What test measures the electrical activity of the brain?

The test that measures the brain’s electrical activity is an electroencephalogram (EEG). It records voltage changes produced by synchronized activity in groups of neurons, using electrodes placed on the scalp, usually with conductive gel or a fitted cap.

EEG is especially useful for detecting abnormal electrical discharges associated with epilepsy and seizures. It can also help evaluate sleep disorders, encephalopathies, coma, anesthesia depth, and brain activity after cardiac arrest. Because EEG captures changes within milliseconds, it has excellent temporal resolution.

A common mix-up is confusing EEG with MRI. MRI creates detailed anatomical images using magnetic fields and radio waves, whereas EEG measures electrical activity directly. An electromyogram records muscle activity, and an electrocardiogram records the heart’s electrical activity. The modern scalp EEG method developed from early 20th-century experiments, and Hans Berger’s first human recordings in 1924 helped establish clinical electroencephalography.