About a decade ago, Karl Deisseroth of Stanford University developed a technology called optogenetics. It allows scientists to stimulate individual nerve cells using light beams within the brains of live and moving animals. Now, this technology has been used to generate visual hallucinations within lab mice, causing them to act as though the things they’re seeing are actually there.
As the name implies, optogenetics relies on introducing genes for light sensitive proteins into neurons. When light at a specific frequency illuminates such neurons, they become active as though they were naturally triggered to do so. In their latest study, published in Science, Deisseroth and colleagues introduced two sets of genes into neurons within the visual cortexes of mice. One gene led to the production of a light sensitive protein, while the other gene resulted in a fluorescent protein that glows green whenever the neuron it’s inside fires.
The mice had tiny glass windows placed within their skulls so that the scientists could illuminate their visual cortexes and watch for fluorescence. This was performed using holograms that can shoot photons in precise configurations over the visual cortexes and at specific neurons.
The researchers trained the mice to respond differently to horizontal and vertical lines and they also studied which holographic projections would generate a resemblance to horizontal and vertical lines in the mice.
Once everything was set up and the mice trained, the researchers were able to simply shine light onto the brains of the mice and the mice would react accordingly, depending on which lines they hallucinated. What’s particularly exciting is that very few neurons have to be stimulated to generate the hallucinations. In some cases fewer than 20 were enough to induce the animals to see something that wasn’t there.
The study with mice is already incredible, but the research will hopefully lead to new understanding of how the brain functions, how conditions such as schizophrenia arise, and how to stop them.
Study in journal Science: Pinpoint brain stimulation probes perception