Stanford's Loh lab traces the front and back of the brain to two separate progenitor cells

The finding came out of a failure. "It was actually a summer student's failed experiment that got us into this," Kyle Loh of Stanford University told New Scientist ^[9]. Labs trying to grow hindbrain neurons had typically started from progenitor cells destined to become forebrain and midbrain neurons, and, according to Loh, that does not work ^[10]. Starting from the GBX2 population instead, his group grew functional human hindbrain motor neurons in a dish, which the report describes as a first ^[11].

That matters for two diseases. ALS is the most common motor neuron disease, and both ALS and spinal muscular atrophy cause speech and swallowing difficulties because they affect the hindbrain ^[13]. Loh said the easier route to hindbrain neurons should assist research into both ^[15]. The mouse work was done in embryos, the human work in culture ^[4][7]. New Scientist's report does not name the journal or give the number of embryos staged.

The evolutionary claim rests on a different kind of evidence. Chicken, zebrafish and acorn worm embryos showed the same two-progenitor pattern ^[16], and on that basis the researchers suggest the two-origin arrangement is at least 550 million years old ^[17]. Jellyfish, which have two separate nervous systems, diverged from our lineage 600 to 700 million years ago ^[18]. Subtract one figure from the other and any merger has to sit between 550 and 700 million years ago, a bracket as much as 150 million years wide ^[1].

"Our research suggests that evolution took two existing neural systems and pushed them together spatially," Loh said ^[2]. He put the design cost plainly: "Having the brain as one organ would probably be more efficient, but we rely on this primordial way to make the brain as two separate pieces" ^[3]. On what the split may have bought, with the hindbrain handling breathing, sleeping, eating and the beating of the heart ^[12], he said "evolution could play around with the forebrain, and make mistakes and give rise to all the fancy things like memory and creativity" ^[20]. Those are hypotheses about selection, and what the experiments measured was progenitor identity.

The other use Loh named is pharmacological. GLP-1 drugs including Ozempic and Wegovy suppress appetite in mice by acting on the hindbrain ^[14], and Loh said human hindbrain neurons in a dish should let researchers investigate how those drugs work in people ^[15]. The cell type his group reports making is the motor neuron ^[11], which is what ALS and spinal muscular atrophy attack ^[13]; the appetite question would need other hindbrain neurons grown from the same GBX2 lineage.