Loss of Flexibility

During infancy, the brain is exceptionally plastic, with sensory neuronal activity continuously shaping and refining the brain’s circuitry. By adolescence, however, this plasticity reduces and pathways become increasingly fixed. Astrocytes, like the one pictured, appear to be responsible for this restriction. Neuroscientists have discovered that the stress hormone cortisol acts on these cells during mouse development, prompting them to produce factors that promote maturation of the extracellular matrix around neurons, which in turn restrains the neurons from making new connections. Indeed, blocking cortisol’s action on astrocytes leads to increased brain plasticity in adult mice. In humans, aberrations in plasticity are thought to contribute to neurodevelopmental conditions including autism spectrum disorder and schizophrenia. Since the cortisol-astrocyte pathway seems to be conserved in humans too, the big question is, could modifying adult plasticity, via astrocyte manipulation, help treat such disorders?

Written by Ruth Williams

Ruth Williams

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Ruth is a freelance science journalist based in the US. She's a regular correspondent for The Scientist, and her work has appeared in The Lancet, Nature, Scientific American Mind, BBC Focus and elsewhere. Twitter @rooph

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• Image from work by Bruno Gegenhuber and colleagues, Greenberg Lab
• Department of Neurobiology, Harvard Medical School, Boston, MA, USA
• Image originally published with no restrictions – hence published here with as Creative Commons Attribution 4.0 International (CC BY 4.0)
• Research published in Nature, May 2026