Research

Comparative study of nonlinear properties of EEG signals of normal persons and epileptic patients

Md Nurujjaman¹ , Ramesh Narayanan^1,2 and AN Sekar Iyengar¹

¹  Plasma Physics Division, Saha Institute of Nuclear Physics, 1/AF, Bidhannagar, Kolkata – 700064, India

²  Current address: Laboratorio Associado de Plasma, Instituto Nacional de Pesquisas Espaciais, Av. dos Astronautas, 1758 – Jardim da Granja 12227-010 Sao Jose dos Campos, SP, Brazil

author email corresponding author email

Nonlinear Biomedical Physics 2009, 3:6doi:10.1186/1753-4631-3-6

Published:	20 July 2009

Abstract

Background

Investigation of the functioning of the brain in living systems has been a major effort amongst scientists and medical practitioners. Amongst the various disorder of the brain, epilepsy has drawn the most attention because this disorder can affect the quality of life of a person. In this paper we have reinvestigated the EEGs for normal and epileptic patients using surrogate analysis, probability distribution function and Hurst exponent.

Results

Using random shuffled surrogate analysis, we have obtained some of the nonlinear features that was obtained by Andrzejak et al. [Phys Rev E 2001, 64:061907], for the epileptic patients during seizure. Probability distribution function shows that the activity of an epileptic brain is nongaussian in nature. Hurst exponent has been shown to be useful to characterize a normal and an epileptic brain and it shows that the epileptic brain is long term anticorrelated whereas, the normal brain is more or less stochastic. Among all the techniques, used here, Hurst exponent is found very useful for characterization different cases.

Conclusion

In this article, differences in characteristics for normal subjects with eyes open and closed, epileptic subjects during seizure and seizure free intervals have been shown mainly using Hurst exponent. The H shows that the brain activity of a normal man is uncorrelated in nature whereas, epileptic brain activity shows long range anticorrelation.