Team Meticulously Counts Insect Brain Cells

Scientists at Johns Hopkins Medicine have meticulously counted the brain cells in fruit flies and three species of mosquitos, and found that, on average, the insects’ brains have about 200,000 neurons and other cells. By comparison, a human brain has 86 billion neurons, and a rodent brain contains about 12 billion.

"Even though these brains are simple [in contrast to mammalian brains], they can do a lot of processing, even more than a supercomputer," says Christopher Potter, senior author on the study published today in PLOS ONE.  "They enable the insects to navigate, find food and perform other complicated tasks at the same time, and our study offers one answer to the question of how many brain cells come together to conduct these behaviors."

Those who study insect behavior and brain function have long suspected these insects must have hundreds of thousands of brain cells, says Potter, but when he and postdoctoral fellow Joshua Raji followed chains of scientific papers that referenced the count, they did not find proof for it.

In response, they report, they set out to find proof using a relatively simple counting method called an isotropic fractionator. First, they used a plastic pestle to break down all the brain tissue of the individual insects. Then, they used a pipette to break apart the tissue and distribute the cells evenly through a buffered solution. Knowing the precise total volume of the solution, they could then count cells within a small fraction of the solution, and scale it up to account for and estimate the total number of cells in the entire solution. To make the actual count, the small amount of solution was spread on a microscope slide and placed on top of a small grid. With painstaking precision, they counted the cells on each slide, one by one.

The researchers concluded that the total sum of brain cells was 199,380 plus or minus 3,400 for Drosophila melanogaster. For three species of mosquito, the researchers found 217,910 plus or minus 6,180 in Aedes aegypti; 223,020 plus or minus 4,650 in Anopheles coluzzii; and 225,911 plus or minus 7,220 in Culex quinquefasciatus.