Nanoparticles could allow researchers to manipulate mouse neurons with light — without opening the skull.

Optogenetics uses light to activate proteins on the surfaces of neurons in the brain. The proteins then stimulate activity in the neurons. The most widely applied method requires probes to be implanted into the brain, prompting Shuo Chen of the RIKEN Brain Science Institute in Wakoshi, Japan, and his colleagues to seek a less-invasive technique.

Working in mice, the team injected light-responsive nanoparticles deep into a brain region involved in memory. The researchers then shone near-infrared light — which can pass through bone and tissue — onto the animals’ heads. The nanoparticles converted the beam into blue-green light, which in turn stimulated neurons that affect how mice respond to a perceived threat.

The technique will enable less-invasive optogenetic manipulation of deep brain regions compared to what was previously possible, the authors say.