A Color-Coded Guide to the Brain

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. 

       A region of the hippocampus where new memories are often formed.
         Photo Courtesy T. Weissman, J. Livet, and J. W. Lichtman

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. 

The auditory region of the brain stem.
Photo Courtesy J. Livet, and J. W. Lichtman

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.

Hannah Krakauer is a research intern at NOVA and a student at Stanford University. 

User Comments:

This is exciting and hopeful. Nature has a use for everything, in its own way and time. Excellent article.

This is really neat, and the images are beautiful! I wonder if you could combine this technique with Stanford's light field microscope, which allows you to record chunks of brain in 3D. Perhaps now a real map could be created of the brain.

Although the content of this article is fascinating and extremely hopeful, I was moved by the writer's ability to articulate a very complex biological process in such a way that even a lay person could feel the passion and importance of this body of work!

So do these viruses make the person or being whose brain is being studied sick??

this is ver wonderful though frightening i hope that it succeeds so we can have another method of treati epilepsy.

So what's the virus they use to illuminate the neurons and is there a lasting effect to using this virus?

While in the hospital after having my first child, I had an adverse reaction to medicine that sent me into a grand mal seizure that moved up my right hand and arm. As it travel up, my brain started short-circuiting through massive numbers of tiny, hair-like colorful wires that shut down the entire electrical system in the brain. I remember it "looking" like what is seen in the first picture you show from the area of the hippocampus.
Needless to say, this article fascinated me by validating a frightening but beautifully unforgettable experience 43 years ago.

I loved the house metaphor! Very helpful. Thank you for this wonderful article!

I love to see the brain in all its pretty colors. I have seen how pretty my clon is and my bladder. to see a mouses brain is spectacular. Maybe someday I can see my brain color also.

Double brainbow! Oh my god!!

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