Lasers make mice hallucinate | Science News for Students

Lasers make mice hallucinate

Scientists control brain cells to create fake visions
Aug 7, 2019 — 6:45 am EST
mouse investigating lab equipment

A mouse checks out a tool that focuses lasers on specific nerve cells in the brain. Activating nerve cells with lasers makes mice “see” things that aren’t really there.

Sean Quirin, James Marshel, Cephra Raja and K. Deisseroth/Stanford Univ.

Aiming laser light into a mouse’s brain can make them “see” lines that aren’t there. This is the first time scientists have created a specific visual perception with lab trickery.

The experiment used optogenetics. This technique uses laser light to activate nerve cells in the brain called neurons. Scientists tweak the neurons to have a light-sensitive protein. This protein prompts the cells to send a signal in response to the light.

Optogenetics debuted about 15 years ago. Everyone hoped it would give scientists precise control over perception and the behaviors that follow, says neuroscientist Karl Deisseroth. He helped pioneer the technique. That ability could help unravel big questions, such as how certain groups of brain cells create experiences.

“It’s exciting to get to this point,” says Deisseroth, a Howard Hughes Medical Institute investigator at Stanford University in California.

Seeing things

Deisseroth’s team identified a group of about 20 neurons that activate when mice viewed either horizontal or vertical lines on a screen. Each mouse had been trained to lick water from a spout when it saw the lines it had been trained on.

The researchers then set out to make the mice hallucinate the lines using laser light. When the brain hallucinates, it sees something that isn’t really there.

Mice were first shown very faint real lines. Over time, the lines became so faint that the mice couldn’t see them. They failed to lick the water spouts. Hitting the group of neurons with laser light, though, improved the rodents’ performance. They licked their water spouts more often.

Then the researchers tested the mice in total darkness. The rodents could not see any lines. Shining laser light on the same group of 20 or so neurons caused mice to “see” lines and lick their spouts.

The light-stimulated neurons also prompted other neurons to fire off signals. This suggested that other vision cells acted as if the mouse had seen a real sight. The team reported the findings online July 18 in Science.

Beyond visions

Neuroscientist Conor Liston calls the work technically amazing. “I think every neuroscientist in this area will look at this with great interest,” says Liston, who works at Weill Cornell Medicine in New York City.

A few key advances led to the experiment’s success, Deisseroth says. Among them: Lasers controlled by liquid crystals, and the discovery of a protein called ChRmine. This protein responds to light — even dim light. That’s a helpful trait because too much light can damage the brain.

Similar approaches could let scientists create tastes, touches and smells, Deisseroth says. And this new method may let researchers control groups of neurons that are involved in more complex brain tasks. “You could easily imagine using similar tools to study memory,” Liston says.  

Power Words

(more about Power Words)

activate     (in biology) To turn on, as with a gene or chemical reaction.

behavior     The way something, often a person or other organism, acts towards others, or conducts itself.

cell     The smallest structural and functional unit of an organism. Typically too small to see with the unaided eye, it consists of a watery fluid surrounded by a membrane or wall. Depending on their size, animals are made of anywhere from thousands to trillions of cells. Most organisms, such as yeasts, molds, bacteria and some algae, are composed of only one cell.

horizontal     A line or plane that runs left to right, much as the horizon appears to do when gazing into the distance.

laser     A device that generates an intense beam of coherent light of a single color. Lasers are used in drilling and cutting, alignment and guidance, in data storage and in surgery.

liquid crystal     A liquid made from an organic (carbon-based) material. Its physical structure consists of loosely ordered arrays of its molecular building blocks. Although a liquid, these arrays seem to resemble the ordered lattice seen in true, solid crystals. Also like true crystals, the liquid can refract light in ways that do not look the same from all directions.

nerve     A long, delicate fiber that transmits signals across the body of an animal. An animal’s backbone contains many nerves, some of which control the movement of its legs or fins, and some of which convey sensations such as hot, cold or pain.

neuron     An impulse-conducting cell. Such cells are found in the brain, spinal column and nervous system.

neuroscientist     Someone who studies the structure or function of the brain and other parts of the nervous system.

optogenetics     A technique that uses light to better understand genes and cells in the nervous system, especially the brain. Recent research is using the technology to study other types of cells and tissues too.

perception     The state of being aware of something — or the process of becoming aware of something — through use of the senses.

protein     A compound made from one or more long chains of amino acids. Proteins are an essential part of all living organisms. They form the basis of living cells, muscle and tissues; they also do the work inside of cells. Among the better-known, stand-alone proteins are the hemoglobin (in blood) and the antibodies (also in blood) that attempt to fight infections. Medicines frequently work by latching onto proteins.

rodent     A mammal of the order Rodentia, a group that includes mice, rats, squirrels, guinea pigs, hamsters and porcupines.

taste     One of the basic properties the body uses to sense its environment, especially foods, using receptors (taste buds) on the tongue (and some other organs).

tool     An object that a person or other animal makes or obtains and then uses to carry out some purpose such as reaching food, defending itself or grooming.

trait     A characteristic feature of something. (in genetics) A quality or characteristic that can be inherited.

vertical     A term for the direction of a line or plane that runs up and down, as the vertical post for a streetlight does. It’s the opposite of horizontal, which would run parallel to the ground.

Citation

Journal:​ ​​ J.M. Marshel et al. Cortical layer–specific critical dynamics triggering perceptionScience. Published online July 18, 2019. doi: 10.1126/science.aaw5202 (2019).