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Some insects have more than 200,000 brain cells

Scientists at Johns Hopkins Medicine are describing why insects are much smarter than what you would expect. After meticulously counting the neurons in fruit flies and three species of mosquitos, the experts found that their brains contained an average of 200,000 cells. 

A human brain contains 86 billion neurons, while a rodent brain contains about 12 billion. According to the researchers, the average number of brain cells found in the insects likely represents a “floor” for the number needed to execute complex tasks. 

“Even though these brains are simple (in contrast to mammalian brains), they can do a lot of processing, even more than a supercomputer,” said Dr. Christopher Potter.

“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.”

According to Dr. Potter, those who study insect behavior and brain function have long suspected these insects must have hundreds of thousands of brain cells. In collaboration with Dr. Joshua Raji, he searched for documentation to support this theory, but came up without any proof.

The experts set out to find their own proof using a relatively simple counting method called an isotropic fractionator, which is a method used to determine the cellular composition of nervous tissue.

First, Dr. Raji broke down all of the brain tissue of individual insects. Then, he used a pipette to break apart the tissue and distribute the cells evenly through a buffered solution.

Dr. Potter said the most challenging part of the technique was the microdissection of a brain that is smaller than the tip of a pencil. “It takes a really steady hand and lots of practice.”

The solution that contained the brain cells was spread on a microscope slide and placed on top of a small grid. Dr. Raji thoroughly counted the cells on each slide.

The experiment revealed that the fruit fly, Drosophila melanogaster, had 199,380 brain cells plus or minus 3,400. 

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.

The brain cells in each species were made up of about 90 percent neurons, while the rest are most likely supportive cells called glia, explained the experts. 

Dr. Potter said that researchers have determined the number of brain cells in only a few species of insects, including wasps and ants. “It would be interesting to apply this approach to social insects like bees, and see if there are differences between queens and drones.”

The counting technique used for this study is a simple one that most researchers could perform, said Dr. Potter, and it is an opportunity for any researcher to contribute the counts to scientific literature.

The study is published in the journal PLOS ONE.

By Chrissy Sexton, Staff Writer

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