Abstracts

To investigate to what extent EEG slow activity can contribute to the clinical evaluation of epilepsy patients., Ten patients with focal or generalized epileptogenic discharges were studied. The data was collected on an XLTEK system with an acquisition range of 0.1-150 Hz. Initially, the recordings had been evaluated for diagnostic purposes with a default filter setting of 1-70 Hz. For this study, power spectra on one-minute of artifact free data were investigated. The areas of maximum power for delta and subdelta activity were compared with the distribution of the epileptogenic discharges., Subdelta power increased over delta by a factor of 2-5 in six patients. The average delta frequency in these patients was 2.1 Hz (range 1-3 Hz) and that of subdelta 0.2 Hz (range 0.1-0.5 Hz). The topography of subdelta was similar to that of delta but the maximum was shifted to a neighboring electrode in four instances. In one case, subdelta activity was maximal in the contralateral low temporal area but the patient[apos]s epileptogenic discharges consisted only of sharp waves that were not followed by a slow wave. In the other instance, there were likewise only bi-temporal low amplitude sharp discharges. In three patients, subdelta power was less by a factor of 2 when compared with delta and in one patient with generalized slow-wave discharges there was no major difference between delta and subdelta., Frequencies below the usually sampled range can be demonstrated in the area of an epileptogenic process. Subdelta power tends to be increased over delta in the presence of well developed spikes that are followed by a higher amplitude slow wave, but can be maximal in the adjacent electrode to the spike. Low amplitude sharp waves tend to show more delta than subdelta power.
The data suggest EEG analysis of seizure patients may be improved and the epileptogenic process further defined by using extended frequency ranges of delta and subdelta. Further investigation is warranted to evaluate the strength of delta and subdelta activity in improving the demarcation of the epileptogenic process.,