FROM DC SHIFT TO ISA : SLOW EEG ON THE ROAD TO GLIA (GIN, Grenoble, le 22/9/2014)

Setting 
Presentation at the Gin-team 9 (SYMONNE) monday meeting

Introduction
Slow EEG encompasses Slow (<0.5Hz) and InfraSlow (<0.01Hz) activities that could be recorded during intracranial or scalp-EEG. Since the discovery of spreading cortical depression by Leao (1940), and the subsequent demonstration that behind cortical depression an infraslow depolarization due to increased extracellular potassium could be evidenced using DC amplifier, several works, during the 60s showed slow and sustained shifts in EEG during ischemia, migraine, hyperventilation, or seizures. More recently, and following the works of Ikeda, it could be demonstrated that current EEG devices could allow studying so-called "DC-shift", by removing digitalized high-pass filters. 
Thus, "ictal onset baseline shifts" and "infraslow activities" have been shown during focal and generalized non convulsive seizures (absence), albeit rather inconstantly. Moreover, ISA were shown to occur either before, at or after seizure onset in many types of seizures. 

Powerpoint is here (click on the front slide) :

References (click on titles)

• Wu et al, Epilepsia 2014 : a careful comparison of Ictal Baseline Shifts, Ictal HFO and Ictal conventional stereo-EEG in 15 patients with intracranial EEG : 
• Rodin et al., Clin EEG 2008 : Absence and focal seizures with AC amplifiers
• A textbook on EEG describing ISA (read from page 300):