Sight Recovery After Blindness Offers New Insights on Brain
Reorganization

Studies of the brains of blind persons whose sight was partially
restored later
in life have produced a compelling example of the brain's ability to
adapt to
new circumstances and rewire and reconfigure itself.

The research, conducted by postdoctoral researcher Melissa Saenz of
the
California Institute of Technology along with Christof Koch, the Lois
and Victor
Troendle Professor of Cognitive and Behavioral Biology and professor
of
computation and neural systems, and their colleagues, shows that the
part of the
brain that processes visual information in normal individuals can be
co-opted to
respond to both visual and auditory information. That brain
reorganization
persists even if the blind subjects later regain their vision--for
example,
through technologies such as corneal stem-cell transplants, retinal
prosthetics,
and gene therapy.

"Sight-recovery patients can face many challenges in using restored
vision
because of brain reorganization that occurs during prolonged
blindness.
Understanding this brain adaptation will be useful for helping
patients make the
best use of their restored vision," says Saenz.

Researchers scanned the brains of two individuals whose sight had been
recovered
decades after having been lost. One volunteer, Michael May, was
blinded in a
chemical accident at the age of three, and then he had his vision
partially
restored in his left eye at age 46 through a corneal stem-cell
transplant. The
second subject, a 53-year-old woman, had been blind since birth
because of
damage to the retina and cataracts. At age 43, sight in her right eye
was
partially restored by cataract removal.

Each subject listened through headphones to several types of sounds
including
speech, frequency sweeps (simple tones whose frequency changes), and
sounds that
appeared to be "moving" horizontally from one side of the head to the
other (the
illusion was created by increasing the volume or timing of sounds
delivered to
either the left or the right speaker) while lying in a magnetic
scanner.

This allowed Saenz to monitor changes in blood flow that are closely
linked to
the underlying neuronal activity in a region of the brain called MT+/
V5, which
is specifically involved in visual motion processing. Ten test
subjects with
normal vision were similarly studied.

Only in the two individuals with recovered sight did the MT+/V5 region
light up
in response to sound. No response was seen in the control subjects.

"Previous studies had shown that a variety of new sensory functions
move into
the visual cortex when a person loses their vision, especially when
vision is
lost as a young child, when the brain is very adaptable," says Saenz.
"Our data
show for the first time what happens to the new sensory responses if a
blind
person has the chance to see again. The sound responses didn't go
away. They
persisted together with the restored visual responses, even after many
years
with regained sight."

Most interestingly, the MT+/V5 region reacted only to auditory motion,
but not
to other types of auditory stimuli. In other words, moving sound
activated a
part of the brain that is normally reserved for processing moving
visual images.

"This wasn't a random takeover. We didn't find responses to all types
of sounds,
but specifically to moving sounds. This brain reorganization was
efficient and
took advantage of this region's specialized role in motion
processing," she
says.

"Our volunteers with sight recovery gave us the unique opportunity to
answer the
question of whether the different sensory response in a blind person
activates a
specific visual area (MT+/V5). Normally, the location of this area is
variable
and is identified in sighted people by how it responds to visual
stimulation,
not based on anatomical landmarks alone. So we couldn't convince a
critic that
we identified this area in someone who was still blind."

In fact, According to Saenz, such multitasking may contribute to the
strong
ability to perceive motion--as opposed to the poor visual acuity--that
has been
seen before among patients who have recovered their sight after a
lifetime of
blindness.

"This study demonstrates the plasticity inherent in even adult brains
and the
very tight linkage between neural activity in particular pieces of
gray matter
and the subject's perception in the privacy of his and her mind," Koch
says.

"When my vision was restored after 43 years of being totally blind, I
had no
idea of the complexity of how our brain sees," says test subject
Michael May.
"It is through vision scientists that I have had a front-row seat in
learning
about how I perceive the world with my new vision. Turns out that the
integration of all my senses, tools, and techniques has been the key
to a
maximum life experience."

The paper, "Visual motion area MT+/V5 responds to auditory motion in
human
sight-recovery subjects," was published in the May 14 issue of the
Journal of
Neuroscience.

Source: Caltech
http://www.physorg.com/news130163759.html