Scientists show how the brain responds differently to seeing the same thing under different conditions – ScienceDaily

For years, the brain was thought of as a biological computer that processes information through traditional circuits, with data transmitted directly from one cell to another. While this model remains accurate, a new study led by Salk professor Thomas Albright and faculty scientist Sergei Gepstein shows that there is also a second, entirely different way in which the brain distributes information: through the interactions of neural activity waves. The results are published in science progress On April 22, 2022, it helped researchers better understand how the brain processes information.

“We now have a new understanding of how the brain’s computational machinery works,” says Albright, Konrad T. Prebis chair in vision research and director of the Salk Vision Center Laboratory. “The model helps explain how the base state of the brain can change, affecting people’s attention, focus, or ability to process information.”

Researchers have long known that there are waves of electrical activity in the brain, both during sleep and wakefulness. But the basic theories about how the brain processes information — especially sensory information, such as the sight of a light or the sound of a bell — revolves around information that is detected by specialized brain cells and then transmitted from one neuron to another like a relay.

However, this traditional brain model does not explain how a single sensory cell can react differently to the same thing under different conditions. A cell may be activated, for example, in response to a rapid flash of light when the animal is particularly alert, but remain inactive in response to the same light if the animal’s attention is focused on something else.

Gepshtein likens the new understanding of wave-particle duality in physics and chemistry – the idea that light and matter have properties of both particles and waves. 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. The particles are confined to a specific location, and the waves are distributed across many locations. Both views are necessary to explain its complex behaviour.

“The traditional view of brain function describes brain activity as an interaction between neurons. Because each neuron is confined to a specific location, this view is like describing light as a particle,” says Gepshtein, director of Salk’s Collaboratory for Adaptive Sensory. techniques. “We have found that in some situations, brain activity is better described as an interaction of waves, which is similar to describing light as a wave. Both views are essential to understanding the brain.”

Some of the characteristics of sensory cells observed in the past were not easy to explain by looking at the way the “particle” is in the brain. In the new study, the team observed the activity of 139 neurons in an animal model to better understand how cells coordinate their response to visual information. Together with physicist Sergey Savelyev of Loughborough University, they created a mathematical framework for interpreting neuronal activity and predicting new phenomena.

They discovered that the best way to explain how neurons behave was through the interaction of microscopic waves of activity rather than the interaction of individual neurons. Instead of a flash of light activating specialized sensory cells, the researchers showed how they create distributed patterns: waves of activity across many neighboring cells, with alternating peaks and troughs of activation — like ocean waves.

When these waves are simultaneously generated in different places in the brain, they inevitably collide with each other. If two activity peaks meet, they generate higher activity, while if a lower activity trough meets peak activity, it may cancel it out. This process is called wave interference.

“When you’re outside, there are many, many inputs, and so all these different waves are generated,” Albright says. “The brain’s pure response to the world around you has to do with how all of these waves interact.”

To test their mathematical model of how nerve waves occur in the brain, the team designed an accompanying visual experiment. Two people were asked to detect a thin faint line (“probe”) located on a screen surrounded by other light patterns. The researchers found that how well people performed this task depended on where the probe was located. The ability to detect the probe was raised in some locations and low in others, forming a spatial wave predicted by the model.

“Your ability to see this probe in each location will depend on how the neuronal waves are superimposed at that location,” says Gepshtein, who is also a member of Salk’s Neurobiology Center of Vision. “And we have now suggested how the brain mediates this.”

Exploring how nerve waves interact goes far beyond explaining this optical illusion. The researchers hypothesize that the same types of waves are generated – and interact with each other – in every part of the brain’s cortex, not just the part responsible for analyzing visual information. This means that the waves generated by the brain itself, through subtle cues in the environment or internal mood, can alter the waves generated by sensory input.

The researchers say this may explain how the brain’s response to something can change from day to day.

Other co-authors on the research include Ambarish Bawar of Salk and Snow Kwon of the University of California, Berkeley.

The work was supported in part by the Salk Institute’s Sloan Schwartz Center for Theoretical Neurobiology, the Kavli Institute for the Brain and Mind, the Conrad T. Prebys Foundation, the National Institutes of Health (R01-EY018613, R01-EY029117) and the Engineering and Physical Sciences Research Council (EP/S032843/1). ).

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