1Rob Nicolson, 1Timothy J. DeVito, 2Christine N. Vidal, 2Yihong Sui, 2Kiralee M. Hayashi, 1Dick J. Drost, 1Peter C. Williamson, 1Beth Craven-Thuss, 1William Pavlosky, 2Arthur W. Toga, 2Paul M. Thompson
1Lawson Health Research Institute, University of Western Ontario, Canada
2Laboratory of Neuroimaging, UCLA School of Medicine, Los Angeles, CA, USA
Fourteen male patients with autism (age: 9.8+/-3.4 years) and 12 male controls (age: 10.0+/-2.2 years) underwent a magnetic resonance imaging scan. T1-weighted 3D MP-RAGE images (1.2-mm isotropic resolution) were acquired at 3.0-Tesla (IMRIS, Winnipeg, Canada). The groups did not differ significantly in terms of age, sex, race, or non-verbal intelligence. Four patients were left-handed while no controls were. Scans were digitally transformed into the ICBM standardized stereotactic space, and the transformation parameters were retained for native space analyses. The hippocampus was delineated, using an anatomical protocol with quantified reliability, and traces were converted into 3D parametric surface meshes. Average anatomical maps were also created to visualize the mean 3D shape of the hippocampus in both diagnostic groups. The volume of both hippocampi and hippocampal asymmetry ([r-l]/[r+l]) was compared between the two groups using ANOVA.
The groups did not differ significantly in the volume of either the left hippocampus (F=0.03, df=1,25, p=0.9) or the right hippocampus (F=0.06, df=1,25, p=0.8). There was also no significant difference in the pattern of hippocampal asymmetry between the groups (F=1.0, df=1,24, p=0.8).
Although the results of this study must be interpreted cautiously in light of several limitations (small sample size, possible medication effects), we did not detect a difference in the volume of the hippocampus. This result is similar to that found in most imaging studies of the hippocampus in autism and suggests that, although a reduction in cell size and an increase in cell density has been reported in neuropathological studies of the hippocampus, these changes are not reflected in the volume of the structure.
Paul Thompson, Ph.D.
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