Higher Electrode Density Improves Epilepsy Surgery by Pinpointing Where Seizures Begin

In an effort to improve the precision of determining which tissue should be removed during epilepsy surgery, researchers at UC San Francisco (San Francisco, CA, USA) utilized intracranial electroencephalogram (EEG) recordings, which measure the brain's electrical activity. They recreated electrode arrays of varying densities to identify the SOZ more effectively. The researchers then created seizure activity heatmap videos based on the EEG recordings and projected these heatmaps onto reconstructed brain images. By studying the heatmap videos, they were able to explore how different electrode densities influenced epileptologists’ ability to identify SOZs. The findings, published in the open-access journal eBioMedicine, revealed that higher-density intracranial EEG recordings improved the accuracy and agreement among epileptologists regarding the location of SOZs, compared to lower-density recordings.

The study involved placing high-density electrode grids onto the brains of patients with drug-resistant epilepsy. After implantation, the patients were observed in the hospital for several days to allow seizures to occur, enabling researchers to pinpoint the locations where they originated. The team asked trained epileptologists to locate the SOZ for these patients using both high-density array recordings (with 4 to 5 mm inter-electrode spacing) and lower-density recordings (with 8 to 10 mm spacing), both derived from the same seizure data. Seizure activity data was visualized as heatmap videos overlaid on reconstructed brain scans, with electrode locations hidden. Using a randomized crossover design, six epileptologists viewed the video visualizations under both higher and lower-density conditions, utilizing a custom computer program to outline the SOZ on the brain.

The results showed that higher-density depth and subdural intracranial EEG recordings led to greater agreement among the epileptologists and helped them identify a larger extent of the SOZ compared to lower-density recordings. The researchers noted that high-density electrode arrays could also allow for more precise mapping of brain function regions, which is typically done by physicians using electrical stimulation. While not assessed in this study, the researchers suggested that additional electrode details might help surgeons more accurately define surgical margins, ensuring the removal of abnormal tissue while preserving healthy tissue. The team emphasized that further studies with more patients are necessary to determine if higher electrode densities lead to better surgical outcomes. Nevertheless, the findings clearly suggest that increasing electrode density on implanted hardware provides clearer insights into the location and full extent of SOZs.

“One of the worst feelings we get is when a patient who underwent surgery begins having seizures again. It suggests some of the bad, seizure-generating tissue is still present,” said senior study author Jon Kleen, MD, PhD, an epilepsy specialist and UCSF assistant professor of neurology in the Weill Institute for Neurosciences. “We’re hopeful this may enable better appraisals of pathophysiological tissue margins and move the needle in the effectiveness epilepsy surgery.”

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