Researchers at Harvard University have developed a new method for setting the brain aglow in a rainbow of colors.

The ability to paint individual brain cells with such a broad palette will allow neuroscientists to explore neural circuits like never before.

Jean Livet, Jeff Lichtman, and their collaborators at Harvard genetically engineered mice to carry numerous copies of genes that code for fluorescent proteins of three different colors–yellow, red, and cyan–as well as an enzyme that can randomly block any subset of these genes from producing their fluorescent tag.

When the mice are fed a compound that activates the enzyme, each cell undergoes a random molecular process in which subsets of the color-coding genes are knocked out. The remaining genes produce the three colored fluorescent compounds in different amounts, which combine to form a unique new hue.