Ventral and dorsal pathways for language

TLDR

Dual‑stream language processing models posit a dorsal pathway for mapping sound to articulation and a ventral pathway for mapping sound to meaning, analogous to visual and auditory systems. This study aimed to test the neuroanatomical basis of that dual‑stream model. Using fMRI combined with a novel DTI‑based tractography method, the authors identified the most probable anatomical pathways linking regions activated during two prototypical language tasks. The findings showed that sublexical repetition is mediated by a dorsal pathway connecting the superior temporal lobe to premotor cortices via the arcuate and superior longitudinal fasciculus, whereas higher‑level comprehension relies on a ventral pathway linking the middle temporal lobe to ventrolateral prefrontal cortex through the extreme capsule, indicating the dorsal route is mainly for sensory‑motor mapping and the ventral route for sound‑to‑meaning processing.

Abstract

Built on an analogy between the visual and auditory systems, the following dual stream model for language processing was suggested recently: a dorsal stream is involved in mapping sound to articulation, and a ventral stream in mapping sound to meaning. The goal of the study presented here was to test the neuroanatomical basis of this model. Combining functional magnetic resonance imaging (fMRI) with a novel diffusion tensor imaging (DTI)-based tractography method we were able to identify the most probable anatomical pathways connecting brain regions activated during two prototypical language tasks. Sublexical repetition of speech is subserved by a dorsal pathway, connecting the superior temporal lobe and premotor cortices in the frontal lobe via the arcuate and superior longitudinal fascicle. In contrast, higher-level language comprehension is mediated by a ventral pathway connecting the middle temporal lobe and the ventrolateral prefrontal cortex via the extreme capsule. Thus, according to our findings, the function of the dorsal route, traditionally considered to be the major language pathway, is mainly restricted to sensory-motor mapping of sound to articulation, whereas linguistic processing of sound to meaning requires temporofrontal interaction transmitted via the ventral route.