Technique for recording electrical activity in the brain, whose cells emit distinct patterns of rhythmic electrical impulses. Pairs of electrodes on the scalp transmit signals to an electroencephalograph, which records them as peaks and troughs on a tracing called an electroencephalogram (EEG). Different wave patterns on the EEG are associated with normal and abnormal waking and sleeping states. They help diagnose conditions such as tumours, infections, and epilepsy. The electroencephalograph was invented in the 1920s by Hans Berger (1873–1941).

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