electroencephalogram

a record of the BRAIN'S electrical activity measured on an electroencephalograph. Electrodes on the scalp record the charge of electric potential - or brain waves. There are four main types of waves: alpha, beta, theta and delta. Alpha waves, with a frequency of ten per second, occur when the person is awake and DELTA WAVES (seven or fewer per second) occur in sleeping adults. The occurrence of delta waves in wakeful adults indicates brain damage or cerebral tumours.