Visual Development according to
www.sfn.org/index.cfm?pagename=brainBriefings_visualDevelopment
with comments added by DPM in Book Antigua
Scientists studying the visual cortex discovered columns of neurons that selectively
respond to visual information from one eye or the other. They learned that normal visual
experience during a critical period in early childhood is crucial for these columns to form
properly. These discoveries shed light on normal brain development and revolutionized
treatment of a childhood eye disease called strabismus.
How do we see? How does the brain make sense of what we see? How does what we see
affect our brain?
Only in the past several decades have scientists begun to uncover answers to these
questions. Landmark basic research led to the understanding of visual brain development.
It also shed light on how the brain adapts to new information and greatly improved
treatment for certain childhood visual diseases.
The key research on visual development began during the 1950s and 1960s, when
scientists began to explore the visual cortex in cats and monkeys. The visual cortex is
located in the occipital lobe, or lower rear portion, of the brain's hemispheres.
Neuroscientists found that specific types of nerve cells, or neurons, of the mature visual
cortex respond to specific shapes or orientations of light. They also discovered that
isolated within the visual cortex are sets of alternating columns of cells that process
information sent from either the left or right eye.
These columns called ocular dominance columns, are a major feature of the organization of
the visual cortex. They are part of the neural circuitry that gives us one unified view of the
visual world, even though the brain gets information from both eyes. Using radioactive
molecules to make neurons that respond to each eye, researchers found that ocular
dominance columns run across the cortex as a series of alternating stripes, like a zebra's
black and white stripes.
With research on cats and monkeys, scientists discovered that ocular-dominance columns
are not fully wired at birth, but take shape during the first several months of life. If one eye
is not used during this critical period of visual cortex development, neurons in the ocular
dominance column that should receive visual information from the unused eye do not
develop normally, and instead become wired to the normal eye. The ocular dominance
columns representing the eye that is not used waste away. Once the critical period ends,
sight is permanently impaired.
These findings help show that:
Sensory experience from the external world can influence how the brain wires
itself up after birth. Visual experience is crucial for a child's vision to develop
normally -- a "use it or lose it" situation. Treatment of common childhood eye
diseases should begin much earlier than standard practice.
One childhood eye disease, strabismus, is an abnormality in which children cannot align
their eyes properly or fuse the images from the two eyes. Children with this condition --
which affects at least 30,000 babies each year -- typically stop using one of their eyes to
avoid double vision. This results in deprived sensory input to that eye.
Until the 1970s, strabismus -- while treatable with surgery, exercises, or an eye patch --
often led to incurable visual impairment in one eye.
Because diagnosing and treating strabismus is slightly more difficult in infants than older
children, doctors typically delayed treatment until the children were four or older --
inadvertently increasing the degree of permanent vision loss.
Janice Megan Jensen was born on May 13, 1952. Her mother, Virginia Jensen (born June 3,
1919) had Janice's eyes operated on "before Christmas in second grade." I believe this
would indicate that Janice was 7 years and 7 months old at the time of her strabismus
operation. This is now considered too late to avoid damage to the visual cortex
development.
Shawna Diane Jensen was born June 3, 1978 if I remember correctly. By the time I met
Shawna, she was three years old and should have had an operation for strabismus
immediately. I convince Janice to take Shawna to an eye doctor. I cannot remember her
name at this point. The eye doctor was to set up an operation with a surgeon in Tennessee,
as I remember, it could have been another state near Tennessee. Conflicts arose and the
operation never happened. As you can see from the next paragraph, it was inevitable that
Shawna would become blind in one eye without that operation. Since she lacked normal
development of her visual cortex, there may never be a cure to her problem.
Armed with knowledge of ocular dominance columns and the critical period of visual cortex
development, doctors now treat strabismus early in life, well before age four, when normal
vision can be restored.
This basic research has helped thousands of children. It also demonstrates that the saying
"use it or lose it" applies to early childhood development as well as aging.
--------------------------------------------------------------------------------
Nerve connections from the eye to the visual cortex, where visual information is processed,
are shown in the graphic whose link is below. In normal development (above), visual stimuli
cause the connections to separate and form ocular dominance columns of equal size in the
cortex. When one eye is deprived of sensory information (below), the columns from the
deprived eye shrink and the connections of the normal eye take over more than their fair
share of territory, resulting in permanent visual impairment.
