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[♩INTRO]
The feeling of a kicking fetus is perhaps one of the more fun parts
of having a baby.
And these movements serve a purpose well beyond letting you know
that that little thing is in there.
Like the pilots in Pacific Rim learning to control their giant robotic Jaegers,
these movements are evidence that your tiny incipient human’s brain
is learning to control its body.
When a fetus is in the womb, it’s not just sitting around waiting to be born.
It’s actually working really hard to learn everything it needs to survive
in the outside world, including breathing, swallowing, and, of course, moving.
There are over six hundred muscles in the human body,
which makes for a lot of controls to master.
So fetuses need to get an early start,
and the womb is the perfect place to get some practice in.
The first fetal movements happen around seven weeks after the parent’s last period.
Which is pretty early!
They consist of slow bending movements of the head and trunk,
and eventually simple movements of the arms and legs.
Things start to change at a postmenstrual age of nine to ten weeks.
That’s when the fetus starts to move with all the parts of its body,
and the directions and speeds of these movements start to vary.
These movement patterns are called general movements,
and their purpose is to explore all the possible combinations of movements
the fetus’s tiny body can make.
These movements generate proprioceptive sensory signals,
that is, sensory information about the position and movement of the body.
Every possible general movement has its own set of proprioceptive signals,
which helps the brain learn what these movements feel like.
So not only is the brain sending out all sorts of commands
to the muscles in the body, but the body is teaching the brain
the consequences of those commands.
The brain is learning what groups of neurons
are responsible for what movements.
It’s essentially the equivalent of learning to control a Jaeger
by flailing your arms and seeing what happens.
It doesn’t end there, though.
General movements continue to evolve and change
throughout pregnancy and into the first few months after birth.
More or less.
See, these changes in general movements occur at fairly predictable
postmenstrual ages, but are not affected by birth.
Infants who are born prematurely tend to follow the same
motor development patterns as their counterparts who are still in utero,
but are the same postmenstrual age.
It seems like the brain still needs about the same amount of time
to learn to control the body, regardless of whether or not it is still in the uterus.
It’s not until several months after birth that these general movements
are replaced with goal-directed movements,
movements used to accomplish specific goals, like rolling over or reaching.
However, there are a few goal-directed movements
that have to be learned in the uterus.
Sucking and swallowing are vital because they help a newborn eat,
and therefore survive.
So they have to develop before birth.
Fetuses have to learn to breathe, too, which they seem to do via hiccuping.
Other than that, infants tend to learn goal-directed movements
in a consistent order after birth,
starting with eye tracking and head balance,
and advancing to rolling over, grasping objects,
crawling, sitting, standing, and eventually walking.
Turns out it’s hard work learning to pilot a human body.
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[♩OUTRO]