DETERMINATION OF BRAIN ACTIVITY BY THRESHOLD OF WAVELET POWER SPECTRUM OF TTG BASED ON KRAWTCHOUK FUNCTIONS

Abstract

Based on the EEG analysis, a method for determining the set of time parameters of brain activity maxima in different leads and in different frequency ranges was proposed, which determines the functional connectivity of the brain. To counteract the power difference for different frequencies and people with different background activation, a procedure for normalizing the power of the wavelet spectra was proposed. It has been found that the power of normalized wavelet spectra based on the Kravchuk functions for different frequency ranges and for different people is in the range 0.01... 0.9. To determine the power threshold above which the corresponding maximum power can be considered a brain response to an external or internal stimulus, EEG wavelet spectra were constructed based on Krawtchouk functions for 10 people aged 20–22, right-handed students of Taras Shevchenko National University of Kyiv. The Neuron-Spectrum-4 / EP complex was used for EEG registration (NeuroSoft, Certificate of EUROCAT Institute for Certification and Testing, Quarat Center, Darmstadt, Germany); EEG registration was carried out at a frequency of 500 Hz, 19 electrodes placed on the international 10/20 system were used. The length of the EEG recording is 16000 points, ie 32 s. The SOM-Ward method clustered the obtained power of the wavelet spectra by 171 attributes. Power attributes of the wavelet spectra in 19 standard leads F1, F2, Fz, F3, F4, F7, F8, Cz, C3, C4, T3, T4, T5, T6, Pz, P3, P4, O1 and O2 were used as attributes. for frequencies 0.5Hz, 1Hz, 2Hz, 4Hz, 8Hz, 16Hz, 31Hz, 63Hz and 125Hz. As a result of clustering, the smallest number of clusters was obtained — 3 and the largest number was — 5. Wavelet Spectrum Analysis 10 surveyed found that the maximum value of the average wavelet power for clusters attributable to background activity was 0.012, and the minimum value of the average wavelet power for clusters attributable to brain reaction was 0.033. Thus, a threshold value of the wavelet spectrum power was detected, namely 0.033, above which the corresponding maximum of the power can be considered as a brain response to an external or internal stimulus.