Shannon, a 14-year-old who lives in Massachusetts, has amblyopia, a condition sometimes referred to as “lazy eye.”
You can’t tell by looking at her, though. Unlike some amblyopic patients, whose eyes visibly wander, Shannon simply has extremely poor eyesight.
Patients’ best hope for correcting amblyopia is before they turn about 8 years old. Those who don’t get treatment early enough—or for whom treatment doesn’t work—usually end up living with the problem forever.
Shannon is one of those people. Her entire life, she’s worn glasses with a thin non-prescription lens on one side, and a thick corrective lens on the other. As a toddler, her parents tried to make her wear therapeutic eye patches, but she would fling them off.
A few months ago, Shannon enrolled in a clinical study at Boston Children’s Hospital for which she’s taking donepezil, a drug that’s typically used to treat Alzheimer’s. Donepezil is a cholinesterase inhibitor, meaning it increases the amount of acetylcholine circulating around nerve endings. It's been shown to improve memory function in some patients with dementia.
But of course, Shannon doesn’t have memory problems. Her team of doctors is instead using the donepezil to encourage her brain to learn new skills as quickly and nimbly as an infant’s would. Shannon's vision has improved markedly over the past four months, her mother told me by phone.
Takao Hensch, a Harvard professor of cellular biology who is part of the Boston Children’s team, has found that behavioral drugs like donepezil can help return the chemistry of the brain to so-called “critical periods” in its development—the times during early childhood when the brain was rapidly growing. Critical periods help explain why children younger than about 7 can pick up new skills, like language and music, much faster than adults can. This is why you see parents attempting to plant foreign languages in their kids while they’re still in Pampers. It’s much easier than trying to conjugate French verbs for the first time when you’re 30.
Hensch and his colleagues have already found that valproate, an epilepsy drug, can help tone-deaf adults learn to differentiate music notes. In a study published in December in the journal Frontiers in Systems Neuroscience, a team of researchers including Hensch administered valproate or a placebo to 24 men with no music experience and then trained them to label music notes. Those who took the valproate were later able to correctly identify 5.09 music notes on average, compared with 3.5 in the control group.
There were several flaws in the study—the sample size was small, and it’s possible that some of the men had a genetic predisposition toward music.
Still, the effect size was promising enough for Hensch to attempt new experiments with other drugs and different types of traits.
In Shannon's case, the donepezil helped her mis-wired brain learn how to process visual stimuli from the amblyopic eye, just like a newborn’s would.
“Our main interest is not really to create super humans but to help with developmental disorders or brain injury in adulthood,” he told me.
Hensch’s research is one of the more intriguing recent examples of how our understanding of neuroplasticity has evolved. Until about 20 years ago, scientists thought that after we reached puberty the structure of our brains more or less froze. But more recent studies have shown that our brains continue to transform throughout our lives, though not to the extent they did when we were children.