Light Pulses Control Neuron Activity

Researchers used ultrafast pulses of tailored light to make neurons fire in different patterns, the first example of coherent control in a living cell. (Source: S. Boppart)

Specially tailored, ultrafast pulses of light can trigger neurons to fire and could one day help patients with light-sensi­tive circadian or mood problems, according to a new study in mice at the Univer­sity of Illinois. Chemists have used coherent light beams to regulate chemical reactions, but this study is the first demon­stration of using them to control function in a living cell. The researchers used opto­genetic mouse neurons, that had a gene added to make them respond to light. However, the researchers say the same technique could be used on cells that are naturally respon­sive to light, such as those in the retina.

“Photo­receptors in our retinas connect to different parts in the brain that control mood, metabolic rhythms and circadian rhythms,” said Stephen Boppart, Illinois professor of electrical and computer engineering and of bioengineering. The researchers used light to excite a light-sensitive channel in the membrane of neurons. When the channels were excited, they allowed ions through, which caused the neurons to fire. While most bio­logical systems in nature are accus­tomed to the conti­nuous light from the sun, Boppart’s team used a flurry of very short light pulses – less than 100 femto­seconds. This delivers a lot of energy in a short period of time, exciting the molecules to different energy states. Along with control­ling the length of the light pulses, Boppart’s team controls the order of wave­lengths in each light pulse.

“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,” Boppart said. “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 researchers demon­strated using patterns of tailored light pulses to make the neurons fire in different patterns.

Boppart says coherent control could give opto­genetics studies more flexi­bility, since changing proper­ties of the light used can give researchers more avenues than having to engineer mice with new genes every time they want a different neuron behavior. Outside of opto­genetics, the researchers are working to test their coherent control technique with naturally light-respon­sive cells and processes – retinal cells and photo­synthesis, for example. “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,” Boppart said. “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.” (Source: U. Illinois)

Reference: K. Paul et al.: Coherent control of an opsin in living brain tissue, Nat. Phys. 13, 1111 (2017); DOI: 10.1038/nphys4257

Link: Beckman Inst. for Advanced Science and Technology, Univ. of Illinois at Urbana-Champaign, Urbana, USA

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