For many years, the brain has been thought of as a biological computer that processes information via traditional circuits, with data zipping directly from one cell to the next. While that model remains correct, a new study conducted by Salk Professor Thomas Albright and Staff Scientist Sergei Gepshtein shows that the brain also parses information in a second, quite distinct way: through the interplay of waves of neuronal activity. The findings, which will be published in Science Advances on April 22, 2022, will aid researchers’ understanding of how the brain processes information.
Salk’s Vision Center Laboratory says that “we now have a fresh knowledge of how the computational machinery of the brain works,” says Albright, the Conrad T. Prebys Chair in Vision Research and director of the Vision Center Laboratory. “The model helps explain how the brain’s basic conditions might alter, impacting people’s attention, focus, or ability to comprehend information.”
“We now have a new understanding of how the computational machinery of the brain is working. The model helps explain how the brain’s underlying state can change, affecting people’s attention, focus, or ability to process information.”says Albright, the Conrad T. Prebys Chair in Vision Research and director of Salk’s Vision Center Laboratory.
Researchers have long known that electrical activity waves exist in the brain during both sleep and waking. However, the basic theories of how the brain processes information—particularly sensory information such as the sight of a light or the ring of a bell—have revolved around information being detected by specialized brain cells and then relayed from one neuron to the next.
However, this classic model of the brain could not explain how a single sensory cell might react so differently to the same item under different conditions. When an animal is especially vigilant, a cell may become activated in reaction to a brief flash of light, but will remain inactive in response to the same light if the animal’s attention is focused on something else.
Gepshtein compares the new knowledge to wave-particle duality in physics and chemistry, which holds that light and matter have both particle and wave qualities. In some cases, light behaves as if it were a particle (also known as a photon). In other cases, it behaves as if it were a wave. Particles are restricted to a single area, whereas waves are spread across multiple locations. Both perspectives on light are required to describe its complex behavior.
“The classic understanding of brain function defines brain activity as a neuron-to-neuron connection. Because each neuron is constrained to a certain area, this viewpoint is analogous to describing light as a particle. “Gepshtein, head of the Salk Institute’s Collaboratory for Adaptive Sensory Technologies, agrees. We discovered that in some cases, brain activity is better represented as a wave interaction, similar to how light is described as a wave. Understanding the brain requires both perspectives. “
Given the “particle” approach to the brain, some sensory cell features discovered in the past were difficult to explain. The team analyzed the activity of 139 neurons in an animal model to better understand how the cells coordinated their response to visual information in the current study. They developed a mathematical framework to evaluate neuron activity and forecast novel events in partnership with Loughborough University physicist Sergey Savel’ev.
They discovered that the interaction of tiny waves of activity, rather than individual neurons, was the best method to explain how neurons behaved. Instead of a burst of light activating specialized sensory cells, the researchers demonstrated how it generates distributed patterns of activity over several nearby cells, with alternating peaks and troughs of activation—much like ocean waves.
When these waves are created in separate parts of the brain at the same time, they unavoidably collide. When two peaks of activity collide, they generate even more activity, but when a trough of low activity collides with a peak, it may wipe it out. This is known as “wave interference.”
So when you’re out in the world, all these different waves are formed. “There are many, many inputs when you’re out in the world, and so all these different waves are formed,” Albright explains.”How all these waves interact determines the net response of the brain to the world around you.”
The researchers created an accompanying visual experiment to evaluate its mathematical model of how neural waves occur in the brain. Two subjects were asked to find a thin, faint line (“probe”) on a screen that was surrounded by various light patterns. The researchers discovered that how well participants did this task depended on where the probe was located. The ability to detect the probe increased in some places and decreased in others, generating a spatial wave predicted by the model.
“Your ability to see this probe at every site will be determined by how brain waves superimpose at that location,” says Gepshtein, who is also a member of Salk’s Center for the Neurobiology of Vision. “And we’ve now proposed how the brain mediates that.”
The knowledge of how brain waves interact is significantly more important than describing this optical illusion. The researchers assume that the same types of waves are created and interact with each other in all parts of the brain’s cortex, not only in the area responsible for visual information analysis. That is, waves generated by the brain, as well as tiny cues in the surroundings or internal moods, can alter the waves generated by sensory inputs.
According to the researchers, this could explain why the brain’s response to something can change from day to day.
Ambarish Pawar of Salk and Sunwoo Kwon of the University of California, Berkeley are also co-authors of the paper.