A large international collaboration of scientists known as the FlyWire Consortium worked on the project, which detailed more than 50 million connections between more than 139,000 neurons — brain nerve cells — in the insect.

The research sought to decipher how brains are wired and the signals underlying healthy brain functions. It could also pave the way for mapping the brains of other species.

"You might be asking why we should care about the brain of a fruit fly," Princeton University Neuroscience Professor Sebastian Seung, who worked on the project, said.

Scientists imaged 7,000 'salami-sliced' sections of fruit fly brain

The fruit fly used in the study, whose scientific name is Drosophila melanogaster, is often used in neurobiological studies.

While some people may be more interested in swatting flies than studying them, some of the researchers found aesthetic satisfaction peering at the fruit fly brain — though it's less than one millimetre wide.

"It's beautiful," University of Cambridge neuroscientist and research co-leader Gregory Jefferis said.

"When you dive inside the brain it's just incredibly complicated and intricate at this microscopic level," he told ABC News.

The map devised by the researchers provided a wiring diagram, known as a connectome, for the brain of an adult fruit fly.

The researchers fashioned a map tracking the organisation of the hemispheres and behavioural circuits inside the fly's brain.

They also identified the full set of cell classes in its brain, pinpointing different varieties of neurons and chemical connections — synapses — between these nerve cells, and looked at the types of chemicals secreted by the neurons.

Dr Jefferis said the project began "10 years ago" with imaging of 7,000 "salami-sliced" sections of a fruit fly brain.

While dozens of researchers put in hours of work over a decade for the project, they also used artificial intelligence to trace out the sections automatically with machine vision, Dr Jefferis said.

He said the scientists could look at sensations, reflexes and memory in the fruit fly brain.

Sight, taste, motion analysed

Similar research was previously conducted on simpler organisms, such as the worm Caenorhabditis elegans and the fruit fly's larval stage. But the adult fruit fly has more complicated brain wiring to study.

"One of the major questions we're addressing is how the wiring in the brain, its neurons and connections, can give rise to animal behaviour," Princeton neuroscientist Mala Murthy, another research co-leader, said.

"They're capable of sophisticated behaviours like the execution of walking and flying, learning and memory behaviours, navigation, feeding and even social interactions, which is a behaviour that we studied in my lab at Princeton."

One of the studies analysed brain circuits underlying walking and discovered how flies halt.

Another analysed the fly's taste network and grooming circuits behind behaviour, such as when it uses a leg to remove dirt from its antennae.

Another looked at the visual system including how the fly's eyes process motion and colour information.

Still another one analysed connectivity through the brain, discovering a large assemblage of "hub neurons" that may speed up information flow.

"These kind of maps really let us think about the mechanics of thought," Dr Jefferis said.

However, he noted "the difference is pretty dramatic" between human and fruit fly brains. 

"The human brain is a million times bigger than the fly brain in terms of neurons," he said, so scientists have a ways to go before mapping it.

Reuters/ABC