Intraoperative microseizure detection using a high-density micro-electrocorticography electrode array

Abstract

One-third of epilepsy patients suffer from medication-resistant seizures. While surgery to remove epileptogenic tissue helps some patients, 30–70% of patients continue to experience seizures following resection. Surgical outcomes may be improved with more accurate localization of epileptogenic tissue. We have previously developed novel thin-film, subdural electrode arrays with hundreds of microelectrodes over a 100–1000 mm2 area to enable high-resolution mapping of neural activity. Here, we used these high-density arrays to study microscale properties of human epileptiform activity. We performed intraoperative micro-electrocorticographic recordings in nine patients with epilepsy. In addition, we recorded from four patients with movement disorders undergoing deep brain stimulator implantation as non-epileptic controls. A board-certified epileptologist identified microseizures, which resembled electrographic seizures normally observed with clinical macroelectrodes. Recordings in epileptic patients had a significantly higher microseizure rate (2.01 events/min) than recordings in non-epileptic subjects (0.01 events/min; permutation test, P = 0.0068). Using spatial averaging to simulate recordings from larger electrode contacts, we found that the number of detected microseizures decreased rapidly with increasing contact diameter and decreasing contact density. In cases in which microseizures were spatially distributed across multiple channels, the approximate onset region was identified. Our results suggest that micro-electrocorticographic electrode arrays with a high density of contacts and large coverage are essential for capturing microseizures in epilepsy patients and may be beneficial for localizing epileptogenic tissue to plan surgery or target brain stimulation.

Flexible, high‐resolution cortical arrays with large coverage capture microscale high‐frequency oscillations in patients with epilepsy

“…It should also be noted that although studies of interictal activity from recordings in the epilepsy monitoring unit have indicated that HFOs coincident with interictal discharges, or "spikes," may be especially clinically valuable, we did not find sufficient instances of HFOs coincident with interictal discharges in our recordings to investigate their spatial scale in the present study 56,57 . Interestingly, our previous work also identified intraoperative microseizures in epilepsy patients using the same LCP‐TF μECoG arrays 35 . Thus, future work using implantable μECoG arrays to record for longer durations during presurgical monitoring under various states of consciousness will be essential to further understand the clinical relevance of microscale HFOs and their relationship over time to other interictal activity such as interictal discharges and microseizures.…”

“…56,57 Interestingly, our previous work also identified intraoperative microseizures in epilepsy patients using the same LCP-TF μECoG arrays. 35 Thus, future work using implantable μECoG arrays to record for longer durations during presurgical monitoring under various states of consciousness will be essential to further understand the clinical relevance of microscale HFOs and their relationship over time to other interictal activity such as interictal discharges and microseizures.…”

“…(G) The custom headstage board, which uses a 64‐channel Intan RHD chip for amplification and analog to digital conversion. This figure is adapted from Sun et al 35 …”

“…We used LCP-TF μECoG arrays described previously to record intraoperatively from the surface of the brain in each subject (Figure 1). 34,35,40 Custom arrays were fabricated by DYCONEX (Micro Systems Technologies). We used three μECoG array designs with different center-to-center spacings (pitches) and coverages to fit each craniotomy and recording target.…”

“…We captured HFOs during brief intraoperative recordings from patients undergoing resection surgery for epilepsy using liquid crystal polymer thin-film (LCP-TF) μECoG arrays with high resolution (.76-1.72-mm pitch) and large spatial coverage (144-1596 mm 2 ) designed for use in the intraoperative setting. 34,35 We identified ripple and fast ripple HFO events using a common automated detection algorithm along with artifact rejection methods. [36][37][38][39] We found microscale heterogeneity in HFO characteristics across the arrays, with distinct subregions of elevated activity.…”