Estimação da resposta evocada à estimulação somatossensorial elétrica senoidal de 5 Hz e 2 kHz, utilizando Wavelets e análise em componentes independentes

Abstract

The psychophysical evaluation of the sensibility of the thin and thick fibers with sinusoidal current stimulation was proposed in the 80s. The 5 Hz stimulus would be related to the thin unmyelinated fiber and the 2 kHz to the thick myelinated fiber. Aiming a quantitative analysis of the cerebral cortex response to those stimuli, the evoked potential (EP) was estimatedwith the coherent mean and the Cyclic Shift Tree Denoising using Wavelet (CSTD). The evaluation of performance of both technique was made with simulated subrogate data. These techniques were applied to EEG signals (5 volunteers with 5 Hz and 3 for 2 kHz) collected on theCz electrode (10-20 International Standard System), during 100 stimuli of 20s each, with interval between stimuli of 10s. The stimulus intensity was twice the sensitivity threshold (ST) for 5 Hz and 2 kHz. The signals were sampled at 500 Hz and 20 kHz, for 5 Hz and 2 kHz, respectively. Toremove the 2 kHz stimulus artifact, a low-pass filter at 1 kHz was applied, and for 5 Hz stimulus artifact was applied the Independent Component Analysis using second order statistics (SOBIRO). The simulated data showed a better performance of the CSTD technique for EP estimation.The EP estimated with 5 Hz stimulus presented the following components: N104 (one volunteer), P179 (four volunteers) and N234 (three volunteers), P280 (three volunteers) and N493 (all volunteers). The EP with 2 kHz stimulus presented the P31, N82, P129, N224 and P389components in all volunteers. The results indicate shorter latency in the first components of the 2 kHz EP. This fact suggests more speed of the information transmission as expected by thick fibers stimulation. The CSTD and SOBI-RO techniques can be very useful tools for the EPestimation.