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Neuropsychologia. 2014 Jan;53:137-45. doi: 10.1016/j.neuropsychologia.2013.11.008. Epub 2013 Nov 21.

Longitudinal processing speed impairments in males with autism and the effects of white matter microstructure.

Author information

  • 1Waisman Laboratory for Brain Imaging and Behavior, University of Wisconsin-Madison, 1500 Highland Avenue, Madison, WI 53705, USA. Electronic address: btravers@wisc.edu.
  • 2Department of Psychology and Neuroscience Center, Brigham Young University, Provo, UT 84602, USA; The Brain Institute of Utah, University of Utah, 36 South Wasatch Drive, Salt Lake City, UT 84112, USA; Department of Psychiatry, University of Utah, 501 Chipeta Way, Salt Lake City, UT 84108, USA.
  • 3Waisman Laboratory for Brain Imaging and Behavior, University of Wisconsin-Madison, 1500 Highland Avenue, Madison, WI 53705, USA.
  • 4Department of Radiology, University of Utah, 30 North 1900 East #1A071, Salt Lake City, UT, USA.
  • 5Departments of Psychiatry and Biostatistics, Harvard University, 677 Huntington Avenue, Boston, MA 02115, USA; Neurostatistics Laboratory, McLean Hospital, 115 Mill Street, Belmont, MA 02478, USA.
  • 6Interdepartmental Program in Neuroscience, University of Utah, 401 MREB, 20 North 1900 East, Salt Lake City, UT 84132, USA.
  • 7Waisman Laboratory for Brain Imaging and Behavior, University of Wisconsin-Madison, 1500 Highland Avenue, Madison, WI 53705, USA; Department of Psychiatry, University of Wisconsin-Madison, 6001 Research Park Blvd., Madison, WI 53719, USA; Department of Medical Physics, University of Wisconsin-Madison, 1111 Highland Avenue, Room 1005 Madison, WI 53705, USA.

Abstract

The present study used an accelerated longitudinal design to examine group differences and age-related changes in processing speed in 81 individuals with autism spectrum disorder (ASD) compared to 56 age-matched individuals with typical development (ages 6-39 years). Processing speed was assessed using the Wechsler Intelligence Scale for Children-3rd edition (WISC-III) and the Wechsler Adult Intelligence Scale-3rd edition (WAIS-III). Follow-up analyses examined processing speed subtest performance and relations between processing speed and white matter microstructure (as measured with diffusion tensor imaging [DTI] in a subset of these participants). After controlling for full scale IQ, the present results show that processing speed index standard scores were on average 12 points lower in the group with ASD compared to the group with typical development. There were, however, no significant group differences in standard score age-related changes within this age range. For subtest raw scores, the group with ASD demonstrated robustly slower processing speeds in the adult versions of the IQ test (i.e., WAIS-III) but not in the child versions (WISC-III), even though age-related changes were similar in both the ASD and typically developing groups. This pattern of results may reflect difficulties that become increasingly evident in ASD on more complex measures of processing speed. Finally, DTI measures of whole-brain white matter microstructure suggested that fractional anisotropy (but not mean diffusivity, radial diffusivity, or axial diffusivity) made significant but small-sized contributions to processing speed standard scores across our entire sample. Taken together, the present findings suggest that robust decreases in processing speed may be present in ASD, more pronounced in adulthood, and partially attributable to white matter microstructural integrity.

KEYWORDS:

Autism; Diffusion tensor imaging; Executive function; Processing speed; White matter

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