Cortical representations and major white matter tracts of dual stream language model annotated on MRI of a patient with normal imaging findings.
Language: cortical representations & white matter tracts
Specifications of cortical areas and white matter tracts involved in dual stream models of language processing
Case Discussion
The contemporary understanding of language processing is based on dual stream models, i.e. dorsal and ventral. While the field is continuously evolving, it is generally believed that the dorsal stream is responsible for phonological processing and language production (sound/sign to action). The ventral stream is responsible for orthographic and semantic processing (sound/sign to meaning). The two pathways overlap both in anatomical representations and function 1.
The ventral pathway is active in both cerebral hemispheres during visual, auditory and possibly tactile language input 2,3; the dorsal pathway, on the other hand, is specialized in the dominant (left) hemisphere for speech output 3.
In dual stream language models, the white matter pathways are as important as the cortical representations and damage to these tracts can result in various types of speech disorders. Furthermore, neuroplasticity is only observed in the cortical area, but not in the white matter tracts. Neighboring cortical areas can assume the role of the damaged sites during recovery, while damage to the white matter tracts usually results in permanent speech disorder 2.