AAN 2026 | Altered hippocampal gamma oscillations as a neural biomarker for cognitive impairment in MTLE

Our study looked at the patients with the mesial temporal lobe epilepsy and in those patients we looked, at we questioned ourselves like usually those patients with the mesial temporal lobe epilepsy they have a memory impairment and yet we don’t have a clear electrophysiological marker which can predict the outcome of those memory impairment for after the epilepsy surgery. So we asked ourselves a question can the gamma oscillations can be a useful marker to predict the memory outcome following the epilepsy surgery in the mesial temporal of epilepsy. So quickly few words on why gamma. So gamma oscillations are the fast brain waves at the frequency of 30 to 100 hertz in the hippocampus which is responsible for the memory impairment, memory encoding, memory retrieval, and memory processing. And also it is responsible for the synchronization of the memory network in between the mesial temporal lobe. So for our study we reviewed the 34 mesial temporal lobe epilepsy patients who underwent the stereo EEG video recording and then we used that recording data with the hippocampal recording, we use those data to analyze their gamma oscillations and compared with their pre-op neuropsychological data. And we quantified the gamma power using the Currie [9] software and then we classified them into mainly four categories: bilaterally preserved, gamma power reduced more than 50% bilaterally, then unilaterally absent or bilaterally absent. Then we matched that gamma profile with the patient’s pre-surgical neuropsychological data and we saw a striking difference in the verbal memory when we saw there was a significant gamma loss on the left side patient had a significant memory loss in the verbal domain, while the visual spatial memory showed the same trend but it wasn’t statistically significant with the right-sided gamma loss. Why does this matter clinically? First of all it was suggestive of a dose-response relationship where the more impairment of the gamma oscillations in the hippocampus related to the more impairment of the memory in the patients with the mesial temporal lobe epilepsy and second it followed the lateralization model where the patient with the left-sided gamma loss had a verbal memory loss and patient who had a right-sided gamma loss patient had visual spatial memory loss. And with this biomarker we can predict patients who are undergoing some kind of surgical intervention with the mesial temporal structure, what type of memory loss they will have or what kind of memory impairment they have after the surgical intervention and based on this marker we can predict their memory impairment and we can use this data to counsel the patient pre-surgically. Which can also guide us for the long-term cognitive outcome following the epilepsy surgery.

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