Optogenetics is a techniques that unites light and the genetic modification of cells. Ultimately, the technology makes brain cells photosensitive and allows scientists to manipulate, or “activate, cells by using flashes of light. In this respect, optogenetics is like a switch that is used by scientists to turn brain cells off and on like a light.
Typically, the cells involved are neurons that have been genetically modified to express light-sensitive ion channels. For the technique, a gene for a light-sensitive protein, such as channelrhodopsin, is inserted into cells so that the protein is produced on their surfaces. When these cells are later exposed to light, channels open and charged particles rush inside. This causes the modified cells to release a “spike,” which causes an electrical signal to be sent to other cells.
The approach has the potential to reveal the relationship between brain activity, on one hand, and cognition, behavior, and emotion, on the other. Already, the technology can be used to remotely control motor circuits, such as having an animal perform specific physical actions at the flick of a switch. It can even label and alter memories that form as a mouse explores different environments.
In short, the technique has allowed neuroscientists to achieve feats that were previously inconceivable.
It has made such an impact that two of its inventors, Karl Deisseroth of Stanford University and the Howard Hughes Medical Institute and Ed Boyden of Massachusetts Institute of Technology, received a Breakthrough Prize in the life sciences. It’s a remarkable field that has already made unique contributions and has an amazing amount of, as yet, unlocked potential.
At the recent Society for Neuroscience meeting in Chicago, several leading researchers spoke about their current projects using the technique, as well as the obstacles they’re facing. The biggest obstacle is the fact that both stimulating and recording activity with light causes problems if (and when) wavelengths overlap. This is especially challenging because the proteins that are used as indicators need to be excited by light in order to emit light.
Indicator proteins generally consist of a protein that is sensitive to cell activity which is linked to a fluorescent protein, so they light up in response to a cell’s stimulation. Much work in the field is, therefore, now focused on finding proteins whose wavelengths don’t overlap. If these challenges are overcome, all-optical techniques in optogenetics could further revolutionize neuroscience by allowing researchers to simultaneously monitor and control single spikes from both single neurons or large ensembles of neurons as experimental animals move freely about.
“This approach will open a whole new range of experiments,” says Michael Hausser, a neuroscientist at University College London, in a statement. “Unlocking the full potential of optogenetics requires going beyond targeting genetically-defined cell-types, to targeting cells according to functional properties, rather than just genetic identity.”