"A major push is under way to figure out the molecular basis of those "critical" or "sensitive" periods, to figure out how the brain changes as certain learning abilities come and go. In some, if not all, of those mammals that have the alternating stripes in the visual cortex known as ocular dominance columns, those columns can be adjusted early in development, but not in adulthood. A juvenile monkey that has one eye covered for an extended period of time can gradually readjust its brain wiring to favor the open eye; an adult monkey cannot adjust its wiring. At the end of a critical period, a set of sticky sugar-protein hybrids known as proteoglycans condenses into a tight net around the dendrites and cell bodies of some of the relevant neurons, and in so doing those proteoglycans appear to impede axons that would otherwise be wriggling around as part of the process of readjusting the ocular dominance columns; no wriggling, no learning. In a 2002 study with rats, Italian neuroscientist Tommaso Pizzorusso and his colleagues dissolved the excess proteoglycans with an antiproteoglycan enzyme known as "chABC," and in so doing managed to reopen the critical period. After the chABC treatment, even adult rats could recalibrate their ocular dominance columns. ChABC probably won't help us learn second languages anytime soon, but its antiproteoglycan function may have important medical implications in the not-too-distant future. Another 2002 study, also with rats, showed that chABC can also promote functional recovery after spinal cord injury."
"How does the body push the comparatively tiny genome so far? Many researchers want to put the weight on learning and experience, apparently believing that the contribution of the genes is relatively unimportant. But though the ability to learn is clearly one of the genome's most important products, such views overemphasize learning and significantly underestimate the extent to which the genome can in fact guide the construction of enormous complexity. If the tools of biological self-assembly are powerful enough to build the intricacies of the circulatory system or the eye without requiring lessons from the outside world, they are also powerful enough to build the initial complexity of the nervous system without relying on external lessons.
The discrepancy melts away as we appreciate the true power of the genome. We could start by considering the fact that the currently accepted figure of 30,000 could well prove to be too low. Thirty thousand (or thereabouts) is, at press time, the best estimate for how many protein-coding genes are in the human genome. But not all genes code for proteins; some, not counted in the 30,000 estimate, code for small pieces of RNA that are not converted into proteins (called microRNA), of "pseudogenes," stretches of DNA, apparently relics of evolution, that do not properly encode proteins. Neither entity is fully understood, but recent reports (from 2002 and 2003) suggest that both may play some role in the all-important process of regulating the IFS that control whether or not genes are expressed. Since the "gene-finding" programs that search the human genome sequence for genes are not attuned to such things-we don't yet know how to identify them reliably-it is quite possible that the genome contains more buried treasure."
Our sense of a composition largely inheres in how we feel about the individual parts; narrative arcs are almost always essential in drama but (unless there are lyrics involved) often less essential in music. All of this is, I suspect, again symptomatic of human memory limitations. We live, to a remarkable degree, in the present; what happened thirty seconds ago is already rapidly fading from our memory (or at least rapidly becomes harder for us to retrieve).
The psychologist Abraham Maslow famously suggested that after we take care of our most basic needs, such as food, shelter, and sex, we eventually strive for “ self-actualization,” or the realization of our full potential; in his words, “[Even if all our other] needs are satisfied, we may still often (if not always) expect that a new discontent and restlessness will soon develop, unless the individual is doing what he [or she] is fitted for. A musician must make music, an artist must paint, a poet must write. What a [person] can be, he [or she] must be.
"Sometimes guitar riffs get repeated over and over ("vamping," in the lingo of musicians), but generally there is a soloist proving variation that runs above that background, lest the song sound monotonous. Philip Glass's minimalist compositions (such as the soundtrack to 'Koyaanisqatsi') deviate from much of the classical music that preceded them, with much less obvious movement than, say, the Romantic-era compositions that his work seems to rebel against, yet his works, too, consist not only of extensive repetition but also of constant (though subtle) variation. Virtually every song you've ever heard consists of exactly that: themes that recur over and over, overlaid with variations."
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Honey bees, too, use a highly specialized learning mechanism to help them figure out where they are going: the difference is that their system works based on the trajectory of a single star, our very own sun. Once again, part of the system is prewired, but part of it requires learning. The prewired bit is a mathematical function that relates the sun's position on the horizon to to a bee's orientation-but some of the values of the equation must be set, which is where learning comes in. What the bee learns is a highly specific bit of information about the sun's trajectory at the bee's particular latitude at a particular time of year. A five o'clock winter sun in Boston means something very different from a five o'clock summer sun in California, and a highly focused learning mechanism allows honeybees to take advantage of that information. We know that bees don't simply memorize a correspondence between particular places on the horizon and particular headings, because bees that have been raised in conditions in which they are exposed only to morning light can accurately use the sun as a guide during evening light.