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Ira J. Chasnoff, M.D.
Ira J. Chasnoff M.D.

The Common Sense

Humans have five senses; most also have “the common sense.”

I received a call from an adoptive parent this week. "Nick's 19 years old," said the frustrated father. "And he doesn't have an ounce of sense!"

It seems that Nick had been out with friends when a 16-year-old girl said, "Nick, why don't you come over to my house sometime, and we'll hang out?"

Nick is an imposing young man with jet-black hair, a winning grin, and an innocent demeanor that leads him to take people at their word. So it was that at three in the morning that same night, Nick got up, got dressed, and went to her house.

Entering through an unlocked back door, he climbed the stairs to her bedroom and shook her awake. When she awoke, there was Nick, 6 feet tall, looming over her in the dark. She began to scream.

Her parents rushed in, threw on the lights, and found Nick standing unconcerned in their daughter's bedroom. They called the police.

After hours of questioning, the police were ready to throw the book at Nick, because every time they asked, "What the hell do you think you were doing?" Nick calmly responded, "But she invited me over."

Thomas Aquinas was a 13th-century philosopher and theologian. Although he had no understanding of brain anatomy, he did offer a very insightful description of what we might now refer to as information processing: that is, how the brain takes in and uses information.

Aquinas observed that all people have five senses: sight, hearing, touch, taste, and smell. He then added the notion of "the common sense."

Aquinas used the term differently than what it has come to mean for most people today. Now a person is said to have common sense if that person can see through the clutter of daily life and make good decisions.

But Aquinas had something quite different in mind. He used the term to describe a function of the brain, which allowed for integrating the various forms of sensory input so that things "made sense."

For him, "the common sense" was that aspect of human thinking that took the input from the five physical senses and formed a full, integrated concept. He accurately inferred the necessary role of the corpus callosum, a central component of the substructure of the brain. The corpus callosum is responsible for connecting the right and left sides of the brain, thereby allowing the individual to take the information he or she knows and use it to guide and inform behavior.

A human being without a corpus callosum would lack the brain structure needed for "the common sense." In another time, Aquinas might have made a good neuroscientist, but as it is, he serves us well as an articulate thinker capable of bridging the gap between modern neuroscience and an early philosophical understanding of what it meant to be a fully functioning person.

The pieces fall into place in Nick's case when we come to know the extent of his prenatal exposure to alcohol. Alcohol use in early pregnancy has been shown to change the structure and shape of the corpus callosum, in some cases prohibiting the corpus callosum from forming at all.

On looking at an MRI of Nick's brain, a trained physician can see the thinning and shifting of the corpus callosum induced by his birth mother's use of alcohol in the first weeks after conception—most likely before she ever realized she was pregnant.

Changes in this part of the brain explain, in large part, why Nick cannot connect what he hears, sees, smells, tastes, and feels into coherent patterns that can actually help him make good decisions and manage his behaviors. Although his IQ is well into the 90s, and he is not willfully impulsive or indifferent to danger, Nick lacks the common sense to unify disparate forms of sensory input.

Every community has young people like Nick, children with dramatic and urgent needs. Health care professionals, teachers, and others see them on a regular basis, but the children often do not get what they need. They go undiagnosed and untreated, and most often they and their parents are blamed for the behaviors. Punitive approaches are taken, and, statistically, the majority of these children will end up in jail.

The logic of prevention and early intervention is never clearer than when it is applied to children who have been prenatally exposed to alcohol or other drugs. The challenge is to begin to reshape how we think about human behavior: to recognize the biologically based causes at the root of many of the difficulties we see in children today. It is nothing more than simple 13th-century common sense.

About the Author
Ira J. Chasnoff, M.D.

Ira J. Chasnoff, M.D., is a Professor of Clinical Pediatrics at the University of Illinois College of Medicine in Chicago. His most recent work is The Mystery of Risk.

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