The electrical oscillations we call brain waves have fascinated scientists and the public for more than a century. But it is still controversial whether they have functions or just represent the activity of the brain like the buzz of an engine. Many neuroscientists hypothesize that if brain waves have functions, they are also achieved through synchronous oscillation at different locations. However, as the research continues to deepen, researchers have discovered that many brain waves are actually "moving waves" that move like ocean waves.

Now a research team at Columbia University in the United States has conducted a new study. Joshua Jacobs, a neurological scientist who heads the team, proposed that travel waves are very common in the human cortex and show varying degrees of organization according to the degree of performance of the brain performing tasks. This shows that brain waves are behavior-related and are in line with previous studies. Previous research has proposed that brain waves are an important but neglected brain mechanism, which has an impact on memory, perception, attention and even consciousness.

Brain waves were first discovered through EEG technology. Researchers have noticed a range of brain wave activities at different frequencies. The slowest brain waves appear in deep sleep and continue to improve as consciousness and attention levels improve. Deciphering EEG data is very difficult because it is difficult to determine the location of brain wave activity, and transmission in the brain can blur the signal. The latest study leverages a new technology called electrocortical grammar (ECoG). This technology directly places electrodes on the brain surface, minimizing signal distortion and greatly improving spatial resolution.

Scientists have proposed many points to describe the possible role of brain waves. A mainstream theory believes that synchronous oscillation binds information from different locations of the brain to describe the same event, such as different characteristics of an object (shape, color, and movement, etc.). There is also a similar view that they can promote information transmission between different regions. But these assumptions require brain wave synchronization and produce standing waves, not traveling waves.

But this is impossible because traveling waves have different characteristics, which may represent information about past states in other brain regions. The propagation of brain waves in the brain is similar to that of sounds in the air, which makes them a potential mechanism for conveying information between different regions.

These views have been around for decades, but most neurologic scientists rarely care about them. One possible reason is that most of the reports of traveling waves before this described such waves only without determining their significance. "If you ask a general neuroscientist, they would say it's a collateral phenomenon, like a buzz of an engine," said Terry Sejnowski, a neuroscientist at the Salk Institute of Biology. "And since no one has ever linked it directly to any behavior or function, it's not considered an important thing."

The research tools used by researchers may also have some relationship. Today's mainstream neurologic scientists explored the origin of brain waves when studying neuronal behavior with needle-shaped microelectrodes. In one experiment, pioneers in this field noticed that neurons send brain waves differently than other neurons. They infer that this time must be important, and combined the responses of multiple experiments to obtain an "average brain wave sending rate." This has also become a standard way to quantify neural activity, but the cycle of neurons may bring variability, so researchers habitually ignore the time information needed to reveal the traveling waves.

Sejnowski said this conceptual framework comes from the activity of a single neuron, but brain function is actually accomplished through the interaction of countless neurons. Since traveling waves are composed of many neuronal activities in the brain, techniques applied to single neurons cannot detect them. But new technologies that have emerged over the past decade have enabled us to monitor multiple neurons simultaneously. "This opens another door for us," said Sejnowski. "For the first time we have tools and technologies to understand what is really going on, but it will take a generation to be accepted into the already solidified field of neuroscience."

Optical methods such as pressure sensitive chromatography allow researchers to see electrical changes in thousands of neurons at the same time, but these methods cannot be applied to humans due to risks. Electrocorticography is usually used in patients with epilepsy to check for epilepsy. Therefore, the scientists who conducted the latest study recruited 77 epilepsy patients with cortical EEG electrodes and explored the travel waves. They first look for groups of electrodes that vibrate at the same frequency, and then evaluate which groups of electrodes truly represent the traveling wave by analyzing the time of the vibration.

Next, the research team gave the testers a memory task, and when the testers were prompted to recall the memory information, the travel waves in their frontal and temporal lobes became more organized. These brain waves go from moving in all directions to being consistent in most directions. Importantly, this trend change is correlated with their response rate. "The better the task performance, the more consistent the brain waves are. This suggests that we have discovered a new way to measure brain activity, and this study may also lead to new brain-computer interface technologies," Jacobs said.

These findings should help some researchers to dispel doubts about the importance of this brain wave. David Alexander, a psychologist at the University of Lefen, Belgium, said: "This study is a huge contribution to the study of cortical travel waves and increases our understanding of their role in human cognition. This study will really help people to eliminate the concern that these brain waves are just vague signals that are transmitted in the head." But he also believes that the authors of the research paper made erroneous judgments about the novelty of these findings and did not acknowledge some previous studies.

He claims that previous research on travel waves has shown that they can be induced in memory tasks. He pointed out that a 2002 brain wave study has found that the time of wave direction reversal is related to memory performance. Interestingly, in a 2008 brainwave study, he found that people who had already had schizophrenia had fewer brainwaves in memory tasks than healthy individuals. This indicates that there is a correlation between differences in travel wave performance and psychiatric symptoms.

He also claimed that the research team's method of evaluating travel waves is similar to the one he used in a 2016 study. "Alexander's research is really interesting, but we are not sure if his findings involve the same signal as our study. His report says it involves the entire brain region, and our findings are limited to specific areas." He also pointed out that there are also differences between the signal recording techniques of the two studies and the recorded signal characteristics.

Determining the importance of traveling waves brings new directions to the field of neuroscience. "The discovery of such a wide range of oscillations originated from moving waves, suggesting that they are involved in the coordination activities of different areas of the brain. These findings have also opened up new areas of research for research, such as letting us understand the composition of this coordination," Jacobs said. He believes that moving waves can convey information, at least the current research conclusion is.

There is another theory that traveling waves regulate neuron sensitivity by constantly moving back and forth across the cortex, just like an attention searchlight that shuttles through virtual information processing areas of the brain. "The concept of travel waves is related to how you maintain the state where the cortex is most sensitive to other input information. There is no doubt that people's interest in travel waves will continue to grow. What you are seeing now is a transition from one conceptual framework to another completely new framework. It's a shift in thinking mode."