulties and problems with automatic re-orienting to sound are well documented in autism spectrum disorders (ASD). Abnormal preattentive arousal processes may contribute to these deficits. In this study, we investigated components of the cortical auditory evoked potential (CAEP) reflecting preattentive arousal in children with ASD and typically developing (TD) children aged 3-8 years. Pairs of clicks ('S1' and 'S2') separated by a 1 sec S1-S2 interstimulus interval (ISI) and much longer (8-10 sec) S1-S1 ISIs were presented monaurally to either the left or right ear. In TD children, the P50, P100 and N1c CAEP components were strongly influenced by temporal novelty of clicks and were much greater in response to the S1 than the S2 click. Irrespective of the stimulation side, the 'tangential' P100 component was rightward lateralized in TD children, whereas the 'radial' N1c component had higher amplitude contralaterally to the stimulated ear. Compared to the TD children, children with ASD demonstrated 1) reduced amplitude of the P100 component under the condition of temporal novelty (S1) and 2) an attenuated P100 repetition suppression effect. The abnormalities were lateralized and depended on the presentation side. They were evident in the case of the left but not the right ear stimulation. The P100 abnormalities in ASD correlated with the degree of developmental delay and with the severity of auditory sensory modulation difficulties observed in early life. The results suggest that some rightward-lateralized brain networks that are crucially important for arousal and attention re-orienting are compromised in children with ASD and that this deficit contributes to sensory modulation difficulties and possibly even other behavioral deficits in ASD.
Subject(s)
Auditory Cortex/physiopathology , Auditory Perception/physiology , Child Development Disorders, Pervasive/physiopathology , Evoked Potentials, Auditory/physiology , Functional Laterality , Acoustic Stimulation , Arousal , Attention , Case-Control Studies , Child , Child Development Disorders, Pervasive/psychology , Child, Preschool , Electroencephalography , Female , Humans , Male , Reaction Time/physiology , SoundABSTRACT
BACKGROUND: An elevated excitation/inhibition ratio has been suggested as one mechanism underpinning autism. An imbalance between cortical excitation and inhibition may manifest itself in electroencephalogram (EEG) abnormalities in the high frequency range. The aim of this study was to investigate whether beta and gamma range EEG abnormalities are characteristic for young boys with autism (BWA). METHODS: EEG was recorded during sustained visual attention in two independent samples of BWA from Moscow and Gothenburg, aged 3 to 8 years, and in age matched typically developing boys (TDB). High frequency EEG spectral power was analyzed. RESULTS: In both samples, BWA demonstrated a pathological increase of gamma (24.4-44.0 Hz) activity at the electrode locations distant from the sources of myogenic artefacts. In both samples, the amount of gamma activity correlated positively with degree of developmental delay in BWA. CONCLUSIONS: The excess of high frequency oscillations may reflect imbalance in the excitation-inhibition homeostasis in the cortex. Given the important role of high frequency EEG rhythms for perceptual and cognitive processes, early and probably genetically determined abnormalities in the neuronal mechanisms generating high frequency EEG rhythms may contribute to development of the disorder. Further studies are needed to investigate the specificity of the findings for autism.
Subject(s)
Autistic Disorder/physiopathology , Cerebral Cortex/physiopathology , Electroencephalography , Autistic Disorder/diagnosis , Beta Rhythm , Brain Mapping , Child , Child, Preschool , Cortical Synchronization , Humans , Male , Russia , Statistics, NonparametricABSTRACT
OBJECTIVE: Functional brain abnormalities associated with autism in 3-8-year-old boys were studied with EEG recorded under controlled experimental condition of sustained visual attention and behavioral stillness. METHODS: EEG was recorded in two independent samples of boys with autism (BWA) from Moscow (N=21) and Gothenburg (N=23) and a corresponding number of age-matched typically developing boys (TDB). EEG spectral power (SP) and SP interhemispheric asymmetry within delta, theta and alpha bands were analyzed. RESULTS: BWA comprised a non-homogeneous group in relation to theta and alpha SP. When four outliers were excluded the only between-group difference in absolute SP was a higher amount of prefrontal delta in BWA. BWA of both samples demonstrated atypical leftward broadband EEG asymmetry with a maximum effect over the mid-temporal regions. Concurrently, the normal leftward asymmetry of mu rhythm was absent in BWA. CONCLUSIONS: The abnormal broadband EEG asymmetry in autism may point to a diminished capacity of right temporal cortex to generate EEG rhythms. The concurrent lack of normal leftward asymmetry of mu rhythm suggests that abnormalities in EEG lateralization in autism may be regionally/functionally specific. SIGNIFICANCE: The data provide evidence for abnormal functional brain lateralization in autism.
Subject(s)
Autistic Disorder/physiopathology , Dominance, Cerebral , Electroencephalography , Alpha Rhythm , Autistic Disorder/diagnosis , Child , Child, Preschool , Delta Rhythm , Humans , Male , Temporal Lobe/physiopathology , Theta RhythmABSTRACT
We examined the hypothesis of lower-level processing abnormalities related to perceptual grouping in boys with autism aged 3-6 years. We investigated event-related potentials response to visual elements that either formed perceptually coherent illusory contour or were arranged in a noncoherent way. The results showed that in healthy boys the illusory contour as compared with control stimulus elicited enhanced negativity of N1 peak (C effect), which has been previously found in adults. Autistic boys demonstrated the reliable inverted illusory contour effect, that is, more positive N1 amplitude to illusory contour. We hypothesized that boys with autism were sensitive to difference between illusory contour and control figures basing on collinearity processing mechanisms implemented in neural circuitry of primary visual cortex.
Subject(s)
Autistic Disorder/physiopathology , Evoked Potentials, Visual/physiology , Illusions/physiology , Child , Child, Preschool , Humans , Male , Photic Stimulation , Psychiatric Status Rating Scales , Visual Cortex/physiopathologyABSTRACT
We estimated relative contribution of genetic and environmental factors to electroencephalogram (EEG) frequency and amplitude parameters in infants. EEG was registered in 49 pairs of monozygotic and 45 pairs of dizygotic twins aged 7-12 months during (1) visual attention and (2) darkness. The variability of occipital alpha frequency depended mainly on genetic, probably nonadditive factors. The mean heritability for the spectral amplitudes in the delta, theta, and alpha bands were 0.37, 0.13, and 0.22 during visual attention, and 0.22, 0.40, and 0.10 during darkness. The influence of shared environment was probable for many of the EEG parameters. It was greatest for the amplitude of the theta rhythm during visual attention. The theta amplitude depended on such a parameter of early social environmental enrichment as the number of caregivers in the family. The possible relationship between infant theta rhythm and developmental outcome is discussed. For many of the EEG parameters, heritability increased during the second half of the first year of life, thus supporting the hypothesis about amplification of genetic effects and decrease of common environmental influences with age.
