CUTTING EDGE RESEARCH IS UNLOCKING THE SECRETS OFBEHAVIORAL
DEVELOPMENT
HATCHING A CHICK THAT CROWS LIKE A QUAIL TEACHES US A THING OR TWO
ABOUT THE FUNCTIONING BRAIN. KEVIN LONG, PH.D., OF THE NEUROSCIENCES
INSTITUTE IN SAN DIEGO, TALKS ABOUT THE LATEST RE, SEARCH ON HOW THE
DEVELOPING BRAIN COMES TO CONTROL BEHAVIOR.
Nancy K. Dess [NKD]: Your work has been described as "brain
transplantation." Is that what you do?
Kevin Long [KL]: No. We take a small portion of developing brain
tissue from a quail--before the embryo even has mature neurons or
blood--and put it in the corresponding place of a chicken embryo.
NKD: And the tissue "takes?"
KL: Yes. When the chick hatches it has both quail and chicken
neurons.
NKD: Live cells are one thing, a working brain is another. Does the
transplant do anything?
KL: It does, but it depends on what is transplanted. For instance,
Evan Balaban, Ph.D., showed that transplanting certain cells produces a
chicken that crows like a quail, and transplanting others produces a
chicken that bobs its head like a quail.
NKD: Do they need to have heard or seen a quail crowing or
bobbing?
KL: Amazingly, no exposure to birds is necessary.
NKD: So the behavior is innate, coded in the genes?
KL: "Innateness" is a difficult concept. We don't yet understand
how genes and the cellular environment during development underlie these
behaviors--and both do. In this case, though, learning by the birds is
not strongly involved.
NKD: Are you genetically manipulating these birds?
KL: We transplant developing neural tissue, not genes that get
passed to offspring. A poultry producer, who attended one of my talks,
was excited at the thought of chicken-sized birds that taste like quail.
I burst his bubble by reminding him that when the birds grew and mated,
they would have 100 percent baby chickens. He was so defeated.
NKD: How then do the transplants code for the behavior?
KL: Something intrinsic to the tissue is critical to its behavioral
function. But those cells might send signals elsewhere during development
to induce other cells to change what they do. Take my work on perception:
Baby chickens normally approach a chicken sound more often than a quail
sound, without having heard either before. Transplanting developing quail
midbrain tissue, however, results in a chick that prefers the sound of a
quail.
NKD: The midbrain controls the preference?
KL: Not necessarily. We have evidence that forebrain nuclei are
very much involved. The transplanted cells might not do much locally to
produce the preference, but rather, as they develop, they begin to send
signals to the forebrain region responsible for deciding what is
important. So the behavior is not controlled by the quail midbrain cells
or by the chicken forebrain cells, but by a developmental dance they
do.
NKD: Does the success of that dance depend on evolutionary
relatedness?
KL: Chickens and quail are related, and we do the transplant at a
developmental stage at which they aren't much different. Success probably
depends on both facts. But that begs the profound question of what
"related" really means. How different does tissue need to be to make a
chicken prefer a quail? What makes one species different from
another?
NKD: And what makes humans the same as or different from other
animals?
KL: Humans, like chickens and quail, have some inborn reflexes and
preferences, like infant grasping and preference for language. Now, that
doesn't necessarily mean that a bit of transplanted tissue would change
human reflexes--much less complex behavior. Mammals develop differently
from birds and experience shapes all sorts of behaviors. While
implications for humans are not yet clear, this is a useful technique for
figuring how, in general, behaviors are controlled. If we can figure that
out, we might understand some neurological and developmental
disorders--and more about what it means to be uniquely human.
Nancy K. Dess is a professor of psychology at Occidental College
and former senior scientist at the American Psychological
Association.
