Sentence comprehension in autism: thinking in pictures with decreased functional connectivity

Abstract

Comprehending high-imagery sentences like The number eight when rotated 90 degrees looks like a pair of eyeglasses involves the participation and integration of several cortical regions. The linguistic content must be processed to determine what is to be mentally imaged, and then the mental image must be evaluated and related to the sentence. A theory of cortical underconnectivity in autism predicts that the interregional collaboration required between linguistic and imaginal processing in this task would be underserved in autism. This functional MRI study examined brain activation in 12 participants with autism and 13 age- and IQ-matched control participants while they processed sentences with either high- or low-imagery content. The analysis of functional connectivity among cortical regions showed that the language and spatial centres in the participants with autism were not as well synchronized as in controls. In addition to the functional connectivity differences, there was also a group difference in activation. In the processing of low-imagery sentences (e.g. Addition, subtraction and multiplication are all math skills), the use of imagery is not essential to comprehension. Nevertheless, the autism group activated parietal and occipital brain regions associated with imagery for comprehending both the low and high-imagery sentences, suggesting that they were using mental imagery in both conditions. In contrast, the control group showed imagery-related activation primarily in the high-imagery condition. The findings provide further evidence of underintegration of language and imagery in autism (and hence expand the understanding of underconnectivity) but also show that people with autism are more reliant on visualization to support language comprehension.

Fig. 1

Within-group contrasts showing greater activation for high imagery than low imagery. The participants with autism showed little difference between the high- and low-imagery conditions, in contrast to the control participants, who showed more activation in the high-imagery condition than the low-imagery condition.

Fig. 2

Between-group contrasts of activation in each condition. (A) In the high-imagery condition, the autism group showed more activation than controls only in lingual gyrus. (B) In the high-imagery condition, the control group showed higher brain activation in left inferior frontal, middle frontal and left angular regions than the participants with autism. (C) In the low-imagery condition, the autism group showed more activation in L IPS and in left lingual gyrus in comparison with controls. (D) In the low-imagery condition, the control group did not show higher activation than the autism group; and (E) coronal view of higher activation in autism in L IPS than controls in the low-imagery condition.