Letter re: Practice guideline summary: Use of fMRI in the presurgical evaluation of patients with epilepsy: Report of the Guideline Development, Dissemination, and Implementation Subcommittee of the American Academy of Neurology.

Abstract

The American Academy of Neurology (AAN) endorsement for the use of fMRI evaluation of hemispheric dominance for language in epilepsy surgery candidates1 appears as an odd and disconcerting sequel to the article by Eckland et al.,2 which reported that the clustering approach in functional MRI (fMRI) data processing may be responsible for an excessively high rate of false-positive findings. The latter report implied that up to 70% of the significant fMRI effects reported in approximately 40,000 peer-reviewed publications could represent no brain physiology facts, but type I statistical errors to the degree that they employed clustering of activated voxels.2 Consequently, it is fitting to suggest users of these popular fMRI software packages (SPM, FSL, AFNI) reconsider conclusions based on differences in activation levels of voxel clusters between task conditions. This raises the question of whether those who use the clustering procedure for the purpose of assessing hemisphere dominance for language should be alarmed for having made incorrect assessments in the past and refrain from using them for the same purpose in the future. Our answer is no, since language laterality judgments are typically made on the basis of laterality indices (i.e., the relative degree of activation defined as the ratio of left- and right-hemisphere activated voxels that are equally likely or unlikely to be activated). However, depending on how users of these automated software packages derive estimates of localization of the language network hubs (a practice not endorsed by the AAN),1 they may need to exercise more caution now that the shortcomings of these data reduction and analysis procedures were directly demonstrated and made widely known.