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Tractography of the language network in prelingually deaf patients
Finkl T. , Anwander A. , Friederici A.D. , Gerber J. , Mainka A. , Mürbe D. , Hahne A.
Saxonian Cochlear Implant Centre, University Hospital Dresden, Dresden, Germany, 2Max Planck Institute for Human Cognitive and Brain
Sciences, Leipzig, Germany, 3Department of Neuroradiology, University Hospital Dresden, Dresden, Germany
Introduction: Prelingually deaf adults who receive a cochlear implant (CI) usually develop only a limited ability
to understand spoken language. In these patients, missing stimulation via the auditory pathway in early
childhood leads to a cortical reorganization in such a way that the processing of other sensory modalities, e.g.
visual information, takes over regions that are normally occupied by the auditory system. In order to investigate
to what extent this reorganization is reflected in the white matter, we visualized fiber tracts of the language
network by means of diffusion tensor imaging (DTI). In the past, DTI studies dealing with deaf patients focused
on subcortical structures relevant for auditory processing. Since understanding speech, however, requires not
only an intact auditory pathway, but also a well-developed language network, we applied tractography to study
the relationship between prelingual deafness and white matter anatomy of language-associated tracts.
Methods: Five prelingually deaf adults with bilateral hearing loss (mean age 29; 3 women) and five normalhearing controls (mean age 27; 3 women) took part in the study. Each subject underwent one MR scanning
session, in which a T1- and a diffusion-weighted data set was acquired. Subsequent tractography was carried
out using ROI-analyses (region of interest).
Results: None of the participants displayed neuroanatomical pathologies. Tractography revealed a shorter left
arcuate fasciculus in patients compared to controls. In addition, the left uncinate fasciculus was less pronounced
in the deaf.
Discussion: Representing one of the major pathways in language processing, the left arcuate fasciculus
connects Broca and Wernicke area and is involved in both language production and perception. The uncinate
fasciculus plays a role in auditory-verbal memory and semantic tasks, which is also essential for successful
language comprehension. Our results confirm the importance of these tracts for the processing of spoken
language and underline the significance of a sensitive period for the acquisition of spoken language and the
development of the language network in early childhood. By means of DTI we could show that missing auditory
stimulation during this critical time window leads to a reorganization of neuronal connections, which impedes the
possibilities of speech rehabilitation in prelingually deaf CI users despite the ameliorated hearing conditions
provided by the implant.
Conclusion: The arcuate and the uncinate fasciculus in prelingually deaf adults are insufficiently developed,
which impairs successful comprehension of spoken language despite the benefits of a CI on hearing. In order to
investigate this and employ it for diagnostic purposes, DTI serves as a good instrument. It is easy to integrate
into routine examinations and reveals additional information about the neuroanatomical prerequisites for the
hearing and speech rehabilitation of CI patients.