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In a new study, scientists experimented with memories in mice models. The team was able to erase and then restore memories by using different types of lights on a specific region of nerve connections in the brains of rats.

"We can form a memory, erase that memory and we can reactivate it, at will, by applying a stimulus that selectively strengthens or weakens synaptic connections," study senior researcher, Dr. Roberto Malinow, a professor of neurosciences the University of California, San Diego, said reported by Philly.

For this study, Malinow and colleagues focused on stimulating synapses in the rats' brains. Synapses are connections that exist between the brain's nerve cells, also known as neurons. The team first created a painful memory for the rats. The rats were already genetically altered to have nerves that were sensitive to different frequencies of light.

The researchers administered an electric shock to the rats' foot while simultaneously stimulating a bundle of nerves in the rats' brains. After repeated exposure to the shock, the rats developed a connection between shock and nerve stimulation. The rats exhibited fear behaviors every time their nerves were stimulated, even if there was no shock.

The team then removed the association, or the memory, of fear by weakening the connections in the nerves. They used low-frequency light pulses directed at the same nerves. Now, when the nerves were stimulated, the mice no longer remembered to be fearful. The researchers were also able to restore fearful behaviors by exposing the nerves to high frequency light pulses. Now, when the nerves were stimulated, the mice became fearful again without the use of a shock to the foot.

"We can cause an animal to have fear and then not have fear and then to have fear again by stimulating the nerves at frequencies that strengthen or weaken the synapses," lead study author Sadegh Nabavi, a postdoctoral researcher in the Malinow lab, stated.

The study was published in Nature. The press release can be found here.