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Researchers have used light to erase specific memories in mice, proving a basic theory of how different parts of the brain work together to retrieve episodic memories, according to a new study. 

Optogenetics is a new technique for manipulating and studying nerve cells using light. It is rapidly becoming the standard method for investigating brain function. 

 "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," Brian Wiltgen, one of the authors of the study, said in the press release. 

If the hippocampus is damaged, patients can lose decades of memories, Wiltgen added. 

Researchers were able to switch off the specific nerve cells in the hippocampus, and showed that the mice lost their memories of the unpleasant event. They further observed that turning off other cells in the hippocampus did not affect the retrieval of that 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."

Researchers also observed how the specific cells in the cortex were connected to the amygdala, a structure in the brain that is involved in emotion and in generating the freezing response.

The study was carried out at  UC Davis.