What device records the human brain’s electrical activity from electrodes placed on the scalp?

An electroencephalograph records the human brain’s electrical activity from electrodes placed on the scalp.

The resulting recording is called an electroencephalogram, or EEG. Electrodes detect voltage differences produced mainly by the synchronized activity of large groups of cortical neurons. The signals are amplified and displayed as waveforms over time.

German psychiatrist Hans Berger made the first human EEG recordings in 1924 and published his findings in 1929. His work established that the brain produces measurable electrical rhythms without opening the skull.

An electroencephalograph is the recording instrument, while electroencephalography is the method and an electroencephalogram is the trace itself. EEG is especially useful for examining seizures, sleep stages, and broad changes in brain function, although it provides less precise information about the location of activity than many brain-imaging techniques.