There is no anatomical indication that memories could have survived, he added. VijayRaghavan, an emeritus professor and former director of India’s National Center for Biological Sciences who was the main editor of the paper and was not involved in the study. “It’s almost as if you would deliberately unplug and replug” the machine.Īs a result, the adult brain’s mushroom body is “fundamentally … a completely new structure,” said K. The mushroom body in the larva looks very similar to the adult version, Thum said, but “the rewiring is really intense.” It’s as if the inputs and outputs of a computational machine all got disrupted but still somehow maintained their wireless functionality, Gerber said. These neurons are not used by the larva, but at metamorphosis they mature to become input and output neurons for nine new computational compartments that are adult-specific. In addition to the remodeled larval neurons, many new neurons are born as the larva grows. At this transformation stage, “it’s kind of this ultimate Buddhistic situation where you have no inputs, you have no outputs,” Gerber said.

All the connections between the neurons in the mushroom body and their input and output neurons are dissolved. Within those seven, some neurons die, and some are remodeled to perform new adult functions. Truman and his team found that when the larvae undergo metamorphosis, only seven of their 10 neural compartments are incorporated into the adult mushroom body. Each compartment has a task, such as guiding a fly toward or away from something. These networks are arranged in distinct computational compartments, like the spaces between the frets on the guitar. These neurons communicate with the rest of the brain through input and output neurons that weave in and out of the strings, creating a network of connections that allow the insect to associate odors with good or bad experiences. The region consists of a bunch of neurons with long axonal tails that lie in parallel lines like the strings of a guitar. The researchers zoned in on the mushroom body, a region of the brain critical for learning and memory in fruit fly larvae and adults. It allows you to look at not just one, two, or three neurons but an entire network of cells. It’s a “pretty cool method,” said Andreas Thum, a neuroscientist at Leipzig University and coauthor of the commentary with Gerber. So even as nearly all the other cells in the fruit fly’s larval body are eliminated, most of the original neurons are recycled to function anew in the adult. That process is older than metamorphosis itself and not easily modified after a certain stage of development.

That’s partly because the nervous system in all insects arises from an array of stem cells called neuroblasts that mature into neurons. “The nervous system has never been able to change the way it makes neurons,” Truman said. The nervous system of a fruit fly offered a practical opportunity to do that: Although most of the fruit fly larva’s body cells die as it transforms into an adult, many of the neurons in its brain don’t. Truman knew that to really understand what’s happening to the brain, he had to be able to trace individual cells and circuits through the process.

“We didn’t have much of a big picture,” Truman said.

Since then, numerous studies have detailed different neurons and parts of the brains of larvae and adults, but they are either anecdotal or focused on very small aspects of the process. In 1974, he published the first paper on what happens to the brain during metamorphosis, for which he tracked the number of motor neurons in hornworm larvae and adults. While Riddiford focused her work on the effect of hormones on metamorphosis, Truman was most interested in the brain.

Metamorphosis franz