Comparison of Frequency Bands Using Spectral Entropy for Epileptic Seizure Prediction

Introduction. Under the hypothesis that the uncontrolled neuronal synchronization propagates recruiting more and more neurons, the aim is to detect its onset as early as possible by signal analysis. This synchronization is not noticeable just by looking at the EEG, so mathematical tools are needed for its identification. Objective. The aim of this study is to compare the results of spectral entropies calculated in different frequency bands of the EEG signals to decide which band may be a better tool to predict an epileptic seizure. Materials and Methods. Invasive ictal records were used. We measured the Fourier spectrum entropy of the electroencephalographic signals 4 to 32 minutes before the attack in low, medium and high frequencies. Results. The high-frequency band shows a markedly rate of increase of the entropy, with positive slopes and low correlation coefficient. The entropy rate of growth in the low-frequency band is practically zero, with a correlation around 0.2 and mostly positive slopes. The mid-frequency band showed both positive and negative slopes with low correlation. Conclusions. The entropy in the high frequencies could be predictor, because it shows changes in the previous moments of the attack. Its main problem is the variability, which makes it difficult to set the threshold that ensures an adequate prediction. 1. Introduction Epilepsy is considered by some authors as a symptom that responds to different neurological disorders. These disorders may be strokes, head traumas, brain malformations, and the effect of neurotoxic substances among others [1]. All of them are discontinuities that affect normal brain activity, enabling the creation of conditions for the occurrence of the attack. The mechanism of the attack is not clear yet, although there are several hypotheses based on the incorrect communication between neurons [2]. For some reason, this results in synchronizing the activation of a mass of neurons which generates the crisis. According to the more accepted postulates, the problem of the epilepsy occurs when an error in the communication between neurons is not blocked by the inhibition system that controls them. In this case one neuron excites another neuron causing a cascade of stimulation that grows and propagates recruiting other neurons. If during that propagation neither factor inhibits the recruitment of neurons, that small initial failure takes a critical mass of neurons and ends in an epileptic seizure [3]. Under the hypothesis that the uncontrolled neuronal synchronization propagates and recruits more neurons each