PANTHEON, JANUARY 2016We have a tendency to judge craziness at face value. Why do people scream at invisible entities, eat dirt and paper, or loiter on street corners muttering about the Devil? Well, because they’re crazy, right?

But what if we didn’t accept that answer so easily and instead asked the question: Why is that person acting so bizarrely? For neurologists, “crazy” isn’t a diagnosis. It’s a symptom. The key is to look into the brain and pinpoint the cause of that symptom. What I have found, time after time, is that once we discover that underlying cause, abnormal behavior can be viewed as a reasonable, even logical, form of compensation.

I discuss this perspective on mental illness in my latest book, NeuroLogic: The Brain’s Hidden Rationale Behind Our Irrational Behavior.

Consider the following two people, each of whom exhibits a unique form of mental illness....

Surprisingly, both disorders have the same underlying neurological deficit: damage to the border between the temporal and parietal lobes. Injuries to this region disrupt crucial communication between the sensory system, responsible for perception, and the limbic system, which is responsible for emotional processing.

Normally, these two systems in the brain cooperate to process not only the appearance of a familiar face, but also a vast array of emotions ranging from overt feelings of love, fear, or jealousy to the subtlest sense of familiarity and shared experience. But when a schism develops between the appearance of faces and that intimate feeling of recognition they’re supposed to trigger, you feel a cold, emotional distance from everyone you know. The person in bed with you looks like your spouse, but you know in your heart that she isn’t. Family and friends who should look familiar don’t feel familiar. No longer connected to anyone in your life, you feel removed from the world. How would you logically explain that scenario to yourself?

It sounds a lot like death, at least the way death is represented in popular culture. Hence, some patients begin to believe that they have passed from this world, and eventually end up with a diagnosis of Cotard delusion. Another subset of patients might reasonably conclude that it is not they themselves who have changed, but the people around them. The patient thinks to himself: “This woman doesn’t feel like my wife, so she must not be my wife. So who is she, and why is she in my bed? I must be cheating.” Arriving at this explanation earns him the diagnosis of Capgras syndrome.

Seen this way, these two diagnoses are surprisingly logical ways to explain the same pathology. Those with a tendency toward depression and nihilism tend to claim that they are dead. Those with a more paranoid personality tends to direct the blame outward, believing that the people around them have been replaced by imposters (or, in this case, a mistress). In both cases, the perceived situation is far more bizarre than the patient. The stories they come up with are a form of compensation—coping mechanisms that help make sense of an utterly confusing situation. Given such bewildering circumstances, the behaviors aren’t that unreasonable. You might even call them logical.

The brain’s inner workings can be disturbed in countless ways, many of which we have only begun to study. When one views the behavioral manifestation of mental illness within this context, it becomes clear that words like “crazy” and “insane” are simply admissions of ignorance. They are empty categories for a vast array of illnesses we barely understand, and they trivialize the subtlety of the underlying neurological dysfunction. As research continues to unveil the defects that produce mental illness, and to dissolve some of the mystery, perhaps we can learn to look past the symptoms, and instead look into the brain. 

Eliezer J. Sternberg is a resident neurologist at Yale-New Haven Hospital. With a background in neuroscience and philosophy, he studies how brain research can shed light on the mysteries of consciousness and decision-making. Read an excerpt of NeuroLogic.

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