Journal of the International Neuropsychological Society

Symposium

Neuronal fiber pathway abnormalities in autism: An initial MRI diffusion tensor tracking study of hippocampo-fusiform and amygdalo-fusiform pathways

THOMAS E. CONTUROa1 c1, DIANE L. WILLIAMSa2, CHARLES D. SMITHa3, EREN GULTEPEa1, ERBIL AKBUDAKa1 and NANCY J. MINSHEWa4

a1 Mallinckrodt Institute of Radiology, Washington University School of Medicine, St. Louis, Missouri

a2 Department of Speech-Language Pathology, Duquesne University, Pittsburgh, Pennsylvania

a3 Department of Neurology, University of Kentucky, Lexington, Kentucky

a4 Departments of Psychiatry and Neurology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania

Abstract

MRI diffusion-tensor tracking (DTT) was performed in 17 high-functioning adolescents/adults with autism and 17 pairwise-matched controls. White matter pathways involved in face processing were examined due to the relevance of face perception to the social symptoms of autism, and due to known behavioral and functional imaging findings in autism. The hippocampo-fusiform (HF) and amygdalo-fusiform (AF) pathways had normal size and shape but abnormal microstructure in the autism group. The right HF had reduced across-fiber diffusivity (D-min) compared with controls, opposite to the whole-brain effect of increased D-min. In contrast, left HF, right AF, and left AF had increased D-min and increased along-fiber diffusivity (D-max), more consistent with the whole-brain effect. There was a general loss of lateralization compared with controls. The right HF D-min was markedly low in the autism subgroup with lower Benton face recognition scores, compared with the lower-Benton control subgroup, and compared with the higher-Benton autism subgroup. Similar behavioral relationships were found for performance IQ. Such results suggest an early functionally-significant pathological process in right HF consistent with small-diameter axons (with correspondingly slower neural transmission) and/or higher packing density. In left AF and HF, changes were interpreted as secondary, possibly reflecting axonal loss and/or decreased myelination. (JINS, 2008, 14, 933–946.)

(Received February 01 2008)

(Revised August 04 2008)

(Accepted August 05 2008)

Correspondence:

c1 Correspondence and reprint requests to: Thomas E. Conturo, Mallinckrodt Institute of Radiology, Washington University School of Medicine, 4525 Scott Avenue, Campus Box 8225, St. Louis, MO 63110. E-mail: tconturo@wustl.edu

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