Language networks in anophthalmia: maintained hierarchy of processing in 'visual' cortex

Area of Science:

• Neuroscience
• Cognitive Neuroscience
• Neuroimaging

Background:

• The occipital cortex, typically visual, shows cross-modal activation in blind individuals.
• The degree of activation varies with the cause and onset of blindness.

Purpose of the Study:

• To investigate the cortical language network in bilaterally anophthalmic subjects (never had visual input) at rest and during an auditory covert naming task.
• To compare their brain activity patterns with sighted controls and other forms of congenital blindness.

Main Methods:

• Functional magnetic resonance imaging (fMRI) was used to study five bilaterally anophthalmic subjects.
• Resting-state and auditory covert naming tasks (using definitions and reversed speech) were employed.

Main Results:

• Bilaterally anophthalmic subjects activated lateral occipital cortex during auditory naming, exceeding activation seen with reversed speech.
• The lateral occipital cortex was incorporated into a resting-state language network.
• Primary visual (calcarine) cortex showed no differential activation and maintained high interhemispheric correlation, unlike extrastriate areas.

Conclusions:

• The findings suggest that the lateral occipital cortex can be recruited for auditory language processing in the absence of any visual input.
• Unlike other congenital blindness forms, anophthalmia does not show a reversal of the typical visual processing hierarchy.
• Cortical organization in anophthalmia may reflect subcortical auditory input to the geniculo-striate pathway.