Think of your most horrible, unpleasant memory. If you could, would you want to erase that from your brain? You can’t do it now, but new research is moving in that direction.

In a study at the University of California-Davis Center for Neuroscience and Department of Psychology scientists were able to use light to erase specific memories in mice, providing proof for a long-standing theory of how memories work by making them forget a painful experience.

The mice used in the experiment weren’t run-of-the mill squeakers. They were genetically modified so that when their nerve cells are activated they flouresce green and express a protein that allows them to be switched off by light. The scientists could see which nerve cells were being activated when the mice made memories, and switch them off with a fiber-optic cable inserted into the mouse’s brain.

Having a clear map of what was happening in the brain was important, because the scientists wanted to test the long-standing theory that retrieving memories requires a coordinated effort between the brain’s cerebral cortex and a small structure deep within called the hippocampus.

“The theory is that learning involves processing in the cortex, and the hippocampus reproduces this pattern of activity during retrieval, allowing you to re-experience the event,” researcher Brian Wiltgen said.

The study created by Wiltgen, Kazumasa Tanaka and colleagues placed the mice in a box with a floor that gave a mild electric shock. Normally mice check out a new area when placed inside, but if they remember that the box shocked them before they will freeze in fear when placed inside.

The scientists identified which cells were being activated in the hippocampus during this fear response and switched them off. The mice lost their fear of the box.

The effect only worked when those specific hippocampus cells were shut off. Scientists could trace the connection between those cells back to corresponding cells in the cortex and also see how those cortex cells activated another part of the brain called the amygdala, a brain structure that helps generate the fear associated with the memory.

“The cortex can’t do it alone, it needs input from the hippocampus,” Wiltgen said. “This has been a fundamental assumption in our field for a long time and Kazu’s data provides the first direct evidence that it is true.”

[Source: UC – Davis]

Image of lab mice via Wikimedia Commons



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