International Meeting for Autism Research (May 7 - 9, 2009): Relationship Between Corpus Callosum Structure and Intelligence in Autism and Typical Development

Thursday, May 7, 2009

Northwest Hall (Chicago Hilton)

12:00 PM

M. DuBray , Interdepartmental Program in Neuroscience, University of Utah, Salt Lake City, UT

T. L. Merkley , Psychology, Brigham Young University, Provo, UT

E. Bigler , Psychology & Neuroscience, Brigham Young University, Provo, UT

A. L. Alexander , Department of Medical Physics, Department of Psychiatry, Waisman Laboratory for Brain Imaging & Behavior, University of Wisconsin, Madison, WI

A. Froehlich , Psychiatry, University of Utah, Salt Lake City, UT

J. E. Lee , Medical Physics, Waisman Laboratory for Brain Imaging & Behavior, University of Wisconsin, Madison, WI

J. E. Lainhart , Psychiatry, Neuroscience, & The Brain Institute, University of Utah, Salt Lake City, UT

N. Lange , Departments of Psychiatry and Biostatistics, Harvard University, Belmont, MA

Background: IQ is often decreased or uneven in autism, and may be related to corpus callosum (CC) development. A number of studies suggest that the corpus callosum is smaller in autism than in typical controls relative to total brain volume. We previously found smaller CC volumes and abnormal microstructure in individuals with autism. Aberrant growth of the CC could contribute to reduced interhemispheric connectivity and variations in intelligence.
Objectives: The present study examines the relationship between corpus callosum morphology and measures of intelligence and processing speed in high functioning individuals with autism.
Methods: 3T MRI T1-weighted images were used to calculate midsagittal area of the corpus callosum according to the Witelson methodology. 47 right handed males with autism (pIQ>74) were compared to 37 typically developing males (mean age: autism=12 years, controls=13.5 years).

Results: While controlling for age and total intracranial volume, significantly positive correlations were found between measures of intelligence and total callosal and subregional areas in the autism group only. In contrast, correlations were negative in controls; higher performance IQ and processing speed were related to smaller posterior callosal areas.

Conclusions: The relationship between midsagittal callosal area and intelligence differs in autism and typical development. In autism, “more is better”: larger midsagittal area is related to higher IQ in autism. The opposite is found in controls in posterior CC regions. The findings suggest a fundamental difference in the relationship between the development of the corpus callosum and development of IQ in autism. Our longitudinal work, examining the trajectories of CC growth, white matter microstructural development, and the development of processing speed and intellectual skills, seeks to pinpoint what is going on in the CC and how it affects functioning in autism.

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