Prism goggles trick the brain into rewiring the visual cortex, providing insight into its plasticityBy John Westcott
The first thing you notice after you strap on Dr. Alyssa Brewer’s prism goggles is the nausea.
A roiling hits the stomach and grows worse as you begin to move. The world is strangely out of kilter. You reach out to grab hold of something, but it’s not there. Just putting one foot in front of the other takes an enormous effort.
“Welcome to the world of unreality” is what the UCI associate professor of cognitive sciences likes to say when unlucky subjects first peer out of the goggles. They’re an ingenious way to unhinge a person’s sense of reality. The environment one sees is completely flipped; the two prisms inside are tilted so that what you see on the left is really on the right, and what’s on the right is really left.
Brewer is intentionally tricking the brain, forcing it to find a way to adapt to this strange new reality. Her subjects stumble and lurch, grasping at air. It’s the supreme test of the visual and vestibular systems, pathways in the brain that use what you feel and see to enable navigation of the three-dimensional world around you.
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Such mind boggling helps Brewer and other scientists learn how the brain works. She hopes experiments like this will lead to new treatments for post-traumatic stress disorder and stroke, perhaps even Alzheimer’s disease and chronic pain.
Paradoxically, flipping reality right to left is a far bigger challenge to the brain than turning things upside down. That’s apparently because of the way its two hemispheres communicate with each other.
“We are not entirely sure why this is the case, but one hypothesis is that the difference is due to the wiring and connectivity of the brain,” Brewer explains.
“The representation of the body is split between the two hemispheres. The left side of the brain is controlling the right side, and vice versa. The visual information from both sides of visual space, for the most part, doesn’t come together until pretty far along the visual processing pathways. We were actually surprised by how different the experiences are.”
The brain is also surprised. When someone wears the goggles, the cerebellum – or lower brain – protests, sending urgent signals of distress and disequilibrium to the cerebral cortex. In turn, the visual and motor regions of the cerebral cortex – or higher brain – frantically try to realign what you see with commands for how to move through space.
“You get this warning from your brain that something is very wrong,” Brewer says. “You get motion sickness, and every head movement you make multiplies the motion sickness.”
But just as she suspected, the brain does adapt. Usually, after a week or so of using only the prism goggles to view the world, subjects who were initially so disoriented they could hardly stand, let alone walk, find their footing and become quite adroit at navigating their new environment.
“You’re forcing the brain to rewire itself,” Brewer says. “And you end up with two different maps in your visual cortex: one that matches the normal visual world to spatial movements and one that matches the flipped visual world to the same movements. When subjects came back three months later and did the study again, it only took about a day for them to readjust to the goggles, suggesting that these changes persist for extended periods of time.”
It’s a form of neuroplasticity in which the brain develops new neuronal connections in response to altered circumstances. Scientists used to believe the adult brain was mostly static, that it couldn’t change in significant ways after an early developmental period. But the explosion of brain research that Brewer and others have fostered in recent decades shows that the lump of gray matter sitting atop our shoulders is far more resilient than we once thought.
Brewer and her colleagues first began fiddling with prism goggles in 2008, shortly after she arrived at UCI. Subjects in the two-week experiments were required to view the world exclusively through the contraptions and wear blackout masks for sleeping and showering.
Brewer found that the prisms caused more than just visual confusion. The brain employs a broad network of input to discern reality, including sound and touch.
As a result, a goggle wearer’s hand almost instinctively reaches for an object seen on, say, the right, even though he or she knows it’s on the left. An hour after one woman took off her goggles, she still automatically turned her head to the right when someone to the left called her name.
Individual reactions to the goggles can vary greatly. Brewer says she personally can’t handle more than a few minutes of wear. And that’s an improvement. “I couldn’t even get out of the chair,” she recalls of her first time.
“You’re forcing the brain to rewire itself. And you end up with two different maps in your visual cortex.”
On the other hand, her colleague Brian Barton, a postdoctoral fellow who has worked with Brewer on several research projects over the years, adapted to the goggles with lightning speed. He can accomplish such difficult tasks as walking through a maze or preparing cupcake batter with relative ease.
“I was in the lab with a graduate student and Dr. Brewer, both of whom had just tried the goggles on and were unable to navigate the roughly 15-foot walk to the nearest doorway,” Barton says. “To everyone’s surprise, I was able to navigate not only to the first door, but through another, down the hallway and back, through the two doors to my chair.”
