Scientists Erase Specific Memories in Mice with Light

Can you imagine targeting specific memories to forget? Scientists have found a way to erase specific memories in mice, which proves a basic theory of how different parts of the brain work together to retrieve episodic memories.

In this case, the scientists used optogenetics, which is a new technique for manipulating and studying nerve cells using light. This allows the researchers to better investigate brain function.

The scientists used optogenetics in order to test a long-standing idea about memory retrieval. Researchers had previously theorized that retrieving episodic memories, which are memories about specific places and events, involves coordinated activity between the cerebral cortex and the hippocampus, a small structure deep in the brain.

"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," said Brian Wiltgen, one of the researchers, in a news release.

In order to test this particular theory, the researchers used genetically modified mice. These mice were modified so that when nerve cells are activated, they fluoresce green and express a protein that allows the cells to be switched off by light. This allowed the scientists to follow exactly which nerve cells in the cortex and hippocampus were activated in learning and memory retrieval, and then switch them off with light directed through a fiber-optic cable.

The scientists then trained the mice by placing them in a cage where they received a mild electric shock. The mice eventually learned to freeze in place when placed in the cage.

What was interesting was that when the researchers switched off specific nerve cells in the hippocampus, the mice lost their memories of the unpleasant event. In contrast, turning off other cells in the hippocampus didn't affect their retrieval of that memory.

"The cortex can't do it alone, it needs input from the hippocampus," said Wiltgen. "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."

The findings are published in the journal Neuron.