Your brain contains approximately 80 billion nerve cells, called neurons, which make connections with parts of other neurons, called dendrites, to form networks. Neurons have been known to communicate with each other by passing small chemical signals through these connections, but now we know that they also can spread messages more widely by releasing chemical signals from other parts of the neuron.
A Brainbow is the result of a process in which individual neurons in the brain can be seen seperately from other neurons using fluorescent proteins. By randomly expressing different ratios of red, green, and blue derivatives of green fluorescent protein in individual neurons, it is possible to flag each neuron with a distinctive color. This process has been a major contribution to the field of neural connectomics. The technique was originally developed in 2007 by a team led by Jeff W. Lichtman and Joshua R. Sanes, both at Harvard University.