Research

Nonlinear analysis of EEG signals at different mental states

Kannathal Natarajan¹ , Rajendra Acharya U¹ , Fadhilah Alias¹ , Thelma Tiboleng¹ and Sadasivan K Puthusserypady²

¹  ECE Division, Ngee Ann Polytechnic, 535 Clementi Road, Singapore 599489

²  Department of ECE, National University of Singapore, Singapore 119260

author email corresponding author email

BioMedical Engineering OnLine 2004, 3:7doi:10.1186/1475-925X-3-7

Published:	16 March 2004

Abstract

Background

The EEG (Electroencephalogram) is a representative signal containing information about the condition of the brain. The shape of the wave may contain useful information about the state of the brain. However, the human observer can not directly monitor these subtle details. Besides, since bio-signals are highly subjective, the symptoms may appear at random in the time scale. Therefore, the EEG signal parameters, extracted and analyzed using computers, are highly useful in diagnostics. This work discusses the effect on the EEG signal due to music and reflexological stimulation.

Methods

In this work, nonlinear parameters like Correlation Dimension (CD), Largest Lyapunov Exponent (LLE), Hurst Exponent (H) and Approximate Entropy (ApEn) are evaluated from the EEG signals under different mental states.

Results

The results obtained show that EEG to become less complex relative to the normal state with a confidence level of more than 85% due to stimulation.

Conclusions

It is found that the measures are significantly lower when the subjects are under sound or reflexologic stimulation as compared to the normal state. The dimension increases with the degree of the cognitive activity. This suggests that when the subjects are under sound or reflexologic stimuli, the number of parallel functional processes active in the brain is less and the brain goes to a more relaxed state