Increased discharge threshold after an interictal spike in human focal epilepsy.
It is commonly assumed that interictal spikes (ISs) in focal epilepsies set off a period of inhibition that transiently reduces tissue excitability. Post-spike inhibition was described in experimental models but was never demonstrated in the human epileptic cortex. In the present study post-spike excitability was retrospectively evaluated on intracerebral stereo-electroencephalographic recordings performed in the epileptogenic cortex of five patients suffering from drug-resistant focal epilepsy secondary to Taylor-type neocortical dysplasias. Patients typically presented with highly periodic interictal spiking activity at 2.33 +/- 0.87 Hz (mean +/- SD) in the dysplastic region. During the stereo-electroencephalographic procedure, low-frequency stimulation at 1 Hz was systematically performed for diagnostic purposes to identify the epileptogenic zone. The probability of evoking an IS during the interspike period in response to 1-Hz stimuli delivered close to the ictal-onset zone was examined. Stimuli that occurred early after a spontaneous IS (within 70% of the inter-IS period) had a very low probability of generating a further IS. On the contrary, stimuli delivered during the late inter-IS period had the highest probability of evoking a further IS. The generation of stimulus-evoked ISs is occluded for several hundred milliseconds after the occurrence of a preceding spike discharge. As previously shown in animal models, these findings suggest that, during focal, periodic interictal spiking, human neocortical excitability is phasically controlled by post-spike inhibition.
Curtis
Marco
M
Department of Experimental Neurophysiology, Istituto Nazionale Neurologico, via Celoria 11, 20133 Milano, Italy. decurtis@istituto-besta.it
Tassi
Laura
L
Lo Russo
Giorgio
G
Mai
Roberto
R
Cossu
Massimo
M
Francione
Stefano
S
D000293:Adolescent; D000328:Adult; D002648:Child; D004351:Drug Resistance; D004558:Electric Stimulation; D004567:Electrodes, Implanted; D004569:Electroencephalography; D004828:Epilepsies, Partial / Q000503:physiopathology*; D005260:Female; D006801:Humans; D008297:Male; D019579:Neocortex / Q000002:abnormalities / Q000473:pathology; D012189:Retrospective Studies; D013238:Stereotaxic Techniques