Format

Send to

Choose Destination
Brain Struct Funct. 2016 Jul;221(6):3337-45. doi: 10.1007/s00429-015-1104-x. Epub 2015 Sep 28.

Anatomy and lateralization of the human corticobulbar tracts: an fMRI-guided tractography study.

Author information

1
Cognitive Neuroscience and Neuropsychiatry Section, University College London Institute of Child Health, 30 Guilford Street, London, WC1N1EH, UK. f.liegeois@ucl.ac.uk.
2
Cognitive Neuroscience and Neuropsychiatry Section, University College London Institute of Child Health, 30 Guilford Street, London, WC1N1EH, UK.
3
Department of Audiology and Speech Pathology, University of Melbourne, Melbourne, Australia.
4
Murdoch Children's Research Institute, Melbourne, Australia.
5
Developmental Imaging and Biophysics Section, University College London Institute of Child Health, London, UK.

Abstract

The left hemisphere lateralization bias for language functions, such as syntactic processing and semantic retrieval, is well known. Although several theories and clinical data indicate a link between speech motor execution and language, the functional and structural brain lateralization for these functions has never been examined concomitantly in the same individuals. Here, we used functional MRI during rapid silent syllable repetition (/lalala/, /papapa/ and /pataka/, known as oral diadochokinesis or DDK) to map the cortical representation of the articulators in 17 healthy adults. In these same participants, functional lateralization for language production was assessed using the well-established verb generation task. We then used DDK-related fMRI activation clusters to guide tractography of the corticobulbar tract from diffusion-weighted MRI. Functional MRI revealed a wide inter-individual variability of hemispheric asymmetry patterns (left and right dominant, as well as bilateral) for DDK in the motor cortex, despite predominantly left hemisphere dominance for language-related activity in Broca's area. Tractography revealed no evidence for structural asymmetry (based on fractional anisotropy) within the corticobulbar tract. To our knowledge, this study is the first to reveal that motor brain activation for syllable repetition is unrelated to functional asymmetry for language production in adult humans. In addition, we found no evidence that the human corticobulbar tract is an asymmetric white matter pathway. We suggest that the predominance of dysarthria following left hemisphere infarct is probably a consequence of disrupted feedback or input from left hemisphere language and speech planning regions, rather than structural asymmetry of the corticobulbar tract itself.

KEYWORDS:

Corticobulbar tract; Diffusion-weighted MRI; Functional MRI; Lateralization; Speech; Tractography

PMID:
26411871
DOI:
10.1007/s00429-015-1104-x
[Indexed for MEDLINE]

Supplemental Content

Full text links

Icon for Springer
Loading ...
Support Center