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.

A common ornamental tree planted along sidewalks and in gardens throughout the world, Ginkgo biloba–also called the maidenhair tree–has been considered a source of herbal medicine for millennia. During the 1990s, several studies showed the extracts helped improve memory in patients with dementia (ScienceNOW, 30 May). And today, ginkgo is a popular remedy sold not just for memory loss but also for ailments ranging from depression to hemorrhoids.
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further investigation indicated that live ginkgo cells were harboring algal “ghosts”: nondescript cell bodies that lacked a nucleus or chloroplast. When ginkgo cells died, these ghosts came back to life, transforming themselves into free-living, photosynthesizing algae.
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In living cells, the algae depend on the ginkgo for food. In return, it’s possible that the algae somehow help produce the ginkgo’s medicinal compounds, he suggests. Not much is known about the synthesis of these unique compounds except that making them requires two compartments–the cytosol–and “some unknown organelle,” says Huss. That organelle might be the algae.

Whatever the nature of the partnership, it could be more than a hundred million years old. Ginkgos date back to the dinosaurs, and researchers know already that the two other plants dating back that far back depend on symbiosis to survive. “That makes me think that symbiosis is part of an ancient story,”