Background EEG power effects of a cumulative dose of alcohol were investigated as subjects drank three glasses of alcoholic, 1 h apart. Subjects completed a task battery composed of digit span tests, 3 min each of eyes-open and eyes-closed resting EEG, and two blocks of an auditory N-back working memory task for measuring brain function of different segmental features in monosyllabic Thai words. The changes in cognitive effort caused by the difficulty manipulation in the N-back task were reflected in specific EEG signals. Measuring EEG activity before and after alcohol consumption, during the performance of difficulty manipulation in N-back task of working memory indicate that neuronal populations needed for working memory processing were less available after alcohol consumption because of increased background oscillatory activity as evidenced by increased background EEG power.