..The circuits that survived were already partly tuned to the world beyond. At birth, she was already predisposed to the sound of her mother's voice over that of strangers; to the cadence of nursery rhymes she might have overheard in the womb; and perhaps to the tastes of her mother's Mexican cuisine, which she had sampled generously in the amniotic fluid. The last of her senses to develop fully was her vision. Even so, she clearly recognized her mother's face at just two days old.
For the next 18 months, Corina was a learning machine. While older brains need some sort of context for learning—a reason, such as a reward, to pay attention to one stimulus over another—
baby brains soak up everything coming through their senses.
"They may look like they're just sitting there staring at things," says Mark Johnson of the Centre for Brain and Cognitive Development at Birkbeck, University of London. "But right from the start, babies are born to seek information." As Corina experienced her new world, neural circuits that received repeated stimulation developed stronger synaptic connections, while those that lay dormant atrophied. At birth, for instance, she was able to hear every sound of every language on Earth. As the syllables of Spanish (and later English) filled her ears, the language areas of her brain became more sensitive to just those sounds, while losing their responsiveness to the sounds of, say, Arabic or Swahili.
If there is one part of the brain where the "self" part of Corina's mind began, it would be in the prefrontal cortex—a region just behind her forehead that extends to about her ears. By the age of two or so, circuits here have started to develop. Before the prefrontal cortex comes on line, a child with a smudge on her cheek will try to wipe the spot off her reflection in a mirror, rather than understand that the image in the mirror is herself, and wipe her own cheek.
But as scientists are learning about all higher cognitive functions, they're discovering that
a sense of self is not a discrete part of the mind that resides in a particular location, like the carburetor in a car, or that matures all at once, like a flower blooming.
It may involve various regions and circuits in the brain, depending on what specific sense one is talking about, and the circuits may develop at different times.
So while Corina may have recognized herself in a mirror before she was three years old, it might have been another year before she understood that the self she saw in the mirror persists intact through time. In studies conducted by Daniel Povinelli and his colleagues at the University of Louisiana at Lafayette, young children were videotaped playing a game, during which an experimenter secretly put a large sticker in their hair. When shown the videotape a few minutes later, most children over the age of three reached up to their own hair to remove the sticker, demonstrating that they understood the self in the video was the same as the one in the present moment.
Younger children did not make the connection.
If Corina had a sticker caught in her hair when she was three, she doesn't remember it. Her first memory is of the thrill of going to the store with her mother to pick out a special dress, pink and lacy. She was four years old. She does not recall anything earlier because her hippocampus, part of the limbic system deep in the brain that stores long-term memories, had not yet matured.
That doesn't mean earlier memories don't exist in Corina's mind. Because her father left when she was just two, she can't consciously remember how he got drunk sometimes and abused her mother. But
the emotions associated with the memory might be stored in her amygdala, another structure in the brain's limbic system that may be functional as early as birth. While highly emotional memories etched in the amygdala may not be accessible to the conscious mind, they might still influence the way we act and feel beyond our awareness.Source:
http://science.nationalgeographic.com/science/health-and-human-body/human-body/mind-brain.html
