Enriched Environments and Sensory Loss Reshape Synapse Populations Across the Mouse Brain

Researchers at the University of Edinburgh have mapped billions of individual connections between brain cells in mice and found that experience reshapes them far more broadly than earlier work could show. The study appears in the journal Nature Communications.

The connections in question are synapses, the junctions through which nerve cells communicate. It has long been known that experience changes the brain: learning and sensory input can alter how strongly neurons talk to one another, and synapses can form, vanish or change structure. But earlier studies tended to look at relatively small numbers of synapses in confined regions, which gave a limited picture of what happens across the whole organ.

The Edinburgh-led team used a technique called synaptome mapping, which pairs high-resolution microscopy with automated image analysis, to survey synapses across the entire mouse brain. They studied mice kept in enriched environments, which included running wheels, mazes that changed, and more opportunities for social interaction. Some animals experienced this during development and others in adulthood.

The enriched mice showed changes in distinct populations of synapses across many brain regions. Different types of synapse responded differently: some became more numerous, some fewer, and others did not change at all. Yet the overall density of synapses in the brain did not rise. The researchers read this as a sign that the type and quality of connections matter more than their sheer number.

To test how sensory change plays out across the brain, the team also closed one eye of a group of mice for a week. The effects did not stay within the visual system. Synapse changes appeared in areas tied to other senses and to memory. Experts involved say this suggests that a change in one kind of sensory experience can trigger molecular adaptations widely, underlining how interconnected brain functions are.

The team suggests the findings could help explain why some events help the brain adapt while others may contribute to impaired function. Synapse changes have previously been linked to sleep deprivation, brain injury, and genetic variants associated with autism, schizophrenia and other disorders. Alterations to the brain's varied synapse populations could be a shared mechanism through which it responds to both inherited and environmental influences. If so, understanding how experience shifts these populations might eventually point to ways of modifying synapses disrupted by environment, genetics or injury, the researchers add.

Dr Hanan Woods, the study's first author, from the University of Edinburgh's Institute for Neuroscience and Cardiovascular Research, said the results suggest sensory and environmental experiences reshape the molecular landscape of synapses throughout the brain, and that this diversity and capacity for adaptation may offer a foundation for understanding resilience and vulnerability to disease across life.

Seth Grant, Professor of Molecular Neuroscience at Edinburgh, said the work raises questions for development and education about how combinations of sensory, physical, social and learning experiences shape the brain's molecular architecture. He added that it gives a basis for future questions about how factors such as prolonged phone or tablet use might modify the brain.

The research team also included scientists from Cardiff University and the University of Strathclyde, and the work was supported by Wellcome, the European Research Council and the Simons Foundation. The findings are in mice, and the human implications raised by the authors remain questions for future work.