PhD Project 30

Anatomical and Connectopic Adaptations to Language: A Comparative Approach




PIs: Christian Beckmann (DCCN) and Rogier Mars (DCC)
PhD-candidate: Guilherme Freches
Start date: November 01, 2017

(last update 2019-07-01)

Research Content

A number of specialisations for language have been described in the human brain, including lateralisation of temporal and frontal brain areas, expansion of particular white matter pathways, and changes at the micro-anatomical level. To date, however, it has been very difficult to relate any of these changes to specific aspects of language. Although precursors of different aspects of language are assumed to be present in some other primates, progress has been hampered by a lack of data beyond the human brain and one or two model species. The purpose of the present project is to develop a large-scale comparative approach to tackle this problem, by studying the architecture of connections across the brains of a range of different primates that differ in their communicative abilities and strategies.

In this PhD project, measures of functional and structural connectivity will be utilized to shed light on the underlying building blocks that support the features for the connectome of language. Abstracting from specific language tasks, the connectomic description will be used at the systems neuroscience level to enable cross-species comparisons in order to characterize the unique features that enable human connectivity over and beyond levels of communication found in other species. The project will look at the temporal-frontal tracts across a wider range of species post mortem, including humans, apes (chimpanzee and gorilla), and monkeys (macaque and baboon) to test which innovations occurred where on the evolutionary tree.

Highlight

Anatomical and Connectopic Adaptations to Language
Team members: Freches, Beckmann, and Mars

The purpose of this project is to develop a large-scale comparative approach to studying the architecture of connections across the brains of a range of different primates that differ in their communicative abilities and strategies. The project utilizes measures of functional and structural connectivity to shed light on underlying building blocks that support the features for the connectome of language. The pipeline for connectopic mapping using white matter tractography data has been developed. Thus far the pipeline has been used for mapping the connectopies in Brodmann areas 44/45, V1, and Temporal Lobe in humans and primates. In BA44/45, two overlapping modes of connectivity were disentangled:  the first mode (G1) showing gradual connectivity change when moving along the BA44/45 posterior-anterior axis; the second mode (G2) highlighting separate contribution of dorsal and ventral tracts towards this region’s connectivity fingerprint. Preliminary results on the temporal lobe show that humans and chimpanzees share the first mode of connectivity, but start to diverge on their connectivity fingerprints when higher order gradients are explored. Differences seem to be driven by expansion of the arcuate fasciculus towards the anterior temporal lobe in humans.

This project is at the forefront of methods development with a strong focus on brain connectivity across species.  It directly addresses a core question of the BQ2: what characteristics of human brains support our unique abilities to acquire/use language.
This project brings together expertise from neuroimaging, specifically related to novel approaches to mapping functional and structural connectivity, and a cross-species comparative perspective.  Such a large-scale cross-species comparative project would not be possible without extensive sharing of data (especially primate) and expertise.

 

First two overlapping gradients of white matter connectivity present in BA 44/45 for each hemisphere. G1 (first gradient) separates BA44 from BA45. G2 (second gradient) separates contributions from dorsal and ventral white matter tracts. Colours indicate relative similarity in patterns of connectivity.

Progress 2018

In 2018 the pipeline for connectopic mapping using tractography data was developed. The pipeline was used for mapping the connectopies in Brodmann areas 44/45, V1 and Temporal Lobe in humans and primates. A poster was presented at the Champalimaud Research Symposium 2018 under the name "Connectivity gradients in diffusion weighted imaging". Two abstracts were submitted to the 2019 OHBM meeting under the names “Connectivity Gradients in diffusion weighted imaging” and “Laplacian Eigenmaps reveal two distinct modes of connectivity in the human temporal Cortex”.

Groundbreaking characteristics

This project brings together expertise from neuroimaging, specifically related to mapping functional and structural connectivity, and a cross-species comparative perspective. This project is at the forefront of methods development and has a strong focus on methods that can be meaningfully applied to measure brain connectivity across a variety of species.  In this sense it directly addresses one of the core questions of the BQ2, namely what about the human brain sets us apart from closely related species in supporting our unique abilities to acquire and use language.