Unlocking the brain’s secrets what happens in the brain when someone is thinking, sleeping, or focusing on an object? The first person to record activity within the human brain in response to various stimuli was Hans Berger, a German psychiatrist. Electroencephalography as he termed his procedure, would revolutionize our understanding of mental processes.
People had known of the existence of electrical currents in the brain since 1875 when Richard Caton, a Liverpool surgeon, and medical school lecturer, discovered brain signals by measuring electrical potentials on the exposed cortex of rabbits and monkeys.
But the true nature of these impulses was not revealed until 6 July 1924, when the German psychiatrist Hans Berger identified for the first time a cortical current on the surface of the brain in a patient at the psychiatric clinic that he ran in Jena.
Faint Stirrings
The apparatus Berger employed, which he dubbed an ‘electroencephalograph’, was fairly primitive. Silver foil electrodes were attached to the skin of the patient’s scalp by means of an elastic bandage; wires from these electrodes ran to an amplifier and a string galvanometer.
Any oscillations detected by the galvanometer were to be reflected in the movement of a needle and recorded graphically as a trace on a long-moving strip of paper. To achieve a visual recording was a real challenge, since the electrical currents coursing through the brain are extremely weak, measuring barely one ten-thousandth of a volt.
As the anxious researcher looked on, the recording needle began to flicker slightly, tracing a line made up of hundreds of peaks and troughs. Faint though the trace was, Berger was delighted with the result, having expended great effort and gone through many inconclusive trials to get to this point.
Even so, to be sure that the electroencephalogram really was recording an electrical brain phenomenon, he continued with the experiments for five more years in the small laboratory in the basement of his clinic, using his patients, his son Klaus and even himself as guinea pigs for study.
Berger always conducted his testing on Sundays when the electrical devices in the hospital were switched off, so they could not interfere with the registration of the tiny impulses on the encephalograms.
Electroencephalogram – Berger always conducted his testing on Sundays when the electrical devices in the hospital were switched off, so they could not interfere with the registration of the tiny impulses on the encephalograms.
From Scepticism to Recognition
By 1929 Berger had identified two types of oscillation, which he termed ‘alpha’ and ‘beta’ waves, and was sufficiently convinced of his findings to publish his first paper that July, entitled ‘On the electroencephalogram in man’.
But his results were greeted with scepticism by his peers, despite the fact that they confirmed similar readings of brain waves in dogs, made in 1912 by the Russian physiologist Vladimir Pravdich-Neminski. Professional snobbery played a part in the rejection; the medical establishment looked down on Berger and his work because he was not a neurophysiologist.
In 1934 Edgar Adrian, a neurophysiologist at Cambridge who had recently been awarded the Nobel prize for physiology, also recorded the alpha wave, employing an improved EEG apparatus that used copper-gauze electrodes wrapped in saline-soaked lint. In a paper describing this research, published jointly with his assistant B HC Matthews, Adrian cited Berger’s seminal work, acknowledging his influence.
In a further mark of recognition, Adrian invited Berger to be co-president of the first international symposium on electrical activity in the nervous system, held in Paris in 1937. Despite this belated recognition Berger, who was prone to bouts of deep depression, took his own life in 1941 in the clinic where he had done his groundbreaking experiments.
Since the 1950s, the EEG has become the standard method of studying the brain and diagnosing its disorders. It can reveal tumors, vascular deformities, and infections in brain tissue, and is a vital first step before a more thorough investigation using an MRI or CAT scanner.
It has also helped in the identification and investigation of different forms of epilepsy, a disease that is related to chronic or temporary hyperactivity in certain regions of the brain.
Painless procedure
Taking an EEG is a non-invasive procedure that involves attaching electrodes to the scalp – usually 16–20, far fewer than in the photograph above. The test generally lasts no more than an hour, during which the patient is subjected to visual stimuli that stimulate particular types of brain activity.
States of the Urban
In his 1929 paper, Berger described two very distinct types of brain waves that he had identified: The electroencephalogram represents a continuous curve with continuous oscillations in which one can distinguish larger first-order waves with an average duration of 90 milliseconds and smaller second-order waves of an average duration of 35 milliseconds.’
The first-order (alpha) waves are seen in states of relaxation, especially when the eyes are closed, while beta waves are associated with mental concentration and with startle reactions. Later neurophysiologists also identified low-frequency delta waves, which occur in deep sleep (the phase when people are most likely to talk or sleepwalk).
After 60-70 minutes of sleep, these are superseded by a rapid, low-voltage EEG, accompanied by rapid eye movement (REM) and low muscle tone. This is the so-called ‘paradoxical sleep’ (also known as the ‘third state’ of brain functioning, after alpha and beta waves), during which sleepers customarily dream.
The Electroencephalogram – 1924- A person undergoing an EEG Test in the1950s. Around this time the procedure was first used to look foreign of epilepsy in patients.
