Fluid intelligence and the cerebellum in autism spectrum disorders

Abstract

Executive functioning abilities, including abstract reasoning, are often reported as weaknesses in autism spectrum disorders (ASDs). The current study examines reasoning through a different approach by utilizing the Cattell-Horn-Carroll (CHC) theory of intelligence, which is a widely accepted, research-based model that defines reasoning or fluid intelligence (Gf) and outlines those smaller skills of which it is composed. The Woodcock-Johnson, Third Edition (WJ III) is a test battery based on CHC theory, assessing the broad and narrow abilities of the model.

Young men with high-functioning autism spectrum disorders (HFASDs) and neurotypical controls were given the WJ III tasks that assess the four narrow abilities of fluid intelligence - general sequential reasoning/deductive reasoning (RG), induction/inductive reasoning (I), speed of reasoning (RE), and quantitative reasoning/math reasoning (RQ). It was hypothesized that while deductive reasoning, inductive reasoning, and reasoning speed would be lower for HFASD, math reasoning would be comparable between groups. This expectation was based on previous autism research, which has found reasoning and processing speed deficits but preserved math skills.

The present study also sought to examine cerebellar volume, through structural brain imaging, and its relationship to reasoning abilities. The HFASD group was expected to have reduced cerebellar volume when compared to controls. The ASD literature contains many examples of this pattern of brain structure, with the cerebellum being the most commonly cited region of abnormality. Additionally, the cerebellum has been implicated in studies of executive functioning, and a relationship between size and performance on nonverbal reasoning tasks has been reported. Therefore, a positive correlation was hypothesized between cerebellar volume and scores on WJ III reasoning tasks.

Twenty-one young adult male HFASD subjects and 21 neurotypical controls were included in the current study. The data was analyzed through the use of MANOVA/MANCOVA, t-tests, and Pearson correlations. Results supported fluid intelligence weaknesses in the HFASD sample, with significantly lower performance in speed of reasoning. Deductive and inductive reasoning abilities were also lower, though these findings did not reach significance. The data did not support decreased cerebellar volume in HFASD, nor was a relationship between fluid reasoning and volume of the cerebellum found.