A new study demonstrates that competition between cells improves memory circuits in the brain.
The findings, published in Neuron, will aid the search for the causes of neurological disorders such as Alzheimer’s disease, autism and schizophrenia.
“Much of our understanding of the brain’s wiring has come from studying our sensory and motor systems, but far less is understood about the mechanisms that organize neural circuits involved in higher brain functions, like learning and memory,” said senior author Hisashi Umemori, M.D., Ph.D.
Brain cells grow and extend along pathways to link different parts of the brain, Umemori said. As the brain develops, these connections fine-tune themselves and become more efficient. Problems with this refinement process may be responsible for some neurological disorders.
“We wanted to know how brain circuits become more efficient during the brain’s development,” Umemori said. “Does the brain choose to keep good connections and get rid of bad ones and, if so, how?”
To examine how neural activity organizes memory circuits, researchers used mice that had been genetically modified so that neurons of interest purposefully could be switched off.
Scientists studied the connection between the hippocampus, which is crucial for learning and memory, and the cerebral cortex, which is key for perception and awareness, as well as other cognitive functions. They deactivated about 40 percent of the neurons in the connection and, over a matter of days, watched as the brain eliminated the inactive neural connections and kept only the active ones.
A subsequent part of the experiment showed that if all the neurons were deactivated, their connections were not eliminated.
“This tells us that the brain has a way of telling among a group of neurons which connections are better than others,” Umemori said. “The neurons are in competition with each other. So when they’re all equally bad, none can be eliminated.”
The researchers also looked at a part of the hippocampus called the dentate gyrus, which is only one of two areas of the brain that continues to generate new neurons throughout life. Here they found a second distinct type of competition: newborn cells were competing with mature cells, rather than competition occurring between mature cells.
When scientists blocked the dentate gyrus’ ability to make new cells, the elimination stopped and the brain kept the existing cells even if they were deactivated.
The message from this is that efficient learning and memory occurs when the brain eliminates bad connections, Umemori explains.
He added, “The better we understand how these mechanisms work, the better we’ll be able to understand what’s happening when they aren’t working.”
Source: University of Michigan