A subset of neurons found in the mouse’s retina.

To a large extent the brain remains a mystery. In comparison to Astronomy, Neuroscietist and author of Portraits of the Mind, Carl Schoonover believes we are at the stage stargazing was before the invention of the telescope.He says, “We are still seeing very small parts of things, we have some interesting and great tools that in their own way are very powerful but we don’t yet have the defining tools we need to look at the brain.”

Golgi’s Stain

Drawing of a dog’s olfactory bulb by Camillo Golgi.

Despite our lack of an overall understanding of the mind, in the last 140 years significant advances have been made. In fact the birth of modern neuroscience dates back to 1873 with the discovery of a staining technique by Camillo Golgi. The physician applied a mixture of Silver Nitrate and Potassium Dichromate to a slice of the brain which had the effect of staining certain neurons black.

This technique was put to great use by a man considered by many to be the father of modern neuroscience, Santiago Ramón y Cajal. The process only stained a few cells, which gave a clear picture of the shape and form of a single neuron hidden among the billions of brain cells that make up the mind.

What our brain does is effortlessly, automatically and extremely quickly organize that information and it is an open question how that works

Schoonover says, “Nobody actually knows how it works but the outcome is, for whatever reason, only about 1 out of 100 nerve cells in brain tissue get labeled (stained). What’s interesting is that the entire cell gets labeled, so it can be hundreds of microns, maybe even millimeters of neuron, that gets filled with black.”

Green fluorescent protein

Brainbow enables neuroscientists to distinguish between neighbouring, densely packed neurons.

In today’s study of the brain scientists are still using techniques that highlight individual neurons, but instead of staining them black they are now lighting them up from the inside. One example of this is the use of green fluorescent protein (GFP) which has proved incredibly useful in highlighting neural networks to show how they communicate with each other.

Schoonover explains, “Green fluorescent protein was discovered in jellyfish which happened to glow green and people always wondered why that was. After many years studying this question people worked out the gene that encodes this protein that glows green. Using very common genetic engineering techniques, you can insert that gene into any cell that you want to study… and you can get that cell to glow green.”

You can insert that gene into any cell that you want to study… and you can get the cell to glow green

What is especially important about GFP is that it is applied to the brains of live animals such as mice and rats so you can study the brain as the animal grows. Schoonover says, “Let’s say I want to study neurons x in area y of the brain and I want to know what they look like and I want to know how they develop over time while the animal is developing and growing, I can deliver the gene- triggering fluorescent protein to those cells during development and just look. They are lighting up for me because they are expressing that gene, it’s that simple.”


A few of the many neurons that are found in the neocortex.

Scientists have gone on to develop a range of different coloured fluorescent proteins that can be encoded into neurons highlighting with even more clarity individual cells in dense samples. This technique has been rather aptly named Brainbow.

Schoonover has been using these techniques in studying the brains of rats for his PhD, in an attempt to understand how information transfers through the brain. He says, “Information comes in from the world, through our eyes, hands, noses, it is very raw unstructured noisy information and what our brain does is effortlessly, automatically and extremely quickly, organize that information and it is an open question how that works.”

The use of the Brainbow technique is helping neuroscientists like Schoonover get ever closer to understanding how these neuron circuits communicate with each other when processing information from the outside world. This may still be a very nascent field in the grand scheme of things but scientists like Schoonover are inching ever closer to understanding  how this complex  bundle of neurons actually works.

Watch Carl Shoonover’s TED talk:

Picture credits: TheBrain-1 by Michael Hendricks and Suresh Jesuthasan (2008); TheBrain-2 by In-Jung Kim and Joshua R. Sanes (2008); TheBrain-3 by Ryan Draft, Jeff Lichtman and Joshua Sanes (2007); TheBrain-4 by Tamily Weissman, Jeff Lichtman, and Joshua Sanes (2007); TheBrain-6 by Camillo Golgi (1875).

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