Stanford researchers find human brain consists of two distinct organs

Researchers at Stanford University have discovered that the human brain is not a single unified organ, but a composite of two distinct nervous systems that evolved independently over approximately 550 million years. The study, published in Nature Neuroscience, reveals that the brain originates from two separate populations of progenitor cells during embryonic development.

One system, the forebrain and midbrain, is responsible for higher cognitive functions such as language, consciousness, and abstract reasoning. The other, the hindbrain (or rhombencephalon), is a more primitive system that regulates vital physiological processes including heart rate, breathing, sleep, and hunger.

This discovery overturns the long-held scientific model that the entire brain develops from a single progenitor cell. It also provides a potential explanation for why scientists have historically struggled to grow specific hindbrain neurons in laboratory settings. The findings open new avenues for researching neurodegenerative diseases that affect the brain stem, such as amyotrophic lateral sclerosis (ALS) and spinal muscular atrophy (SMA).