Delineating In-Vivo T1-Weighted Intensity Profiles Within the Human Insula Cortex Using 7-Tesla MRI

The integral role of the insula cortex in sensory and cognitive function has been well documented in humans, and fine anatomical details characterising the insula have been extensively investigated ex-vivo in both human and non-human primates. However, in-vivo studies of insula anatomy in humans (in general), and within-insula parcellation (in particular) have been limited. The current study leverages 7 tesla magnetic resonance imaging to delineate T1-weighted intensity profiles within the human cortex, serving as an indirect proxy of myelination. Our analysis revealed two separate clusters of relatively high and low T1-weighted signal intensity across the insula cortex located in three distinct cortical locations within the posterior, anterior, and middle insula. The posterior and anterior cortical locations are characterised by elevated T1-weighted signal intensities, contrasting with lower intensity observed in the middle insular cortical location, compatible with ex-vivo studies. Importantly, the detection of the high T1-weighted anterior cluster is determined by the choice of brain atlas employed to define the insular ROI. We obtain reliable in-vivo within-insula parcellation at the individual and group levels, across two separate cohorts acquired in two separate sites (n1 = 21, Glasgow, UK; n2 = 101, Amsterdam, NL). These results reflect new insights into the insula anatomical structure, in-vivo, while highlighting the use of 7 tesla in neuroimaging. Specifically, the current study also paves the way to study within-insula parcellation at 7 tesla and above, and discusses further implications for individualised medicine approaches.