The graphic is available here.
www.sfn.org/index.cfm?pagename=brainBriefings_visualDevelopment
with comments added by DPM in Book Antigua
Scientists studying the visual cortex discovered columns of neurons that selectively
respond to visual information from one eye or the other. They learned that normal visual
experience during a critical period in early childhood is crucial for these columns to form
properly. These discoveries shed light on normal brain development and revolutionized
treatment of a childhood eye disease called strabismus.
How do we see? How does the brain make sense of what we see? How does what we see
affect our brain?
Only in the past several decades have scientists begun to uncover answers to these
questions. Landmark basic research led to the understanding of visual brain development.
It also shed light on how the brain adapts to new information and greatly improved
treatment for certain childhood visual diseases.
The key research on visual development began during the 1950s and 1960s, when
scientists began to explore the visual cortex in cats and monkeys. The visual cortex is
located in the occipital lobe, or lower rear portion, of the brain's hemispheres.
Neuroscientists found that specific types of nerve cells, or neurons, of the mature visual
cortex respond to specific shapes or orientations of light. They also discovered that
isolated within the visual cortex are sets of alternating columns of cells that process
information sent from either the left or right eye.
These columns called ocular dominance columns, are a major feature of the organization of
the visual cortex. They are part of the neural circuitry that gives us one unified view of the
visual world, even though the brain gets information from both eyes. Using radioactive
molecules to make neurons that respond to each eye, researchers found that ocular
dominance columns run across the cortex as a series of alternating stripes, like a zebra's
black and white stripes.
With research on cats and monkeys, scientists discovered that ocular-dominance columns
are not fully wired at birth, but take shape during the first several months of life. If one eye
is not used during this critical period of visual cortex development, neurons in the ocular
dominance column that should receive visual information from the unused eye do not
develop normally, and instead become wired to the normal eye. The ocular dominance
columns representing the eye that is not used waste away. Once the critical period ends,
sight is permanently impaired.
These findings help show that:
Sensory experience from the external world can influence how the brain wires
itself up after birth. Visual experience is crucial for a child's vision to develop
normally -- a "use it or lose it" situation. Treatment of common childhood eye
diseases should begin much earlier than standard practice.
One childhood eye disease, strabismus, is an abnormality in which children cannot align
their eyes properly or fuse the images from the two eyes. Children with this condition --
which affects at least 30,000 babies each year -- typically stop using one of their eyes to
avoid double vision. This results in deprived sensory input to that eye.
Until the 1970s, strabismus -- while treatable with surgery, exercises, or an eye patch --
often led to incurable visual impairment in one eye.
Because diagnosing and treating strabismus is slightly more difficult in infants than older
children, doctors typically delayed treatment until the children were four or older --
inadvertently increasing the degree of permanent vision loss.
Janice Megan Jensen was born on May 13, 1952. Her mother, Virginia Jensen (born June 3,
1919) had Janice's eyes operated on "before Christmas in second grade." I believe this
would indicate that Janice was 7 years and 7 months old at the time of her strabismus
operation. This is now considered too late to avoid damage to the visual cortex
development.
Shawna Diane Jensen was born June 3, 1978 if I remember correctly. By the time I met
Shawna, she was three years old and should have had an operation for strabismus
immediately. I convince Janice to take Shawna to an eye doctor. I cannot remember her
name at this point. The eye doctor was to set up an operation with a surgeon in Tennessee,
as I remember, it could have been another state near Tennessee. Conflicts arose and the
operation never happened. As you can see from the next paragraph, it was inevitable that
Shawna would become blind in one eye without that operation. Since she lacked normal
development of her visual cortex, there may never be a cure to her problem.
Armed with knowledge of ocular dominance columns and the critical period of visual cortex
development, doctors now treat strabismus early in life, well before age four, when normal
vision can be restored.
This basic research has helped thousands of children. It also demonstrates that the saying
"use it or lose it" applies to early childhood development as well as aging.
--------------------------------------------------------------------------------
Nerve connections from the eye to the visual cortex, where visual information is processed,
are shown in the graphic whose link is below. In normal development (above), visual stimuli
cause the connections to separate and form ocular dominance columns of equal size in the
cortex. When one eye is deprived of sensory information (below), the columns from the
deprived eye shrink and the connections of the normal eye take over more than their fair
share of territory, resulting in permanent visual impairment.
The graphic is available here.
CU Boulder is my current home