Introduction: The visual word form area (VWFA) is a left basal temporal region that exhibits differentially strong neural responses to printed words compared to other complex visual stimuli. Focal lesions to the VWFA have been shown to cause alexia or alexia without agraphia and preserved letter-by-letter reading. Multimodal mapping with functional MRI (fMRI), diffusion MRI (dMRI), stereo EEG/intraoperative direct electrical stimulation (DES) can help preserve this structure, provide direct tests of neurocognitive dynamics driving VWFA specialization, and can inform surgical management around the VWFA.
Methods: All three patient participant underwent detailed longitudinal behavioral testing of neuropsychological function including reading and dMRI/fMRI. Two patients had awake surgeries with DES. FMRI analyses isolated left basal temporal regions with specific specificity for words in all individuals, while dMRI identified the location of the inferior longitudinal fasciculus (ILF) with respect to functional activity and the surgical resection. Mapping strategy and surgical approach was dictated by each patient’s pathology (1 tumor, 2 EZ).
Results: In all three patients, multimodal mapping permitted accurate delineation of the VWFA. In the two patients with VWFA preservation (confirmed on postoperative fMRI), word reading was unaffected (100%>100%, 100%>96%, p=0.41). Reading in the teenaged third patient was impaired post-operatively (100%>3%, p< 0.001), characterized by letter-by-letter reading. This patient could read length-matched Arabic numerals (not a general visual agnosia). Long-term follow-up (8 years) showed the emergence of a new functional VWFA in the contralesional (right) basal temporal regions and increased left posterior parietal activity, with an improvement in reading accuracy to 70% at 1 year, and 94% at 8 years.
Conclusion : These findings provide causal evidence of the specificity of the VWFA for reading and provide a strategy for multimodal mapping. In cases where resection of VWFA is necessary, reading can recover through recruitment of the contralateral basal temporal and left parietal regions involved in letter processing.
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