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Slide Slam P11 Sandbox Series

A retrospective comparison of language lateralization as assessed with the Wada test and functional MRI

Slide Slam Session P, Thursday, October 7, 2021, 2:30 - 4:30 pm PDT Log In to set Timezone

Sarah M. Schneck1, Victoria L. Morgan1, Monica L. Jacobs1, Jonah Fox1, Musab Ali1, Stephen M. Wilson1; 1Vanderbilt University Medical Center

There is considerable variability between individuals in the extent of activity observed in the subdominant hemisphere when language areas are mapped with fMRI, with some individuals demonstrating a complete absence of activity and others demonstrating activity similar to that of the dominant hemisphere [1]. It has been speculated that this variability in subdominant activation may explain recovery patterns in post-stroke aphasia [2], and a transcranial magnetic stimulation (TMS) study showed that subdominant activity in neurologically normal individuals was protective when a virtual lesion was created in the dominant hemisphere [3]. Does the presence of activation in the subdominant hemisphere reflect an independent ability of that hemisphere to process language? In this “sandbox series” presentation, we describe our plans to address this question using a retrospective comparison of fMRI and Wada findings [4] obtained as part of presurgical workups for epilepsy and brain tumor patients. The Wada test provides a measure of the independent linguistic capacity of each hemisphere. Specifically, we plan to ask the following primary question: is there a correlation between subdominant hemisphere activation on fMRI and that respective hemisphere’s demonstrated independent capacity during the Wada test? Results from the Wada test in the medical record are typically recorded in narrative form, documenting whether or not patients are able to complete various language tasks when each hemisphere is anesthetized (e.g., follow one–step commands, follow two–step commands, name objects, etc.). In order to quantify the results from the Wada test to be used in a statistical analysis, we developed a coding scheme in which receptive and expressive language are rated separately. Receptive language is rated on a 0–2 scale, and expressive language is rated on a 0–3 scale. From the fMRI data, lateralization indices will be calculated to quantify the relative levels of activity in each hemisphere. Because we are using archival fMRI protocols that have not always had tightly controlled baselines, we plan to use language area masks to exclude potentially confounding sensorimotor activations. We have a working cohort of 92 participants who have undergone both fMRI and the Wada test. At the present time, we have coded the Wada results from 54 participants. Of these 54, 43 have demonstrated independent language ability in just one hemisphere, 6 have demonstrated at least partial ability in both hemispheres, and 5 did not show independent capacity for language in either hemisphere. After we complete coding of the Wada studies and analysis of the fMRI data, we will determine whether activation in the subdominant hemisphere observed on fMRI is associated with independent capacity for language processing by the subdominant hemisphere. This study may provide insight into the role of the subdominant hemisphere in recovery from aphasia following damage to the dominant hemisphere. [1] Wilson et al. Hum Brain Mapp 2018; 39: 3285-307. [2] Crinion & Price. Brain 2005; 128: 2858-71. [3] Knecht et al. Nat Neurosci 2002; 5: 695-9. [4] Wada & Rasmussen. J Neurosurg 1960; 17: 266-82.

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