The brain of the fruit fly larva has been comprehensively mapped by researchers for the first time, revealing the connectivity of each and every neuron.

This groundbreaking achievement in science will contribute to our comprehension of how neural signals operate in the brain, leading to behaviors and learning.

The connectome of the larva’s brain encompasses the circuitry of neural pathways and all of its 3016 neurons, making it the most extensive complete brain connectome documented thus far.

This groundbreaking study was carried out under the direction of Professor Marta Zlatic and Professor Albert Cardona of the Medical Research Council Laboratory of Molecular Biology and the University of Cambridge, together with colleagues from the US and the UK. 

The study was published today in Science.

The nervous system of an organism, including the brain, is made up of neurons that are linked together via synapses. Chemical information is transferred from one neuron to another through these contact sites.

According to Professor Zlatic, the organization of brain circuits has a direct impact on the brain’s computational capabilities. Thus far, the structure of only a few brains, such as those of the roundworm C. elegans, the larva of a marine annelid, and a low chordate tadpole, all of which have only a few hundred neurons, have been studied.

“This means neuroscience has been mostly operating without circuit maps. Without knowing the structure of a brain, we’re guessing on the way computations are implemented. But now, we can start gaining a mechanistic understanding of how the brain works.”

Although current technology is insufficient to map the connectome of higher animals such as large mammals, Professor Zlatic explained that all brains share a similar structure, consisting of interconnected networks of neurons.

In addition, all species must engage in various complex behaviors, such as processing sensory information, learning, selecting actions, navigating their surroundings, choosing food, recognizing others of their kind, and escaping from predators.

Like genes, which are conserved across the animal kingdom, she believes that the fundamental circuit motifs responsible for implementing these behaviors will also be conserved.

Zlatic, Cardona, and colleagues used a high-resolution electron microscope to scan hundreds of slices of the fruit fly larva’s brain in order to create a representation of the connectome. Scientists meticulously labeled the connections between neurons and painstakingly assembled the resultant photos into a map of the fly’s brain. They not only mapped the 3016 neurons but also an astounding 548,000 synapses.

The researchers also created computational techniques to uncover potential information flow channels and circuit patterns in the insect’s brain. Also, they discovered that several structural elements closely resemble modern deep-learning architecture.

According to Professor Zlatic, the most challenging aspect of this research was comprehending and interpreting the complex neural circuitry observed in the fruit fly larva brain connectome. To address this challenge, her team collaborated with Professor Priebe and Professor Vogestein’s groups at Johns Hopkins University, developing computational tools to extract and predict the relevant circuit motifs from the neural structure. By analyzing this biological system, it may also be possible to generate inspiration for the development of more effective artificial networks.

Head of Neurosciences and Mental Health at the Medical Research Council, Jo Latimer, expressed enthusiasm for the significant achievement of the MRC Laboratory of Molecular Biology and their collaborators in comprehensively mapping every neuron in the fruit fly larva brain connectome and understanding the connectivity between them. This breakthrough provides valuable insights into how neural signals traverse through neurons and synapses, leading to behavior, and may contribute to future therapeutic interventions.

The next stage will be to explore further into the architecture necessary for certain behavioral processes like learning and decision-making, as well as look at activity in the whole connectome when the insect is doing things.

Source: 10.1126/science.add9330