Electroencephalography, or EEG, was invented over 100 years ago. In the years since this device for monitoring brain electricity was invented, 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, and has also been important in guiding the diagnosis and treatment of 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 importance of this discovery in neuroscience and medicine.
Discovery of EEG
On July 6, 1924, a psychiatrist Hans Berger He made his first EEG recording on a 17-year-old boy who was undergoing brain surgery. At the time, Berger and other researchers were making electrical recordings in animals’ brains.
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 spanning the early years of his career, Berger measured brain volume and temperature to study changes in mental processes such as intellectual work, attention, and desire.
He then turned to recording electrical activity. Although he recorded the first traces of an EEG in the human brain in 1924, he did not publish his results until 1929. The intervening five years were a time of self-doubt about the source of the EEG signal in the brain and a tortuous process of developing experimental setups. Berger recorded hundreds of EEGs on multiple subjects, including his own children, with both experimental successes and failures.
Eventually convinced of his results, he published a series of papers in the journal Archiv für Psychiatrie and hoped to win the Nobel Prize. Unfortunately, the research community doubted his results, and it took years before anyone else began using EEG in their own research.
Berger was eventually nominated for the 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 throughout the conductive tissue of the brain, skull, and scalp. EEG electrodes placed on the head can record these electrical signals.
Since the discovery of the EEG, researchers have shown that neural activity oscillates at specific frequencies. Berger, in his first EEG recordings in 1924, noted a predominance of oscillatory activity that varied between eight and 12 times per second, or 8 to 12 hertz, which he 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 regions. For example, theta oscillations, which rotate at 4 to 8 hertz, are important for communication between brain regions involved in memory encoding and retrieval in animals and humans.
The researchers then looked at whether these could alter neural oscillations and therefore affect how neurons talk to each other. Studies have shown that many behavioral and noninvasive methods can alter neural oscillations and lead to changes in cognitive performance. Engaging in certain mental activities can cause neural oscillations at the frequencies used by those mental activities. For example, my team’s research found that mindfulness meditation can increase theta frequency oscillations and improve memory recall.
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 improve memory recall.
EEG has also led to important discoveries about how the brain processes information in many other cognitive areas, including how people perceive the world around them, focus their attention, communicate through language, and process emotions.
Diagnosis and treatment of brain disorders
EEG is now widely used in the diagnosis of sleep disorders and epilepsy and in guiding the treatment of brain disorders.
Scientists are using EEG to see if memory can be improved with noninvasive brain stimulation. While the research is still in its infancy, there have been 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 cause neural activity equal to the difference between the stimulation frequencies. Higher frequencies can better penetrate the brain and reach the targeted area. Researchers recently tested this method in humans using 2,000 hertz and 2,005 hertz, and delivered a 5-hertz theta frequency to the hippocampus, a brain region important for memory. This led to improvements in remembering a name associated with a face.
While these results are promising, more research is needed to understand the exact role 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 this technique has taught us about brain function and what this technique may do in the future.
In a survey 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 technique. What will be possible in the next 100 years of EEG?
Some researchers, including myself, predict that we will use EEG to diagnose and create targeted treatments for brain disorders. Others predict that an affordable, wearable EEG will be widely used to enhance cognitive function at home or seamlessly integrated into virtual reality applications. The possibilities are vast.
This article is republished from The Conversation, a nonprofit, independent news organization that brings you facts and trusted analysis to help you understand our complex world. By Erika Nyhus Bowdoin College
Read more:
Erika Nyhus receives funding from the National Institutes of Health and the National Institute of Mental Health.