Abstract
To establish the link between structure and function of any large area of the neocortex, it is helpful to identify its principles of organisation. One way to establish such principles is to investigate how differences in whole-brain connectivity are structured across the area. Here, we use Laplacian eigenmaps on diffusion MRI tractography data to investigate the organisational principles of the human temporal association cortex. We identify three overlapping gradients of connectivity that are, for the most part, consistent across hemispheres. The first gradient reveals an inferior–superior organisation of predominantly longitudinal tracts and separates visual and auditory unimodal and multimodal cortices. The second gradient radiates outward from the posterior middle temporal cortex with the arcuate fascicle as a distinguishing feature; the third gradient is concentrated in the anterior temporal lobe and emanates towards its posterior end. We describe the functional relevance of each of these gradients through the meta-analysis of data from the neuroimaging literature. Together, these results unravel the overlapping dimensions of structural organization of the human temporal cortex and provide a framework underlying its functional multiplicity.
Highlights
Understanding the relationship between brain structure and function is one of the main challenges of neuroscience (Honey et al 2009)
These results are in complete agreement with previous studies assigning key roles to the inferior longitudinal fasciculus (ILF) (Herbet et al 2018) in vision-related tasks and the involvement of middle longitudinal fasciculus (MdLF) (Wang et al 2013) and the acoustic radiation (Maffei et al 2019) in the auditory pathway
Similar inferior–superior gradients have been found when looking at the anterior temporal lobe (ATL) with its inferior end showing peak activations for semantic tasks using picture stimuli, and its superior end being active in semantic tasks using verbal stimuli (Visser et al 2010)
Summary
Understanding the relationship between brain structure and function is one of the main challenges of neuroscience (Honey et al 2009). Brain Structure and Function (2020) 225:1245–1260 be found in the posterior parietal cortex, where functional organisation follows spatially ordered patterns, ranging from projection of environment onto the body on its rostral pole to projection of the body onto the environment on its caudal pole (Medendorp et al 2019) Such an understanding of principles of connectivity has not yet been reached for the temporal association cortex. Even within the primate order, the temporal lobe is thought to have undergone significant expansion and reorganisation, in the great ape and human lineage (Bryant et al 2019; Mars et al 2013) where it might underlie the uniquely human specialization for language (Eichert et al 2018) This variety of functional areas within the temporal lobe and its variability across species makes the need for an understanding of its overarching organisational principles all the more pressing. The precise link between the anatomical reorganization of the temporal lobe throughout evolution and its higher functional multiplicity remains poorly understood
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