Cortical Thickness in Adults with Autism

Background:

Grey matter (GM) volume and cortical thickness (CT) have been shown to correlate with performance and expertise on a number of tasks in typically developed individuals (e.g., Maguire et al., 2003). In people with ASDs it has been suggested that GM abnormalities are linked to behavioural deficits (Hadjikhani et al., 2006).  Structural magnetic resonance imaging (MRI) studies have revealed various different patterns of CT/GM volume in adults and adolescents with ASDs, predominantly finding decreases on both measures in areas of the frontal, parietal and temporal lobe (e.g., Scheel et al., 2011; Toal et al., 2010). However, increases in CT/GM volume in areas across the brain have also been reported (e.g., Hyde et al., 2010).

Objectives:

Despite being a more reliable measure of underlying GM thickness (Kim et al., 2005), studies on CT in people with ASDs are underrepresented in the literature.  Our objective was to utilise new semi-automatic cortical thickness analysis (CTA) tools in BrainVoyager QX (Goebel et al., 2006), which have not yet been applied to whole brain CT measurements in a group with ASDs and a matched control group.

Methods:

Participants: 10 males with ASDs and 10 age, sex and IQ- matched controls (McKay et al. 2011).Data Collection:  Sagittal T1-weighted anatomical images were obtained using a Siemens 3T Tim Trio MRI scanner (Parameters -T1 weighted MPRAGE sequence; TR = 1900ms, TE = 2.52ms, TI = 900ms with a flip angle = 9°; 192 slices; resolution = 1 mm³; FOV = 256.

Data Processing: White matter (WM)/GM border and the GM/cerebrospinal fluid (CSF) border was extracted for each brain using the advanced segmentation tools in BrainVoyager QX.  From these, individual CT maps were calculated for each subject.  Reconstructed surfaces of the GM/WM boundary for each hemisphere were aligned using cortex-based alignment (CBA) in order to better account for anatomical variability across all brains. The CT maps were then transformed from volume space into each subject's corresponding surface space. 

Analysis: Independent between groups t-tests were carried out using the CT of each subject at every vertex on the surface. Cluster size threshold estimation was used to control for multiple comparisons.

Results:

The analysis revealed that males with ASDs had significantly reduced CT bilaterally in the fusiform gyrus, in the left precentral sulcus and in the right postcentral sulcus, superior temporal sulcus, posterior cingulate, uncus and parahippocampal gyrus. There were no areas found to have significantly increased CT in the ASD group. These results are in line with previous studies reporting reduced CT/GM volumes in people with ASDs.

Conclusions:

The regions found to have reduced CT in the ASD group, namely the fusiform gyrus, posterior cingulate, and posterior temporal lobe, have been implicated in social cognition (Adolphs, 2001; Redcay, 2008). Similarly, the fusiform gyrus, precentral and postcentral sulcus have been linked to face and emotional face processing (Kanwisher et al., 1999; Adolphs et al., 1996).  As such, the reduced CT found in these regions may correspond to functional abnormalities in the aforementioned domains in individuals with ASDs.