fMRI Task: Semantic Decision Making
Jeff Binder's version of this task (1995) is perhaps the best-studied and comprehensively validated fMRI task for language lateralization. The task alternates blocks of task and control. In the task the patient hears animal names, and respond to a semantic judgment about them (e.g., pressing a button if the animal lives in the US and is used by humans). In the control they hear strings of tones, and press a button if they hear two high tones.
The method has been directly contrasted with the Wada test in the largest patient series to date. Janecek and colleagues (2013) compared language laterality per fMRI (semantic decision) and a Wada protocol (Loring) in 229 patients (Wada language L/Bi/R=184/30/15). Overall fMRI-Wada agreement was 86% with the only measures predicting discordance in a given patient being the degree to which fMRI (and, less so) Wada laterality index trended right. This concordance rate approximated the (weighted) rate from prior studies (85%). Using slightly different criteria to define discordance, when fMRI classified cases as left dominant (n=182), Wada testing typically also did so (92%). fMRI bilateral cases (n=28) were variably left (46%), bilateral (36%) or right (18%) dominanton Wada. fMRI right cases were also most often right dominant on Wada (53%) or bilateral (26%), though 4 of these cases were Wada left dominant. While the only factor predicting discordance was the degree to which fMRI and (less so) Wada trended right, all 4 discordant cases were right handed and had right hemisphere pathology.
At least as importantly, the ability of the method to predict language change following surgery has also been examined (Sabsevitz et al., 2003). In a set of 56 patients undergoing a tailored anterior temporal lobectomy, fMRI was more effective than the Wada test at predicting post-surgical outcome when defined as a drop in the patient's raw score on a naming task (Boston Naming Task). When marked decline–a drop of more than 2 standard deviations relative to the right temporal patients' mean performance–occurred, fMRI predicted this with 100% sensitivity and 73% specificity (Wada 92% and 45%, respectively) in predicting outcome. Forty one percent of post-surgical naming variance was predicted.
Sabsevitz et al. 2003. Use of preoperative functional neuroimaging to predict language deficits from epilepsy surgery. Neurology 60:1788–1792.
- Janecek et al. 2013. Language Lateralization by fMRI and Wada Testing in 229 Epilepsy Patients: Rates and Predictors of Discordance. Epilepsia. 2013 February ; 54(2): 314–322. See also on Researchgate (free).