Diffusion tensor imaging in the study of language and aphasia

Abstract

Background: Diffusion tensor imaging (DTI) is an emerging research technique that is used to map and characterise white matter tracts in the healthy and damaged brain.

Aims: The aim of this paper is to familiarise the readers with DTI while giving the tools to understand and evaluate recent developments in aphasia research that use DTI methodology.

Main Contribution: Principles of DTI technology as well as its main caveats are described. An overview of studies that used DTI to explore the language system and aphasia is given. Future directions and the potential contribution of DTI to the understanding of aphasia diagnosis and recovery are highlighted.

Conclusions: DTI is an emerging technology, increasingly being applied to further our understanding of aphasia and its recovery. So far it has contributed to our knowledge in four areas of research. In the area of brain anatomy it is used to redefine the borders between various parts of the cortex based on their structural connectivity, to acquire a more accurate map of the tracts connecting the various parts of the language system, and to measure hemispheric asymmetry. Future studies might be able to further our understanding of language anatomy and relate hemispheric asymmetry to recovery potential. Second, DTI can help in relating structure to function. So far many studies focused on repetition deficits and conduction aphasia. Future studies can explore the anatomy of other language deficits. Third, DTI has been used in the study of brain damage and recovery. Studies have documented the damage that occurs to white matter following stroke and other insults, and the spontaneous reorganisation that follows. In the future DTI might contribute to the debate about the role of the right hemisphere in recovery from aphasia. Lastly, in the area of aphasia rehabilitation there is great lack of data. The studies reviewed here have shown that rehabilitation potential is dependent on white matter integrity and that white matter changes can occur as a result of therapy. Future studies should further our understanding of the role of white matter integrity in recovery, therefore contributing to the question of why some patients show good recovery while others do not. Future studies should also try and map white matter changes that are associated with successful versus unsuccessful rehabilitation, and with different stages of recovery.

Keywords:

• Diffusion tensor imaging

Acknowledgments

SG was supported by the Pinsent-Darwin Fellowship, Wingate scholarship, The Cambridge Overseas Trust and B'nai Brith Scholarship. EAW received support from the Biomedical Centre Grant (BMC) to Cambridge from the UK National Institute of Health Research (NIHR).