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Causal parametric language mapping using electrical stimulation
Poster Session B, Friday, September 12, 4:30 - 6:00 pm, Field House
Raouf Belkhir1,2, Frank Garcea3, Eduardo Navarrete4, Benjamin Chernoff1, Max Sims5, Sam Haber6, Arka Mallela7, Matthew Pease8, Thandar Aung7, Susan Smith3, Eliza Reedy7, Eric Hintz9, Kevin Walter3, Tyler Schmidt3, Jorge Gonzalez-Martinez7, Nduka Amankulor10, Webster Pilcher3, Bradford Mahon1,3; 1Carnegie Mellon University, 2University of Pittsburgh Medical School, 3University of Rochester Medical Center, 4University of Padova, 5MindTrace Technologies, 6Albany Medical Center, 7University of Pittsburgh Medical Center, 8Indiana University, 9Penn Medicine Lancaster General Health, 10University of Pennsylvania
Introduction: Direct Electrical Stimulation (DES) is the standard for functional language mapping during awake brain surgery. Mapping is based on a binary measure of performance: regions are ‘eloquent’ if DES elicits errors in naming, or ‘safe to remove’ if it does not. This approach assumes DES has no impact on language processing on correct (negative mapping) trials. Methods: We analyzed 2,498 picture-naming trials from awake surgeries in 19 patients, targeting left perisylvian areas. Response times were measured from picture onset to spoken response on correct trials. Variance in DES intensity, location, duration, and timing (relative to picture onset) was assessed. Parallel analyses spatially mapped the relation of DES parameters to performance at the group level using ‘searchlight’ analyses. Results: Higher stimulation intensity was associated with increased error rate (p<0.0004) and slower response times (p<0.0002). Closer proximity to errors (within or across patients) predicted slower response times on correct trials (p<0.0001, p<0.005). DES duration was positively related to error rate (p<0.0001) and response times (p<0.0001); this relation is location-dependent, with the strongest effect in speech motor cortex and anterior supramarginal gyrus. When DES (relative to picture onset) caused the greatest delay varied by region, and the neurophysiological time course of activity (measured in 14 SEEG patients) accounted for 28% of the variance in when DES had its strongest effect in each region. A cross-validated predictive model found that DES intensity, location, duration, and timing collectively predicted 54% of response time variance on negative mapping trials. Discussion: Causal Parametric Mapping provides a novel approach to integrate positive and negative mapping trials into a graded measure reflecting each region’s role in language. These findings suggest that binary mapping methods may underestimate the extent of ‘eloquent’ cortex. An ongoing multisite trial will assess whether indices from negative mapping trials explain unique variance in language outcomes 3months post-surgery.
Topic Areas: Language Production, Speech Motor Control