Abstracts

Rationale: Most seizures self-terminate through complex interregional interactions. Increased synchrony (phase and amplitude correlation) just prior to termination is a common phenomenon. Generalized partial directed coherence (GPDC) measures directed functional connectivity (dFC) between brain regions [1]. Indegree from a dFC provides valuable information to the state change affecting each region depending on synchrony in the local milieu. Here we measured indegree derived from windowed analysis of GPDC starting at 20 seconds before seizure termination and continued 20 seconds postictally, to quantify: 1) difference in the synchrony within the onset, spread and least involved channels (ON, SP and LI), 2) whether this interaction was significantly different between pre-termination (PrT) and post termination (PoT) states. Methods: Twenty seizures from 7 patients with intractable partial epilepsy underwent IEEG/SEEG placement for localizing the seizure onset zone (SOZ) were used for analysis. After the removal of artifactual channels, the data was converted to adjacency bipolar derivatives. GPDC was calculated using a window of 5 seconds with 50% overlap (SR: 2048Hz model order: 25) for each bandwidth (Delta:1-4Hz, Theta:4-8Hz, Alpha:8-13Hz, Beta:13-30Hz, Low Gamma:30-40Hz and High Gamma:45-95Hz) for all 3 types of channels. The indegree calculated across the stages and the bipolar derivations were tested with a two-way interaction ANOVA (LSD corrected p-value  Results: It was found that the onset and spread channels had a significant difference between the PrT and PoT in all the band widths. However this difference was not very significant in the channels not involved. There was a significant decrease in indegree following seizure termination and this was maximum in the onset and spread channels but no on the least involved channels (p=0.041). The decrease in indegree was maximum at delta and higher gamma band in the onset and spread channels. When we tested the interaction between the seizure state and the onset channel type it was found that the indegree showed a significant reduction (Table 1)(Figure 1). Conclusions: PrT is a state of heightened synchronization with increased cross talk between the different electrodes, following which there is a catastrophic drop in synchronization in a wide range of brain electrical activity with all cannels a similar post ictal state with little variance between them.[1] “The Concept of Effective Inflow: Application to Interictal Localization of the Epileptogenic Focus from iEEG.” IVlachos I, Krishnan B, Treiman D, Tsakalis K, Kugiumtzis D, Iasemidis LD.  IEEE Transactions on Biomedical Engineering (2016) Funding: This study was supported by NSF grant OIA 1632891.