Impact of Autism Diagnosis on Neural Systems of Nonverbal Fluid Reasoning in Adolescent Male Monozygotic Twins

Background:   Characterizing neural trajectories of fluid reasoning in special populations (including gifted) and in neurotypical children will sharpen our understanding of the influence of reasoning on the acquisition of a range of intellectual skills and talents. This skill is one of those enhanced or preserved at certain high levels of function in autism (Soulieres et al., 2009). Matrix reasoning, an identified construct of intelligence, has been acknowledged as a chief marker of changes in crystallized abilities, in addition to changes seen within real-world contextual thinking when you have enough information but not sufficient time to make decision (Kalbfleisch, Van Meter, and Zeffiro, 2006), and in academic settings including quantitative ability, declarative knowledge, and reading (Ferrer et al., 2009; Soulieres et al., 2009; Wright et al., 2008).  Matrix reasoning tests have also been shown to better identify giftedness (i.e. intellectual aptitude in disadvantaged populations) at higher rates than culturally biased traditional intelligence tests (Naglieri, 1997).  Furthermore, aspects of metacognitive ability are untouched in twice exceptional children with autism (Kalbfleisch & Loughan, 2011).

Objectives:   The present study investigated the impact of two types of autism diagnoses (high-functioning autism versus Asperger’s syndrome) on fluid reasoning (Ferrer, O’Hare, & Bunge, 2009; Kalbfleisch, Van Meter, & Zeffiro, 2006; Wright, Matlen, Baym, Ferrer, & Bunge, 2008) in a pair of adolescent male monozygotic twins. We report psychometric, behavioral, and neuro-functional differences of fluid reasoning assessed with a novel matrix reasoning task in the pair who presented as volunteers for an ongoing study of higher-level cognition in children with high-functioning autism. We report them here as a separate case due to their genetic identity, which lends an opportunity to examine demonstrative functional consequences of autism diagnosis on fluid reasoning. 

Methods:  We evaluated the impact of autism diagnosis on neural systems of nonverbal fluid reasoning in adolescent male monozygotic twins, age 16.3 years, using psychometric (WISC-IV, BRIEF) and functional neuroimaging methods utilizing a novel matrix reasoning task.

Results:   Twin with high-functioning autism (HFA) displayed lower Full Scale IQ resulting from decreased verbal aptitude and clinically significant executive function deficits compared to the twin with Asperger’s (ASP). Twins displayed comparable behavioral accuracy and speed during fluid reasoning. Conversely, neural systems in ASP correlated with right medial frontal cortex, posterior cingulate gyrus, and precuneus. Neural systems in HFA correlated with right superior and middle frontal gyri, right superior temporal gyrus and bilateral precuneus.

Conclusions:  These functional results coincide with brain structure changes that currently define differential conditions on the autism spectrum in the medical literature. Our findings potentially demonstrate the functional consequences of differences in verbal ability and executive function in twins with two forms of autism.  Furthermore, this approach presents a format for exploring the nature of twice exceptionality within a larger framework for mapping atypical brain development. We consider implications for the role of intelligence in the context of preserved and enhanced fluid reasoning ability in autism that leads to the presence and expression of certain talents and skills, sometimes described as twice exceptionality.