Optogenetics is a cutting edge technique being used by neuroscientists to determine the functions of specific brain cells. This technique involves inserting a light-sensitive gene into specific brain cells using a virus as a vector. The gene makes a protein called channelrhodopsin-2, which reacts to blue light by admitting ions into the brain cells, causing them to activate. In this way, researchers can activate individual brain cells by exposing them to light and then study the resulting physiological and behavioral effects.

So far, optogenetic methods have mostly been used in invertebrate and rodent studies. Previous studies using nonhuman primates only tested the technique on single isolated neurons and did not find any related behavioral effects. Wim Vanduffel and his team at Massachusetts General Hospital in Charlestown, MA, wanted to see if they could extend this research by studying the effect of optogenetically activating an entire network of cells.

First, the scientists scanned the brains of two rhesus macaques using functional magnetic resonance imaging (fMRI) while they performed a visual task. From the scans, they could determine which area of the brain was required for performing the task. Next, they inserted the light-reacting gene into multiple cells of this brain area and guided light-conducting needles into the same brain area so that light could be shone on the cells to boost their activity.

The researchers found that stimulating the brain cells with light improved the mental performance of the two macaques; the monkeys performed the visual task 10% faster (Curr. Biol. published online 26 July 2012 doi:10.1016/j.cub.2012.07.023). These results show that pre-stimulating an area of the brain necessary for a task can lead to faster processing involved in performing the task. Vanduffel told New Scientist, “For the first time, we were able to change behavior in primates with our technique.”

The team also observed optogenetically induced changes in fMRI activity in several specific brain networks during the task. The study also marks the first time that whole networks of cells were activated by optogenetic methods. This research opens up the possibility that the technique could be used to treat conditions in humans, such as epilepsy or Parkinson's disease, by activating populations of nonfunctioning brain cells. The researchers caution that much more work is to be done. “This is just proof of principle, and there's a very, very long way to go before we can start using it in humans,” Vanduffel said.