Scientists have created the most complete image of a brain to date and it is a glorious, rainbow-colored masterpiece. The research has been published in the journal Cell. 

The brain that has been mapped belongs to a fruit fly (Drosophila melanogaster), those pesky little insects that like to hang around overripe fruit. These bugs have brains the size of a poppy seed and roughly 100,000 neurons. In comparison, human brains are thought to contain 100 billion neurons, though this hasn't been proven in a peer-reviewed study and recent research suggests this is actually an overestimation. Still, there is a big difference in scale between a fruit fly brain and a human brain. 

The reconstruction was built using 21 million images, 7,062 brain slices, and a technique called serial selection transmission microscopy. The end result is an intricate 3D map that can be explored from every angle and zoomed in on, allowing you to revel in the most stunning detail.

“The entire fly brain has never been imaged before at this resolution that lets you see connections between neurons,” Davi Bock, a group leader at the Howard Hughes Medical Institute's Janelia Research Campus, said in a statement.

 ^{Z. Zheng et al./Cell 2018}

The endeavor was only possible because of advances in electron microscopy technology. According to Bock, the study would have been such a painfully slow process that it would have been out of the question 10 years ago. 

“Imagine taking 21 million pictures with your iPhone,” he explained. “You’d be sitting and clicking for decades.” Now it is possible to image a complete brain slice in fewer than 7 minutes. 

But before the team could take images of the neurons, they first had to inject heavy metals into the brain. These metals coat the tissue and leave behind a residue on the cell membranes and synapses, which can later be picked up by the camera. The brain is then sliced and a beam of electrons is directed at each slice. The electrons pass through all but the metal-loaded sections (i.e., the neurons), exposing the brain's architecture.

"It’s the same way that X-rays go through your body except where they hit bone,” Bock added.

Sewing together millions of images, the team was able to map out the entire brain of a fruit fly. Already, they are making new discoveries.

Fruit flies are surprisingly sophisticated, Bock says. As well as being able to learn, remember, and recognize where is safe and where is not, they have impressive mating displays and grooming behavior. Now, the team is identifying new neurons and discovering how different cells in the fly's brain communicate with one another.

The ultimate end goal is to map out the human brain in a similar fashion, but this could be years in the making.