It's not-- despite its electric acid cool aid look, this slice of mouse brain gets it psychedelic colors from biotech researchers inserting four genes encoding fluorescent proteins into its parental DNA. Neurons randomly expressing various combinations and levels of the resulting proteins can turn any of 90 colors report Jean Livet et al . in Nature. They say this "brainbow" technology greatly facilitates mapping of neural circuits in healthy and diseased brains.:
"In Brainbow transgenes, Cre/lox recombination is used to create a stochastic choice of expression between three or more fluorescent proteins (XFPs). Integration of tandem Brainbow copies in transgenic mice yielded combinatorial XFP expression, and thus many colours, thereby providing a way to distinguish adjacent neurons and visualize other cellular interactions."