Feeling in Tongues
Study: Learning to feel again akin to learning a second language
FRIDAY, Sept. 7, 2001 (HealthDayNews) -- Re-training severed nerves is much like learning a second language, a new study says: It's easier and more successful when you're younger.
Swedish hand surgeons say people who undergo nerve repair of the wrist are more likely to recover normal or nearly normal sensation if they're 10 or younger. The age patterns for recovery have a "striking analogy" in the ability of immigrants to learn a second language, which is easier early in life but becomes progressively harder with age, the researchers say.
Indeed, a plot of the pattern of regained sensation after nerve-repair surgery matches almost perfectly a graph of grammar test scores and ages of immigrants learning English as a second language. Both show the best gains among the very young, followed by a steep fall-off into the teen years and an adult plateau that's far beneath childhood proficiency. The findings appear as a research letter in the Sept. 8 issue of The Lancet.
The results help explain why nerve-repair surgery in adults almost always produces discouraging results when it comes to re-learning how to use the damaged limb, the researchers say. Rather than reflecting inadequate surgical technique, they say the adult brain may simply be too set in its ways to adapt to the scrambled nerves.
Dr. Goran Lundborg and Birgitta Rosen of Malmo University Hospital studied 54 patients, ages 4 to 72, who underwent surgery to repair severed median or ulnar nerves in their wrists. The nerves control the hands and fingers.
Using standard tests to measure tactile sensation, such as shape and texture, the researchers say that children under age 10 had the best recoveries from the operations, regaining nearly complete "tactile gnosis," or the ability of the hand and fingers to "see" an object.
After about age 10, however, the extent of recovery dropped sharply until it leveled off after age 18. The researchers saw a brief spike among patients in their early- and mid-20s, but that tailed off in the 30s and beyond.
"We have defined a critical age period for regaining functional sensibility after nerve repair, ending in the late teen ages," Lundborg and Rosen write. "The critical period is closely associated with a corresponding critical period for language acquisition, indicating a strong learning component in acquisition of functional sensibility."
"Tactile gnosis may be permanently lost in adult patients," when "the hand speaks a new language to the brain," they write.
Dr. Rudy Buntic, a microsurgeon at the California Pacific Medical Center's Buncke Clinic in San Francisco says the latest work is "interesting, but not particularly earth-shattering."
"It's nothing new that patients who are younger tend to do a lot better with peripheral nerve repairs," says Buntic, a hand specialist. He says with microsurgery techniques, older people also can recover significant function.
"It's not as gloomy as they lead you to believe," Buntic says.
Unfortunately, he says the Swedish scientists didn't include any information about what kinds of surgical methods the doctors used, nor the nature of the nerve injuries to the patients. Children, for example, often suffer lacerating, "sharp" wounds to nerves that heal better than the crushing injuries adult patients frequently present with, Buntic says.
Dr. A. Lee Dellon, a Baltimore neurosurgeon who has studied the "reeducation" of nerves, says you can teach an old nerve new tricks. "Although it's certainly true that the younger do better, it is not absolutely related to age," says Dellon, who also is professor of plastic surgery and neurosurgery at Johns Hopkins University.
Intensive exercises that focus on the fingers can help the adult brain remap repaired nerves and generate more accurate pictures of what the hands are touching, Dellon says. "I can get people who are 60, with re-training, to understand what this new pattern is in their fingers," he says.