Abstracts

Rationale: Identifying eloquent cortex is a critical goal in epilepsy surgery planning. Task-based functional MRI (fMRI) is used to lateralize language function pre-surgically but can be subject to participant noncompliance. Resting state fMRI is a promising alternative to collect data from children or patients unable to complete task paradigms. Methods comparable to task-based fMRI for calculating language laterality index (LI) at rest in patients with epilepsy are not well-developed. We aimed to compare resting state functional connectivity and task-based fMRI activation to lateralize language dominance in patients with epilepsy. Methods: We collected 6-minute eyes open resting state fMRI and auditory description decision language task fMRI in 30 epilepsy patients (mean age=33; SD=11; 12 female). LI was calculated from task fMRI using SPM12 bootstrap method in three regional masks: frontal, temporal, and frontal+temporal. Resting state functional connectivity analysis was conducted using seed-based methods with a 6mm sphere seed in left and right Broca's area. For resting state, two novel language LI calculation methods were assessed in regional masks and at multiple thresholds (p<0.05, p<0.01, p<0.001, top 10% connections). LI continuous values and dominance classifications were compared between task and resting state. Clinical factors, including resection side, seizure onset age, and outcome after surgery were evaluated. Results: Twenty-five patients showed a consistent pattern of left language dominance during task fMRI on all three regional masks. Five patients had mixed or atypical language dominance. Significant positive correlations were found between task LI and resting state LI when functional connectivity thresholds were set to the top 10% of connections. Concordance of dominance classifications ranged from 20% to 30% for the intra-hemispheric resting state LI method and 50% to 63% for the resting state LI intra- minus inter-hemispheric difference method. Approximately 40% of patients left dominant on task showed bilateral dominance at rest. There was no difference in LI concordance between patients with right-sided and left-sided resections. Early seizure onset (<6 years old) was not associated with atypical language dominance during task-based or resting state fMRI. Conclusions: We introduced two new resting state fMRI seed-based LI calculation methods. While a relationship between task and resting state LI exists in epilepsy patients, language dominance is less lateralized on resting state than task fMRI. Language dominance concordance classifications depends on brain regions surveyed and resting state LI calculation method. Further investigation is needed before resting state fMRI can be applied for pre-surgical functional mapping. Funding: Study Funded by NIH (ZIANS002236)