Presentation
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Causal Dissociation of Reading and Naming
Poster A122 in Poster Session A, Tuesday, October 24, 10:15 am - 12:00 pm CEST, Espace Vieux-Port
Oscar Woolnough1, Nitin Tandon1; 1University of Texas Health Science Center at Houston
Lesions in language-dominant ventral occipitotemporal cortex (vOTC) carry the risk of causing impairment to both reading and naming, resulting in alexia or anomia. At population level, lesions resulting in reading or naming deficits display highly comparable localizations raising questions on how distinct the representations of these two visual language functions truly are. Prior stimulation studies in vOTC have provided evidence that reading and naming are partially dissociable within individuals, however these studies have all been performed in small populations (<5 individuals), due to the relative inaccessibility of this region to direct cortical stimulation, reducing the ability to generalise the localisation of these effects across individuals. Here, we present data collected from 51 language mapping sessions performed with 49 adult patients (18-62 years). Stimulation was performed in the context of the preservation of function prior to resections in the language dominant hemisphere. We co-registered 2,829 direct cortical stimulation sites during reading and naming to create population-level, probabilistic, surface-based maps of stimulation-induced language disruption. Further, in 8 patients we used chronometric stimulation during single word reading or lexical semantic judgements, to better characterise the temporal profile of vOTC’s causal involvement in reading. Chronometric stimulation was triggered with a pseudorandom delay from the onset of the word, with delays from 0 to 800ms in steps of 200 ms. Language testing was performed using passage reading (216 disruption sites) and visual naming (304 disruption sites). Within vOTC we were able to dissociate sites that selectively disrupted reading (24 sites in 11 patients) or naming (27 sites in 12 patients), or disrupted both tasks (75 sites in 21 patients). Posterolateral vOTC had a higher probability of producing reading-selective disruptions while more anteromedial regions resulted in greater naming disruption. This resulted in a distinct causally-reading-selective region posterior to a multi-modal region that disrupted both reading and naming. Chronometric stimulation of reading in vOTC demonstrated greatest disruption of function when stimulation was applied 200-400ms after word onset, inducing reading errors and slowing word production of both words and pseudowords. Induced reading errors included reading arrests, letter substitutions and regularization errors. We also demonstrated significant disruption of lexical semantic processing during a concreteness judgement task. This work provides a comprehensive causal dissociation between the reading-specific visual word form area and the classical multi-modal basal temporal language area. The causally reading selective region shows a highly comparable localisation to functional definitions of visual word form area from intracranial and fMRI recordings. This work further demonstrates that pre-surgical mapping of both reading and naming should be essential for patients requiring vOTC resections, as these functions are not co-localized.
Topic Areas: Reading, Disorders: Acquired