Autistic fluid intelligence: Increased reliance on visual functional connectivity with diminished modulation of coupling by task difficulty

Abstract

Different test types lead to different intelligence estimates in autism, as illustrated by the fact that autistic individuals obtain higher scores on the Raven's Progressive Matrices (RSPM) test than they do on the Wechsler IQ, in contrast to relatively similar performance on both tests in non-autistic individuals. However, the cerebral processes underlying these differences are not well understood. This study investigated whether activity in the fluid "reasoning" network, which includes frontal, parietal, temporal and occipital regions, is differently modulated by task complexity in autistic and non-autistic individuals during the RSPM. In this purpose, we used fMRI to study autistic and non-autistic participants solving the 60 RSPM problems focussing on regions and networks involved in reasoning complexity. As complexity increased, activity in the left superior occipital gyrus and the left middle occipital gyrus increased for autistic participants, whereas non-autistic participants showed increased activity in the left middle frontal gyrus and bilateral precuneus. Using psychophysiological interaction analyses (PPI), we then verified in which regions did functional connectivity increase as a function of reasoning complexity. PPI analyses revealed greater connectivity in autistic, compared to non-autistic participants, between the left inferior occipital gyrus and areas in the left superior frontal gyrus, right superior parietal lobe, right middle occipital gyrus and right inferior temporal gyrus. We also observed generally less modulation of the reasoning network as complexity increased in autistic participants. These results suggest that autistic individuals, when confronted with increasing task complexity, rely mainly on visuospatial processes when solving more complex matrices. In addition to the now well-established enhanced activity observed in visual areas in a range of tasks, these results suggest that the enhanced reliance on visual perception has a central role in autistic cognition.

Keywords: Autism; Connectivity; Intelligence; PPI; Reasoning; fMRI.

Fig. 1

Examples similar to items from the Raven's Standard Progressive Matrices. This fluid reasoning test is composed of 60 matrix problems of increasing complexity. To solve the matrices, participants have to choose among 8 choices the one that best fill in the missing entry (bottom right of the matrix). The three examples represent the three complexity levels included in our study: figural, analytical and complex analytical.

Fig. 2

Complexity contrast. A. Non-autistic > autistic contrast (in blue): increased activity in left middle frontal gyrus and bilateral precuneus as complexity increased. AUT > non-AUT contrast (in red): increased activity in the left superior occipital gyrus and the left middle occipital gyrus as complexity increased (p < 0.001 unc, K = 50 contiguous voxels). B, C, D. Percent signal change in the three regions of between-group differences displayed for each task complexity level, in the autistic group (in red) and non-autistic group (in blue).

Fig. 3

PPI analyses based on common areas of activity (conjunction seeds). Non-autistic > autistic contrast (in blue): As complexity increased, non-autistic participants exhibited a wider increase in functional connectivity with other elements of the reasoning network for the 3 regions of interest, in comparison with autistic participants. Autistic > non-autistic contrast (in red): As complexity increased, autistic participants showed a higher functional connectivity than non-autistic participants only for the occipital seed, for which they displayed an increase in connectivity between the left inferior occipital gyrus (seed) and areas in the left superior frontal gyrus, right superior parietal lobule, right middle occipital gyrus and right inferior temporal gyrus (p < 0.001, unc.). Green spots indicate seeds.

Fig. 4

PPI analyses based on areas of maximal between-group differences in activity (maximum difference seeds). Non-autistic participants (in blue) demonstrated a wide connectivity with other elements of the reasoning network for the three seeds. Autistic participants (in red) only showed functional connectivity for the occipital seed, which exhibited an interaction with frontal, temporal, occipital and sub-cortical areas (p < 0.001, unc.). Green spots indicate seeds.