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What do nerves need in order to grow? That question first caught Rita Levi-Montalcini’s attention in the 1930s, when she came across a recent paper by embryologist Viktor Hamburger. After observing that clipping the wing bud off chicken embryos stunted the growth of spinal nerves and ganglia on the side of the body with the excision, Hamburger reported that signals from the limb drove the growth and differentiation of immature cells in the central nervous system. Levi-Montalcini was intrigued. But after repeating the embryo experiments and finding that the chick’s nerve cells continued to develop after amputation and died later—just before reaching their target tissue—she came to a different conclusion. Rather than failing to initiate nerve growth, she hypothesized, the animals were unable to sustain the growing cells, causing a degenerative process that limited their proliferation.
Levi-Montalcini began these experiments at the University of Turin in ...
