Neuroscientists have long believed that vision is processed in the brain along circuits made up of neurons, similar to the way telephone signals are transferred through separate wires from one station to another.
But scientists at Georgetown University Medical Center discovered that visual information is also processed in a different way, like propagating waves oscillating back and forth among brain areas. Their findings are published in the July 5 issue of the journal Neuron.
"What we found is that signals pass through brain areas like progressive waves, back and forth, a little bit like what fans do at baseball games," said the study's corresponding author, Jian-young Wu, Ph.D., an associate professor in the Department of Physiology and Biophysics at Georgetown. Just as the stadium wave is coordinated and travels through the crowd, a collective pattern emerges from the activities of millions of neurons in the visual areas, he said, explaining, "It simply makes sense that brain function is the result of large numbers of neurons working together."
This challenges longstanding notions about how the brain processes sensory information, Wu said. "One traditional model theorizes that neurons are hooked together into specific circuits. However, new imaging methods tell us that there are more than just circuits."
Wu and his colleagues visualized wave-like patterns in the brain cortex using a new method called voltage sensitive dye imaging. They used a special dye that binds to the membrane of neurons and changes color when electrical potential passes along active neurons.
Traditionally, scientists have studied brain activity by placing electrodes in the brain and measuring the electrical currents that are related to neuronal activity. Because it is difficult to put many electrodes into the brain, the spatiotemporal pattern of the neuronal activity has long been ignored. "Now, with optical methods, we can watch sequential activation of different sectors of the visual cortex when the brain is processing sensory information," Wu said.