QUANTITATIVE TOPOGRAPHIC ELECTROENCEPHALOGRAPHIC MAPPING DURING DROWSINESS AND SLEEP ONSET

The topographic EEG features of drowsiness and sleep onset are much le ss well documented than are their temporal aspects. A commercial topog raphical mapping system was used to assess the main EEG features emplo ying all 19 international 10/20 system electrode sites referenced to l inked ears during wakefulness, stages 1A and 1B drowsiness, stage 2 sl eep, and sleep onset REM periods in 19 patients. All patients had been referred for a diagnostic EEG or a Multiple Sleep Latency Test and ha d essentially normal EEGs. Anterior alpha of drowsiness seldom represe nted frontal spread of the occipital alpha rhythm but usually was a di stinct activity of apparent separate origin. Theta activities of drows iness were maximum at CZ and FZ. Vertex sharp waves and sawtooth waves of rapid eye movement (REM) sleep had similar fields maximum at the m idline with a steep decrease laterally. Isolated anterior mainly negat ive waves were identified. Sleep spindles were usually maximal in fron to central, occasionally centro parietal, or even parietal areas.