Language processing in the occipital cortex of congenitally blind adults

TLDR

Humans have evolved language‑specific regions in the left frontal and temporal cortex, yet congenitally blind individuals also recruit visual cortex during verbal tasks. The study demonstrates that visual cortex activity in congenitally blind adults reflects language processing. In congenitally blind adults, left visual cortex shows higher BOLD during sentence comprehension versus degraded controls, is modulated by phonological, lexical semantic, and combinatorial structure, and exhibits increased functional connectivity with left prefrontal cortex and thalamus compared to sighted peers, indicating that vision‑evolved regions can assume language functions without innate microcircuitry.

Abstract

Humans are thought to have evolved brain regions in the left frontal and temporal cortex that are uniquely capable of language processing. However, congenitally blind individuals also activate the visual cortex in some verbal tasks. We provide evidence that this visual cortex activity in fact reflects language processing. We find that in congenitally blind individuals, the left visual cortex behaves similarly to classic language regions: (i) BOLD signal is higher during sentence comprehension than during linguistically degraded control conditions that are more difficult; (ii) BOLD signal is modulated by phonological information, lexical semantic information, and sentence-level combinatorial structure; and (iii) functional connectivity with language regions in the left prefrontal cortex and thalamus are increased relative to sighted individuals. We conclude that brain regions that are thought to have evolved for vision can take on language processing as a result of early experience. Innate microcircuit properties are not necessary for a brain region to become involved in language processing.