Similarities and differences between the interictal epileptiform discharges of green-spikes and red-spikes zones of human neocortex.

OBJECTIVE

This study looks for differences in the waveforms of interictal epileptiform discharges (IEDs) between cortices expressing only isolated discharges (green-spikes zones) vs those manifesting seizures (red-spikes zones): these can help to understand ictogenesis mechanisms and improve clinical decision in surgical epilepsy. Typical IEDs are triphasic, exhibiting in sequence: a negative-sharp-wave, a positive-baseline-shift and a negative-slow-wave. Negative-slow-waves are thought to reflect neurophysiological inhibition: their features at a focus' edge may reflect peripheral inhibition, a mechanism characterized in experimental models, curbing seizures' spread. This might be weakened in red-spikes.

METHODS

A retrospective review of human intracranial EEGs was performed, comparing green- and red-spikes for their peripheral slow-waves' amplitudes. Green- and red-spikes were also compared also for the amplitudes of their negative-sharp-waves and positive-baseline-shifts, as well as for their spread pathways.

RESULTS

Green-spikes exhibit more pronounced peripheral slow-waves than red-spikes. They also exhibit more pronounced positive-baseline-shifts, and more frequent propagation pathways' shifts.

CONCLUSIONS

Peripheral slow-waves' amplitudes correlate with seizures' suppression and may reflect neurophysiological peripheral inhibition.

SIGNIFICANCE

This study suggests a novel approach to reading intracranial EEGs: amplitudes measures of IEDs waveforms are technically simple, may help identifying epileptogenic zones and indicate the spatial distribution of underlying ictogenesis mechanisms.