Diagram of neurons firing during EEG

In this section, we describe the EEG or electroencephalograph, a diagnostic tool used in epilepsy, explain the science behind it, and introduce the person who discovered it.

If you or a loved one has been diagnosed with epilepsy, you’ve most likely had an EEG done. What is an EEG? How does it work? And who came up with this technique? 

Who discovered the EEG?

The first human EEG was recorded by Professor Hans Berger, Chief Psychiatrist of the University of Jena in Germany. Dr. Herbert H. Jasper was a Canadian neuroscientist who studied the mechanisms underlying epilepsy and seizures. His work looked at the EEG or the method of recording electrical signals from neurons to understand sleep, consciousness, and epilepsy. His collaboration with Wilder Penfield, a Canadian neurophysiologist, revolutionized EEG in epilepsy. 

How does an EEG work?

A scalp-EEG is a pain-free, non-invasive technique where electrodes are placed on the person’s skull. The EEG traces represent differences in electrical potential between electrodes. 

What causes these potential differences? Neurons communicate with each other by using electrical signals; however, the contribution of each individual neuron to the resulting EEG trace is extremely small. Hence, the EEG will pick up a signal only when a few thousand neurons are firing simultaneously. 

This signal is amplified to give us the ultimate readout. An EEG cannot be used to tell what someone is thinking. However, it can give us information about whether or not someone is thinking, asleep, or awake. 

In this figure (adapted from Neuroscience: Exploring the Brain, 3rd Edition), we can see the neurons (pyramidal cells) with active synapses. This means that they are actively conducting electricity, which is measured by the EEG electrode placed on the scalp. 

Where can I learn more about EEGs?

This website has information on how to make sense of an EEG, how to prepare for an EEG, and different kinds of EEG recordings.

Authored by: Sloka Iyengar PhD | Basic Science Editor on 9/2015
Reviewed by: Patricia O. Shafer RN MN | Associate Editor / Community Manager on 2/2017