CHICAGO, March 29 (Xinhua) -- By studying electrical activity in mouse brains, researchers at Washington University School of Medicine in St. Louis found that the ultra-slow waves detected on an MRI scan of the brain play a central role in how the complex brain coordinates itself and that the waves are directly linked to consciousness.
The study is published on March 29 in the journal Neuron.
The researchers approached the mystery of the ultra-slow waves using two techniques that directly measure electrical activity in mice brains. In one, they measured such activity on the cellular level. In the other, they measured electrical activity layer by layer along the outer surface of the brain.
They found that the ultra-slow waves spontaneously started in a deep layer of mice's brains and spread in a predictable trajectory. As the waves passed through each area of the brain, they enhanced the electrical activity there. Neurons fired more enthusiastically when a wave was in the vicinity.
Moreover, the ultra-slow waves persisted when the mice were put under general anesthesia, but with the direction of the waves reversed.
"There is a very slow process that moves through the brain to create temporary windows of opportunity for long-distance signaling," said first author Anish Mitra at Washington University. "The way these ultra-slow waves move through the cortex is correlated with enormous changes in behavior, such as the difference between conscious and unconscious states."
The fact that the waves' trajectory changed so dramatically with state of consciousness suggests that ultra-slow waves could be fundamental to how the brain functions.
"Your brain has 100 billion neurons or so, and they have to be coordinated," said senior author Marcus Raichle, a professor of medicine as well as a professor of radiology at the School of Medicine. "These slowly varying signals in the brain are a way to get a very large-scale coordination of the activities in all the diverse areas of the brain. When the wave goes up, areas become more excitable; when it goes down, they become less so."
The researchers now are studying whether abnormalities in the trajectory of such ultra-slow waves could explain some of the differences seen on MRI scans between healthy people and people with neuropsychiatric conditions such as dementia and depression.
"If you look at the brain of someone with schizophrenia, you don't see a big lesion, but something is not right in how the whole beautiful machinery of the brain is organized," said Raichle. "What we've found here could help us figure out what is going wrong."
