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Fw: Ferrets

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  • Paul Okami
    ... From: Jack Drescher To: sexnet@listserv.acns.nwu.edu Sent: Sunday, April 30, 2000 5:26 PM Subject: Ferrets From:
    Message 1 of 2 , Apr 30, 2000
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      ----- Original Message -----
      Sent: Sunday, April 30, 2000 5:26 PM
      Subject: Ferrets

      From:
      http://www.nytimes.com/library/national/science/042500sci-animal-ferret.
      html
      '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.
    • Timo Jarvilehto
      ... This may be surprising for those who believe that the brain is capable of cognitive operations and that it is the brain who sees or hears. However, if we
      Message 2 of 2 , May 1, 2000
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        Paul Okami forwarded a message:

        > 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.

        This may be surprising for those who believe that the brain is
        capable of cognitive operations and that it is the brain who sees or
        hears. However, if we think that the brain is only a part of the
        system of hearing, then this result can be predicted. I don't want to
        be magisterial, but perhaps you allow a citation from a recent
        article:

        "The question of subjectivity of consciousness is the question of the
        contents of consciousness. What determines the content - the qualia -
        of the conscious experience? It is nowadays usual in cognitive science
        to answer this question by referring to a certain area of the brain: a
        visual sensation differs qualitatively from a tactile one, because the
        former is processed in the visual cortex and the latter in the
        somatosensory one. Such an answer, however, is only a repetition of
        Muller's law of specific nerve energies from the 19th century in a
        modern form. Muller thought that each nerve contains its own specific
        energy which makes it understandable why, for example, any stimulation
        of a visual nerve produces a visual sensation. According to Muller,
        the nerve contains a "specific energy" related to the evoked
        sensation. Nowadays nobody believes in such energies, but in fact this
        concept has been replaced by the concept of the locus of activation.
        Visual sensation appears, because neurons in the visual cortex are
        activated.

        However, the neurons in the different parts of the brain function in a
        similar way even if there are some anatomical differences in their
        constitution. There is nothing "visual" in the visual cortex, or
        nothing "tactile" in the tactile cortex, and there is no reason to
        think that the quality of the sensation would be determined by the
        locus of activation per se. Thus, Muller's original problem has still
        not been adequately answered in cognitive science.

        According to the present consideration the problem is wrongly
        formulated. If I ask "What determines the content of my
        consciousness?", the answer cannot deal only with the brain, but must
        include much more. What makes me feel like a human being does? The
        first condition for this possibility is precisely that I am a human
        being, that I belong to the human species. I am a human being only if
        the contents of my consciousness are typically human; if they are
        something totally different then I am no more a human being. According
        to the present formulation this is self-evident, because the content
        of consciousness is determined by the common results, by the
        possibility of co-operation with other human beings. Thus, the content
        of consciousness is shared with other human beings; otherwise
        co-operation would not be possible. "
        (Jarvilehto, Integrative Physiological and Behavioral Science
        2000,35: 35-57.)

        TJ
        ===================================================
        Timo Jarvilehto
        http://wwwedu.oulu.fi/homepage/tjarvile/indexe.htm
        Professor of psychology
        University of Oulu
        PB 2000, 90014 Oulun yliopisto, Finland
        tjarvile@...
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