Frequency Power of the brain waves before, during and after SDs
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SD is presented as a negative near DC-shift (NDCS) and as a decrease in power in the ECoG bands in adjacent electrodes using an AC recorder. For SD examination, 5-min signal segments before and after the NDCS of the SDs were analyzed. Moreover, the NDCS of the SDs were studied, presenting a mean duration of 51.3 s (σ = ± 14.1 s). For reliable SD evaluation, the SDs included in the analysis had signal segments of 5 min before and after the NDCS free of artifacts and other SDs. The ECoG recording segments before, during, and after the NDCS were referred to as “preSD,” “SD,” and “postSD”. For signal decomposition, the discrete 512-point Fourier transform (Hanning window) was computed for each data segment and, subsequently, the power spectrum. For each segment, we estimated the mean power spectrum corresponding to each frequency band: delta (0.1–4 HZ), theta (4–7 Hz), alpha (8–12 Hz), beta (13–31 Hz), and gamma (32–45 Hz). The power calculation was performed using customized MATLAB programs (MathWorks, Natick, MA). The SDs were collected and analyzed in periods of 3 h per electrode, with eight time lapses in total. The power spectrum of each brain wave was computed for each SD phase (preSD, SD, and postSD), resulting in a dataset of eight elements for each phase.