In the BRAIN there is a regular, rhythmical change of electric potential, due to the rhythmic discharge of energy by nerve cells. These changes can be recorded graphically and the ‘brain waves’ examined – a procedure introduced to medicine in the 1920s. These records
– electroencephalograms – are useful in DIAGNOSIS: for example, the abnormal electroencephalogram occurring in EPILEPSY is characteristic of this disease. The normal waves, known as alpha waves, occur with a frequency of 10 per second. Abnormal waves, with a frequency of 7 or fewer per second, are known as delta waves and occur in the region of cerebral tumours and in the brains of epileptics. An electroencephalogram can assess whether an individual is awake, alert or asleep. It may also be used during surgery to monitor the depth of unconsciousness in anaesthetised patients.
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