Imagine going to the orchestra and instead of a symphony, each musician plays solo, one movement at a time – a violinist during one piece, a cellist during the next, perhaps a clarinetist after that.
Until recently, that is the equivalent of what neuroscientists have done: recording the spikes of each neuron individually.
However, a shift is underway as researchers embrace a grander perspective that has led to a remarkable discovery: mysterious spiral brain waves that dance in the outer layer of the brain – the cerebral cortex – which may play a crucial role in organizing complex brain activity.
The cerebral cortex, a convoluted outer region of the brain, takes center stage in numerous high-level functions including reasoning, emotion, thought, memory, language and consciousness. This intricately folded area accounts for nearly half of the brain's mass, playing an integral role in our cognitive experience.
The research, published in June by University of Sydney and Fudan University scientists in Nature Human Behaviour, may lead to fresh pathways of understanding brain disorders, like Alzheimer's disease and cerebral palsy, the authors say.
"These emergent waves enable us to understand how different brain regions or networks are effectively coordinated during cognitive processing," senior author and University of Sydney Associate Professor Pulin Gong told Salon. "These emergent waves enable us to understand how different brain regions or networks are effectively coordinated during cognitive processing."
The scientists took magnetic resonance imaging (fMRI) brain scans of 100 young adults between the ages 22 and 35. Participants engaged in cognitive tasks, such as solving math problems, leading to a fascinating observation: the waves exhibited a mesmerizing interplay of clockwise and counterclockwise rotations across diverse brain regions, frequently converging at the intersections of distinct brain networks.
The team analyzed the imaging data collected as part of the Human Connectome Project (HCP) using methods employed by fluid physicists studying wave patterns in turbulent flows. What has been used to, for example, create more efficient piping systems, is now helping scientists understand the brain better. The HCP is an open science project containing brain scans from hundreds of participants, who are monitored either while sitting quietly in the scanner in a resting state or performing one of several simple tasks.
The spiral waves are brain signals emerging from the collective activities of millions – potentially even billions – of neurons at the microscopic level.
"One key characteristic of these brain spirals is that they often emerge at the boundaries that separate different functional networks in the brain," Ph.D. student and lead author Yiben Xu said in a statement. "Through their rotational motion, they effectively coordinate the flow of activity between these networks. In our research we observed that these interacting brain spirals allow for flexible reconfiguration of brain activity during various tasks involving natural language processing and working memory, which they achieve by changing their rotational directions."
This large-scale approach to neuroscience could uncover various mechanisms underlying disorders of the nervous system, and potentially even lead to new diagnostic tests, the authors say.
In future work, the authors plan to integrate experimental recordings with modeling studies to better understand the mechanisms underlying the brain spirals and delve deeper into their functional roles in cognition.
The scientists behind this recent paper are not alone in their study of brain waves. Lyle Muller, assistant professor of applied mathematics at the University of Western Ontario, leads a lab that has been exploring the links between traveling waves during sleep and neural plasticity – the process through which the brain learns and integrates new memories. This critical function deteriorates during neurodegenerative diseases.
Muller and his colleagues found that rotating wave patterns called spindles that occur during non-REM sleep – when our brains, breathing and heart rate slow – could enable plasticity required for storing memories during sleep. Because these spindles change with aging, understanding these wave patterns better could provide insights into how plasticity breaks down with disease, Muller said.
"While this is a fundamentally new way of studying the brain, understanding neural activity with a dynamic, systems-level approach has a lot of promise for understanding disorders of the nervous system," Muller told Salon. "Understanding the link between traveling waves, sleep and the aging process, by analyzing direct electrical recordings that have a strong link to the activity of single neurons, is a priority for future research in my lab."
The spiral waves seen by Gong and his team span several brain areas, Muller said and could represent an interesting mechanism for coordinating flow of information through the neural circuits of the brain.But, he said it is not yet clear how.
"Testing whether these spiral wave patterns can lead to new predictions of neural circuit dynamics and behavior, and confirming their specific underlying mechanism through computational modeling, will tell us whether these new spiral wave patterns are telling us something interesting about the symphony of neurons in the human brain," Muller said, "or whether they may be more related to supplementary functions, like the tuning of the instruments or the lighting in the performance hall."
