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Electroencephalograph or EEG machines measure the brain’s electrical activity using electrodes attached to the scalp. Brain activity is visually recorded by the machines as wavy lines called ‘traces’. EEG machines can identify brain conditions such as epilepsy and monitor changes in brain activity during sleep or coma.

In the 1800s, Richard Caton and Adolf Beck performed research on animals to understand electrical brain activity. The electrocardiograph machine was developed in 1902. Medical scientists applied this equipment to the brain.

During the 1920s, German psychiatrist Hans Berger developed the electroencephalograph to detect electrical activity from the surface of a human skull. Berger used electrodes to develop a safe, non-invasive technique to record brain function.

In 1936, EEGs were used to establish patterns to diagnose epilepsy and other conditions. By the 1940s scientists were using EEGs to try to diagnose criminal behaviour and some mental illnesses. Some thought EEGs could be used in eugenics to screen those with such disorders and prevent them reproducing. EEGs were also used in ‘lie detector’ machines. By the 1960s most psychiatrists and psychologists accepted EEG data could not reliably diagnose dishonesty, criminality or mental illness. Since then, EEGs have been used in sleep research. They help us understand the relationship between deep sleep, light sleep, dreaming and wakefulness. They also help legally define ‘brain death’.

During the 20th century EEGs demonstrated the absence of brain activity. In 1963 an EEG was used as an indicator of brain death by R S Schwab. Using EEG to define death remains controversial.



Related links

Techniques and Technologies:

External links:


R Bud and D J Warner (eds), Instruments of Science, An Historical Encyclopedia (London: Science Museum, 1998)

J Empson, Human brainwaves: the psychological significance of the electroencephalogram (Basingstoke: Macmillan; New York: Stockton, 1986)

D Millett, ‘Wiring the brain: from the excitable cortex to the EEG, 1870-1940’, unpublished PhD thesis, University of Chicago, 2001



A conductor which enables a current to go in or out of a particular object, substance or region.


A disorder of brain function characterized by seizures that occur suddenly. The seizures can be triggered by fast flashing lights, especially strobe lighting.


The study of human improvement by selective breeding, founded in the 1800s by English scientist Sir Francis Galton. Widely discredited after its use by the Nazi regime.


a machine designed to detect and record changes in physiological characteristics, such as a person's pulse and breathing rates, used especially as a lie detector.