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| Archive : Fall
2006 |
FROM BACH TO BEDOUINS, MANY STONES WERE TURNED IN SEARCH OF CLUES TO HOW PUBERTY BEGINS:
An eighteenth-century choir // A gene that “kisses” // Harry Potter // Saudi cousins // Songbirds //
And, of course,
pimply faced adolescents.
To Grow Hairy [page 4]
 By Stephen S. Hall |
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One of the biggest questions in neuroscience today is whether puberty “seals off” brain growth the way sex hormones seal off the ends of bones. During the physical growth that typifies the adolescent growth spurt, height is achieved through a continual, incremental lengthening of skeletal bones at the growth plates, small disks of tissue at the ends of long bones like those of the upper arm or thigh. With increasing sexual maturity, however, an adolescent body produces more sex hormones, and these hormones ultimately “seal” the growth plates at the conclusion of puberty, so that growth effectively stops and adult height is achieved.
One hypothesis is that as the amount of testosterone generally increases in boys and estradiol increases in girls, wiring patterns in the brain, sculpted by a childhood’s worth of highly personal and individual experiences—nurture, nutrition, fights, flute practice, all sorts of large and small endeavors and behaviors—become more or less permanently fixed. It is as if a neuropsychological circuitry is tentatively mapped out by the experiences of childhood and adolescence, then the reproductive hormones of puberty solder that circuitry in a much more permanent fashion. Not rigidly and irrevocably—otherwise, education would be useless once the ends of our bones fuse—but tentatively. Thus a basic architecture, contributing to a basic probability of neurocognitive tendencies, may well be fixed by the end of adolescence.
This process remains inadequately understood in humans. But researchers have found that in birds, for example, an animal’s flexibility in learning its song system can be extended when testosterone is removed from immature males. Sisk, the Michigan State psychologist, suspects there is a neural equivalent to the way puberty seals bone growth. “I’m betting there is, based on our behavioral data,” she says, “but we don’t yet have empirical evidence for permanent structural changes.”
If her hypothesis is correct, this change would be among the most profound in terms of adult behavior. So while it’s clearly not true that puberty is all in your head, it certainly starts there, and some of its most lasting effects may be cemented into place there as well. The biology promises to be fascinating but also a little frightening, especially if we find that our “inner teenager” is hardwired into our adult brain.
This story is based on an excerpt from Stephen S. Hall’s upcoming book,
Size Matters, to be published by Houghton Mifflin in November. Copyright © 2006
by Stephen S. Hall. Used by permission of the Melanie Jackson Agency, LLC.
 Dossier
1.“The GPR54 Gene as a Regulator of Puberty,” by Stephanie B. Seminara, Sophie Messager, Emmanouella E. Chatzidaki, Rosemary R. Thresher et al., New England Journal of Medicine, Oct. 23, 2003. An account of experiments that showed that a defect in the gene prevents puberty in mice and humans, thus revealing the gene’s pivotal role.
2.“The Adolescent Brain: A Work in Progress,” by Daniel R. Weinberger, Brita Elvevåg and Jay N. Giedd, June 2005 [The National Campaign to Prevent Teen Pregnancy]. A highly readable exploration of how the teenage brain undergoes refining and restructuring. |
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