Scientists discover anatomical changes in the brains of the newly
sighted
Following cataract removal, some of the brain's visual pathways seem to
be more malleable than previously thought.

Date:
May 1, 2023
Source:
Massachusetts Institute of Technology
Summary:
Neuroscientists discovered anatomical changes that occur in the
white matter of visual-processing areas of the brain, in children
who have congenital cataracts surgically removed.


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For many decades, neuroscientists believed there was a "critical period"
in which the brain could learn to make sense of visual input, and that
this window closed around the age of 6 or 7.

Recent work from MIT Professor Pawan Sinha has shown that the picture
is more nuanced than that. In many studies of children in India who had
surgery to remove congenital cataracts beyond the age of 7, he has found
that older children can learn visual tasks such as recognizing faces, distinguishing objects from a background, and discerning motion.

In a new study, Sinha and his colleagues have now discovered anatomical
changes that occur in the brains of these patients after their sight is restored. These changes, seen in the structure and organization of the
brain's white matter, appear to underlie some of the visual improvements
that the researchers also observed in these patients.

The findings further support the idea that the window of brain plasticity,
for at least some visual tasks, extends much further than previously
thought.

"Given the remarkable level of remodeling of brain structure that we are seeing, it reinforces the point that we have been trying to make with our behavioral results, that all children ought to be provided treatment,"
says Pawan Sinha, an MIT professor of brain and cognitive sciences and
one of the authors of the study.

Bas Rokers, an associate professor and director of the Neuroimaging Center
at New York University Abu Dhabi, is the senior author of the study,
which appears this week in the Proceedings of the National Academy of
Sciences. The paper's lead authors are Caterina Pedersini, a postdoc
at New York University Abu Dhabi; Nathaniel Miller, who is studying
medicine at the University of Minnesota Medical School; and Tapan Gandhi,
a former postdoc in the Sinha Lab who is now an associate professor at
the Indian Institute of Technology. Sharon Gilad-Gutnick, an MIT research scientist, and Vidur Mahajan, director of the Center for Advanced Research
on Imaging, Neuroscience, and Genomics, are also authors of the paper.

White matter plasticity In developed nations such as the United
States, infants born with cataracts are treated within a few weeks of
birth. However, in developing nations such as India, a higher percentage
of these cases go untreated.

Nearly 20 years ago, Sinha launched an initiative called Project Prakash,
with the mission to offer medical treatment to blind and vision-impaired children in India. Each year, the project screens thousands of children,
many of whom are provided with glasses or more advanced interventions
such as surgical removal of cataracts. Some of these children, with
their families' permission, also participate in studies of how the
brain's visual system responds after sight is restored.

In the new study, the researchers wanted to explore whether they could
detect any anatomical changes in the brain that might correlate with
the behavioral changes that they have previously seen in children who
received treatment. They scanned 19 participants, ranging in age from
7 to 17 years of age, at several time points after they had surgery to
remove congenital cataracts.

To analyze anatomical changes in the brain, the researchers used a
specialized type of magnetic resonance imaging called diffusion tensor
imaging. This type of imaging can reveal changes in the organization
of the white matter - - bundles of nerve fibers that connect different
regions of the brain.

Diffusion tensor imaging, which tracks the movement of hydrogen nuclei in
water molecules, produces two measurements: mean diffusivity, a measure
of how freely water molecules can move, and fractional anisotropy, which reveals the extent to which water is forced to move in one direction
over another.

An increase in fractional anisotropy suggests that water molecules are
more constrained because nerve fibers in the white matter are oriented
in a particular direction.

"If you see increasing fractional anisotropy and decreasing mean
diffusivity, then you can infer that what's happening is that the nerve
fibers are growing in volume and they're getting more organized in terms
of their alignment," Sinha says. "When we look at the white matter of the brain, then we see precisely these kinds of changes in some of the white
matter bundles." The researchers observed these changes specifically
in white matter pathways that are part of the later stages of the visual system, which is believed to be involved in higher-order functions such
as face perception. These improvements occurred gradually over several
months following the surgery.

"You see anatomical changes in the white matter, but in separate studies
using functional neuroimaging, you also see increasing specialization,
as a function of visual experience, similar to what happens in typical development," Gilad- Gutnick says.

The researchers also tested the participants' performance on a variety
of visual tasks and found that their ability to distinguish faces from
other objects was correlated with the amount of structural change in
the white matter pathways associated with higher-order visual function.

In comparison, while the treated children showed some improvements in
visual acuity -- the ability to clearly see details of objects at a
distance -- their acuity never fully recovered, and they showed only
minimal changes in the white matter organization of the early visual
pathways.

"The notion that plasticity is a time-limited resource and that past
a certain window we can't expect much improvement, that does seem to
hold true for low- level visual function like acuity," Sinha says. "But
when we talk about a higher-order visual skill, like telling a face
from a non-face, there we do see behavioral improvements over time,
and we also find there to be a correlation between the improvement that
we are seeing behaviorally and the changes that we see anatomically."
Benefits of treatment The researchers also found that children who had cataracts removed at a younger age showed greater, and faster, gains in face-perception ability than older children. However, all of the children showed at least some improvement in this skill, along with changes in
the structure of the white matter.

The findings suggest that older children can benefit from this kind of
surgery and offers further evidence that it should be offered to them,
Sinha says.

"If the brain has such outstanding abilities to reconfigure itself and
even to change its structure, then we really ought to capitalize on that plasticity and provide children with treatment, irrespective of age,"
he says.

Sinha's lab is now analyzing additional imaging data from Project Prakash patients. In one study, the researchers are investigating whether
the patients show any changes in the thickness of their gray matter,
especially in the brain's sensory processing areas, after treatment. The researchers are also using functional MRI to try to localize visual
functions such as face perception, to see if they arise in the same
parts of the brain that they do in people born with normal sight.

The research was funded by the National Eye Institute.

* RELATED_TOPICS
o Mind_&_Brain
# Neuroscience # Intelligence # Brain-Computer_Interfaces
# Child_Development # Perception # Brain_Injury #
Psychology # Child_Psychology
* RELATED_TERMS
o Occipital_lobe o Brain o Visual_perception o Motion_perception
o Neocortex_(brain) o Sensory_system o Retina o Brain_damage

========================================================================== Story Source: Materials provided by
Massachusetts_Institute_of_Technology. Original written by Anne
Trafton. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Caterina A. Pedersini, Nathaniel P. Miller, Tapan K. Gandhi, Sharon
Gilad-Gutnick, Vidur Mahajan, Pawan Sinha, Bas Rokers. White
matter plasticity following cataract surgery in congenitally
blind patients.

Proceedings of the National Academy of Sciences, 2023; 120 (19)
DOI: 10.1073/pnas.2207025120 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2023/05/230501164006.htm

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