Neocortical propagation in temporal lobe spike foci on magnetoencephalography and electroencephalography

Propagation of the neuronal population of the interictal epileptic spike was quantified in 5 patients with complex partial epilepsy arising from temporal lobe using electroencephalography and magnetoencephalography. During the spike complex in each patient there was a spike at the deep sphenoidal electrode and a spike at the superficial scalp electrode on spontaneous electroencephalography. In each patient the sphenoidal spike had a different peak latency than the scalp spike, consistent with spike propagation. Electroencephalography was used to trigger two magnetoencephalographic averages of stereotyped spikes during the sphenoidal peak and the scalp peak. Magnetoencephalography discriminated the centers of two cortical spike populations at different latencies, showing deeper localization with sphenoidal trigger and more superficial localization with scalp trigger in each patient (p less than 0.05). Latency differences and propagation distances of spikes were consistent with the conduction velocity of corticocortical fibers. Noninvasive estimates of the cortical surface area of the spikes agreed with estimates obtained by electrocorticography over temporal neocortex. These findings indicate propagation of neuronal populations active during human interictal spikes between deep and superficial cortex of temporal lobe, likely by monosynaptic or oligosynaptic pathways. This interictal system appears to be partly independent of the hippocampal interictal system in complex partial epilepsy.