Brewer is not sure why, but she suspects Barton’s frequent forays into three-dimensional video games have primed his brain for the imaginary goggle world. Barton agrees, saying that video games probably gave him practice in dealing with conflicting visual information. They have also identified a genetic difference that affects brain plasticity. These are the types of insights Brewer hopes will illuminate brain function.
Brewer’s journey into the world of science wasn’t always a smooth one, though she knew as early as second grade that she was destined to be a scientist. Later in elementary school, she was the odd girl out in her rocketry class – not because she was odd, but because she was a girl. The only one.
“No one else in the class would talk to me,” she recollects. “Even the teacher never spoke to me once during the whole class.”
But the shunning did not discourage Brewer. She was determined to do what she loved. “I discovered I can be really stubborn,” she says. “It just made me work harder.”
That stubbornness helped her persevere through isolation and other annoyances, such as suggestions that a woman should pursue a more suitable – and easier – profession in order to raise a family.
Brewer, a mother of two, proved all the doubters wrong. She earned dual degrees in medicine and neurosciences at Stanford University, believing both would be valuable in pursuing her ultimate goal: using brain research to find unorthodox solutions to intractable medical problems. The two fields put her in a position to search for new answers.
Her research sometimes took her in unexpected directions. She briefly worked with scientists studying radiation effects on specific cancer markers and imaging changes in the heart during exercise.
But Brewer was more fascinated by the brain, and by the time she arrived at UCI in 2007, Brewer was looking for new ways to study neuroplasticity. She had worked with patients with retinal damage and developmental deficits in graduate school. But it occurred to her that working directly on the brain held the greatest promise for future treatments.
Brewer had encountered a professor during grad school at Stanford who shifted the visual field of owls using prisms, making their hunting swoops frustratingly inaccurate until they eventually adapted to the new match between their visual and motor worlds.
She began testing humans to see if they responded in similar ways. In the beginning, her subjects sometimes unwittingly walked in circles as they tried to navigate their altered environment.
Contagious – in a Good Way
“It’s a lot like looking through a camera while you’re walking,” Brewer says. “You get this jittery effect. Then you go in the wrong direction because of the prisms, and that makes the jittery effect even worse. You also can’t see your feet because of the goggles, which adds to the disorientation.”
Simply sitting in a chair was initially a trying experience for some of her subjects. Scribbling a word was almost impossible. “Writing the letter ‘m’ in the dark is easy,” she says, “but when you try to write it while watching, your hand appears to move in the opposite direction. You write the letter ‘n,’ and then you find yourself writing backward over it.”
But by the end of the two-week test, participants were negotiating their new environment about as well as they had their more familiar world.
In addition to observing the behavioral improvement, Brewer employs groundbreaking neuroimaging techniques that map the physical changes in the brain as it adapts. Images from functional MRIs – which measure the fluctuating oxygen levels in clusters of neurons – indicate changes in the visual and motor brain regions after someone has worn the goggles. Brewer and her colleagues have spent hundreds of hours sifting through the raw data.
“An increase in this plasticity could make other treatments more successful, especially for conditions like PTSD and drug addiction.”
It’s painstaking work, but it’s proving that the visual cortex is capable of profound change even in adulthood. This is promising news for those seeking solutions to disorders such as stroke, which often causes vision loss or other visual disturbances.
“We are starting related studies exploring how different types of visual training could be effective for rehabilitation of visual deficits,” she says. “Perhaps the still-healthy brain hemisphere could take on the function of the damaged hemisphere for a particular visual behavior. We see this type of interhemispheric change in the normal brains of our subjects who adapted to two weeks of reversed vision.”
There is even tantalizing evidence from other studies that neuroplasticity can be contagious, in a good way. Once it takes hold in certain areas of the brain, as it appears to do in the goggle experiments, neighboring tissue may become more receptive to change.
Brewer is teaming up with researchers at Stanford University, Baylor College of Medicine and the University of Texas Health Science Center at Houston to dig deeper into these and associated issues. And her experiments with the goggles continue, now with the new goal of determining how different senses, like hearing and touch, interact with the visual adaptations that her subject’s brains undergo.
“Because the prism goggles produce such dramatic changes in part of the visual cortex,” she says, “we are hopeful that these changes make the brain as a whole more susceptible to restructuring – to being more ‘plastic.’ Such an increase in this plasticity could make other treatments more successful, especially for conditions like PTSD and drug addiction.”
To conquer such intractable disorders, Brewer notes, it helps to view them from a different perspective.