Carefully Controlled Light Pulses Can Trigger Neurons to Fire

Researchers at the University of Illinois have developed a technique of using a flurry of very short light pulses of different wavelengths to control how mouse neurons fire. Eventually, the technique might be useful for influencing cells in the body that respond to light, such as those in the retina, to treat light-sensitive circadian or mood problems.

The researchers developed this method using mouse neurons that had been genetically modified so that they respond to light, but the technique is also applicable to light-sensitive cells in the body, such as those in the retina. Being able to treat disease by shining a light into your eye sounds like the stuff of science fiction, but this new technique brings that possibility one step closer to reality.

"The saying, 'The eye is the window to the soul' has some merit, because our bodies respond to light. Photoreceptors in our retinas connect to different parts in the brain that control mood, metabolic rhythms and circadian rhythms," says Stephen Boppart, a researcher involved in the study.

The research team used light to activate a light-sensitive channel on the mouse neurons, causing them to fire. However, the key to the technique involved using a stream of very short pulses of light, less than less than 100 femtoseconds in duration. However, the team was not just able to control the duration of each light pulse, but could also change the light's wavelength each time, which meant that they could make the neurons fire in different patterns.

"When you have an ultrashort or ultrafast pulse of light, there's many colors in that pulse. We can control which colors come first and how bright each color will be," explains Boppart. "For example, blue wavelengths are much higher energy than red wavelengths. If we choose which color comes first, we can control what energy the molecule sees at what time, to drive the excitement higher or back down to the base line. If we create a pulse where the red comes before the blue, it's very different than if the blue comes before the red."

The team is investigating the potential of the technique to control cells that naturally respond to light, and are also looking at its effect in processes that are light dependent, such as photosynthesis. "What we're doing for the very first time is using light and coherent control to regulate biological function. This is fundamentally more universal than optogenetics – that's just the first example we used," says Boppart. "Ultimately, this could be a gene-free, drug-free way of regulating cell and tissue function. We think there could be 'opto-ceuticals,' methods of treating patients with light."

Study in Nature Physics: Coherent control of an opsin in living brain tissue…

Via: University of Illinois…

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