Abstracts

Rationale: The current tools available for localization of expressive language, including functional magnetic resonance imaging (fMRI) and cortical stimulation mapping (CSM), require that the patient remain stationary and follow language commands with precise timing. Many pediatric epilepsy patients, however, have intact language skills but are unable to participate in these tasks due to cognitive impairments or young age. Resting state fMRI (RS) is a technique which measures changes in the blood oxygen level dependent (BOLD) response while the subject is not performing a task. In adult subjects, there is evidence that language laterality as determined by RS activity, by quantifying differences in correlated activity between brain regions forming putative functional networks, is comparable to the laterality index obtained from task-based fMRI. While RS has shown promise in lateralizing language in adults, there have been no prior studies determining if RS may accurately predict language laterality in children. Methods: A retrospective review of pediatric patients at Texas Children’s Hospital was performed to identify patients who have undergone epilepsy surgical planning over the past 5 years with language localization using traditional methods of Wada testing, CSM, or task-based fMRI with calculated laterality index. 22 patients (12 female, mean age 13.5 years) were identified to have had language localization performed with one of these three methods in addition to RS. For each subject, the expressive language areas (“Broca’s area”) were defined as pars opercularis in the left and right hemisphere using the Destrieux cortical atlas with Freesurfer. The full RS timecourse of activity was averaged across all of the voxels in each of the left and right Broca’s areas, to create two seed regions per patient. Next, the receptive language regions (“Wernicke’s area”) were defined broadly to include the posterior half of the superior temporal gyrus, middle temporal gyrus, superior temporal sulcus, angular and supramarginal gyri in the left and right hemispheres. As a proxy for strength of connectivity between these two regions (Broca’s and Wernicke’s areas), the maximum correlation value was found between the Broca’s area seed regions on the left with the left and right Wernicke’s voxels (4 values total per patient). These 4 correlation values for each patient, as well as the predetermined laterality of left or right hemisphere language dominance based on the more traditional technique, were used to create a logistical regression classifier. Results: The language laterality as determined by traditional methods was left-hemispheric in 13 patients in right-hemispheric in 9 patients. Using a leave one out cross validation, the logistical regression classifier using Broca-Wernicke connectivity successfully classified language laterality in 17 out of 22 patients, significantly greater than would be expected by chance (binomial test p = 0.0169). Conclusions: Broca-Wernicke connectivity using RS may be a useful technique to lateralize language function in pediatric epilepsy patients who are unable to participate in traditional task-based methods. Funding: 5R00MH103479-04, SPATIOTEMPORAL INVESTIGATIONS OF PARIETAL CORTEX CONTRIBUTIONS TO EPISODIC MEMORY, Principal Investigator Brett Foster