The Agile Gene: How Nature Turns on Nurture by Ridley Matt

The Agile Gene: How Nature Turns on Nurture by Ridley Matt

Author:Ridley, Matt [Ridley, Matt]
Language: eng
Format: mobi
Publisher: Harper Perennial
Published: 2012-02-13T21:00:00+00:00

THROWING SWITCHES IN THE BRAIN

It is easy to infer the existence of critical periods during which the wet cement of character can be set. It is less easy to conceive of how they work. What can possibly occur inside a brain to imprint a gosling on to a professor soon after hatching? Even to ask such a question reveals me to be a reductionist, and reductionists are bad. We are supposed to glory in the holistic experience and not try to take it apart. To which I could reply that there is often more beauty, poetry, and mystery in the circuit design of a microchip or the workings of a well-made vacuum cleaner than there is in a roomful of conceptual art, but I would not want to be called a philistine, so I will merely claim that reductionism takes nothing from the whole; it adds new layers of wonder to the experience. That applies whether the designer of the parts was a human being or the GOD.

How does a gosling’s brain imprint on a professor? Until very recently this was a complete mystery. Within the past few years, though, the veils of mystery have begun to lift, revealing new veils beneath. The first veil concerns which part of the brain is involved. When a chick imprints on its parents, experiments reveal that memories are laid down first and most rapidly in a part of the brain called the left intermediate and medial hyperstriatum ventrale (IMHV). In this part of the brain, and only on the left side, many changes accompany imprinting: neurons change shape, synapses form, and genes are switched on. If the left IMHV is damaged, the chick fails to imprint on its mother.

The second veil to lift reveals which chemical is necessary for “filial” imprinting of this kind. By examining the brains of chicks after they had or had not imprinted on an object, Brian McCabe found that a neurotransmitter called GABA is released from brain cells in the left IMHV during imprinting. He had previously noticed that a gene for a GABA receptor is switched off about 10 hours after the chick has been trained to imprint on an object.21

So something happens in one part of the left side of the chick’s brain during imprinting, first to release GABA and then to reduce sensitivity to GABA at the end of the critical period. To take the story further, it is time to leave baby birds for a different kind of critical period, one that is a little easier to study: the development of binocular vision. Babies are occasionally born with cataracts in both eyes that render them blind. Until the 1930s surgeons thought it wise not to operate to remove such cataracts until after the child reached age 10, because of the risks of surgery on small children. But it became apparent that such children never managed to perceive depth or shape properly even after the removal of the cataracts. It was simply too late for the visual system to learn how to see.



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