US scientists have developed a new method that turns the mouse scalp transparent, making it possible to image the living brain during its development. 

The brain is constantly changing from birth – new connections are being formed and broken in brain cells, with the formation of new networks in response to different stimuli with rapid changes in structure. Until now brain development was not possible to observe in real time or to be tracked over longer periods in the same animal. 

Researchers at Stanford University applied ampyrone, a chemical compound with anti-inflammatory properties, to the mouse scalp, making the skin transparent by changing how light passed through it. Because ampyrone doesn’t block any colours of light we can see, the team could clearly observe green and yellow fluorescent proteins, commonly used to track brain activity, until the mouse was about four weeks old (the equivalent of a human teenager or early adult).

The researchers were able to observe the same brain cells over time in juvenile mice to see how brain activity changed when responding to external stimuli, like a puff of air on their whiskers. Unless the ampyrone solution is reapplied, the effect wears off after about 20 minutes, and the researchers found no evidence that it caused irritation to the skin. 

“This opens a literal window to peek into the brain’s development,” said Guosong Hong, senior author of the paper published in PNAS. “In the future, this approach could enable us to look at how [brain] circuits form during the development of an animal.”