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Making memories takes time

You really should stop when you smell the roses, at least if you want to remember where they are and how they smell.

At the Society for Neuroscience annual meeting in San Diego, California, Loren Frank from the University of California-San Francisco reported results of experiments showing that the slower rats moved, the better they cemented memories.

The experiments focused on the hippocampus, which is known to be involved in memory formation. Using a technique called optogenetics, Frank’s team made hippocampal neurons sensitive to light and then used lasers to measure the synaptic activity in the rats’ brains. In particular, they looked at synaptic connections between two areas known as the entorhinal cortex (EC) and CA1.

In times of rapid movement, when the rats were familiar with their surroundings and moved quickly to grab food, there was a direct synaptic connection between EC and CA1. But when the rats were unfamiliar and moved slowly, taking time to sniff about and check things out, the two regions were linked by a more indirect route.

Frank thinks that the faster the animals moved, the more they focused on taking in and processing sensory information in the rapid, direct pathway. This suppressed the extra steps of the indirect pathway, which are likely involved in information processing that is necessary for memory consolidation. When the rats moved slowly, and could sniff around a bit, they could consolidate the memories better.

“When in motion, the system is just trying to keep up. It’s hard to form memories,” says Frank. “There’s a trade-off between internal processing mode and external mode. It’s true — you need to stop and smell the roses.”

In some ways the result are not surprising. We have known that we learn when awake and consolidate when sleeping. Frank says this research, in combination with experiments published last year, suggests that the brain will undergo constant refreshing: any time the brain has time to rest, it will start consolidating. If a rat, or you, is running around all day, neither of you will have time to remember.


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