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Does Our Window for Learning New Things Really Close? Dr. McKhann Discusses Neuroplasticity at the World Science Festival

Each year in New York, some of the top minds in science and the arts gather for the World Science Festival (WSF). The annual weeklong event has drawn a total of 2.5 million visitors since its inception in 2008, with a mission to cultivate a general public informed by science, inspired by its wonder, convinced of its value and prepared to engage with its implications for the future.” Through moderated panels and debate, theatrical and musical performances, intimate discussions and outdoor experiences, participants enjoy science beyond the lab, against a backdrop of daily life.

For several years Dr. Guy M. McKhann, a neurosurgeon with Columbia University Irving Medical Center/NewYork-Presbyterian Hospital, has participated in WSF. In 2016 he took part in a presentation on Neuroprosthetics, the use of brain implants to restore and improve function, and in 2017 he moderated a gathering on Engineering the Brain.

In 2018, Dr. McKhann returned to WSF as moderator of a panel on neuroplasticity. He was fortunate to have three amazing neuroscientists on the panel to discuss this fascinating topic: Carla Shatz Ph.D. of Stanford University, Alvaro Pascual-Leone, M.D., Ph.D., of Harvard Medical School, and Nim Tottenham, Ph.D of Columbia University. The program, The Nuts and Bolts of Better Brains: Harnessing the Power of Neuroplasticity, focused on the differences between young brains and older brains and how age affects our ability to learn new things.

Let’s take a look at these differences.

In the brain, for every skill we develop (like learning to walk as a baby or to knit as an adult) electrical signals carve paths along nerve fibers and through the many synapses (connections between nerves) in the brain. These paths, called synaptic pathways, are created because of experience and exposure, so a newborn baby’s brain has an infinite number of pathways it can potentially create. Because there are so many options, scientists say that at this point the brain is flexible—or plastic. As the baby has more experiences and acquires new skills, these neural pathways are established. Each time the baby needs to take a particular path, the route is a little more obvious and automatic. Think about a toddler walking compared with a kindergarten-age child. The 5-year-old no longer has to carefully direct each step like the brand-new walker does, because the synaptic pathway for walking has been well-established. Staying on the path is automatic, or habitual.  

Now consider what happens when you try to get off the path you’ve established for a particular skill. It’s difficult to escape the established pathways as you get older because alternative pathways, once an option, are less accessible. When neural connections aren’t used, the brain takes them out of commission to preserve valuable energy, and they become less available to create new connections and pathways. So as the brain becomes more stable, it also becomes less plastic. Dr. Tottenham explained that there are windows of plasticity—or critical periods during which it is easiest to acquire a type of skill. Sensory pathways are developed in infancy, then motor and language pathways in early childhood. Higher cognitive pathways are open and available later.

A great example of this phenomenon is the backwards bicycle. In this video, an engineer who learned to ride a bike at a young age tries to ride one with the steering mechanism reversed. Normally you turn the wheel to the right to turn right, left to turn left. That is a well-worn synaptic pathway in the brain of anyone who can comfortably ride a bike. But when this engineer tried to ride the reconfigured bike (turn the wheel right to go left and vice versa), his brain’s established neural pathways for bike riding didn’t work. He had to bushwhack a new path for riding the re-engineered bike, which is why it took him eight long months to make the change. (Not so surprising, his 6-year-old son was able to learn to ride the new bike in just two weeks.)

Now, these well-worn paths may sound like a downside of aging, but they actually work in our favor, as Dr. McKhann explained at WSF. Habits result from the stability of the pathways we build in our brain—the very opposite of plasticity. As adults, we have a lot of things to think about, such as paying bills and raising children. We don’t have time to think about every step we take or how far to turn the steering wheel to make the corner. Stable pathways allow us to perform hundreds or thousands of routine tasks habitually, freeing us up to focus on higher-level problem-solving.

Neuroscientists would like to preserve the young brain’s plasticity, or ability to acquire new skills with relative ease, while retaining the older brain’s stability, or ability to perform daily tasks without conscious planning. Dr. McKhann calls this one of the “Holy Grails” of neuroscience research.

Wouldn’t it be great to be able to learn a new skill as easily as you did as a child? For those with neurologic disorders—say, Alzheimer disease or damage from stroke—that idea holds particular appeal and may even prove life-altering.

If someone has a stroke, for example, it would be helpful to access plasticity for relearning some of the skills lost because of damaged pathways and open the door to building new pathways, say, for walking and talking. Dr. Shatz is pursuing this line of research. There appears to be a chemical braking mechanism that shifts certain pathways from plastic to stable. Dr. Shatz is investigating how blocking these chemicals could reopen these pathways and allow people to regain lost skills.

On the other end of the spectrum is the theory that the autistic brain is too plastic—that it has difficulty establishing stable pathways. Individuals with autism can experience the world as chaotic because they aren’t able to easily manage the constant input via established, well-worn pathways. Dr. Pascual-Leone is studying the differences in plasticity between brains with autism and neurotypical brains and how those differences might be used to direct therapy to help people with autism function more easily on a daily basis.

Scientists also suspect that other neurological disorders may be the result of an imbalance in plasticity and stability. These include depression, obsessive-compulsive disorder, and even tinnitus (ringing in the ears).

According to Dr. McKhann and the WSF panelists, the potential uses of manipulating this balance between stability and plasticity are numerous. They can be used in treatment of diseases and in rehabilitation. Healthy individuals could use this concept to boost memory or learn new things such as improved musical pitch or a foreign language. There is even the suggestion that we can improve our happiness “setpoint,” or our baseline level of happiness. Manipulating this balance may even allow us to become more compassionate.

We are still a long way from being able to flip a switch between a stable brain and a plastic brain, says Dr. McKhann. But we are learning more about brain plasticity, and the path to using it to treat disease and improve lives is becoming clearer.

Learn more about Dr. McKhann on his bio page here.

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