Abstracts

Rationale: Fourteen- and 6-second positive spikes (14&6PS) are a normal variant EEG pattern of no clinical significance.  The bursts of arch-shaped surface positive waves at 14 and /or 6 Hz are best seen during drowsiness and light sleep in the posterior temporal lead of a monopolar recording using an ipsilateral ear reference.  Currently, its exact origin is unknown. A prior single study using intracranial subdural electrodes identified the 14&6PS in the posterior mesial temporal cortex of 4 patients without available simultaneous scalp recordings. There is no present localizing data with depth recordings.  Methods: These waveforms were observed and analyzed in recordings from 2 patients with drug resistant epilepsy admitted to the University of Pittsburgh Epilepsy Monitoring Unit for presurgical evaluation with simultaneous scalp and Stereo-EEG (SEEG). Results: 14&6PS were identified on scalp EEG of 2 patients aged 26 (Patient #1; P1) and 35 (Patient #2; P2) year old with epilepsy for 10 and 22 years, respectively. P1 was on 4 antiepileptic medications (levetiracetam, clobazam, lacosamide and lamotrigine).  Recording was obtained with a reduced number of bilateral scalp electrodes (#22) and SEEG included 7 left depth electrodes sampling parietal (anterior and posterior), hippocampal body and frontal (superior, inferior and two posterior). Seizure onset was localized in the left parietal region with ENGEL class I outcome at 4 years post-resection. We recognized gamma oscillations in the mesial contacts of the left hippocampus that correlated with the appearance of the 14&6PS on the scalp electrodes.  P2 was on 3 antiepileptic medications (oxcarbazepine, valproic acid and zonisamide).  Recording was obtained with a reduced number of bilateral scalp electrodes (#13) and SEEG included 18 depth electrodes placed in bilateral symmetrical fashion recording from amygdala, hippocampal head, insular (3 depths each), anterior cingulate (2 depths each), superior frontal and orbitofrontal.  Seizure onset was localized in the left frontal region with no seizures at 1 month post-resection. Similarly, gamma oscillations were identified in the mesial contacts of the right hippocampus that correlated with the appearance of the variant on the scalp electrodes.The 14&6PS variant appeared to be correlated exclusively with the right hippocampal gamma oscillation although present bilaterally in the scalp.  The variant was seen mainly during sleep, occasionally during K complexes.  The 14&6PS stopped appearing on the scalp when the hippocampal gamma activity ceased. Conclusions: Both patients intracranial recording revealed extratemporal seizure onset zone. We identified gamma oscillations in the mesial contacts of hippocampus that correlated to the appearance of the 14&6PS normal EEG variant of the scalp electrodes. The validity of the findings is enhanced by bilateral recordings and scalp EEG to verify the correlation with the observed variant.  To the best of our knowledge, this is the first report of simultaneous scalp and SEEG recording of the 14&6PS. Funding: None