Presentation
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Invasive and noninvasive mapping of the visual word form area in neurosurgery patients
Poster A123 in Poster Session A, Tuesday, October 24, 10:15 am - 12:00 pm CEST, Espace Vieux-Port
Bradford Mahon1,3, Arka Mallela2, Thandar Aung2, Catherine Liegeois-Chauvel2, Florence Bouhali4, Emefa Akwayena1, Raouf Belkhir2, Alyssa Kersey1, Jessica Barrios Martinez2, Frank Garcea3, Webster Pilcher3, Jorge Gonzalez-Martinez1; 1Carnegie Mellon University, 2University of Pittsburgh, 3University of Rochester Medical Center, 4University of California San Francisco
The visual word form area (VWFA), typically in or around the left temporo-occipital sulcus, exhibits differentially strong neural responses to printed words compared to other complex visual stimuli (objects, faces, places). Focal lesions to the VWFA can cause pure alexia, or letter-by-letter reading. Mapping this cortical region and its associated white matter fibers is thus critical to preserve reading function during neurosurgical procedures in the posterior-basal temporal lobe. Here we present longitudinal studies of two neurosurgery patients (PI & AX) consisting of pre- and post-operative i) functional MRI mapping of the VWFA and adjacent category-preferring regions of temporal-occipital cortex, ii) diffusion tractography of major white matter pathways, and iii) detailed neuropsychological testing. Each patient had an fMRI-localized VWFA in their left posterior temporal-occipital cortex and normal (or above normal) reading ability, prior to surgery. Patient PI’s lesion was in the left parahippocampal gyrus, medial to the VWFA; the location of the lesion compelled resection of the fMRI-localized VWFA to access the lesion in its entirety. PI developed a dense and pure alexia without agraphia post-operatively that largely recovered over the first year after surgery, but remained as a clinically significant reading difficulty 5 years after surgery. Over the first 6 months after surgery, Patient PI could read printed words only using a slow and deliberate letter-by-letter strategy. At the same time, she remained able to fluently name complex Arabic digits (302,432 as ‘three hundred and two thousand, four hundred and thirty-two’). The second patient, Patient AX, underwent a focal resection of a lesion that was just lateral to his fMRI-localized VWFA. Patient AX underwent an awake craniotomy with specific reading and object naming tasks. The fMRI-defined VWFA was confirmed using electrical stimulation mapping and intraoperative monitoring of his reading performance, and the surgery spared AX’s VWFA. Patient AX had no discernable impairments in reading when formally tested several months after surgery. A comparison of pre- and post-operative fMRI in both patients indicates substantial reorganization in Patient PI, with the emergence of a ‘new’ VWFA in homologous right posterior temporal occipital cortex after surgery. By contrast, for Patient AX, who had no discernable changes in reading abilities after surgery, the location of his left VWFA, as well as other temporal-occipital category-preferring regions remained the same. These findings demonstrate, with two types of causal evidence, the anatomical localization of the VWFA using fMRI in individual patients in left posterior temporal occipital cortex. Patient PI, whose VWFA had to be removed to access a parahippocampal lesion, exhibited a dense and selective pure alexia that spared complex arabic numeral reading. Those findings imply a segregation of cortical regions for reading printed words versus arabic numerals. By contrast, Patient AX’s VWFA, which was confirmed with causal evidence provided by electrical stimulation mapping, was surgically spared, and he consequently retained his ability to read. These findings may also suggest that the involvement of right posterior temporal-occipital regions in reading increases after resection of the VWFA and remains unchanged when the VWFA is surgically spared.
Topic Areas: Reading, Disorders: Acquired