we know the answer to this question. In one example in July 2005, police in Plant City, Florida, pulled up outside a dilapidated house to perform an investigation. They had been alerted by a neighbor who had seen a girl in the window on a few occasions but had never seen the girl exit the house and had never seen any adults with her in the window.
The officers knocked on the door for a while and were eventually greeted by a woman. They told the woman they had a warrant to search for her daughter inside the house. They walked down the hallways, probed several rooms, and finally entered a small bedroom. There was the girl. One of the officers vomited.
Danielle, a feral child discovered in 2005 in Florida. Although the photograph displays a child’s beautiful face, the behaviors and expressions inherent to normal human interaction are absent in her: she missed the critical window for proper input from the world.
Danielle Crockett, an undersized girl of almost seven years old, had been locked away in a dark closet for her entire childhood. She was flecked with fecal matter and cockroaches. Beyond basic sustenance, she had never received physical affection, never engaged in normal conversation, and in all likelihood had never been let outdoors. She was fully incapable of speech. When she met the police officers (and later the social workers and psychologists), she appeared to look right through them; she had no glimmer of recognition or indications of normal human interaction. She could not chew solid food, did not know how to use a toilet, could not nod yes or no, and one year later had not mastered the use of a sippy cup. After many tests, physicians were able to verify that she had no genetic problems such as cerebral palsy, autism, or Down syndrome. Instead, the normal development of her brain had been derailed by severe social deprivation.
Despite the best attempts of doctors and social workers, the prognosis for Danielle is poor; the likely scenario is that she will live in a nursing home and may eventually be able to live without diapers.11 Heartbreakingly, hers is a real-life Kaspar Hauser story, with the real-life consequences.
Danielle’s outcome is grim because the human brain arrives in the world unfinished. Proper development requires proper input. The brain absorbs experience to unpack its programs, and only during a rapidly closing window of time. Once the window is missed, it is difficult or impossible to reopen.
Danielle’s story is paralleled by a set of animal experiments in the early 1970s. Harry Harlow, a scientist at the University of Wisconsin, used monkeys to study the bonding between mothers and their children. He had an active scientific career, but when his wife died of cancer in 1971, Harlow sank into a depression. He continued to work, but his friends and co-workers sensed that he was not the same. He turned his scientific interests to the study of depression.
Using monkeys to model human depression, he developed a study of isolation. He put a baby monkey into a steel-walled cage with no windows. A two-way mirror allowed Harlow to look in but prevented the monkey from seeing out. Harlow tried this with a monkey for thirty days. Then another monkey for six months. Other monkeys were incarcerated for a full year.
Because the baby monkeys never had the chance to develop normal bonds (they were put in the cage shortly after birth), they emerged with deep-seated disturbances. Those who were isolated the longest ended up much like Danielle: they showed no normal interaction with other monkeys and did not engage in recreation, cooperation, or competition. They barely moved. Two would no longer eat.
Harlow also noted that the monkeys were incapable of having normal sexual relations. Even so, he took some of the isolated females and had them impregnated to see how these disturbed monkeys would interact with children of their own. The results were disastrous. The isolated monkeys were completely unable to raise children. In the best cases, they ignored the children entirely; in the worst cases, they injured them.12
The lesson of Harlow’s monkeys is the same as the lesson from Danielle: Mother Nature’s strategy of unpacking a brain relies on proper world experience. Without it, the brain becomes malformed and pathological. Like a tree that needs nutrient-rich soil to arborize, a brain requires the rich soil of social and sensory interaction.
With this background in hand, we now see that the brain leverages its environment to shape itself. But how, exactly, does it absorb the world—especially from inside its dark cave? What happens when a person loses an arm or goes deaf? Does a blind person actually enjoy better hearing? And what does any of this have to do with why we dream?
3
THE INSIDE MIRRORS THE OUTSIDE
THE CASE OF THE SILVER SPRING MONKEYS
In 1951, the neurosurgeon Wilder Penfield sank the tip of a fine electrode into the brain of a man undergoing surgery.1 Along the brain tissue just beneath where one might wear headphones, Penfield discovered something surprising. If he gave a small shock of electricity at a particular spot, the patient would feel as though his hand were being touched. If Penfield stimulated a nearby spot, the patient would feel the touch on his torso. A different spot, the knee. Every spot on the patient’s body was represented in the brain.
Then Penfield made a deeper realization: neighboring parts of the body were represented by neighboring spots on the brain. The hand was represented near the forearm, which was represented near the elbow, which was represented near the upper arm, and so on. Along this strip of the brain, there was a detailed map of the body. By moving from spot to spot slowly along the somatosensory cortex, he could find the whole human figure.2
And this wasn’t the only map he found. Along the motor cortex (the strip just in front of the somatosensory cortex), he discovered the same kind of result: a little zap of electricity caused muscles to twitch in specific, neighboring areas of the body. Again, it was laid out in an orderly manner.
Maps of the body are found where inputs enter the brain (somatosensory cortex, top) and outputs leave the brain (motor cortex, bottom). Areas with more detailed sensation, and those that are more finely controlled, command more real estate.
He named these maps of the body the homunculus, or “little man.”
But the existence of the maps is strange and unexpected. How do they exist? After all, the brain is locked in total darkness within the skull. These three pounds of tissue don’t know what your body looks like; the brain has no way to directly see your body. It has access to nothing but a chattering stream of electrical pulses racing up the thick bundles of data cables we call nerves. Stowed away in its bony prison, the brain should have no idea what limbs are connected where, or which are next to which others. So how is there a depiction of the body’s layout in this lightless vault?
A moment of thought will likely lead you to the most straightforward solution: the map of the body must be genetically preprogrammed. Good guess!
But wrong.
Instead, the answer to the mystery is more fiendishly clever.
A clue to the map mystery came decades later, in an unexpected turn of events. Edward Taub, a scientist at the Institute of Behavioral Research in Silver Spring, Maryland, wanted to understand how victims of brain injury could recover movement. To that end, he obtained seventeen monkeys and studied whether severed nerves could regenerate. In each, he carefully cut a nerve bundle that linked the brain to one of the arms or one of the legs. As expected, the unfortunate monkeys lost all sensation from the affected limbs, and Taub set about studying whether there was a way to get the monkeys to regain use.
In 1981, a young volunteer named Alex Pacheco began to work in the lab. Although he presented himself as an intrigued student, in fact he was there to spy for a budding organization,