"The miracle of plasticity and redeployment of the nervous system excites me very much," wrote neurologist and acclaimed science writer Oliver Sacks, author of the best-selling book The Man Who Mistook His Wife For A Hat.
Indeed, our brains' ability to repair themselves after injury is a thing of wonder.
Called neuroplasticity, or brain plasticity, this fascinating aptitude is what makes our brains capable of rerouting their connections to compensate for lost abilities.
A well-known phenomenon caused by neuroplasticity is the fact that losing one's sight often leads to a heightened sense of hearing.
Also, studies have shown that losing one's tactile sense can heighten the sense of smell, which suggests that the brain rewires existing senses to make up for those lost.
Recovery after stroke would also not be possible without the brain's plasticity. Because the brain processes sensory information and motor signals in parallel, motor function loss can be made up for by stimulating the brain with sensory and motor signals and "teaching" it to process them via another pathway.
But there are also more rare, lesser-known manifestations of neuroplasticity, and new research documents one such case.
In a study worthy of one of Sacks's "clinical tales," researchers have mapped the brain of a woman who can only see objects when they are in motion.
Researchers led by Prof. Jody Culham, from the Department of Psychology and Graduate Program in Neuroscience at Western University in London, Canada, set out to investigate this case more deeply by mapping out the woman's brain. The findings were published in the journal Neuropsychologia.
Studying a brain with Riddoch syndrome
Milena Canning lost her vision at 30, following a series of strokes and a respiratory infection. After waking up from an 8-week coma, Canning started to perceive flickers of objects in motion, but never when they were still.
So, she could see rain on a window because it was dripping, but couldn't see anything else through the window. If water was swirling down a drain, she could see it, but if a bathtub was already filled with standing water, she could not.
Now, a team led by Prof. Culham used functional MRI to study the neural pathways in Canning's brain. The investigation revealed that she has a rare condition called Riddoch syndrome.
Riddoch syndrome, also known as statokinetic dissociation, describes the ability of visually impaired people to see an object if it moves but not if it stands still.
The syndrome "has been observed in individuals with lesions in the anterior visual pathways or the occipital lobe."
In Canning's case, explains Prof. Culham, the woman "is missing a piece of brain tissue about the size of an apple at the back of her brain — almost her entire occipital lobes, which process vision."
Brain develops 'back roads' to create vision
For the study, the researchers asked Canning to take part in some tests. They rolled balls — whose "motion, direction, size, and speed" Canning was able to recognize — at her.
The woman was also able to stop and grab the balls at the right time, and she could move around chairs.
"[W]e think the 'superhighway' for the visual system reached a dead end," explains Prof. Culham.
"But rather than shutting down her whole visual system," she says, "she developed some 'back roads' that could bypass the superhighway to bring some vision — especially motion — to other parts of the brain."
So, Canning's brain took an unpredictable route in an attempt to bypass the injury, showcasing neuroplasticity at its most surprising. The study's lead investigator comments on the findings.
"This work may be the richest characterization ever conducted of a single patient's visual system [...] Patients like Milena give us a sense of what is possible and, even more importantly, they give us a sense of what visual and cognitive functions go together."
Prof. Jody Culham