Abstracts

We recently described noninvasive techniques to perform longterm DC-coupled EEG recordings at the bedside, and have used these methods to demonstrate that inspection of infraslow ([lt] 0.5 Hz) activity can correctly lateralize temporal lobe seizures (Vanhatalo et al, [italic]Neurology[/italic].60:1098, 2003). To further clarify the underlying cerebral basis for scalp-recorded infraslow activity, we now report on recordings with subdural arrays of platinum electrodes using DC-coupled amplifiers., Recordings were performed on patients receiving invasive monitoring for medically intractable localization related epilepsy with a total of 17 seizures in 6 patients captured during monitoring. Recordings were made by digital acquisition software using a 64-channel commercial DC amplifier coupled to surgically placed subdural arrays. The frequency bandwidth of record was limited to DC to 70 Hz. Afterwards, ictal events were exported to an EEG analysis software package (EEGlab v4.515) for review. The time of onset, location, polarity, duration, and qualitative shape of infraslow signals up to 10 minutes prior to and 10 minutes after clinical onset of seizure (or electrical onset of seizure for subclinical seizures) were catalogued by an investigator blinded to the conventional EEG and presurgical workup. The results were compared to the location and onset of AC electrical seizure discharge as determined by a board-certified electroencephalographer., Unequivocal infraslow signals, of a magnitude from 0.8 to 4 mV, were seen in 14 seizures in 5 patients following the electrical ictal onset determined from the conventional recording, with a delay ranging from 8 s to several minutes. Of these, in 9 seizures the initial infraslow signals included at least one of the channels determined to localize the ictal onset in the conventional recording. Two seizures had the initial infraslow signal in a channel adjacent to location of ictal onset. Moreover, 3 seizures displayed initial infraslow signals only in nonadjacent channels. Two of the six patients had multiple seizures analyzed and the shape and polarity of the localizing infraslow shifts, when seen, were consistent across seizures for each patient (one patient had a negative shift, one positive)., Infraslow activity recorded invasively with DC-coupled amplifiers are significantly higher in voltage than previous reports of invasive recordings performed with AC amplifiers with a long time constant. The high voltage of this activity helps to explain why infraslow can sometimes localize seizures better than conventional EEG on scalp recordings. On invasive recordings, seizure localization using infraslow activity was usually concordant with that obtained from analysis of higher frequency activity.,