Oscillatory and structural measures of connectivity in psychosis, psychosis-risk and the healthy population

Magnetoencephalography (MEG) and Diffusion Tensor Imaging (DTI) are important tools for probing functional and structural properties of the brain. The interactions between the brain’s local and long-range circuitry could provide a key to understanding schizophrenia as a disorder of dysconnectivity and related risk factors in the healthy population. The aim in the first chapters of this thesis was to understand how high frequency local visual circuitry and long-range low frequency connectivity can be best estimated from MEG data. It was shown that using a finer sampling grid in source estimation leads to improved measures of high frequency responses. Furthermore, that networks usually measured in the resting-state can be extracted from task data was another key discovery and has positive implications for data quality and participant comfort going forward. The second aim of this thesis was to understand how specific local and global entities interact by investigating the relationships between local visual circuitry and long-range structural and oscillatory connectivity. An important finding was that the magnitude of local connectivity in the superficial layers of the visual cortex, as probed by gamma amplitude, was associated with reduced long-range connectivity beyond primary visual areas. The other novel finding was that the frequency of local visual oscillations was correlated with structural measures, possibly reflecting increased myelination. The third aim of this work was to better understand how psychosis-risk relates to functional and structural connectivity in health and schizophrenia. Schizotypy was robustly correlated with reduced long-range functional connectivity but not structural connectivity. The opposite was true for correlations between polygenic risk and connectivity. However, the aforementioned risk factors were not robustly correlated with local functional connectivity. The last chapter showed novel but non-significant differences in local and global oscillatory connectivity that were related to excitatory-inhibitory copy number burden in patients