Sunday, 4 September 2016

The brain uses backward instant replays to remember important travel routes

 Experiments with food rewards show how rats form some memories

Date: August 25, 2016
Source: Johns Hopkins Medicine

You're shipwrecked on a desert island. You wander from your base camp in desperation, searching for water. Suddenly, a stream appears! The water is fresh and clear, the best you've ever tasted. There's just one problem: There's no trace of how you got there, and you're not sure you can find it again next time.

Now Johns Hopkins neuroscientists believe they have figured out how some mammals' brains -- in this case, rats -- solve such navigational problems. If there's a "reward" at the end of the trip, like the chocolatey drink used in their study, specialized neurons in the hippocampus of the brain "replay" the route taken to get it, but backward. And the greater the reward, the more often the rats' brains replay it.

According to the researchers, the finding suggests that both the presence and magnitude of rewards influence how and how well the hippocampus forms memories. The hippocampus is a vertebrate brain structure long known to be vital for making and storing memories, and in so-called spatial relations.

A summary of the work will appear online Aug. 25 in the journal Neuron.

"We've long known that the brains of awake animals have these replay events when they pause in their travels. Now we know that the information in those replays is influenced by reward, probably to help solidify those memories," says David Foster, Ph.D., associate professor of neuroscience at the Johns Hopkins University School of Medicine.

As animals -- including humans -- scurry about or otherwise travel through an environment, their brain waves oscillate up and down, Foster notes. When they pause, and when they are in slow-wave sleep, their brain waves calm down, oscillating more gently, except for one or two "sharp wave ripples" per second. The sharp wave ripple pattern -- a deep dive from baseline, followed by several small ripples and a return to baseline -- takes just one-tenth of a second, but it is then that those "replays" occur in hippocampal neurons called place cells, he explains.




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