Our brains are made up of billions of cells called neurons, and those neurons communicate with each other through neural circuits.

Optogenetics allows us, for the first time, to manipulate the messages that those neurons send to each other.

"If you imagine the brain as this city, up until now we have been looking at it as if from space," explains I-Han Chou, Senior Editor, Nature. "We haven't had the tools to do anything beyond seeing what the whole city block is doing. What you actually want to know is what the individual components of the city are, what the people are doing, and what's the information being transported from one part of the city to another.

"Optogenetics is the ability to manipulate individual neuronal circuits, refining our vision of the function of individual circuits and how they relate to different aspects of our behaviour and personality," she explains.

The name optogenetics comes from the fact that scientists are using optics – that is, light – and genetics – the genetically modified cells in the brains of an animal – together. By shining a light on the genetically modified cells in the brain, scientists have been able to switch them on or off.

The research in practice

Experiments so far have been conducted on rodents, but show promising results for future use in humans.

The research could have remarkable consequences, for instance in treating neurological disorders such as Parkinson's disease.

The part of the brain that is damaged in Parkinson's disease is called the basal ganglia. This part of the brain is involved in the coordination of movement, and experiments have shown that optogenetics can be used to affect the way that we move.

"If you activate a certain subset of neurons with optogenetics you can make a rat freeze up and have difficulty walking. If you activate a different subset the rats start to move faster," explains I-Han Chou.

"Imagine if we could use optogenetics or a similar technology to get the input from an artificial sensor into our brain. In principle, we could not only restore function, but we could enhance our current functions," she adds.

We could also use optogenetics to give ourselves ultra violet light detectors, or carbon dioxide detectors so we could automatically sense our air quality.

"When things go wrong with the brain it is just so devastating. One of the hopes for optogenetics is that if it can work in humans, it might be used as a tool for restoring brain function," says I-Han Chou.



The memory

The technique could potentially be used to manipulate memories, emotions and thoughts, raising profound ethical questions.

Scientists have been able to implant false memories into the brain of a mouse using optogenetics. This could have far-reaching consequences for the 350 million people worldwide that suffer from depression, as Susumu Tonegawa, Professor of Biology and Neuroscience at Massachusetts Institute of Technology explained in a talk at Davos 2016.

"Depression is often caused by chronic stress, which precipitates a series of negative memories. We know now that negative and positive memories compete with each other in the brain network. Using this principle we have recently made a very exciting discovery, that is to cure depression with optogenetic technology," he explains.

In other words, optogenetics could be used to switch on the positive memories in the brain, thereby potentially curing the depression.

This technique could also be used in the treatment of early stage Alzheimer’s, by switching on the cells of the brain that retrieve memories.

"Optogenetics has demonstrated the proof of concept for a variety of diseases and for possible therapy. The big question is: can we convert these findings made with animal models into therapy for human patients?" he asks.

Ethical considerations

One of the most important talking points about optogenetics is not the science itself but the consequences, and how far we should pursue research into the "final frontier" of the human brain.

"There's a lot of ethical issues about enhancing your function and making yourself better," concludes I-Huan Chou. "Would there be a side effect of increasing your capacity by 20%? In ten years’ time we might all be enhanced with implants. It's a future that should be very carefully considered. "