Harvard neuroscientists have cultured human brain organoids (miniature tissue structures) in lab dishes for over 5 years—more than triple the previous world record of 694 days—with cells developing on the same molecular timeline as actual brain development in utero and early childhood. Using single-cell RNA sequencing and epigenetic methylation "clocks," researchers tracked 110 organoids containing nearly 425,000 cells across 5+ years, confirming that organoids faithfully recapitulate human cortical development. This breakthrough could enable disease modeling and drug testing without accessing the inaccessible human brain, addressing a critical gap in neuroscience research.