Brain to Z: E is for EEG

To mark 100 years since electroencephalography, or EEG, was invented, and because it starts with the right letter of the alphabet, it’s going to be the subject of this edition of Brain to Z: where we take a subject from the world of neuroscience, and make it as simple as A, B, C...

From the word ‘electro,’ relating to electricity, ‘encephalos,’ the Greek word for brain, and ‘graph’ from the Greek word for something written or drawn, put simply, EEG is a medical test to monitor electrical activity in the brain.

When Hans Berger was first experimenting with the technique in 1924, he was trying to find the physical origin of a phenomenon he called ‘psychic energy.’ He believed that human minds could communicate with each other through space, and so he was searching for the biological mechanism, which led him to record electrical activity.

Using 2 small metallic discs connected by wire, one on the conductive scalp and the other attached to the ear (a neutral reference), Berger observed alternative current flows in the wire which were proportional to the electrical activity sensed by the disc on the scalp.

Thus, EEG provides a window into the living brain, with a continuous electrical readout of what is happening inside our heads. One of the most important advancements in our understanding of the brain to come out of the development of EEG was the revelation that neural activity oscillates at specific frequencies. Berger himself noted that he was seeing patterns of activity that cycled eight to 12 times per second, or 8 to 12 hertz, which are called alpha oscillations, but there is a mix of different frequencies certain parts of the brain can tune into when trying to communicate with each other.

EEG has since been developed to cover a much broader region of the head, using many electrodes, rendering it an invaluable tool for running medical tests to diagnose and to guide treatment for several brain disorders, and for research experiments into which regions of the brain are responsible for certain functions.

On the clinical front, back in 1934, a group of Boston physicians observed the rhythmic EEG spike-wave appearance of seizures in patients with epilepsy. This was the first time the symptoms and behaviour of patients during seizures were correlated to a brain signal occurring in tandem. Now, EEG is commonly used to diagnose epilepsy and sleep disorders by recognising characteristic patterns and matching them up to symptoms of disease.

Theta oscillations, which have a frequency of 4-8 hertz, are important for linking parts of the brain involved in memory encoding and retrieval in animals and humans. This has formed the basis of treatments involving specific mental activities (such as mindfulness meditation) to induce neural oscillations that will improve communication between these regions, helping with memory problems.

All this made possible thanks to the pioneering work of Hans Berger’s work to uncover a potential basis for telepathy. And, in something of a full circle moment, earlier this year on the Naked Scientists, 100 years after the first EEG, Sam Nastase from Princeton University told us about his work using EEG to uncover the identical brain activity observed in people having a conversation. By using AI to analyse the words they were using and the overall context, and comparing this to the electrical activity of both participants’ brains, he proved that they really were ‘on the same wavelength.’

SM: ‘We can see this really beautiful dynamic where just prior to each word, word by word, as I'm speaking like this. Just prior to each word, the model can capture linguistic content starting to emerge in my brain activity prior to the articulation of the word. And then as soon as I say the word, we can see that same linguistic content reemerging in your brain as you hear the word and as you process the meaning of it.’

While it’s not quite telepathy, it looks like Berger was on to something after all!