Researchers at the UC Davis Center for Neuroscience and Department of Psychology have successfully managed to use light to erase specific memories in mice. Through this study, they have proved the basic theory that different parts of the brain work in tandem to retrieve episodic memories.

Karl Diesseroth from the Stanford University pioneered a new technique called optogenetics, which uses light to manipulate and study nerve cells. This new and revolutionary technique is soon becoming the standard method for investigating brain function.

In an attempt to test a long-standing theory about memory retrieval, Brian Wiltgen, Kazumasa Tanaka, and their colleagues at UC Davis applied the technique of optogenetics. Wiltgen said that for the last 40 years, neuroscientists have believed in the theory that the retrieval of episodic memories about specific events and places, involves coordinated activity between the cerebral cortex and the hippocampus, a small structure situated deep in the brain.

Wiltgen said, "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." A patient may lose decades of memories if the hippocampus is damaged. Until the arrival of optogenetics however, this model has been difficult to test directly.

Tanaka and Wiltgen used genetically modified mice which were engineered in such a way, that when their nerve cells were activated, they fluoresce green and express a protein which allows the cells to be switched off by light. This allowed the researchers to follow exactly which nerve cells in the hippocampus and cortex were activated in memory retrieval and learning, and subsequently switch them off with light directed through a fiber-optic cable.

The mice were trained by being placed in a cage where they received a mild electric shock, triggering a "fear response" in which they freeze in place. The researchers were able not only to label the cells involved in learning and demonstrate that they were reactivated during memory recall, but also switch off the specific nerve cells in the hippocampus, to reveal that the mice lost their memories of the unpleasant event, namely the shock. [Imperial Valley]