Autism as impairment in the formation and use of meaning: an attempt to integrate a functional and a neurological model

Neural correlates of verbal and nonverbal semantic integration in children with autism spectrum disorders

BACKGROUND

Autism is a pervasive developmental disorder characterized by deficits in social-emotional, social-communicative, and language skills. Behavioral and neuroimaging studies have found that children with autism spectrum disorders (ASD) evidence abnormalities in semantic processing, with particular difficulties in verbal comprehension. However, it is not known whether these semantic deficits are confined to the verbal domain or represent a more general problem with semantic processing. The focus of the current study was to investigate verbal and meaningful nonverbal semantic processing in high-functioning children with autism (mean age = 5.8 years) using event-related potentials (ERPs).

METHOD

ERPs were recorded while children attended to semantically matching and mismatching picture-word and picture-environmental sound pairs.

RESULTS

ERPs of typically developing children exhibited evidence of semantic incongruency detection in both the word and environmental sound conditions, as indexed by elicitation of an N400 effect. In contrast, children with ASD showed an N400 effect in the environmental sound condition but not in the word condition.

CONCLUSIONS

These results provide evidence for a deficiency in the automatic activation of semantic representations in children with ASD, and suggest that this deficit is somewhat more selective to, or more severe in, the verbal than the nonverbal domain.

Autism, amnesia, hippocampus, and learning

Autism is held to be the result of the failure of a central cognitive processor which is necessary for flexible multidimensional association of sensorial stimuli, memory, and motivational states. Failure of this processor produces rigid, invariant, rote behavior, thought and language and aberrant modulation of emotion. It is argued that this central processing function is critically dependent on the hippocampus. Thus autism is postulated to be the developmental syndrome of hippocampal dysfunction. The hippocampus is postulated to be necessary for normal development in the child of language syntax, semantics, and pragmatics; the capacity for creativity and generativity in language and behavior, and combinatorial possibilities in general; for the integration of motivational states with experience and learning; and for the construction of a complex, useful and flexible structure of meaning. These constructs may become independent of hippocampus for use, but hippocampus is still required to modify or add to them. Finally, this analysis suggests a specific hypothesis of hippocampal organization which I advance as an hypothesis: that the hippocampus can be modelled as a multidimensional system in which the unique intersection of all input dimensions is the resultant.

Infantile autism: a syndrome of multiple primary deficits?

Attempts to explain infantile autism in terms of just one underlying neurological or psychological deficit may be misguided. As in the case of many neurological syndromes, autism may involve multiple functional deficits due to multiple coexistent neurological deficits. Comparison with Asperger's syndrome and the developmental dysphasias suggests that the autistic syndrome results from the coexistence of at least two distinct constellations of functional impairments: deficits in mechanical language skills, as in the developmental dysphasias; and deficits in social relatedness, play, and nonverbal communication, as in Asperger's syndrome. Possible neurological underpinnings are considered, including the relative contribution of the two cerebral hemispheres. Implications for etiology and research are discussed.