Because of the brain’s amazing and incomprehensible complexity, there are billions of neurons that connect and network all the major areas of the brain with the small intricate parts as well. So how can we distinguish one of these neurons from the billions of others?

Well, within the past five years more advanced techniques have been discovered and used on various organisms. The most prevalent, and probably the most revolutionary, has been staining. This process was pioneered in the late nineteenth century by Camillo Golgi and allowed for the staining of whole, random cells.

Since then, much progress has been made and today the viewing of even more complex and minute parts that make up the brain is possible. One extraordinary technique was developed by a team of Harvard researchers a few years ago, and it is truly beautiful.

Known as the Brainbow technique, these investigators were able to use genetics to visualize complete neuronal circuits in unprecedented detail. Up to four differently colored fluorescent proteins were used, generating  a palette of 100 distinct hues that labeled individual neurons.

Here are the fluorescent proteins in their full glory illuminating the many neurons that make up the brain of a mouse.

This technique was developed with the use of the Cre/loxP site-specific recombination system, a sophisticated method that is commonly used to generate mutant mice lacking a specific gene. Basically, this recombination inverts parts of the DNA sequence at specific sites along the genome. The mating of two different mice strands allows for recombination.

Fluorescent proteins were added to certain constructs of cells, all of which were able to emit colors such as red, cyan, yellow, and green. Multiple copies of the constructs were integrated into a stem cell chromosome, and many random combinations of these four genes were then expressed.

Confocal microscopy was used next to generate three-dimensional reconstructions that traced the multi-color palette onto complete neuronal circuits in various regions of the brain. Thanks to this incredible new technique, a large number of neurons and the connections between them have been labelled and led to new systems based on this discovery.

Since its discovery, the Brainbow technique has allowed for unprecedented visualization of neurons and neuronal circuit in many classic model animals, such as the fruit fly and mouse. Hopefully one day, techniques such as this will aide us in our attempt to untangle the interconnections of our own brains and allow us to further appreciate its beautiful intricacies.

The 100 Colours of the Brainbow: Neurophilosophy

Harvard Researchers Illuminate Connections Among Brain Cells in Technicolor -Popular Science

Transgenic Strategies for Combinatorial Expression of Fluorescent Proteins in the Nervous System: Article – Nature

Colorful Images to Help Illuminate the Brain – NYTimes.com

What would happen if humans were like turtles – alone at birth with no mom to guide them back home? We probably would not survive very long before getting attacked and/or eaten by something bigger than us. For many animal species, instinct guides survival. But for humans and other mammal species, nurture as an infant is crucial to our development.

Weaver et al investigated the phenomenon of nurture in rats. They noted that some rat moms extensively licked and groomed their pups, while others ignored their pups. Pups that received attention during the first week of life grew up to be happy and calm, while those that were ignored grew up to be anxious, and were more prone to disease. Epigenetics studies the genomic changes that occur in response to the external environment. The differences in behavior are due to a change in a glucocortocoid receptor (GR) gene during development. At birth, the gene is highly methylated and inactive. If a rat mother is attentive towards her pups, the pups’ GR gene gradually demethylates, making the gene more active. These pups will be more relaxed in response to stress. Those that were not given attention, and do not express the GR gene, respond poorly to stress. You can try being a rat mom in an interactive game here .

A related study by McGowan et al studied hippocampal tissue in humans that had committed suicide and been abused as a child, and humans that had committed suicide with no history of child abuse. When compared to controls and subjects that were not abused, the subjects that had been abused had decreased level of a GR protein. This shows that events later in life (such as those leading to a suicide) do not actually alter genetic makeup, rather, it is the early childhood interactions which cause epigenetic changes leading to adult behavior. These data are consistant with those of the rats and  show the importance and effect of having proper nurture as a child.

But in reality, how important is it to be calm and controlled in response to stress? Rats are found in urban areas as well as in the wild.

What were to happen if one of the calm happy rats were to stumble upon a mouse (or, in this case, rat) trap? It would be less concerned about danger and be more likely to die, whereas an anxious rat would be guarded and could better survive the harsh environment.

What is the significance of these epigenetic changes for humans? Maybe living in a developed society has prevented us from realizing just how much nurture plays a role in development. Do those born into a war-ridden society have an inactive GR gene and thus a guarded and anxious personality? This is probably advantageous for survival.

In our society, we will of course never be left alone immediately after birth to fend for ourselves. But, what degree of nurture must we receive in order to grow up to be productive members of society? Why are species like turtles able to survive without a mom? Epigenetic studies will be key in future questions concerning nature and nurture.

Studying neurological disorders and identifying the brain regions associated with them often involves selective activation and deactivation of neurons. Blue light has been used in the past to activate cells, but recently Stanford University neuroscientists have figured out a way to use different colors of light to inhibit neurons. Their growing area of research, optogenetics, involves the engineering of viruses that insert genetic coding for light-sensitive proteins into cells of interest.

In the 2 April 2010 issue of Cell, Karl Deisseroth and his colleagues at Stanford published a study demonstrating the use of near-infrared wavelengths in neuron inhibition. Infrared light, being at a higher wavelength than blue light, delivers less energy to tissues and is safe at low power. Its ability to reach deeper brain regions, and thus cover more volume, is useful in in-vivo experiments. Additionally, using different colors of light to alter the activity of different brain regions at the same time could provide some answers as to how changes in various regions work in conjunction with each other to cause neurological problems. Optogenetic technology is already being used in research to study motor control, reward, addiction and other neuropsychiatric disorders.

Optogenetics at work in C. elegans

Switching brain cells on and off using multicolored light – Marie Freebody

Molecular and Cellular Approaches for Diversifying and Extending Optogenetics - Article in Cell