For more than two decades, Evan Balaban has honed his skills at manipulating embryonic tissue samples using tiny instruments of his own making. He can cut a small access window into a quail's egg, and using a scalpel no wider than a human hair, excise a few hundred thousand cells from the bird's developing central nervous system. This is only the first step of the intricate process required to place this minuscule brain into another animal's head. Some of these surgeries end in untimely death for brain-transplanted embryos, but Balaban says he has elevated the typical survival rate from less than 20% to more than 60%. That was unimaginable in the 1950s, he says, when success was more along the lines of one or two in 1,000, and some researchers "were doing this with piano wire."

But don't cue the maniacal laughter just yet. As much T.H. Morgan as it...

Far from being a throwback, he insists, brain swapping is "really working at the right level for answering a lot of interesting questions about brain development and behavior," and techniques are improving all the time. Not until two or three decades ago did biologists understand brain circuitry well enough to make good scientific use of brain transplants, though they have been technically feasible since H.G. Wells' time. Since then, researchers have swapped the brains of various species of frogs and salamanders, as well as ducks, in addition to the quails and chicks that Balaban uses. He plans on trying it on songbirds too.

Transferring brain tissue between embryos has enabled Balaban to examine how birds with implants from different bird species innately prefer the other species' songs. "You [can] make chicken that prefer the quail sound, even more than normal quail do ? as if in the chicken, the cells seize more behavioral control," he remarks. Another of his creations, chickens that bobbed their heads up and down like quail while crowing, provides further proof, he says, that some habits are innate rather than learned and can be traced to specific brain structures.

Balaban's work focuses on how nature and nurture blend together to create a seamless set of brain circuits. Other brain-swappers have focused on how brain structure makes males and females different, or how dysfunctional circuitry manifests itself in congenital abnormalities such as epilepsy.

Balaban estimates that there are four or five active brain-swappers worldwide and sees growing interest in the work among molecular biologists. They find "so much good information available about what molecules are doing," he explains, but those data shed little light on "system interactions," the wider context of brain circuitry. Molecular or genetic techniques provide "good information about the role of a particular molecule, but the context and the larger evolutionary questions can be hard to get into."

Brain switching isn't for everyone, says Manfred Gahr, director of the Max Planck Institute for Ornithology in Starnberg-Seewiesen, Germany, and Balaban's former postdoc. "It's a very tedious technique ? you have to make very accurate movements," he notes, adding that it took him roughly six months to learn to do the surgeries.

Balaban has learned to warm and humidify the environment, to properly tape over the hole in the egg, and other tricks of the trade, and he's happy to share the fruits of this labor. "I freely teach these things to anyone who wants to know them," he says. "I'm very anxious to have the technique continue to improve and to have it diffused, because that's the only way it will survive."

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