Researchers from the UC Davis Center for Neuroscience and Department of Psychology have erased specific memories in mice using light. The researchers also proved a basic theory of how separate parts of the brain work together to retrieve episodic memories.

Optogenetics, initially pioneered by Karl Diesseroth at Stanford University, is a new technique that uses light to manipulate and study nerve cells. Optogenetics techniques are quickly become the standard method for investigating brain function.

Kazumasa Tanaka, Brian Wiltgen and UC Davic colleagues used the technique to test a long-standing idea about memory retrieval. Wiltgen noted that for approximately 40 years, neuroscientists have theorized that retrieving episodic memories requires coordinated activity between the cerebral cortex and a small structure deep in the brain called the hippocampus.

Wiltgen said in a statement, “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.” Patients can lose decades of memories if the hippocampus is damaged.

The introduction of optogenetics has made it easier to test this model directly.

The researchers used genetically modified mice where when the nerve cells are activated, they both fluoresce green and express a protein that enables the cells to be turned off by light. This led to the ability in both to follow precisely which nerve cells in the cortex and hippocampus were activated in learning and memory retrieval, and switch them off with light through a fiber-optic cable.

According to the University of California, San Francisco, episodic memory is the memory of an event or “episode.”