For the first time, a complete brain map of a living being has been created

Researchers from England and the USA show how neurons are wired in the brain

Scientists from the UK’s Medical Research Council Laboratory of Molecular Biology and the University of Cambridge, along with colleagues from the UK and the US, have succeeded for the first time in creating the largest complete brain map of a living creature: They mapped the brain of a fruit fly larva, showing not only the 3016 neurons but also an incredible 548,000 synapses. Their study results were published in the renowned journal “Science” on 10 March 2023.

Understanding basic principles of how signals travel through the brain at the neuronal level

The aim of the work, led by neurobiologist Prof. Marta Zlatic and neuroscientist Prof. Albert Cardona, was to understand the basic principles by which signals travel through the brain at the neuronal level and lead to behaviour and learning.

The map of the 3016 neurons that make up the larval brain and the detailed circuits of neural pathways they contain are called “connectomes”. Connectomes represent the totality of connections in the nervous system of a living organism.

The nervous system of every organism, including the brain, consists of neurons that are connected to each other via synapses. Through these contact points, information is passed electrically from one neuron to another in the form of chemicals.

Great progress: How does a brain actually work?

Prof. Zlatic explains: “The way the brain’s circuitry is structured affects the computations that the brain can perform. But until now, we had not been able to see any structure from a brain, except for the roundworm C. elegans, the tadpole of a low chordate and the larva of a marine annelid, all of which have only several hundred neurons. This means that neuroscience has mostly had to work without circuit maps until now. Without knowing the structure of a brain, we could only guess how computations would be implemented. But now we can start to gain a mechanistic understanding of how the brain actually works.”

Waiting for technology: connectome of higher organisms cannot yet be visualised

The neurobiologist laments that current technology is not yet advanced enough to map the connectome for higher animals such as large mammals, but still, “All brains are similar – they are all networks of interconnected neurons – and all brains in all species must perform many complex behaviours: They all have to process sensory information, learn, select actions, navigate their environment, select food, recognise their conspecifics, and so on. Just as genes are fixed throughout the animal kingdom, I think the basic circuitry that implements these basic behaviours is also fixed.”

To create an image of the fruit fly larva’s connectome, Zlatic, Cardona and colleagues scanned thousands of sections of the larva’s brain using a high-resolution electron microscope. They reconstructed the resulting images into a map of the fly brain and documented the connections between neurons. In the process, they mapped not only the 3016 neurons, but also an incredible 548,000 synapses!

The researchers also developed special computer tools to identify likely pathways of information flow and different types of circuit motifs in the insect’s brain. In the process, they found that some of the structural features correspond exactly to state-of-the-art deep learning architecture.

“This is a big step forward in answering important questions about how the brain works, particularly how signals move through the neurons and synapses that lead to behaviour, and this detailed understanding may lead to therapeutic interventions in the future,” the researchers said.

The next step will be to dive even deeper into the brain to understand, for example, the architecture required for certain behavioural functions such as learning and decision-making, and to look at activity throughout the connectome while the insect is active.

Source: UK Research and Innovation.