SURFACE-BASED MORPHOMETRY AND CORTICAL COMPLEXITY: FROM PSYCHIATRIC DISORDERS TO COGNITION AND BEHAVIOR

This thesis aims at investigating cortical surface measures, specifically cortical complexity, and their importance on the understanding of psychiatric disorders, behavior and cognition. We performed three different studies to reach this goal. In Study 1, we aimed to investigate the brain cortical alterations underlying bipolar-schizophrenic spectrum disorders: patients with schizophrenia, patients with bipolar disorder, and healthy subjects were compared investigating SBM based cortical complexity measures (fractal dimension). Then, we proposed to correlate such structural abnormalities with available clinical and cognitive measures. Cortical complexity was reduced in schizophrenia patients compared to healthy controls in the right superior temporal gyrus while bipolar disorder patients showed significantly lower cortical complexity in the left pars opercularis compared to healthy controls. Additionally, bipolar patients had increased cortical complexity in the left lingual gyrus and this measure was positively correlated with the severity of manic symptoms. When compared to schizophrenia, bipolar patients showed significant increases in cortical complexity in the left inferior temporal gyrus, right temporal pole, inferior and superior temporal cortex. In Study 2, the objective was to investigate cortical complexity in patients with cocaine addiction. Since the frontal, parietal, temporal and insular cortices have been shown to play an important role in decision making and impulsivity, we hypothesized that cortical complexity in the brain of patients with cocaine addiction would be altered in these regions. Moreover, impulsivity is commonly associated with cocaine and the development to its addiction, so we expect that these alteration in the cortical surface may be related to measure of impulsiveness. The results showed that patients with cocaine addiction had higher levels of impulsivity and reduced cortical complexity in a cluster encompassing the left insula and supramarginal gyrus, as well as in the left medial orbitofrontal cortex. Additionally, the cortical complexity in the left medial orbitofrontal cortex was correlated with the age of onset of cocaine addiction and with attentional impulsivity. These findings do indeed suggest that chronic cocaine use may be associated with changes in the cortical surface in fronto-parieto-limbic regions involved in emotional regulation, and that these changes may be linked to earlier use of cocaine. Finally, in study 3, our objective was to investigate changes in the brain surface of chess experts using cortical complexity and gyrification measures. We hypothesized that the surface indexes of the brain regions and networks underlying high-order cognition, including fluid intelligence, working memory, processing speed, and visuospatial processing, namely, prefronto-parieto-temporal networks, would be altered. Additionally, since training in the chess game usually starts during childhood, we hypothesized that these indexes would be correlated with the training time of chess practice. The results showed that in chess experts, the cortical complexity was increased in the left frontal operculum and correlated with the starting age of chess practice, and decreased in the right superior parietal lobule. Chess expertise, also investigated through a logistic regression model was indeed predicted by the cortical complexity in a network of fronto-parieto-temporal regions. These findings suggest that the complex properties of the brain surface in a network of transmodal association areas important for flexible high-level cognitive functions are important for chess expertise, and that these changes may develop over time with long-lasting practice.