The human brain continues to produce new nerve cells throughout its life and these neurons may be key to learning new information. But many of these novice neurons wither and die before joining the vast signaling network of their mature peers. Now new research seems to show that the presence or absence of new information–represented by the neurotransmitter glutamate–may determine a young neuron’s survive.

Beginning in 1962, a researcher at MIT named Joseph Altman published several papers claiming that adult rats, cats, and guinea pigs all formed new neurons. Although Altman used the same technique that Rakic would later use in monkey brains—the injection of radioactive thymidine—his results were at first ridiculed, then ignored, and soon forgotten.

As a result, the field of neurogenesis vanished before it began. It would be another decade before Michael Kaplan, at the University of New Mexico, would use an electron microscope to image neurons giving birth. Kaplan discovered new neurons everywhere in the mammalian brain, including the cortex. Yet even with this visual evidence, science remained stubbornly devoted to its doctrine. Kaplan remembers Rakic telling him that “Those [cells] may look like neurons in New Mexico, but they don’t in New Haven.” Faced with this debilitating criticism, Kaplan, like Altman before him, abandoned the field of neurogenesis.