NOTEBOOK: Brain swapping comes of age
By Jack Lucentini

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
is Dr. Moreau, brain-swapping research is coming into its own, with the
potential to answer questions other technologies can't, says Balaban.
This associate professor of behavioral neuroscience at McGill
University in Montreal is unfazed by the contrast between the glitz of
kindred work, such as stem cell implantation, and the whiff of gothic
horror that accompanies his work.

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."

<http://www.the-scientist.com/2006/3/1/18/1/>