Subjects were 17 boys with autism and 14 healthy male controls between 8 and 12 years of age. The diagnosis of autism was established through the administration of the Autism Diagnostic Interview-Revised (ADI-R) and the Autism Diagnostic Observation Schedule (ADOS). Children with secondary autism such as tuberous sclerosis were excluded. Control subjects were screened by face-to face interview, and individuals with family history of any neuropsychiatric disorder, such as autism, learning disability, affective disorders, and schizophrenia, were not included. Potential subjects with a history of birth asphyxia, head injury, or a seizure disorder were excluded. All control subjects had a full scale IQ (FSIQ)>70 and no learning disability as assessed by the Wide Range Achievement Test-R. Exclusions were based on history and physical examination as well as laboratory testing when indicated. The WISC-III was administered to measure FSIQ, verbal IQ, and performance IQ (PIQ). Methodology of the study was approved by the Institutional Review Board. Written informed consent was obtained from parents and assent was obtained from all children.
Scans were obtained on a GE 1.5 Tesla Signa scanner. A T1
-weighted SPGR sequence was first acquired with the following parameters: slice thickness=1.5mm, slice numbers=124; TE 5ms; TR 25ms; flip angle 40, NEX 1; FOV 24cm; matrix 256×192. Proton density and T2
-weighted images were then obtained with the following parameters: slice thickness=5mm; TE 17ms for PD or 102ms for T2
; TR 2500ms; NEX 1; FOV 24cm; matrix 256×192. MRI data were identified by scan number to retain blindness, and analyzed using Brain research: Analysis of images, Networks and Systems software7
(BRAINS) while applying previously published methodologies of cortical thickness and total brain volume (TBV) measurements.6,7
The initial step of surface analysis in BRAINS is the creation of a triangle-based isosurface using the parametric center of the cortex as the outer boundary of the brain. Cortical thickness is calculated from vectors that are normal to each triangular surface, and the shortest distance to the 50% grey matter and 50% white matter is defined as the thickness.6
All measurements from autistic subjects were compared with controls using Student’s t- test. Pearson’s correlations coefficients were used to examine the relationships between TBV, IQ measures and cortical thickness. Spearman’s rho correlation coefficients were used to examine the associations between ADI-R and ADOS scores with cortical thickness measurements. A two-tailed statistical significance level was set at p<0.05.