Flashes of light show how memories are made

Abstract

Researchers confirm cellular basis for memory by implanting and erasing fear into the brains of rats using fibre optics. Neuroscientists can breathe a collective sigh of relief. Experiments have confirmed a long-standing theory for how memories are made and stored in the brain. Researchers have created and erased frightening associations in rats' brains using light, providing the most direct demonstration yet that the strengthening and weakening of connections between neurons is the basis for memory. “This is the best evidence so far available, period,” says Eric Kandel, a neuroscientist at Columbia University in New York. Kandel, who shared the 2000 Nobel Prize in Physiology or Medicine for his work unravelling the molecular basis of memory, was not involved in the latest study, which was published online in Nature1 on 1 June. A team led by Roberto Malinow, a neuroscientist at the University of California, San Diego, therefore turned to a technique that uses light to activate neurons. The researchers inserted a gene that produces a light-sensitive protein into a virus, then injected the virus into the rat brain cells they wanted to study. Once the gene had been translated into protein, the researchers were able to activate that protein with a pulse of blue light, delivered by an optical fibre implanted in the rat's brain. In classic conditioning experiments, researchers play a tone to an animal and quickly follow it with an electric shock; the rats soon learn to associate the tone with a shock, and freeze when they hear the tone, in anticipation of the shock. Malinow’s team found that they could create the same kind of fearful memory using optogenetics, by delivering light to the neurons that connect a brain region involved in processing sound with one that handles fear, and then shocking the rats. "We can make a memory of something that the animal never experienced before,” Malinow says.