Temporal behavior of seizures and interictal bursts in prolonged intracranial recordings from epileptic canines

Abstract

Objective Epilepsy is a chronic disorder, but seizure recordings are usually obtained in the acute setting. The chronic behavior of seizures and the interictal bursts that sometimes initiate them is unknown. We investigate the variability of these electrographic patterns over an extended period of time using chronic intracranial recordings in canine epilepsy. Methods Continuous, yearlong intracranial EEG recordings from four dogs with naturally occurring epilepsy were analyzed for seizures and interictal bursts. Following automated detection and clinician verification of interictal bursts and seizures, temporal trends of seizures, burst count, and burst-burst similarities were determined. One dog developed status epilepticus, the recordings of which were also investigated. Results Multiple seizure types, determined by onset channels, were observed in each dog, with significant temporal variation between types. The first 14 days of invasive recording, analogous to the average duration of clinical invasive recordings in humans, did not capture the entirety of seizure types. Seizures typically occurred in clusters, and isolated seizures were rare. The count and dynamics of interictal bursts form distinct groups and do not stabilize until several weeks after implantation. Significance There is significant temporal variability in seizures and interictal bursts after electrode implantation that requires several weeks to reach steady state. These findings, comparable to those reported in humans implanted with the NeuroPace RNS device 1,2, suggest that transient network changes following electrode implantation may need to be taken into account when interpreting or analyzing intracranial EEG during evaluation for epilepsy surgery. Chronic, ambulatory intracranial EEG may be better suited to accurately map epileptic networks in appropriate individuals.

Seizure pathways change on circadian and slower timescales in individual patients with focal epilepsy

“…Another confounding factor in our data is that the surgical implantation itself could artificially alter seizure dynamics. Using chronic recordings of epileptic canines, Ung et al (72) found variability in seizure onset and interictal burst dynamics, with the most stable dynamics emerging approximately a few weeks after electrode implantation. In agreement with their work, we found that earlier seizure evolutions often recurred later in the recording, making it unlikely that gradual changes in the recording quality or an acute reaction to the surgery underlay the observed variability.…”

“…In agreement with their work, we found that earlier seizure evolutions often recurred later in the recording, making it unlikely that gradual changes in the recording quality or an acute reaction to the surgery underlay the observed variability. Instead, Ung et al (72) hypothesized that seizure variability results from transient, atypical dynamics as the brain recovers from surgery, with later dynamics representing a truer epileptic network. Other stressors, such as medication withdrawal, could similarly elicit abnormal dynamics.…”

“…Additionally, variability in seizure pathways may not be inherently deleterious, as long as it is observed and accounted for when planning the surgical resection. Indeed, due to the short presurgical monitoring time and limited spatial coverage of the recording electrodes, some potential seizure pathways may not have been captured (11,72), leading us to underestimate the level of variability in some patients.…”

Intracranial EEG fluctuates over months after implanting electrodes in human brain

“…However, it has been demonstrated in that seizures can have similar clinical appearance while arising from different parts of an epileptic networks, sometimes with different EEG signatures. A recent study by our group shows this phenomenon in a long-term canine model 46 . Classifying seizures and mapping their temporal trends is an ongoing project in our laboratory.…”

A cross-species approach to disorders affecting brain and behaviour

“…Temporal variability in seizures and interictal bursts after electrode implantation reach steady state after several weeks, similar to humans, which adds to the translational relevance of this model 62 . The interictal bursts in dogs are tenfold more frequent than seizures, which provides insights into the physiological changes that inhibit transformation of interictal into ictal activity 63 .…”