The Plastic Brain

UAB Neuroscientists Stretch the Boundaries of the Mind

By Bob Shepard

Neurogenesis in action

The big news in neuroscience these days is that you can change your mind. Not just in superficial ways, either, such as opting for milk over creamer or paper instead of plastic, although plasticity has a lot to do with it. The field is abuzz with mind-bending research indicating that the adult brain can be shaped—repaired, expanded, optimized—in ways that were unimaginable only a few decades ago.

You can’t teach an old dog new tricks, the saying goes. And for decades, scientists thought the same thing about the human brain. An adult brain, the textbooks said, is not plastic—that is, it has no ability to change, to grow, to repair itself if injured. At birth, in infancy, and through childhood, the central nervous system is malleable; it can grow and change depending on different stimuli. But researchers were certain that this ability fades upon maturity, leaving the adult brain with the capacity to diminish—through injury, disease, or simply old age—but not to grow new cells or structures, or to repair the damage it accumulates over a lifetime. Distinguished Spanish neuroscientist Ramón y Cajal summarized the viewpoint succinctly in 1913: “Everything may die; nothing may be regenerated.”

This view emerged as far back as the 1850s, when scientists began to believe that neuroplasticity ends with childhood—based on what appeared to be credible evidence, says UAB psychologist Edward Taub, Ph.D. But that view is discredited now, thanks to experimental results in the 1970s that began hinting at the possibility that the adult brain has the potential for plastic change. Although there was no definitive proof, neuroplasticity was at least a plausible explanation for those early findings.

An Invasion of Healing

Taub’s own studies in the 1970s and ’80s were among the first to point to neuroplasticity in the brains of adult mammals. Then Michael Merzenich, Ph.D., a colleague of Taub who was working at the University of California-San Francisco, conducted landmark studies in the 1980s that confirmed that the adult brain was, in fact, plastic.

“It had been considered axiomatic that the adult mammalian nervous system had no plasticity,” Taub says. “Intuitively, I thought that could not be correct. When you come right down to it, what is learning? Learning is neuroplasticity. And there are real changes taking place in the nervous system during learning.”

Taub determined that the brain must have the ability to rewire itself after injury—in essence “learning” how to cope with nonfunctioning regions by shuffling its vast network of connections. He theorized that the brain recruits healthy areas to step into the gap left by damaged systems, likening the process to a benign invasion.

Building on his research, Taub developed Constraint-Induced Movement therapy, or CI therapy, to accelerate this recruitment process and began using it to help stroke patients. The therapy, which was the first explicit clinical application of the principle of neuroplasticity in the adult brain, forces patients to accomplish tasks with their poorly functioning limbs through intensive training. In the process, the brain’s self-healing program is kick-started.

Substantial Improvement

Virtually all of the hundreds of patients who have undertaken CI therapy in Taub’s laboratory and clinic have seen substantial improvement in their ability to use their affected limbs; subsequent studies have shown that the therapy actually increases the amount of gray matter in the brain. CI therapy is now in use around the world, and it has been expanded to treat a number of conditions, including cerebral palsy, traumatic brain injury, multiple sclerosis, and spinal cord injury.

The field of neuroplasticity is growing, too. In fact, Taub says it has become so big that it is almost unmanageable, and some new divisions are needed. “I was at a conference with my valued colleague Mike Merzenich, listening to an investigator giving an excellent talk on what he was calling neuroplasticity,” Taub recalls. “I turned to Merzenich and said, ‘The trouble with neuroplasticity is that there are eight different definitions.’ He said, ‘Eight! You mean a hundred!’”

Next week: We'll explore new definitions of neuroplasticity as three more UAB neuroscientists explain their research into Alzheimer's disease, learning and memory, and the growth of new neurons in the adult brain.

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