Decoded: how brain wires up for better social behaviour

In a path-breaking discovery, scientists have identified, for the first time, why different parts of the brain don't talk to each other very well, especially in people with autism and other neurodevelopmental disorders.

It can be caused by cells called microglia failing to trim connections between neurons in the brain, said a global team of researchers from European Molecular Biology Laboratory (EMBL) in Monterotondo, Italy, Istituto Italiano di Tecnologia (IIT) in Rovereto, Italy, and La Sapienza University in Rome.

Microglia cells act as the first form of active immune defence in the central nervous system and reside in the brain and spinal cord.

"We show that a deficit in microglia during development can have widespread and long-lasting effects on brain wiring and behaviour," said Cornelius Gross, who led the study.

"It leads to weak brain connectivity, decreased social behaviour and increased repetitive behaviour, all hallmarks of autism," Gross added.

The findings indicate that by trimming surplus connections in the developing brain, microglia allow the remaining links to grow stronger, like high-speed fibre-optic cables carrying strong signals between brain regions.

But if these cells fail to do their job at that crucial stage of development, those brain regions are left with a weaker communication network, which, in turn, has lifelong effects on behaviour.

Yang Zhan, a postdoctoral fellow in Gross' lab at EMBL, analysed the strength of connections between different areas of brain in mice that were genetically engineered to have fewer microglia during development.

The scientists combined this approach with high-resolution fMRI (functional Magnetic Resonance Imaging) scans of the mice's brains.

The team found that mice with fewer microglia had weaker connections between neurons and less cross-talk between different brain regions.

These mice spent more time repeatedly grooming themselves and avoided social interactions.

This is an exciting time to study as they're turning out to be major players in how our brain gets wired up, said the study published in the journal Nature Neuroscience.