Abstracts

Rationale: The vital role of the hippocampus in memory function has been well-established, but recent studies have also highlighted the direct contributions of the hippocampus to language processing in healthy adults [1-2]. These novel findings suggest that the hippocampus and its connections to language regions may be related to language abilities in patients with hippocampal damage or impairment, like temporal lobe epilepsy (TLE). However, previous studies assessing the relationship between the hippocampus and neurocognitive abilities in TLE have primarily focused on memory tests. The purpose of the present work was to investigate the relationship between functional connectivity of the bilateral hippocampi and cortical language areas to scores on neuropsychological language measures in patients with temporal lobe epilepsy. Methods: Presurgical resting-state 3T fMRI data was acquired from 26 patients with right temporal lobe epilepsy (mean age: 39.8 years, SD: 10.8), 10 patients with left temporal lobe epilepsy (mean age: 36.2 years, SD: 15.7), and 42 healthy controls (mean age: 39.02 years, SD: 13.7). Functional connectivity (FC) was measured as the average connectivity between the hippocampus (right or left) to the following language regions in both the right and left hemispheres: middle frontal gyrus, pars triangularis, angular gyrus, supramarginal gyrus, planum polare, superior temporal gyrus, and transverse temporal gyrus. The average connectivity values were then correlated to patient scores on measures related to language function, including a measure of Verbal IQ, a word generation task, and the Boston Naming Test. Results: There were no significant differences between groups in functional connectivity values between the hippocampus and language regions across both hemispheres. However, within the two patient groups, both right and left TLE patients showed significantly greater functional connectivity between the hippocampus and language regions ipsilateral to their seizure focus compared to the contralateral hemisphere (p < 0.0001). Pearson correlations between FC values and language measures revealed a significant positive correlation only in right TLE patients between Verbal IQ scores and connectivity of the left hippocampus to right hemisphere language regions (r = 0.46, p < 0.05). Conclusions: We found that temporal lobe epilepsy patients showed stronger functional connectivity between the hippocampus and language regions on the same side as their seizure focus, regardless of whether seizures originate in the right or left hemisphere. This finding has implications for the study of seizure propagation networks and their influence on language processing. Furthermore, we found that higher verbal IQ abilities were associated with greater functional connectivity between the left hippocampus and language regions in the right hemisphere in right TLE patients, suggesting a compensatory mechanism in which greater connectivity to the unimpaired left hippocampus may improve overall language ability. Future analyses will investigate these relationships in postsurgical fMRI data in the same patients to determine whether reorganization of functional connectivity patterns is related to language outcomes after surgery. [1] Piai, V., Anderson, K. L., Lin, J. J., Dewar, C., Parvizi, J., Dronkers, N. F., & Knight, R. T. (2016). Proc of the Nat Academy of Sciences, 113(40), 11366-11371.[2] Bonhage, C. E., Mueller, J. L., Friederici, A. D., & Fiebach, C. J. (2015). Cortex, 68, 33-47. Funding: NIH R01 NS075270 (VLM), R01 NS110130 (VLM), R01 NS108445 (VLM), R00 NS097618 (DJE)