Interictal Spikes & Epileptic Seizures

Circadian rhythms

Philippa Karoly, Dean Freestone, Ray Boston, David Grayden, David Himes, Kent Leyde, Udaya Seneviratne, Samuel Berkovic, Terence O'Brien, Mark Cook

Background

Here we analyse spontaneous epileptic "spike-wave discharages" recorded in 15 epilepsy patients. Data were acquired from implanted electrodes during a clinical trial (see here for details). Recording was continuous over 6 months - 3 years. Spike detection was automated using a template matching algorithm.

Epileptic spikes can be detected using EEG and are thought to be due to large populations of neurons firing in sync. Healthy brains also show spike activity, but patients with epilepsy have far more frequent spike events. It is not clear if there is a direct link between spike-waves and seizures. Here we report on patterns of seizures and spike-waves, their relationship to each other, and the evidence of circadian rhythms.

Key Results

Three patients showed a significant preseizure increase in spike rate, six patients showed a significant decrease, and no significant change was found in the remaining six patients.

Comparison in spike rate between interictal and pre seizure times. The x axis indicates different subjects and the y axis is a normalized spike rate


Seizures and spikes showed clear circadian rhythms that were highly patient specific. Importantly there were times when seizures were extremely unlikely

Circadian patterns of seizures


Usually times of high spike and seizure likelihood were aligned for an individual. Alignment indicates a common factor regulating spikes and seizures (see plot below)


Data Visualization

This is an interactive plot to visualize average hourly spike rate and seizure rate over 24 hours. The rate is normalized to a range from 0% (minimum rate) to 100% (maximum rate) for each patient.
The circle segments represent 1 hour (there are 24 segments) and each ring is a different patient (there are 15 rings in total). The rings can also be viewed individually.

My data won't fit on your screen!

Plot patients:

Take home message

Spikes and seizures have a complex, patient-specific relationship

Our findings show that spikes are neither exclusively protective or provocative. We also show that spikes and seizures are linked and are part of a larger continuum of epileptic events.

A major problem treating epilepsy is the intermittent nature of seizures, making it difficult to refine therapies. The circadian patterns and interrelationship between spikes and seizures that we have identified provide new treatment strategies for epilepsy. Understanding times of high and low seizure and spike likelihood could improve patient management, providing a means to titrate therapies, to forecast seizures and monitor new treatments.

Our study highlight a need for devices that can perform chronic and continuous monitoring of neural signals in order to better manage epilepsy

Contact Us

The authors contact details are:

Philippa Karoly
Dean Freestone
Mark Cook