Page 41 - Mind Games The Aging Brain and How to Keep it Healthy

The Intelligent Mind • 25

The basis for these communications connections already
can be identified approximately 10 weeks after conception
3
when the brain is merely one-half inch long. Neurons begin
pushing their way from the neural tube deep within the inte-
rior of the fetus’s brain to the outside margins, with newer
neurons pushing past older neurons. Neurons travel along
glial fibers much like traveling down a highway toward their
final destination with the assistance of proteins and chemical
4
cues. By five months into the pregnancy, the fetus’s brain is
now two inches long, and the migration of neurons to the
outer layers of the brain is almost complete. 5

Early Brain Development
During development, a baby’s brain is a maze of neurons
much different in structure from the adult’s brain. One in-
teresting example is vision development. To develop vision,
nerve fibers from the retina must grow to extend far enough
through the brain to reach the visual thalamus (see Figure
2-2), and from there, axons reach to the outer layers of the
cortex, before the cortex even exists.

cortex—the folded outer layer of the brain

A study by Carla J. Shatz, professor of neurobiology at
6
Stanford University, demonstrated the existence of transient
support “scaffolding” in the developing brain that aids in de-
veloping vision but disappears after the brain’s growth is fin-
ished. Special types of neurons, subplate neurons, suddenly
appear just below the final destination at the visual cortex
and function to bolster and direct the axons to their proper
location. Then these subplate neurons disappear. These and
other neurons that act as temporary support structures,
along with the proteins and chemical cues previously men-
tioned, prevent the axons from wandering into incorrect ar-
eas and impairing brain functions. Some disabilities, such as
cerebral palsy, autism, epilepsy, schizophrenia, and dyslexia
are thought to be a result of wandering axons or improper
connections. 7