Brain cycling on and off all time: study

New research finds that small regions of the brain cycle in and out of sleep, even when awake, on the order of seconds or fractions of seconds.

In addition, findings from the research, published in the journal Science, indicate that neurons are better at responding to the world when they have cycled into the more active, or "on," state, and they spend more time in the on state when paying attention to a task.

"Selective attention is similar to making small parts of your brain a little bit more awake," said Tatiana Engel, co-lead author on the research and a postdoctoral fellow in the lab of Tirin Moore, one of the senior authors and a professor of neurobiology at Stanford University in northern California on the U.S. west coast.

To understand these newly discovered cycles, the researchers, including the other co-lead author and former graduate student Nicholas Steinmetz, used what amounts to sets of very sensitive pins that can record activity from a column of neurons in the brain.

The probe allowed the team to see for the first time that all the neurons in a given column cycled together between firing very rapidly then firing at a much slower rate, similar to coordinated cycles in sleep.

"During an on state the neurons all start firing rapidly," Kwabena Boahen, a professor of bioengineering and electrical engineering at Stanford and a senior author on the paper, was quoted as saying in a news release.

"Then all of a sudden they just switch to a low firing rate. This on and off switching is happening all the time, as if the neurons are flipping a coin to decide if they are going to be on or off."

Those cycles weren't as visible when awake because the wave doesn't propagate much beyond that column, unlike in sleep when the wave spreads across almost the entire brain and is easy to detect.

A question that comes out of the research is why the neurons cycle into a lower activity state when we're awake. Why not just stay in the more active state all the time?

One answer could relate to energy. "There is a metabolic cost associated with neurons firing all the time," Boahen said.

The brain uses a lot of energy and maybe giving the cells a chance to do the energetic equivalent of sitting down allows the brain to save energy.

Also, when neurons are very active, they generate cellular byproducts that can damage the cells. Noting that "this paper suggests places to look for these answers," Engel said the low-activity states could allow time to clear out this neuronal waste. Endit