[Fwd: New info for nature/nurture fans]

[Carrol Cox <cbcox@xxxxxxxxxxxxx>]

This seems to be important in providing new reasons
to reject the reactionary theories of sociobiology
and evolutionary psychology, as well as idealist
claims of innate ideas -- e.g., Chomsky's claims that
the brain is hardwired for language.

Carrol


-------- Original Message --------
Subject: New info for nature/nurture fans
Date: Tue, 25 Apr 2000 16:43:27 -0700
From: Lisa & Ian Murray <seamus@xxxxxxxxxxxxx>
Reply-To: lbo-talk@xxxxxxxxxxxxxxx
To: "Lbo-Talk@Lists. Panix. Com" <lbo-talk@xxxxxxxxxxxxxxx>

[this would seem to put a bit of a crimp in the Pinker{ton's}
armamentarium]

April 25, 2000
'Rewired' Ferrets Overturn Theories of Brain Growth
By SANDRA BLAKESLEE

Like inventive electricians rewiring a house, scientists at the
Massachusetts Institute of Technology have reconfigured newborn ferret
brains so that the animals' eyes are hooked up to brain regions where
hearing normally develops.

The surprising result is that the ferrets develop fully functioning
visual
pathways in the auditory portions of their brains.

In other words, they see the world with brain tissue that was only
thought
capable of hearing sounds.


The findings, reported by Dr. Mriganka Sur and his colleagues in the
April
20 issue of Nature magazine, contradict popular theories on how animal
brains develop specialized regions for seeing, hearing, sensing touch
and,
in humans, generating language and emotional states.

Many scientists claim that genes operating before birth create these
specialized regions or modules, arguing for example that the visual
cortex
is destined to process vision and little else. But the ferret
experiments
show that brain regions are not set in stone at birth.

Rather, they develop specialized functions based on the kind of
information
flowing into them after birth.

"Some scientists are going to have a hard time believing these
experiments,"
said Dr. Jon Kaas, a professor of psychology at Vanderbilt University in
Nashville. They demonstrate, Dr. Kaas said, "that the cortex can develop
in
all sorts of directions."

"It's just waiting for signals from the environment and will wire itself
according to the input it gets," he said.

The findings may shed light on unusual brain patterns observed in people
who
are born deaf or blind, he added.

"If you wanted to create a dream experiment, this would be it," said Dr.
Michael Merzenich, a neuroscientist at the University of California at
San
Francisco and a leading authority on the brain's ability to change and
reorganize, a process known as plasticity. "It's about the most
compelling
demonstration you could have that experience shapes the brain."

The researchers are all members or former members of the department of
brain
and cognitive sciences at M.I.T. The rewiring experiments began more
than 10
years ago, Dr. Sur said. He chose ferrets because their brains are very
immature at birth and undergo a late form of development that the
researchers can exploit.

As in humans, the ferret's optic and auditory nerves travel through a
way
station called the thalamus before reaching areas in the higher brain or
cortex where vision and hearing are perceived.

In humans, this very basic wiring is present at birth, but in ferrets,
these
important nerves grow into the thalamus after the animal is born. Dr.
Sur
found that if he stopped the auditory nerve from entering the thalamus,
the
optic nerve would arrive a few days later and make a double connection.
It
would go on through the thalamus and connect itself up to both seeing
and
hearing regions of the cortex.

The researchers then waited to see what would happen to the hearing
region
of the brain once it was getting all its signals from the retina.

After a ferret or human is born, cells in the brain's primary visual
area
become highly specialized for analyzing the orientation of lines found
in
images or shapes. Some cells fire only in response to vertical lines. If
presented with a horizontal or slanted line, they don't do anything.

Other cells fire exclusively when a horizontal line falls on them and
yet
others fire in response to lines slanted at various angles. These
specialized cells are draped across the primary visual area in a
somewhat
splotchy fashion that resembles a bunch of pinwheels.

The hearing region of the brain is organized very differently, Dr. Sur
said.

Each cell is connected to the next in a kind of single line. There are
no
pinwheel shapes.

After the rewired ferrets matured, researchers looked at the auditory
region
of their brains and found that cells were organized pinwheel fashion.
They
found horizontal connections between cells responding to similar
orientations.

The rewired map was less orderly than the maps found in normal visual
cortex, Dr. Sur said, but looked as if it might be functional.

The researchers then asked, What does the rewired ferret experience?
Does it
see or does it hear with its auditory cortex?

Rewired ferrets were trained to turn their heads one way if they heard a
sound and in the other direction if they saw a flash of light. In these
experiments, one hemisphere was rewired and the other was left normal as
a
control. Thus the animals could always hear with the intact side of
their
brains and were deaf in the rewired side.

Not surprisingly, when the light was presented to the rewired side, the
animals responded correctly.

But when connections to visual areas were severed on the rewired side,
the
animals still responded to the light. It meant that they were seeing
lights
with their rewired auditory cortex, Dr. Sur said.

The research reopens the question of what are the relative contributions
of
genes and experience in building brain structure, according to Dr. Kaas.

Genes, Dr. Kaas suggests, create a basic scaffold but not much
structure.

Thus, in a normal human brain, the optic nerve is an inborn scaffold
connected to the primary visual area. But it is only after images pour
into
this area from the outside world that it becomes the seeing part of the
brain. All the newborn cortex knows about the outside world is from the
electrical activity of these inputs, or images that fall on the retina,
sounds that reach the inner ear or touch sensations that press on the
skin,
Dr. Kaas said.

As the inputs arrive, the cells organize themselves into circuits and
functional regions.

As these circuits grow larger and more complex, Dr. Kaas said, they
become
less malleable and, probably with the help of changes in neurochemistry,
become stabilized. This is why a mature brain is less able to recover
from
injury than a very young brain.

Young brains are astonishingly plastic, Dr. Kaas said. For example, he
said,
children who suffer from a severe form of epilepsy that is treatable
only by
removing one-half of their brains can learn to walk, talk, throw balls
and
otherwise develop normally with only half a brain, if operated on early
in
life, he said.


But in recent years, scientists are also discovering that adult brains,
as
well, can undergo surprising changes in response to experience. For
example,
imaging experiments carried out on blind people show that when they
learn to
read Braille, "visual" areas of their brains light up.

Touch seems to be residing in visual areas. Similar experiments on deaf
people show that they use the auditory cortex to read sign language,
whereas
people who can hear use the visual areas of the brain for this purpose.

Dr. Sur said his laboratory was now searching for molecules that help
produce these kinds of changes in mature and developing brains.

If the chemistry of regrowth and reorganization can be understood, he
said,
it would offer new avenues for helping people recover from damage caused
by
strokes, accidents and various brain diseases.
http://www.nytimes.com/library/national/science/042500sci-animal-ferret.html