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Saturday, November 26, 2022

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Illustration by p.theo Illustration by p.theo

Of Two Minds

Rethinking the brain's potential
By Lauren Coartney

With 101,000,000,000 possible circuits, compared with a mere 1079 particles in the known universe, the human brain has long mystified mankind.

For centuries, people have struggled to decipher it, seeking out comparisons to describe something that has no equal.

“The brain is so complex, we are bewildered and we long for something very familiar to explain it, like a computer or a clock with all sorts of parts,” said Norman Doidge, professor of psychiatry at the University of Toronto.

Even traditional neuroscience has downplayed the singularity of the human brain by likening it to a machine: The term “hard-wired” is borrowed from the technical world.

The changing brain

The mechanical comparison provides a digestible way to understand the brain, but it implies that parts, once broken, are lost forever, dooming victims of stroke, cerebral palsy, traumatic brain injury and other mental limitations to finish out their lives with compromised brain function.

But now, remarkable observations about the brain’s ability to change, and an ever-growing body of evidence in support of a phenomenon called “neuroplasticity,” are forcing researchers to rethink comfortable explanations and embrace this staggeringly complex circuitry. For those seemingly endless permutations give rise to trauma recovery and mental regeneration from the cradle to the grave.

As the saying goes, “to be human is to err.” However, what makes us vulnerable – a delicate brain that refuses fixity and is difficult to predict or repair – may also make us resilient and adaptable. The hemispheres, tracts and neurons work together so dynamically and so surprisingly, they trump any machine.

Experiment in nature

Researchers at San Diego State University's Department of Psychology have been tracking cases of plasticity, in which patients’ brains circumvent injured areas to develop functions thought to be lost. Their research has focused on children with focal brain lesions – often the result of perinatal stroke – to gauge levels of resilience for varying brain functions.

Perinatal stroke can occur anywhere from week 28 of gestation to 28 days after birth and can be caused by infection, dehydration and blood and cardiac disorders, among other things. It affects one of every 5,000 births.

Victims suffer from motor difficulties (the child may favor one hand), cerebral palsy and epilepsy, conditions that cause gaps in development once thought to be irretrievable.

“These children provide an experiment in nature where we can see how language and emotion can develop when you are missing part of your brain,” said SDSU psychology professor Judy Reilly.

Picking up the load

By focusing on brain damage specifically localized to the left or right hemisphere, Reilly can determine how language and emotion manage to bypass injured regions – previously thought to be the only place these functions could grow – to develop normally.

“If language were already in the left hemisphere from the beginning, a kid with a left hemisphere stroke would never be able to talk,” Reilly said. “If emotion were already in the right, then a kid with a right hand stroke would never learn to smile or would have emotional disturbance.”

But clearly, that wasn’t the case, since the babies she studied for more than 15 years learned to speak, albeit at a slower rate. In the case of one little girl who was born missing most of her left hemisphere, language development was on par with her peers by the time she reached the age of seven.

Using the mechanical comparison of the brain, there would not be an acceptable explanation for this kind of recovery, but with a neuroplastic explanation, it makes perfect sense.

“When you think about the fact that this kid developed language with absolutely no left hemisphere, you have to say, number one, [language] can’t be pre-specified to the left side only,” Reilly said. “It may be better suited, but it’s certainly not the only place language can develop. The right hemisphere can in fact assume those language functions, so you have an enormous amount of plasticity for language.”

Life in plastic

Until recently, evidence supporting neuroplasticity had been largely ignored because people were reluctant to disabuse themselves of the comfortable explanation; and, in what Doidge refers to as the “plastic paradox,” the brain uses its infinite potential to think itself into ruts, masking its true limitlessness.

“There were many, many examples of people with brain damage that made recoveries and they were just dismissed because of the mechanistic bias,” Doidge said. “But now we know that these exceptions – and I’ve documented scores of them – are not so unusual.”

Several factors coalesced in recent years to produce a plastic revolution, including the discovery of the machine metaphor’s limits and new technology that records change at the microscopic level.

When the theory first started gaining steam in the 1960s, neuroplasticity was thought to be a privilege of the young because of favorable conditions in the brain’s early developmental stages. Under normal circumstances, a child’s brain uses several locations across both hemispheres to develop function. As the brain finds the fastest, most efficient path for executing cognitive tasks, often in the best-suited side, those connections become “set.”

“It’s an issue of timing,” said SDSU psychology professor Pamela Moses. “Once the connections are laid down (in the mature brain), it is more difficult for functions to be taken over by resources that are already committed to other systems.”

Embracing exceptions

As Reilly found, if there is early injury in the best-suited side, the connection may simply set in one of the various other areas utilized to develop the neural pathways for the function in question. In contrast, an adult brain would have to re-route a long-defined connection, and that would be extremely difficult, but not impossible.

“In recent years we’ve started to realize that the amount of plasticity in the adult brain is much greater than initially believed,” SDSU psychology professor Jennifer Thomas said. “It was a long-held belief that the adult brain does not produce new neurons, but we now know that new neurons are generated even in the adult human brain.”

This understanding has been driven by documenting and embracing – rather than dismissing – exceptions to the mechanical model. In his recently published book, “The Brain That Changes Itself,” Doidge has amassed dozens of case studies of neuroplasticity in adults.

There is the amputee who has an unscratchable itch in his missing right hand. Inexplicable, until a researcher discovers that the brain cells that once received signals from the hand have been rewired to the man’s face. A good scratch to the cheek relieves the itch.

Another man regains use of paralyzed limbs following a stroke by overcoming the mental rut of learned nonuse. A 90-year-old man awakens driving alertness and improves his handwriting by performing mental exercises aimed at sharpening brain maps and stimulating the mechanisms that regulate plasticity.

Redefining ourselves

The impacts of these findings have already generated innovative ways of treating brain injuries and promise even better therapies to come.

“In the future, we might approach [brain damage] therapy cross-modally, rather than targeting a specific domain,” Reilly said.

“For example, if kids are having problems with language, perhaps one could improve language with more sensorimotor tasks on the assumption that the impact would ‘cross over,’ or kids could use one system as a compensatory system for solving problems in another domain.”

When it comes to the brain, researchers at SDSU and elsewhere know there are no pat answers. The very unpredictability of the plastic brain is the basis of human potential.