In a vivid example of how neuroscientists are meticulously tracing the microwiring of the brain, Norwegian researchers have used an optogenetic light switch to see (literally) which neurons communicate with each other in one small section of the brain.

The researchers at the Norwegian University of Science and Technology (NTNU)’s Kavli Institute of Systems Neuroscience use a virus that acts as a pathway for delivering “channelrhodopsin-2” genes to specific “place cells” to create the equivalent of a light switch.

Place cells, located in the hippocampus. are dedicated to recognizing specific physical places.

Then the researchers inserted optical fibers in the rat’s brain to transmit light to the place cells. They also implanted thin microelectrodes down between the cells so they could detect the signals sent through the axons every time the light from the optical fiber was turned on.

The researchers then turned the lights on and off more than ten thousand times while they recorded the activity of hundreds of individual cells in the rats’ grape-sized brains. The researchers did this research while the rats ran around in a meter-square box, gathering treats.

As the rats explored their box and found the treats, the researchers were able to use the light-sensitive cells to reveal how the rat’s brain created the map of where the rat had been.

When the researchers put together all the information afterwards, they concluded that there is a whole range of different specialized cells that together provide place cells their information, such as grid cells, head-direction cells, and border cells. The brain’s GPS — its sense of place — is created by signals from these different types of cells, they found.

They noted that while place cells receive information about the rat’s surroundings and landmarks, they also continuously update their own movement, which is actually independent on sensory input.