Human brain organoids record the passage of time over multiple years.

Human brain organoids maintained for 5 years in culture transcriptionally age with cell type specificity, and their predicted epigenomic age correlates precisely with time in vitro.

• Why it matters: Human postnatal brain maturation over nearly two decades is hard to model in animals, and organoids previously reflected mainly early development.
• What they did: The team optimized culture conditions to extend excitatory neuron viability and used maturation-associated modules plus whole-genome methylation profiling to track aging over years.
• The result: In chimeric organoids, neural progenitors of different ages show a memory of time in vitro by rapidly generating late neuronal fates, implying organoids can mature and record time for many years.

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