Scientists from the Chinese University of Hong Kong have found that in autistic children, the brain area linked to language and social processing responds more weakly to emotionally significant sentences than in children without autism. The work was published in the journal NeuroImage: Clinical.
The study involved 58 children aged approximately 8 to 12 years (mean age 10 years) for whom Cantonese was their native language. Of these, 37 children had a diagnosis of "autism" and 21 did not; 48 participants were boys. Initially 78 children were recruited, but some were excluded because of strong head movements during scanning, which distort the data.
The children were asked simply to listen to sentences in Cantonese without responding. Some phrases described people in emotional situations - half positive, half negative (for example, "The older sister laughed at the joke") - while others described inanimate objects or phenomena ("The banana peel is yellow"). Sentences played backwards were also included, as non-speech sound for comparison. All phrases were the same length of eight syllables and comparable in complexity and word frequency; they were voiced by a single synthetic voice so that intonation would not differ.
Brain activity was measured using functional magnetic resonance imaging (fMRI), a method that shows which brain areas are more active during a task. The researchers were interested in the left superior temporal sulcus, a cortical area involved in processing speech and social information.
It turned out that, overall, in all children this area responded more strongly to "social-emotional" sentences than to phrases about objects. This skew is called the social-emotional bias; it was found to be present already in childhood. However, in a separate analysis, the bias was pronounced in children without autism, while in autistic children it was weaker and not statistically significant.
The difference between the groups appeared in the middle part of the left superior temporal sulcus: in autistic children the response to emotional phrases was weaker. The effect size was assessed as moderate or large. At the same time, responses to reversed speech and to sentences about objects did not differ between the groups - this suggests that their general hearing and basic language processing are similar.
The difference arose mainly due to negative sentences, but the statistical test did not confirm that positive and negative phrases are processed differently, so the authors consider this only a hint.
The weakness of the response was not explained by the children's language abilities. It also could not be statistically separated from the level of autistic symptoms, because diagnosis and symptom severity overlapped strongly. Within the group of autistic children, more severe symptoms were not associated with weaker brain responses.
"Reduced activity of the left superior temporal sulcus in response to social-emotional semantics may contribute to the difficulties in social communication in autistic children," the authors conclude.
The study has limitations. The sample is small by modern neuroimaging standards, especially few children without autism, so only large differences could be reliably detected. When scientists compared the groups across the whole brain rather than in preselected areas, no difference passed statistical correction. Because of head movements, some autistic children were excluded more often than children without autism - meaning the results may not extend to children who find it difficult to lie still. Most participants were boys, and most autistic children had at least one comorbid condition, most often attention deficit hyperactivity disorder (ADHD). Finally, the social-emotional and object sentences differed both in social content and in emotional valence, so the study cannot separate these two factors.