A new study sees researchers from the University of Stanford find another way of causing hallucinations with experiments on mice that involves neither drugs nor any form of disorder.
The study, published in the journal Science, titled, "Cortical layer–specific critical dynamics triggering perception” looks at how scientists made mice hallucinate without any drugs. Notably, the neuroscientists stimulated nerve cells in the visual cortex of mice to induce an illusory image in the animals’ minds.
The study saw the researchers focusing on the visual cortex of the mice where they inserted two genes. One of the two had been encoded with a light-sensitive protein that stimulated the neuron on getting hit with an infrared laser light. The second gene was encoded with a fluorescent protein that glowed green whenever neuron was active. These in turn, stimulated nerve cells in mice, thus inducing an illusory image in the rodent's mind.
Interestingly, the scientists found that only one of the neurons needed to be stimulated to generate hallucinations in the animal. Following the insertion of genes, the rodents were shown a series of horizontal and vertical bars displayed on a screen.
Researchers observed which neurons in the visual cortex were activated by either of the orientation, accordingly, they were able to identify dispersed populations of individual neurons that were “tuned” to either horizontal or vertical visual displays.
Scientists then played back the recordings in the form of holograms that produced spots of infrared light on just neurons that were responsive to horizontal, or vertical bars.
The scientists trained the mice to lick the end of a nearby tube for water when they saw a vertical bar but not when they saw a horizontal one or saw neither.
Once the mice had become adept at discriminating between horizontal and vertical bars, the scientists were able to induce tube-licking behavior in the mice simply by projecting the “vertical” holographic programme onto the mice’s visual cortex. But the mice wouldn’t lick the tube if the “horizontal” program was projected instead.
Speaking about the same, senior author of the study, Kar Deisseroth revealed, "Now, for the first time, we’ve been able to advance this capability to control multiple individually specified cells at once, and make an animal perceive something specific that in fact is not really there — and behave accordingly."