Research Could Hold A Key On
Human Memory Loss
The song of the zebra finch is a pretty simple one, and not particularly
tuneful, but it can tell us a surprising amount about how brains work and
preserve memories.
"One of the biggest hurdles in stem cell research now is directing new
cells to go only to the site where you want them to go; it's like herding cats
almost," said John Kirn, a Wesleyan University neuroscientist who has
studied bird brains since the 1980s.
Birds can create new brain cells through most of their brains, while the
creation of new neurons, known as neurogenesis, can occur in only a few regions
of a mammal's brain. Better understanding of how neurogenesis happens in birds'
brains, Kirn said, could lead to medical breakthroughs for humans.
"If we can understand how they manage to do this on the molecular
level, it might give us some insights that we can use," he said, adding
that stem therapy is one area that could benefit.
"There's something special about the bird brain that might be
important in how we can create therapies for human brain damage," he said.
Kirn recently co-authored a study on neurogenesis in the zebra finch. The
study, published in the May issue of the Journal of Neuroscience, could
influence research into neurodegenerative illnesses in
humans,includingAlzheimer's andParkinson's disease.
Typically, the song of a zebra finch will gradually degrade if it loses its
hearing. But the researchers found that new neurons that developed in zebra
finch brains helped the birds retain their song even after they were surgically
deafened.
"It's completely counterintuitive to what everyone thinks neurogenesis
is, which is to provide the flexibility for change and to learn new
things," Kirn said. "And this is perhaps an example of the opposite
of that. New neurons, in this case at least, are designed to preserve
function."
To arrive at this insight, the research team studied a group of zebra
finches, recorded their songs, injected the birds with a biomarker that would
highlight new neurons, and then deafened half the birds. After 30 days, they
analyzed the songs of the deafened birds to see which ones best preserved their
songs. "We have some really sophisticated software for measuring all sorts
of acoustic parameters," Kirn said.
The birds were then killed and their brains examined to see which birds had
the most neurons. One of the scientists' predictions was shot down immediately.
"There's a lot of evidence that certain kinds of experience including
social enrichment, can augment the number of neurons," Kirn said, adding
that the researchers thought the lack of hearing would have the opposite
effect. "We thought that the hearing birds would have more new neurons
than deaf birds, but there was no difference."
But when the researchers looked at the brains of the deafened birds, he
said, "that's when things got interesting."
"We found that the more new neurons a bird had, the longer it
preserved the song after it was deafened," he said.
This has some implications for the brains of other species — including
humans — and about the possible causes and even treatment of neurodegenerative
disorders.
"On the very abstract scale, it suggests the possibility that in some
brain regions, it might be possible to preserve information by adding new
cells," Kirn said. "If [human patients are] losing cognitive
function, if they're losing memories, this may be a way to not just enable you
to learn new information, but actually preserve old information."
The link between the brains of birds and humans is indirect, Kirn said, but
"not trivial." For instance, it was generally believed that most
animals — including humans — could not produce new neurons later in life. By
the 1990s, though, the idea was well-accepted that the production of new
neurons did occur in certain animals — thanks largely to research on birds.
Eventually, scientists accepted that it happened in humans as well, though only
in certain parts of the brain.
Fernando Nottebohm, a neuroscientist at Rockefeller University in New York
City and a mentor of Kirn's, was among the first to prove that neurogenesis
occurs in birds. His study of bird brains grew out of an interest in figuring
out how humans learn to vocalize.
"Some birds learn their songs much the way that people learn the
sounds of speech," he said. And bird brains are a lot easier to study than
the human brain. "We know much less about what goes on in the human than
in the bird brain."
Kirn studies the zebra finch almost exclusively, although he did a brief
stint concentrating on the canary. Unlike the canary, which learns a new song
each year, the zebra finch has a limited repertoire. It learns one song in its
first 90 days of life — made of four to eight notes "in very specific
order and they don't vary at all" — and then sings it for the rest of its
life.
Nottebohm studies both. He said they each have their advantages as study
subjects. But, aesthetically, the more tuneful canary wins, hands down.
"Zebra finches have a squawky little song," Nottebohm said.
"They sound like a mechanical cat."
Tomado
de:
http://articles.courant.com/2012-07-06/health/hc-zebra-finch-brain-0708-20120706_1_neurons-john-kirn-zebra-finch
