Don’t Look into the Light!: The Dazzling Neuroscience Technique of Optogenetics

ISABELLE RIDDLE – Francis Crick, known by most as the father of modern genetics, once lamented, in a 1979 research article, the serious roadblocks he foresaw for the field of neuroscience due to the seeming impossibility of observing one brain cell while leaving the surrounding cells undisturbed. Flash to the present, and the worries of this luminary have all but dimmed. Scientists can not only observe single neurons without disturbing the surrounding brain cells but can also externally control hand-picked neurons to elicit specific responses from test animals. The secret ingredient behind this advancement? Optics!

This article will shed light on the technique of optogenetics: how it was developed, how it works on the cellular and organismal level, how it can be utilized within the field of neuroscience, and what responses it is able to produce in organisms. 

For all the hype around optogenetics, you may be surprised to learn that its central functionality derives from the humble green alga Chlamydomonas reinhardtii. This alga is equipped with a light-sensitive spot (like an eye, but super dumbed-down) which, when it senses light, propels the algae in order to maximize photosynthetic ability. The eyespot contains ion channels, which allow ions to flow through them when hit with a certain wavelength of light. It just so happens that neurons are triggered in this same way, by moving ions across cell membranes. Once a threshold of ions crosses a neuron’s cell membrane, the neuron fires. And once one neuron fires, it is able to propagate this signal down many neurons in specific pathways (science folks, think neurotransmitters and excitatory/inhibitory responses). This principle is the backbone underpinning every function of an organism’s nervous system. So, if there was some way to patch these light-sensitive ion channels from the algae onto the neurons of a more complex neural system, then we could use light to trigger not only a movement toward or away from a light source, but potentially any function our test animal’s brain normally is able to control, like walking, communicating, and thinking. 

As it turns out, there is a way to perform this amalgamation: transgenic viral delivery systems. This virus, when injected into the brain, recombines its DNA with the DNA of the host cells (as typical viruses do), so all necessary cell machinery to express the ion channel gene is available, and voila! Specificity is achieved by using the promoter specific to a certain type of cell within your transgenic virus. Light-sensitive ion channels will be expressed in just those cells. Further specificity is achieved because of the nature of optics itself: tiny fiber optic cables can send out a very narrow beam of light which is only large enough to target a specific cell or group of cells. Optogenetics is flexible, though: it does not just have to work on the single-cell level but can also stimulate whole brain regions by simply altering the physical properties of the incoming light. 

Optogenetics has been instrumental in a whole host of recent advances, and as scientists hone the tool, the future continues to brighten. In labs across the world, optogenetics is helping to find ways to restore vision loss, preserve movement following spinal cord injury, and dampen circuits that fuel anxiety, depression, and other psychiatric conditions. The possibilities do not end here, however; they have begun to trickle into the realm of what has until now been considered science fiction. 

We all know that the brain is responsible for more perfunctory-level bodily control. It also encapsulates the very essence of us: our thoughts, emotions, mindsets, and consciousnesses. Because optogenetics has such specialized control over brain structures, it can also alter these more complicated brain functions. For example, optogenetics has been used to reactivate and edit memories. Further, mice’s behavior and agitation level can be controlled by an experimenter and a light switch. 

These results beg the question…Could this technology be used against us to commandeer control of our own bodies and minds? The moral implications of such precise control over another’s brain are incredibly complicated, but a discussion of the ways to use this technology for good is imperative, and soon. Crick’s concern dealt with a lack of scientific prowess and control. Now, however, optogenetics raises concerns of a whole new breed: what to do when a scientific technique is more powerful than ever expected.

Copy Editor: Courteney Malin

Photography Source: https://www.scientifica.uk.com/learning-zone/optogenetics-shedding-light-on-the-brains-secrets