Rigorous visual training teaches brain to see
again after stroke
22 April 2009
By doing a set of vigorous visual exercises on a computer every day
for several months, patients who had gone partially blind as a result of
suffering a stroke were able to regain some vision, according to a
study published in the Journal of Neuroscience (1 April issue).
Such rigorous visual retraining is not common for people who suffer
blindness after a stroke. That’s in contrast to other consequences of
stroke, such as speech or movement difficulties, where rehabilitation is
common and successful.
“We were very surprised when we saw the results from our first
patients,” said Krystel Huxlin, PhD, the neuroscientist and associate
professor who led the study of seven patients at the University of
Rochester Eye Institute. “This is a type of brain damage that clinicians
and scientists have long believed you simply can’t recover from. It’s
devastating, and patients are usually sent home to somehow deal with it
the best they can.”
The results are a cause for hope for patients with vision damage from
stroke or other causes, said Huxlin. The work also shows a remarkable
capacity for “plasticity” in damaged, adult brains. It shows that the
brain can change a great deal in older adults and that some brain
regions are capable of covering for other areas that have been damaged.
Huxlin studied seven people who had suffered a stroke that damaged an
area of the brain known as the primary visual cortex or V1, which serves
as the gateway to the rest of the brain for all the visual information
that comes through our eyes. V1 passes visual information along to
dozens of other brain areas, which process and make sense of the
information, ultimately allowing us to see.
Patients with damage to the primary visual cortex have severely
impaired vision — they typically have a difficult or impossible time
reading, driving, or getting out to do ordinary chores like grocery
shopping. Patients may walk into walls, oftentimes cannot navigate
stores without bumping into goods or other people, and they may be
completely unaware of cars on the road coming toward them from the left
Depending on where in the brain the stroke occurred, most patients
will be blind in one-quarter to one-half of their normal field of view.
Everything right or left of centre, depending on the side of the stroke,
might be gray or dark, for instance.
Building on blindsight
Despite the stroke, the patients’ eyes are taking in visual
information. It’s just that the damaged brain cannot make sense of it to
Huxlin’s team sought to build on this “blindsight” — visual
information, of which the patient is unaware, that still reaches the
brain. A few past studies have shown promise for the idea of building on
blindsight to improve a person’s vision.
“The question is whether we can we recruit other, healthy regions of
the brain to benefit the person’s vision. Can we train those brain
regions so hard and stimulate the brain to such a degree that this
visual information is brought to consciousness, so the person is aware
of what they’re seeing?” said Huxlin.
Huxlin began the study with seven people, four women and three men,
ranging from their 30s to their 80s, who had had a stroke anywhere from
eight to 40 months before the experiment began. All had suffered
substantial damage to the primary visual cortex. The funding to support
the work came from Research to Prevent Blindness, the Pfeiffer
Foundation, the Schmitt Foundation, and the National Eye Institute.
A participant in a vision recovery experiment at
the University of Rochester Medical Center performs a visual test. Photo
credit: Richard Baker/ University of Rochester
The team focused on motion perception, since it’s an aspect of vision
critical for most everyday tasks. The team’s aim was to see if the
brain’s middle temporal region, which was healthy in the participants,
could be stimulated so extensively that it could take on some of the
tasks normally handled by the visual cortex.
The five participants who performed the training and completed the
experiment had significantly improved vision. They were able to see in
ways they weren’t able to before the experiment began. A few found the
experiment life-changing – a couple of participants are driving again,
for instance, or have gained the confidence to go shopping and exercise
Following the dancing dots that can’t be 'seen'
To do the experiment, participants fix their gaze on a small black
square in the middle of a computer screen; scientists use a sensitive
eye tracker to make sure patients keep staring at the square.
Every few seconds, a group of about 100 small dots appears within a
circle on the screen, somewhere in the person’s damaged visual field –
in other words, when the patients stare at the square, they don’t
initially see the dots. The dots twinkle into existence, appear to move
as a group either to the left or the right, then disappear after about
one-half second. Then the patient has to choose whether the dots are
moving left or right. A chime indicates whether he or she chose
correctly, providing feedback that lets the brain know whether it made
the right choice and speeding up learning.
But how do patients choose if they can’t consciously see the
“The patients can’t see the dots, but they’re aware that there is
something happening that they can’t quite see. They might say, ‘I know
that there’s something there, but I can’t make any sense of it,’” said
Huxlin, who is also a faculty member in the departments of
Ophthalmology, Neurobiology and Anatomy, Brain and Cognitive Sciences,
and in the Center for Visual Science.
But the brain is able to make some sense of it all, even though the
patient is unaware that he or she is seeing anything. When forced to
make a choice, patients typically start out with a success rate of
around 50 percent by guessing. Over a period of days, weeks or months,
that number goes to 80 or 90 percent, as the brain learns to “see” a new
area, and the visual information moves from blindsight to consciousness.
Patients eventually become aware of the dots and their movement.
As patients improve, researchers move the dots further and further
into what was the patient’s blind area, as a way to challenge the brain,
to coax it to see a new area.
“Basically, it’s exercising the visual part of the brain every day,”
said Huxlin. “It’s very hard work, very gruelling. By forcing patients
to choose, you’re helping the brain re-develop.”
The patients in the study did about 300 tests at a time, which
translated roughly to sitting in front of a computer for 15 to 30
minutes once or twice a day, every day, for nine to 18 months. It’s an
exhausting task, especially for someone whose brain is working
extra-hard to accomplish it.
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