Brain connectivity and networks as the basis of human hemispheric language dominance

The left cerebral hemisphere is dominant for our ability to speak and understand spoken words for the majority of people. The reasons for such lateralised brain function are unknown. One hypothesis is that brain structural asymmetry (i.e. how the two cerebral hemispheres are structurally different) may provide the basis for functional asymmetry, but there is limited support for this. We were the first to document that macroscopic cerebral asymmetry of the insula is related to side of hemispheric language dominance (HLD) in groups of healthy people whereas interhemispheric asymmetry of 'classical' language cortical regions - such as Broca's area - has limited significance. However, using macoscropic brain morphology to determine the functional organisation of the brain provides only limited answers and does not permit the prediction of HLD in individual people. Significant new insights into the functional organisation of the human brain will only be achieved when we consider the structural organisation of the microstructural brain environment, brain connectivity, and brain networks: these principles of brain structural organisation are thought to underpin brain functional organisation and human cognition, and can be determined in-vivo using advanced MRI approaches.
Objectives
The overall aim of this PhD is to determine the architectural basis of HLD in healthy people using advanced connectivity- and network-based MRI techniques.
Specific objectives:
1. Compare 3 T MRI structural and functional connectomes (network matrices) between people with left, bilateral and right HLD, and apply classification algorithms (e.g. machine learning) to determine whether networks can predict the side of HLD in individual people
2. Probe insular structural and functional MRI connectivity to provide deeper insights into the role of this brain structure for HLD
3. Explore whether high-field 7 T MRI offers increased sensitivity for the differentiation of HLD groups
4. Explore whether the side of HLD impacts on cognitive functioning
Plan
All data was previously acquired in context of the Human Connectome Project (HCP; https://www.humanconnectome.org/). The HCP offers high quality anatomical and functional neuroimaging in the healthy human brain using state-of-the-art MRI. All data is publicly available. Data exists for 1200 people aged 22-35, includes 3 T MRI and behavioural data for most and 7 T MRI for a subset of 184 people. HCP data has not previously been used to address the objectives of the proposed study. Based on existing studies, we estimate that over 150 people will have 'atypical' (i.e. right or bilateral) HLD. The student will collect all relevant MRI and behavioural data for people with atypical HLD and an age- and sex-matched cohort of ~150 people with 'typical' (i.e. left) HLD. Whole-brain structural and functional networks (connectomes) will be generated for each subject using established techniques for which we have prior experience. Connectomes will be analysed with respect to HLD using network-based statistics, graph theory and machine learning approaches. We will use targeted analyses of insular connectivity using probabilistic tractography, as applied in our previous work, and determine the relationship between insular connectivity and HLD.