Autism spectrum disorder (ASD) is a neurodevelopmental disorder that is characterized by deficits in social communication. To explore the developmental changes in communication deficits in ASD, a sample of children encompassing a wide age range, from childhood to adolescence, was recruited. Regarding neural substrates of language/communication in ASD, recent studies have shown aberrant neural activity during semantic processing. For example, there is reduced activation in the left inferior frontal gyrus in adults with ASD compared with that in healthy controls. In contrast, individuals with ASD often have a perception-based preference with recruitment of primary sensory cortices.
A meta-analysis (Lai et al. 2014) concluded that, in contrast to typically developing (TD) individuals, who focused on top-down control processing with recruitment of the frontal cortices for language/communication, individuals with ASD usually engaged more in bottom-up processing because they possessed enhanced sensory-perceptual processing of local features of the stimuli. At the neural level, individuals with ASD showed enhanced activity of the primary sensory cortices (i.e., primary visual cortex) and reduced activation in the frontal area, which is involved in top-down processing (Lai et al., 2014). These findings imply that, unlike healthy adults, adults with ASD might recruit an immature, perception-based neural mechanism to support semantic processing instead of engaging in a frontal control mechanism.
We aimed to examine age-dependent neural correlates of semantic processing in boys with ASD and TD boys. We used functional magnetic resonance imaging (MRI) to investigate 37 boys with ASD (mean age = 13.3 years, standard deviation = 2.4) and 35 age-, sex-, intelligence quotient- and handedness-matched TD boys (mean age = 13.3 years, standard deviation = 2.7) from age 8 to 18 years. Previous research has shown that adolescents aged 13-17 might have a better ability to perform semantic tasks than children aged 8-12. Thus, we further divided the participants into adolescent (22 ASD and 21 TD, mean age = 15.07 years, age range = 13-18) and child (15 ASD and 14 TD, mean age = 10.67 years, age range = 8-12) groups.
The participants performed a semantic judgment task while they underwent an MRI scan. They were asked to indicate whether pairs of visually presented Chinese characters were related in meaning. Group (ASD, TD) x age (adolescent, child) ANOVA was performed to examine differences in age-related changes. Direct comparisons between the adolescent group and the child group were also performed. The behavioral results showed that the ASD group had lower accuracy in the related condition than the TD group. The neuroimaging results showed greater activation in the cuneus and less activation in the left inferior frontal gyrus in boys with ASD than in TD boys. Further examination of the developmental changes revealed that children with ASD had greater activation in the cuneus than TD children, whereas adolescents with ASD showed reduced left inferior frontal activation compared with that in TD adolescents.
In conclusion, TD boys may engage more in higher-level processing during the retrieval or selection of semantic features, whereas boys with ASD may rely more on lower-level visual processing during semantic judgments. These findings imply different functional organization of the semantic system between the two groups.
Figure 1. (a) The interaction effect (group by age) for activation. (b) Children with ASD had greater cuneus activation than TD children (blue), whereas adolescents with ASD showed reduced left inferior frontal gyrus (IFG) activation compared with that in TD adolescents (green).
References
1. Pin-Jane Chen, Susan Shur-Fen Gau, Shu-Hui Lee, and Tai-Li Chou (2016). Differences in age-dependent neural correlates of semantic processing between youths with autism spectrum disorder and typically developing youths. Autism Research, 9(12), 1263-1273. DOI:10.1002/aur.1616.
2. Lai, Meng-Chuan, Michael V. Lombardo, and Simon Baron-Cohen (2014). Autism. Lancet, 383(9920), 896-910. DOI:10.1016/s0140-6736(13)61539-1.
Professor Tai-Li Chou
Department of Psychology,
Imaging Center for Integrated Body, Mind and Culture Research
tlchou25@ntu.edu.tw