Algae have provided a new tool to enhance optogenetics – a technique using light to watch and control neurons in the brain.

Optogenetics allows researchers to turn neurons on or off by making them light sensitive and controlling them with a specific frequency of light.

Previously, it was only possible in the blue-green light range, but a team in the US has discovered a substance which should allow it to work with red light as well.

Having a new colour will allow researchers to independently control the activity of two populations of neurons at once, enabling much more complex studies of brain function.

“If you want to see how two different sets of cells interact, or how two populations of the same cell compete against each other, you need to be able to activate those populations independently,
says Ed Boyden, an associate professor of biological engineering and brain and cognitive sciences at MIT and a senior author of the new study.

The light sensitive proteins at the heart of the study are known as ‘opsins’. They occur naturally in algae, which use them to respond to their environment and generate energy.

To achieve optical control of neurons, scientists engineer brain cells to express the gene for an opsin, which transports ions across the cell's membrane to alter its voltage.

Depending on the opsin used, shining light on the cell either lowers the voltage and silences neuron firing, or boosts voltage and provokes the cell to generate an electrical impulse. The effect is virtually instant and easily reversible.

As well as the red option, MIT researchers’ studies have also thrown up a better, more useful version of the previous blue-green opsin.

The new opsins lend themselves to several types of studies that were not possible before.

For example, scientists could not only manipulate activity of a cell population of interest, but now control upstream cells that influence the target population by secreting neurotransmitters as well.

Pairing opsins could also allow scientists to study the functions of different types of cells in the same microcircuit within the brain. Such cells are usually located very close together, but with the new opsins they can be controlled independently with two different colours of light.

The study will be published in the next edition of Nature Methods.