Brain Network Mapping Clarifies Distribution of Cortical Thickness Reductions

Cortical connectivity networks may explain irregular topographic distribution of reduced cortical thickness in patients with schizophrenia, according to research published in American Journal of Psychiatry.

Researchers compared data from 3 cross-sectional schizophrenia cohorts with healthy controls to characterize the extent and location of reductions in cortical thickness, as well as establish whether cortico-cortical connectivity might explain topographic distribution of reductions in the cortex.

Participants included 70 patients with first-episode psychosis (19 with schizophrenia, 38 with schizophreniform disorder, and 13 with schizoaffective disorder), 153 patients with chronic schizophrenia, and 47 patients with treatment-resistant schizophrenia, as well as corresponding healthy controls (57, 168, and 54, respectively). Neuroimaging data were obtained for all patients.

When compared with the healthy control group, 34, 79, and 106 regions showed significant reductions in cortical thickness in the first-episode psychosis, chronic schizophrenia, and treatment-resistant schizophrenia groups, respectively. None of these 3 patient cohorts exhibited increased cortical thickness. Within the chronic and treatment-resistant schizophrenia groups, the most extensive cortical thickness reductions were found in the frontal and temporal lobes and the insula and cingulate cortex, while the posterior regions demonstrated evidence of reductions in the treatment-resistant group.

Researchers then used permutation testing to establish whether structural covariance was increased in regions with reductions in cortical thickness. In each of the 3 patient cohorts, structural covariance was “significantly increased” in regions with cortical thickness reductions (P <.0001) regardless of whether this covariance was measured in the patient or control group. “In other words,” the researchers noted, “cortical regions susceptible to thickness reductions in schizophrenia were interconnected more strongly than arbitrarily chosen regions both in the general population and across schizophrenia subtypes.”

Supplementary analyses found that 81 regions had significant reductions in cortical thickness in at least 2 of the 3 cohorts, with the level of overlap not attributable to chance (P =.006). Structural covariance was also significantly increased in these 81 regions in both patient and control groups, which was consistent with primary analyses.

One noteworthy study limitation is the cross-sectional design; data should be confirmed in a longitudinal sample. Additionally, researchers noted the challenges in determining whether cortical thickness reductions may have been the result of variations in brain tissue microstructural properties. Finally, MRI data were not combined across cohorts for analyses due to the use of different scanners.

“Brain network architecture can explain the irregular topographic distribution of cortical thickness reductions in schizophrenia,” the researchers of the study concluded. They continued with,  “This finding, replicated in 3 distinct schizophrenia cohorts, suggests that the effect is robust and independent of illness stage.”

Reference
Wannan CMJ, Cropley VL, Chakravarty MM, et al. Evidence for network-based cortical thickness reductions in schizophrenia [published online June 5, 2019]. Am J Psychiatry. doi: 10.1176/appi.ajp.2019.18040380