FRACTAL ANALYSIS OF ELECTROENCEPHALOGRAPHIC SIGNALS INTRACEREBRALLY RECORDED DURING 35 EPILEPTIC SEIZURES - EVALUATION OF A NEW METHOD FOR SYNOPTIC VISUALIZATION OF ICTAL EVENTS

Traditional electroencephalography (EEG) produces a large volume displ ay of brain electrical activity, which creates problems particularly i n assessment of long periods of intracranial, stereoelectroencephalogr aphic (SEEG) recording. A method for fractal analysis that describes 1 00 SEEG data points in terms of a single estimate of fractal dimension (1 < FD < 2) is reported; the central processing unit time costs amou nt to approximately 2 min/Mbyte of input signal (using a Sun SPARCstat ion LX). The diagnostic sensitivity of this method, applied to quantif ication and synoptic visualisation of SEEG signals recorded during 35 epileptic seizures in 7 patients, is evaluated. II is found that the m ethod consistently defines ictal onset in terms of rapid relative incr ease in FD across several channels. Clinically severe seizures are cha racterised by more intense and generalised ictal changes in FD than cl inically less severe events. For all 7 patients, and for 75% of indivi dual seizures, ''fractal diagnoses'' of anatomically defined ictal ons et zone coincided closely with ictal onset zone independently determin ed by inspection of traditional EEG displays of the same data. We conc lude that the method is a computationally feasible way to achieve subs tantial reduction in the volume of SEEG data without undue loss of dia gnostically important information in the primary signal.