Abstracts

Rationale: While network studies of temporal lobe epilepsy (TLE) rarely examine the brain stem, we recently demonstrated functional connectivity decreases between ascending reticular activating system (ARAS) and frontoparietal neocortex in TLE patients that may contribute to neurocognitive dysfunction.^1,2 It is not known if these connectivity decreases are driven more by structural abnormalities in ARAS, or the neocortex, or both, but further insight may be garnered by examining the amplitude of low frequency fluctuations (ALFF) of functional MRI (fMRI) signals in either region individually. Furthermore, we have found that ARAS-neocortical functional connectivity disturbances may actually improve after successful epilepsy surgery (AES abstract 2018), but it is unknown if these functional connectivity increases are associated with postoperative changes in ALFF or in structural connectivity. Methods: We evaluated 10 adult TLE patients before surgery and again > 1 year (mean, 3.3 years) after successful surgery resulting in seizure freedom, along with 10 matched healthy controls. We used fMRI to measure ALFF in three ARAS regions and selected frontoparietal neocortical regions, and diffusion tensor imaging (DTI; probabilistic tractography) to measure structural connectivity seeded from the ARAS regions. Results: In TLE patients, ALFF in ARAS structures differed significantly from those in healthy controls, but ALFF in frontoparietal cortex did not differ between patients and controls (Fig. 1). Abnormal ARAS ALFF in patients did not change after successful surgery, and similarly no changes were noted in frontoparietal ALFF postoperatively (Fig. 1). When evaluating structural connectivity patterns from ARAS to subcortical and cortical regions that we previously found to be significantly reduced in TLE,¹ we did not detect any changes (“improvements”) in these structural connectivity patterns after surgery (Fig. 2). Conclusions: We previously reported abnormal functional connectivity between ARAS and frontoparietal neocortex in TLE, and our present ALFF and structural connectivity results suggest this phenomenon may be driven by structural abnormalities in ARAS structures more so than neocortical abnormalities. However, while ARAS-neocortical functional connectivity may improve after successful epilepsy surgery, we did not detect any improvements in these structural abnormalities as estimated here by ALFF and DTI. This raises interesting questions about the relationships between functional and structural network interactions in TLE.References:1. Englot, D. J. et al. Relating structural and functional brain stem connectivity to disease measures in epilepsy. Neurology (In Press).2. Englot, D. J. et al. Functional connectivity disturbances of the ascending reticular activating system in temporal lobe epilepsy. J Neurol Neurosurg Psychiatry 88, 925-932, doi:10.1136/jnnp-2017-315732 (2017). Funding: This work was supported in part by the NIH grants R00 NS097618 (DJE), R01 NS075270 (VLM), T32 EB021937 (HJFG), and T32 GM07347 (HJFG).