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Flies have more complex cognitive capacities than previously thought


The cognitive capacities of common flies are more sophisticated than previously thought. Researchers discovered attention, working memory, and conscious awareness-like skills in fruit flies using a custom-built immersive virtual reality arena, neurogenetics, and real-time brain activity imaging.

Fruit flies seem to have nothing in common with mammals as they swarm about a batch of bananas in our kitchens. However, as a model species for science, researchers are finding more and more parallels between humans and tiny fruit-eating insects.

Fruit flies (Drosophila melanogaster) exhibit more sophisticated cognitive capacities than previously thought, according to researchers at the University of California San Diego’s Kavli Institute for Brain and Mind (KIBM). The scientists publish fresh evidence of the amazing linkages between the cognitive skills of flies and mammals in the journal Nature on Feb. 16 using a custom-built immersive virtual reality environment, neurogenetic modifications, and in vivo real-time brain-activity imaging.

Their multi-tiered technique revealed that fruit flies had attention, working memory, and conscious awareness-like skills, which are generally exclusively examined in mammals. In these little brains, the researchers were able to see the creation, distractibility, and final fading of a memory trace.

“Despite the absence of evident physical similarities, this research speaks to our daily cognitive functioning — what we pay attention to and how we do it,” said study senior author Ralph Greenspan, an assistant director of KIBM and a professor in the UC San Diego Division of Biological Sciences. “We may draw correspondences between fly and mammalian brain areas based on chemical traits and how we store our memories since all brains developed from a similar ancestor.”

The researchers used an immersive virtual reality environment to examine the fly’s behavior through visual stimulation and combined the projected images with an infrared laser as an aversive heat stimulus to arrive at their new results. The nearly 360-degree panoramic arena allowed Drosophila to flap their wings freely while still being tethered, and the virtual reality was constantly updating based on their wing movement (which was analyzed in real time using high-speed machine-vision cameras), giving the flies the illusion of flying freely in the world. Researchers were able to train and test flies for conditioning tasks by enabling them to orient away from a picture linked with a negative heat stimulus and towards a second, non-heated image.

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They tested two types of conditioning: one in which the flies were given visual stimulation that was timed to coincide with the heat (delay conditioning), with both ending at the same time, and a second, trace conditioning, in which the heat was delivered 5 to 20 seconds after the visual stimulation was shown and removed. The “trace” interval is the duration during which the fly keeps a “trace” of the visual input in its brain, which is a trait associated with attention, working memory, and conscious consciousness in mammals.

The researchers also used a fluorescent chemical that they genetically modified into their brain cells to scan the brain in order to detect calcium activity in real time. Since the trace flashing on and off while being kept in the fly’s short-term (working) memory, the researchers were able to capture the development and length of the fly’s living memory. They also discovered that a training distraction — a light puff of air — caused the visual memory to fade faster, marking the first time researchers have been able to demonstrate such distractedness in flies and indicating an attentional need in memory formation in Drosophila.

“Not only does this research show that flies are capable of this higher kind of trace conditioning and that the learning is distractible, much like mammals and humans,” said Dhruv Grover, a UC San Diego KIBM research faculty member and lead author of the new study. “This research shows that fruit flies may be a useful model for studying higher cognitive abilities. Simply told, the fly continues to wow us with its intelligence.”

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The scientists also pinpointed the spot in the fly’s brain where the memory originated and faded: the ellipsoid body of the fly’s central complex, which corresponds to the cerebral cortex in humans.

Furthermore, the researchers revealed that the neurochemical dopamine is essential for higher cognitive tasks like learning. Dopamine responses began to emerge sooner in the learning process, ultimately anticipating the approaching heat stimulation, according to the findings.

The researchers are currently looking at the specifics of how the brain encodes attention physically. Grover believes that the lessons learned from this model system will not only directly inform our understanding of human cognition strategies and the neural disorders that disrupt them, but will also contribute to new engineering approaches that will lead to artificial intelligence performance breakthroughs.

Dhruv Grover, Jen-Yung Chen, Jiayun Xie, Jinfang Li, Jean-Pierre Changeux, and Ralph Greenspan (all of whom are connected with the UC San Diego Kavli Institute for Brain and Mind, with J.-P. Changeux being a member of the Collège de France) are among the study’s coauthors.

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