How do we search a large, non-independent volume (i.e., multiple locations in the brain) for lesion-deficit relationships with adequate specificity (low type I error, false positives) and sensitivity (low type II error, false negatives)? I addressed these issues using a combination of parametric and non-parametric region-based and voxel-based (whole-brain) analyses, including the first-use of permutation testing in lesion-symptom mapping (Schnur et al. 2005; Schnur et al. 2009) to examine why word production in certain contexts fails in persons with aphasia (Harvey & Schnur, 2015). For example, because persons with Broca’s aphasia (a type of language disorder generally caused by brain damage towards the front of the brain) were especially sensitive to naming interference in Schnur et al. (2006), this suggested word selection is resolved by a cognitive control mechanism located in anterior brain regions, specifically the left inferior frontal gyrus (LIFG). Using lesion-symptom mapping, we were the first to demonstrate that the LIFG was related to one specific language deficit (impaired resolution of competition during word selection) in a group of persons with aphasia (Schnur et al., 2009). This work was replicated several times and inspired computational models of word production (i.e. Roelofs, 2018; Oppenheim et al., 2010). Currently, we apply both univariate (e.g. Harvey & Schnur, 2015) and multivariate methods in lesion-symptom mapping (canonical sparse correlation, support vector regression) to understand the relationship between brain damage and behavior in acute stroke (Martin, Ding, Hamilton, & Schnur, 2021; Ding, Martin, Hamilton, & Schnur, 2020; Patterson, Magnotti, & Schnur, 2019).
Schnur, T.T., Lee, E., Coslett, H.B., Schwartz, M.F., & Thompson-Schill, S.L. (2005). When lexical selection gets tough, the LIFG gets going: A lesion analysis study of interference during word production. Brain and Language, 95 (1), 12-13. [Impact Factor 3.4] DOI: 10.1016/j.bandl.2005.07.008
Schnur, T.T., Schwartz, M.F., Kimberg, D., Hirshorn, E., Coslett, H.B., & Thompson-Schill, S.L. (2009). Localizing interference during naming: Convergent neuroimaging and neuropsychological evidence for the function of Broca's area. Proceedings of the National Academy of Sciences, 106, 322-327. [Impact Factor 10.3] PubMed PMID: 19118194
Harvey, D., & Schnur, T.T. (2015). Distinct loci of lexical and semantic access deficits in aphasia: Evidence from voxel-based lesion-symptom mapping and diffusion tensor imaging. Cortex, 67, 37-58. [Impact Factor 4.9] PubMed PMID: 25880795
Ding, J., Martin, R., Hamilton, A.C., & Schnur, T.T. (2020). Dissociation between frontal and temporal-parietal contributions to connected speech in acute stroke. Brain, 143, 862-876. [Impact Factor 14.2] PubMed PMID: 32155246