Electroencephalography, or EEG, was invented 100 years ago. In the years since the invention of this device to monitor the electricity in the brain, it has had an incredible impact on the way scientists study the human brain.
Since its first use, the EEG has shaped researchers’ understanding of cognition, from perception to memory. It has also been important in diagnosing and guiding treatment for multiple brain disorders, including epilepsy.
I am a cognitive neuroscientist who uses EEG to study how people remember events from their past. The 100th anniversary of the EEG is an opportunity to reflect on the significance of this discovery in neuroscience and medicine.
Discovery of EEG
On July 6, 1924, psychiatrist Hans Berger performed the first EEG recording on a human, a 17-year-old boy undergoing neurosurgery. At the time, Berger and other researchers were performing electrical recordings on the brains of animals.
What set Berger apart was his obsession with finding the physical basis of what he called psychic energy, or mental effort, in humans. Through a series of experiments he conducted in his early career, Berger measured brain volume and temperature to study changes in mental processes such as intellectual work, attention, and desire.
He then moved on to recording electrical activity. Although he recorded the first traces of EEG in the human brain in 1924, he did not publish the results until 1929. The intervening five years were a difficult period of self-doubt about the source of the EEG signal in the brain and refining the experimental setup. Berger recorded hundreds of EEGs from multiple subjects, including his own children, with both experimental successes and setbacks.
Finally convinced of his results, he published a series of articles in the journal Archiv für Psychiatrie and hoped to win a Nobel Prize. Unfortunately, the research community doubted his results and years passed before anyone else used EEG in their own research.
Berger was eventually nominated for a Nobel Prize in 1940. However, due to World War II and the German occupation of Norway, no Nobel Prizes were awarded in any category that year.
Neural oscillations
When many neurons are active at the same time, they produce an electrical signal strong enough to spread instantly through the conductive tissue of the brain, skull and scalp. EEG electrodes placed on the head can record these electrical signals.
Since the discovery of EEG, researchers have shown that neural activity oscillates at specific frequencies. In his first EEG recordings in 1924, Berger noted the predominance of oscillatory activity that cycled eight to twelve times per second, or 8 to 12 hertz, called alpha oscillations. Since the discovery of alpha rhythms, many attempts have been made to understand how and why neurons oscillate.
Neural oscillations are thought to be important for effective communication between specialized brain areas. For example, theta oscillations that cycle from 4 to 8 hertz are important for communication between brain areas involved in memory encoding and retrieval in animals and humans.
Researchers then investigated whether they could alter neural oscillations and thus affect the way neurons communicate with each other. Studies have shown that many behavioral and noninvasive methods can alter neural oscillations and lead to changes in cognitive performance. Performing specific mental activities can cause neural oscillations in the frequencies that those mental activities use. For example, my team’s research found that mindfulness meditation can increase theta frequency oscillations and improve memory retrieval.
Noninvasive brain stimulation methods can target frequencies of interest. For example, my team’s ongoing research has found that brain stimulation at theta frequency can lead to improved memory retrieval.
EEG has also led to important discoveries about how the brain processes information in many other cognitive domains, including how people perceive the world around them, how they focus their attention, how they communicate through language, and how they process emotions.
Diagnosing and treating brain disorders
Nowadays, EEG is widely used to diagnose sleep disorders and epilepsy and to guide the treatment of brain disorders.
Scientists are using EEG to see if memory can be improved with noninvasive brain stimulation. Although the research is still in its early stages, there are already some promising results. For example, one study found that noninvasive brain stimulation at gamma frequency – 25 hertz – improved memory and neurotransmitter transmission in Alzheimer’s disease.
A new type of noninvasive brain stimulation called temporal interference uses two high frequencies to induce neural activity equal to the difference between the stimulation frequencies. The high frequencies can better penetrate the brain and reach the target area. Researchers recently tested this method in humans using 2,000 hertz and 2,005 hertz to send 5 hertz of theta frequency to a brain region important for memory, the hippocampus. This led to improvements in remembering the name associated with a face.
While these results are promising, more research is needed to understand the exact role that neural oscillations play in cognition and whether altering them can lead to long-term cognitive improvement.
The future of EEG
The 100th anniversary of the EEG provides an opportunity to reflect on what it has taught us about how the brain works and what this technology could do in the future.
In a study commissioned by the journal Nature Human Behaviour, more than 500 researchers who use EEG in their work were asked to make predictions about the future of the technology. What will be possible in the next 100 years of EEG?
Some researchers, including myself, predict that we will use EEG to diagnose brain disorders and create targeted treatments. Others expect that affordable, portable EEG will be widely used to improve cognitive function at home or be seamlessly integrated into virtual reality applications. The possibilities are enormous.
This article is republished from The Conversation, a nonprofit, independent news organization that brings you facts and reliable analysis to help you understand our complex world. It was written by: Erika Nyhus, Bowdoin College
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Erika Nyhus receives funding from the National Institute of Health and the National Institute of Mental Health.