A Color-Coded Guide to the Brain
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A new brain mapping technique uses viruses to illuminate neurons in beautiful colors, and can give us detailed visuals of how information travels through the brain. Imagine the brain like an old house, full of complex electrical circuits and wires that branch off to every room. Now imagine that you wanted to trace the path electricity takes from the main circuit breaker to the microwave, but you’re not allowed to destroy the house in the process. Hopefully you would have a circuit map, and if you’re really lucky, the circuits might even be drawn out in different colors. Now, scientists have found a way to make the same kinds of maps in the brain of a mouse by literally illuminating the pathways between neurons. A team at Princeton led by Lynn Enquist is pioneering a way to use viruses to target specific neurons and make them glow in bright colors when stimulated by a laser. Scientists first inject a virus into the beginning of a pathway they would like to follow. As the virus spreads from neuron to neuron, it follows the same paths that neurons use to talk to each other. The traveling virus illuminates neurons as it goes, leaving a colorful streak in its wake. Scientists can use those colors to create a computer model of a specific pathway through the brain without hacking away at the brain itself. Researchers like J. Patrick Card at the University of Pittsburgh are using this technology to study the pathway that regulates blood pressure in the brain. So, why use viruses to trace pathways in the brain? It turns out that their frightening ability to rapidly self-replicate is also what makes them useful. Unlike liquid chemicals, which become diluted after they pass through a few neurons, viruses can follow a neural pathway into the innermost parts of the brain. They can therefore provide a more complete picture of the entire neural circuit.
This approach builds on a brain mapping technique developed just a few years ago at Harvard called Brainbow, which allows scientists to engineer mouse brains with neurons that glow in one of almost 100 randomly generated colors. The original Brainbow studies generated beautiful images that gave precise information about how individual neurons connect to one another. The addition of viruses will allow scientists to visualize not just the entire map of brain circuits, but to make a specific neural circuit stand out against the rest.
Photo Courtesy J. Livet, and J. W. Lichtman
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