Abstracts

Rationale: Object naming ability may be adversely affected by surgical resections in the left anterior temporal lobe (ATL), although such effects are highly variable across individuals. Prior studies have linked severity of naming decline to age at surgery, age at epilepsy onset, preoperative language lateralization, and other factors, but these variables collectively explain less than half of the variation in outcome. Variation in the location and extent of the surgical lesion may be an important factor determining naming outcome, but this hypothesis has not been tested using modern voxel-based lesion-symptom mapping (VLSM) methods. We applied these methods in a prospective cohort of left temporal lobe surgery patients to clarify the ATL regions critical for object naming. Major advantages of this approach over lesion correlation in stroke patients include the fact that pre-lesion performance level and language dominance are known, and surgical lesions in this region more often include ventral temporal areas that may be especially critical for object recognition and naming. Methods: Participants were 42 patients (mean age 37, 24 women) with left language dominance confirmed by either fMRI or Wada testing, who underwent partial left temporal lobe resections for drug-resistant temporal lobe epilepsy. They completed pre- and 6-month postoperative neuropsychological testing that included the Boston Naming Test (BNT). Surgical lesions were labeled manually using high-resolution postoperative MRI, then mapped to a common template using nonlinear morphing of non-lesioned structures. Lesions varied widely in location and extent, including standard ATL resections with variable caudal extension and variable superior temporal gyrus sparing, focal lateral or ventral resections, selective temporal pole removals, and selective hippocampal ablations. VLSM analyses identified the lesion correlates of pre- to post-surgery change scores on the BNT. The resulting maps were thresholded at voxel-wise p < .001 and cluster-corrected at FWE p < .05, as determined by randomization testing. Results: Patients showed an average decline of -7.45 points (SD = 8.95) on the BNT (p <.001), which is an average decline of -15.8% relative to preoperative scores. Change scores varied widely across individuals (range -58% to +8%). Eighteen patients (43%) showed large declines of >20%, whereas five patients showed no decline or marginal improvement. Post-operative declines were statistically associated with resections in a focal region centered on the left anterior fusiform gyrus, including adjacent collateral sulcus, perirhinal cortex, and inferior temporal gyrus, but sparing the hippocampus and temporal pole. Conclusions: ATL regions critically necessary for picture naming are located in the anterior-ventral part of the ATL, centered in the anterior fusiform gyrus. This region appears to correspond with previous descriptions of the “basal temporal language area.” We hypothesize that this region is critical for mapping between visual perceptual and abstract conceptual representations. Resection of this critical zone at the anterior end of the ventral visual object recognition pathway is likely the main cause of postoperative naming decline in patients undergoing left temporal lobe surgery. The lack of association between naming decline and hippocampal resection accords with previous data showing little or no naming decline after focal hippocampal ablation. Funding: NINDS R01 NS35929