Building Nerve Circuits

What was puzzling, though, was just how it all got wired up in the first place. Experiments in the 1950s showed that every neuron somehow knew how to reach its intended destination. Scientists such as Roger Sperry, who received the Nobel Prize in 1981, tried 'rewiring' nerves in experimental animals with bizarre results - connecting nerves back to front made the animals see upside down, or walk backwards.

So how then did nerves end up attaching to the right place? Sperry suggested they were like hounds on a scent, drawn by a recipe of chemical signals sent out by the target. Few scientists believed this to be the case, even when Rita Levi-Montalcini discovered a chemical called Nerve Growth Factor, or NGF for short, that seemed to fit the bill. Together with her colleague, Stanley Cohen, Levi-Montalcini eventually proved that the NGF protein stimulates the growth of nerve connections, for which they shared the 1986 Physiology or Medicine Prize. Nerve fibres grow towards the source of NGF, which can be produced in the local neighbourhood by many types of cell, allowing fibres to find their intended destinations, even through the dense thicket of nerves that make up the brain.

Thanks to the pioneering work carried out by Golgi and Cajal, Sperry, Cohen and Levi-Montalcini, and a host of other researchers, we have a remarkably clear picture now of how the nervous system is wired up. But finding out just how messages travel through it required another remarkable voyage of discovery.

related articles:

mapping nervous system Find Gap! Building Nerve Circuits Generating Nerve Signals Acting on Impulses Voltage Regulator Crossing the Gap Sparks Fly Chemical Communication Brain-Enhancing Chemicals Mind Matters