PRIMATE-SCIENCE RESEARCH HIGHLIGHT-- 
 
"Critical period in brain development discovered" 
(Courtesy Yerkes Regional Primate Research Center) 
 
Newborn babies may avoid lifelong vision problems thanks to a
discovery in monkeys at the Yerkes Primate Research Center of Emory
University.  
 
A team led by Ron Boothe, Ph.D., chief of the Visual Science
Division at Yerkes, has found that a dramatic reorganization of
brain cells occurs in infant monkeys in the first three weeks of
life, corresponding to the first three months in humans. These
neural connections turn out to be the building blocks of a healthy
visual system, allowing for a baby's sudden ability to see in
stereovision, or three-dimensionally and, as the months and years
go by, to avoid a series of irreversible visual defects. 
  
Infants make these vital connections only with the help of visual
stimuli from the world around them. If a baby fails to receive
normal visual input in the first three months--usually due to
undetected visual defects at birth, such as cataracts--the baby
will never recover the brain cell connections, and will suffer one
or more of the vision deficits for life. 
 
Boothe calls this critical three-month window the "neonatal"
sensitive period--as compared with the "classical postnatal"
sensitive period which lasts for several years after birth, and was
described by vision scientists David H. Hubel and Tortsen N.
Wiesel, who were awarded the Nobel prize in 1981 for their work. 
 
The irreversible deficits involve problems with controlling eye
movements, such as strabismus, in which the visual axes of the eyes
are not parallel, leaving the child cross-eyed; latent nystagmus,
a rhythmical oscillation of the eyeball; dissociated vertical
deviations, in which a covered eye drifts upward; and deficits in
motion processing, which impairs vision of movements going in a
certain direction 
 
The deficits range in severity from one person to another. Aside
from the aesthetic problems involved with being cross-eyed, for
instance, the deficits make performing many activities a bit
riskier because they are oculomotor problems affecting depth
perception. "They would probably keep someone from becoming a
fighter pilot, or a race car driver," Boothe explains.  
 
Currently, no treatment exists for the deficits once they appear.
However, they are preventable. The clinical message is clear:
newborns and neonates should be carefully screened as early as
possible and treated immediately for cataracts and other problems.

  
"Eye doctors have certainly seen these disorders in the past, and
it was always in children who also had other vision problems, such
as cataracts," notes Boothe. Scientists had assumed that cataracts
and the deficits were caused by the same thing, perhaps some
unknown genetic abnormality. But the new findings in rhesus
monkeys, whose visual systems are almost identical to those of
humans, reveal that the deficits are actually a separate,
neurologic problem occurring during development, rather than a
genetic one. 
 
Boothe was working with rhesus monkeys to find treatments for
cataracts when he noticed that permanent deficits in eye movements
developed when he simulated cataracts experimentally in neonatal
(less than a month old) monkeys--but not when these conditions were
induced just a few weeks later. 
                                                               
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For more information, contact Kate Egan at (404) 727-7709,
yerkes-info@rmy.emory.edu 
 
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References:  
 
O'Dell, C. and R.G. Boothe. 1997. The development of stereoacuity
in infant rhesus monkeys. Vision Research. 37:2675-2684. 
 
Boothe, R.G. 1997. A neonatal visual deprivation syndrome.
Perception. 26:766. 
 
Burrows, A., M.J. Mustari, R.J. Tusa, A. Aiyer, R. Boothe, and J.
Wilson. 1997. The role of early visual experience in gaze holding.
Society for Neuroscience Abstracts. 23:2367. 
 
Boothe, R.G., and A.B. Fulton. 1998. Amblyopia. In: Principles and
Practice of Ophthalmology, 2nd Edition, D.M. Albert and F.A.
Jakobiec, eds. W.B. Saunders Company, Philadelphia, PA (in press).

 
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P-T Research Highlights appears every other week and focuses
broadly on research involving non-human primates. Coverage includes
biomedicine, behavior, conservation and veterinary science. Please
submit highlights for this column to Larry Jacobsen, P-T Research
Highlights editor, at jacobsen@primate.wisc.edu. A 300-word limit and
lay-language style are recommended. P-T Research Highlights are
supported by a grant from the National Institutes of Health,
National Center for Research Resources.  Copyright 1998,
Wisconsin Regional Primate Research Center. No portion of this highlight
may be copied or redistributed without the consent of the editor.

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