Language Mapping Using fMRI and Direct Cortical Stimulation for Brain Tumor Surgery

Abstract

Language functional magnetic resonance imaging for neurosurgical planning is a useful but nuanced technique. Consideration of primary and secondary language anatomy, task selection, and data analysis choices all impact interpretation. In the following chapter, we consider practical considerations and nuances alike for language functional magnetic resonance imaging in the support of and comparison with the neurosurgical gold standard, direct cortical stimulation. Pitfalls and limitations are discussed.

Optimizing Magnetoencephalographic Imaging Estimation of Language Lateralization for Simpler Language Tasks

“…Although both of our novel protocols (NWR, PN) did not have as high of a predictive value to measure laterality as VG, they can still act as reliable measurements of laterality, particularly in clinically affected populations where VG compliance might be challenging, and potentially moreso when combined together ( Table 2). These results confirm many other studies showing that word retrieval tasks such as VG illustrate robust lateralization effects as they strongly activate both expressive and receptive language regions (Bowyer et al, 2005;Price, 2010;Pang et al, 2011;Findlay et al, 2012;Brennan et al, 2016). Regardless, our findings indicate that hemispheric dominance for language can still be gleaned from MEGI reconstructions using tasks that are easier to conduct.…”

“…Application of our optimized VOIs and time windows (as established in our training cohort) when applied independently to our validation cohort replicate the finding that tailored spatial and temporal NWR/PN indices for laterality match well with VG, with concordance being high for both NWR and PN in this validation cohort, respectively 87 and 82%. As task selection may impact the interpretation of results (Brennan et al, 2016;Morrison et al, 2016), the calculated LI's were compared to each other, with VG-LI used as a validated index of laterality ( Figure 5). A stronger correlation between VG and PN LI's (strong correlation: r = 0.65) was found than between VG and NWR LI's (medium correlation: r = 0.45).…”

“…While other language tasks such as verbal fluency (Pirmoradi et al, 2016) and picture naming (Hinkley et al, 2016) have been administered during MEGI, these protocols have yet to be optimized as surrogate replacements for the IAP. As these tasks evoke different processes at different stages in time (compared to verb generation) optimized parameters for these datasets are critical to avoid incorrect interpretation of results, laterality reports and information provided to neurosurgeons (Brennan et al, 2016;Morrison et al, 2016). While the verb generation (VG) task has been optimized for MEGI (Findlay et al, 2012) no such procedure exists for other language tasks that may be easier for patients to handle.…”

Mapping language function with task-based vs. resting-state functional MRI

“…This result is not surprising as the MLP was trained to recover the topography of T-fMRI responses in RS-fMRI data [ 28 ]. Additionally, this outcome may reflect a relative disadvantage of stimulation mapping as speech arrest commonly is taken as the outcome measure, which arguably is a limited indicator of impaired language function [ 63 ]. Moreover, it is well established that language is represented in the frontal operculum [ 64 ], a region of the cerebral cortex not on the brain surface, and therefore, not directly accessible to stimulation mapping.…”

Can We Standardize Clinical Functional Neuroimaging Procedures?

“…Due to this complexity, current clinical functional imaging protocols vary considerably across institutions in non-standardized ways. However, despite this situation, recent reviews of fMRI for presurgical evaluation of patients with epilepsy or brain tumors recommend the application of fMRI in certain contexts showing probable or possible usefulness for patients [levels B and C, (8), (9)]. In this situation and since procedural variability immediately affects validity and repeatability of fMRI results, a burning question for clinical functional neuroimaging is: can we standardize clinical fMRI procedures and to what extent?…”