Análise da Coerência Parcial Direcionada do Eletroencefalograma durante Estimulação Somatossensorial

Partial Directed Coherence (PDC) is a strong mathematical method that gives the concept of Granger causality a frequency domain approach. This method can be used to identify coherence between more than only pairs of signals, decomposing their mutual interactions into "feedback" and "feedforward" aspects. The usage of PDC with multivariate autoregressive models (MAR) has already proved to be efficient in applications to the electroencephalogram (EEG) and can be used to determine causality and information flow between brain regions in different stimulation conditions. This work focuses on the study and analysis of PDC application to the EEG obtained without stimulating the patient (spontaneous EEG) and with somatosensory stimulation (SSEP - Somatosensory Evoked Potential) of the right posterior tibial nerve, aiming to compare both situations. PDC was applied to signals from C3, P3, Cz, Pz, C4, P4 derivations from the International 10-20 System, located near the somatosensory cortex, region where to expect the highest amplitude response while in stimulation. The results have shown that, when the patients are stimulated, there is more information flow (in a frequency range of 0 to 100Hz) from the left hemisphere of the brain cortex, contralateral to the stimulus, to the right hemisphere, ipsilateral to the stimulus, even when it is observed a greater potential in the right side, phenomenon known in literature as paradoxical lateralization.