Chaotic and stochastic dynamics of epileptiform-like activities in sclerotic hippocampus resected from patients with pharmacoresistant epilepsy

Abstract

The types of epileptiform activity occurring in the sclerotic hippocampus with highest incidence are interictal-like events (II) and periodic ictal spiking (PIS). These activities are classified according to their event rates, but it is still unclear if these rate differences are consequences of underlying physiological mechanisms. Identifying new and more specific information related to these two activities may bring insights to a better understanding about the epileptogenic process and new diagnosis. We applied Poincaré map analysis and Recurrence Quantification Analysis (RQA) onto 35 in vitro electrophysiological signals recorded from slices of 12 hippocampal tissues surgically resected from patients with pharmacoresistant temporal lobe epilepsy. These analyzes showed that the II activity is related to chaotic dynamics, whereas the PIS activity is related to deterministic periodic dynamics. Additionally, it indicates that their different rates are consequence of different endogenous dynamics. Finally, by using two computational models we were able to simulate the transition between II and PIS activities. The RQA was applied to different periods of these simulations to compare the recurrences between artificial and real signals, showing that different ranges of regularity-chaoticity can be directly associated with the generation of PIS and II activities.

Epileptic seizure suppression: a computational approach for identification and control using real data

“…However, one of the main goals of the proposed approach is to make the models as simple as possible (specially envisioning the later stages of state-space representation), besides avoiding potential problems of overfitting. In this sense, the models can sufficiently approximate the inherent dynamics of periodic ictal activity (PIS) and interictal activity (II), distinguishing them according to the AR coefficients obtained, thus endorsing previous results using the same signals [50].…”

“…In fact, Ref. [50] used the same signals present in this work, and by applying nonlinear/nonparametric classification techniques, such as logistic regression and confidence intervals, fairly good classifications were obtained. Moreover, within each…”

“…The main difference between ictal (PIS) and interictal (II) spikings concerns the interspike intervals: while the PIS activity presensts more regular evenly-spaced spikes, the spikes of the II activity are more irregular, switching from local bursts to isolated spikes over the whole signal. A previous statistical analysis and classification of the signals used in this work has been carried out [50]. Essentially, according to the authors, the patterns exhibited in PIS signals indicate a more deterministic activity and underlying mechanism, whereas II signals suggest a more complex/chaotic one.…”

“…The raw signals were properly filtered to remove any uncorrelated activity (i.e., shifting baseline, spurious harmonics), as carried out in [50]. By filtering them, the resulting activity consists mainly of only epileptic spiking or bursting behavior over time.…”

“…The electrophysiological data used in this work were recorded from slices of hippocampal subfields 2 that were surgically resected from patients with pharmacoresistent temporal-lobe epilepsy (TLE) [50]. The results show that AR models can, indeed, represent real epileptic seizures fairly well, which is particularly helpful to provide customized models for each patient or time signature.…”