International Meeting for Autism Research (May 7 - 9, 2009): The Limbic System in the Asperger Syndrome: a Preliminary Diffusion Tensor Tractography Study

The Limbic System in the Asperger Syndrome: a Preliminary Diffusion Tensor Tractography Study

Saturday, May 9, 2009: 2:00 PM
Northwest Hall Room 5 (Chicago Hilton)
L. Pugliese , Psychological Medicine and Psychiatry, Section of Brain Maturation, King's College London, Institute of Psychiatry, London, United Kingdom
M. Catani , Psychological Medicine and Psychiatry, Section of Brain Maturation, King's College London, Institute of Psychiatry, London, United Kingdom
M. Thiebaut de Schotten , Psychological Medicine and Psychiatry, Section of Brain Maturation, King's College London, Institute of Psychiatry, London, United Kingdom
C. Murphy , Psychological Medicine and Psychiatry, Section of Brain Maturation, King's College London, Institute of Psychiatry, London, United Kingdom
E. Daly , Section of Brain Maturation, Department of Psychological Medicine and Psychiatry, Institute of Psychiatry, King's College London, London, United Kingdom
D. G. Murphy , Section of Brain Maturation, Department of Psychological Medicine and Psychiatry, Institute of Psychiatry, King's College London, London, United Kingdom
.. MRC UK AIMS Network , Psychological Medicine and Psychiatry, Section of Brain Maturation, King's College London, Institute of Psychiatry, London, United Kingdom
Background: It has been suggested that people with Autistic Spectrum Disorder (ASD) have altered development (and connectivity) of limbic circuits1,2.  However, direct evidence of anatomical differences specific to white matter pathways underlying social behavior and emotions in ASD, is lacking.

Objectives: We used Diffusion Tensor Imaging  (DTI) tractography to compare, in vivo, tract-specific measurements along the principal limbic pathways between people with Asperger syndrome and healthy controls.

Methods: We recruited 66 people: twenty-four males with Asperger Syndrome (mean age 23±12 years, age range: 9-54 years) and 42 age-matched male controls (mean age 25±10 years, age range: 9-54 years).  DTI were acquired on a 1.5 T GE Signa NV/i LX (General Electric, Milwaukee, WI) and processed as described by Jones at al3.  We quantified tract-specific diffusivity measurements as indirect indexes of tract volume (e.g. number of streamlines) and micro-structural organization and integrity (e.g. mean diffusivity, MD; and fractional anisotropy, FA) of the main limbic tracts.  These include the inferior longitudinal fasciculus (ILF), inferior frontal occipital fasciculus (IFOF), uncinate, cingulum and fornix.

Results: DTI measurementsStreamlines: People with Asperger syndrome had a significantly higher number of streamlines in the right (p=0.003) and left (p=0.03) cingulum and in the right (p=0.03) and left (p=0.04) inferior longitudinal fasciculus.  In contrast people with Asperger syndrome had a significantly lower number of streamlines in the right uncinate (p=0.02).  The number of streamlines for the right (but not for the left) cingulum survived Bonferroni correction. Mean Diffusivity: The Asperger group showed significantly increase in the ILF bilaterally, and in the right cingulum and in the right IFOF.  Fractional anisotropy: individuals with Asperger syndrome had a significant decrease in FA within the IFOF bilaterally, and in the right uncinate fasciculus.  Age-related differences.  Streamlines: There were no significant age-related differences between groups.  Mean diffusivity: There was statistically significant age-related difference in mean diffusivity of the left uncinate fasciculus (Zobs=2.05) (p=0.02). Fractional Anisotropy: There were no age-related  between-group differences.

Conclusions: People with Asperger syndrome have significant differences in micro-structural integrity (and maturation) of some, but not all, limbic pathways. This may mostly affect (respectively) the cingulum and uncinate fasciculus. Our findings support previous reports of anatomical, metabolic and functional differences in the limbic regions of people with Asperger and may explain some of the social and emotional4,5 anomalies typically found in the disorder. Further studies linking the involvement of these pathways are required.

References: 1) Courchesne E,et al. Curr. Opin. in Neurobiology. 2005;15(2):225-230. 2) Jones D. Hum.Brain Mapp. 2002;15(4):216-30 3)  Wickelgren I. Science. 2005;308(5730):1856-8. 4) Damasio AR. Arch Neurol. 1978;35(12):777-86. 5) Mundy P. J Child Psychol Psych. 2003;44(6):793-809.

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