Obstructive Sleep Apnea Syndrome (OSAS) is a very common sleep disorder that is associated with several neurocognitive impairments. The present study aims to assess the electroencephalographic (EEG) power before, during and after obstructive apnea episodes, in four frequency bands: delta (
), theta (
), alpha (
) and beta (
). For that purpose, continuous wavelet transform was applied to the EEG signals obtained with polysomnography, and topographic EEG brain mapping (EBM) to visualize the power differences across the whole brain. The results demonstrate that there is a significant decrease in the EEG
power during OSAS that does not totally recover immediately after the episode. Furthermore, a power decrease in a specific brain region was noticed for all EEG frequency ranges.