A graded tractographic parcellation of the temporal lobe

Claude J Bajada,Rebecca L Jackson,Hamied A Haroon,Hojjatollah Azadbakht,Geoff J.M Parker,Matthew A Lambon Ralph,Lauren L Cloutman

doi:10.1016/j.neuroimage.2017.04.016

Abstract

The temporal lobe has been implicated in multiple cognitive domains through lesion studies as well as cognitive neuroimaging research. There has been a recent increased interest in the structural and connective architecture that underlies these functions. However there has not yet been a comprehensive exploration of the patterns of connectivity that appear across the temporal lobe. This article uses a data driven, spectral reordering approach in order to understand the general axes of structural connectivity within the temporal lobe.Two important findings emerge from the study. Firstly, the temporal lobe's overarching patterns of connectivity are organised along two key structural axes: medial to lateral and anteroventral to posterodorsal, mirroring findings in the functional literature. Secondly, the connective organisation of the temporal lobe is graded and transitional; this is reminiscent of the original work of 19th Century neuroanatomists, who posited the existence of some regions which transitioned between one another in a graded fashion. While regions with unique connectivity exist, the boundaries between these are not always sharp. Instead there are zones of graded connectivity reflecting the influence and overlap of shared connectivity.

Highlights

Within the temporal lobe, anteroventral and middle temporal areas have been found to be associated with semantic processing (Binder et al, 2009; Binney et al, 2010; Lambon Ralph et al, 2017), while medial areas have long been implicated in episodic memory (Scoville and Milner, 1957)
An examination of the parcellations reveals that the structural connectivity of the temporal lobe is arranged along two main axes of organisation, one medial to lateral and the other from the anteroventral to posterodorsal temporal lobe
The overarching patterns of connectivity across the temporal lobe are organised along two key structural axes

Summary

Introduction

The temporal lobe is a complex region that supports multiple cognitive domains including language (Cloutman, 2013; Price, 2010), semantic processing (Lambon Ralph, 2014; Lambon Ralph et al, 2017), memory (Scoville and Milner, 1957), audition (Kaas and Hackett, 1999) and vision (Goodale and Milner, 1992; Grill-Spector and Malach, 2004). The cortex does not exist as a detached entity and regions such as the temporal lobe are highly interconnected both locally and to other areas throughout the brain via white matter fibre bundles (Bajada et al, 2015; Catani, 2007; Catani et al, 2012; Catani and Thiebaut de Schotten, 2008; Déjerine and Déjerine-Klumpke, 1895; Duffau, 2015) These structural connections are assumed to be a determinant of the functional capabilities of a cortical area, governing the nature and flow of information to and from an area, and can influence both its underlying neural architecture and its functioning (Anwander et al, 2006; Cloutman and Lambon Ralph, 2012; Johansen-Berg et al, 2004)

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