Did you know our brains glow? Well, not glow exactly—technically it’s called fluorescence—but this phenomenon ends up making the brain look kind of like red and green Christmas lights under a microscope. If you want to impress your family and friends at the holiday dinner table this season, read on to learn more about brain fluorescence.

First, let’s talk a little bit more about why fluorescence is important.

Sometimes scientists use fluorescent dye, or probes attached to “fluorophores” (something that gives off fluorescence), in various techniques to be able to see more easily or precisely and measure proteins and structures in tissue. Using a microscope, researchers can see the fluorescence on whatever the dye binds to and take pictures for further study and measurements. These techniques have been used since the 1940s and have greatly impacted what we scientists have been able to learn about the human body.

Fluorescence can be divided into a couple of different types of colors based on wavelengths. Some of the shades can be seen by the human eye and some can’t. Two of the more common colors used in scientific experiments that can be seen by eye are green and red! In fact, the 2008 Nobel Prize in Chemistry was awarded to three people for the discovery of green fluorescent protein, originally isolated from jellyfish.

Fluorescent dyes play an important part in scientific research, but some tissue in our bodies give off fluorescence naturally without any help from additional dyes. This type of fluorescence is called “autofluorescence.” Blood vessel walls are one example in our body that’s autofluorescent. As we age, our brains seem to accumulate a pigment that gives off a lot of autofluorescence, which means it glows when viewed under a microscope. One challenge for scientists has been to try and block this background autofluorescence in the brain so we can better study what we actually want to see without this background autofluorescence covering it. This may sound a bit contradictory to what we just said about fluorescence helping us see structures more clearly, but fluorescence is more complicated than you might think! Imagine a really bright light shining in your eyes that makes it hard for you to see what’s behind it, but we’ll save more specifics for another time.

Regardless of its complexities, fluorescence—including the “Christmas lights” of our brains—is an interesting and valuable technique we can use to look inside and further study the amazing human body.

Katie Anne Fopiano is a doctoral candidate at the Medical College of Georgia at Augusta University. She researches how various diseases alter the microvasculature and specifically explores the role the microvasculature plays in the development of cardiovascular and cerebral diseases.