“Behavioural evidence suggests that targeting just 20 neurons prompted animals to ‘see’ an image. …
Deisseroth’s team showed mice images of either horizontal or vertical bars, and trained the animals to lick from a tube of water whenever they saw the vertical bars. The scientists monitored the animals’ brains and recorded which neurons fired when the mice saw the vertical bars. They eventually identified about 20 cells per animal that seemed to be consistently associated with the vertical image.
To create the hallucinations, the researchers shone light on only these neurons — stimulating them to fire. This caused the mice to lick the tube of water as if they were seeing vertical bars, even though the animals were sitting in darkness. The mice didn’t lick the tube when the scientists stimulated the neurons linked to the image of horizontal bars.
Christof Koch, president of the Allen Institute for Brain Science in Seattle, Washington, says that the paper is a technical tour de force and an advance in optogenetics. “It’s playing the piano of the mind,” he says. …”
Reardon S: Hallucinations implanted in mouse brains using light. Nature 571: 459-460 (2019); doi: 10.1038/d41586-019-02220-4.