Evaluation of Photic Stimulus Response Based on Comparison with the Normal Database in EEG Routine Examination

Abstract

The aim of our research is the evaluation of the photic driving response, a routine EEG examination for diagnosis. It is well-known the EEG responds not only to the fundamental frequency but also to all sub and higher harmonics of a stimulus. In this study, we propose a method for detecting and evaluating responses in screening data for individuals. This method consists of two comparisons based on statistical tests. One is an intraindividual comparison of the amplitudes between the EEG at rest and the photic stimulation (PS response reflecting enhancement and suppression by PS, and the other is a comparison between data from an individual and a distribution of normals in the normal database. These tests were evaluated using the Zvalue based on the Mann- Whitney Utest. The experiment was conducted using PS frequencies of 3, 6, 7, 10, 14 and 18Hz. We used the measured data at electrode O1 where PS appears the greatest. We measured EEGs from 130 normal subjects and 30 patients with any of schizophrenia, dementia and epilepsy. Normal data were divided into two groups, the first consisting of 100 data for database construction and the second of 30 data for test data. We evaluated amplitudes at a subharmonic frequency, the fundamental frequency, the second harmonic frequency, higher order harmonic frequencies less than 40Hz, and the alpha peak frequency. From the results of the comparison of patients and the normal database, frequencies with Zvalues smaller than those of the normal database could be recognized. At the alpha peak frequency, patient data have higher Zvalues than does the normal database though there were no significant differences for the subharmonics. Moreover, in the patient data, both the enhancement of harmonic components including the fundamental wave by PS and suppression of the alpha component were weak.