In 1845, Edgar Allan Poe wrote an insightful short story called "The Imp of the Perverse." He explains what he means by an "imp" through the story's narrator, who relates what the imp in our mind might do if we were standing at a cliff's edge:

"We stand upon the brink of a precipice. We peer into the abyss-we grow sick and dizzy. Our first impulse is to shrink from the danger. Unaccountably we remain. By slow degrees our sickness and dizziness and horror become merged in a cloud of unnamable feeling. By gradations, still more imperceptible, this cloud assumes shape… far more terrible than any genius or any demon of a tale, and yet it is but a thought… it is merely the idea of what would be our sensations during the sweeping precipitancy of a fall from such a height."

This particular perversity I actually felt while climbing for the first time in Yosemite with my friend, Boreas. At the top of the climb, my imagination ran wild as I gazed down a sheer 800-foot cliff. It wasn't just that I could, and did, vividly imagine my body careening down the rock face—it was that the seed of curiosity, the imp of an actual urge was there; it was inside of me, ready to act, I felt, if I just lost focus for one crucial moment. I found that I was actually afraid not of the height, but of myself. And yet, while these thoughts kept me plastered to the rock surface at the top of an exposed peak, Boreas sat placidly. To this imp he was completely immune. Have you found your imp? Is it the urge to let go of the steering wheel while driving? That tickling impulse to start singing in the middle of a public lecture or sermon? There seem to be an endless array, to each their own. But where do these imps live?

At the beginning of my graduate school , I witnessed a 'brain ' by a neuropathologist. The brain in the first case was of an elderly man who had died recently. Remarkably (and unusually), the social worker who had worked with the man when he was alive was there at the brain cutting. Not five minutes into the procedure, the neuropathologist noted the degeneration in the prefrontal cortex—including heavy degeneration of the dorsolateral prefrontal cortex (in the brain just above the temples and wrapping around the outer edges of the forehead), which is involved in 'cognitive control.' When the neuropathologist turned and asked the social worker about issues of impulsiveness and control, the social worker replied that the man had a tendency later in life to jump out of moving cars. It turns out that stories like these are common. In fact, 57% of people with frontotemporal (neural degeneration that targets the frontal and temporal lobes) violate social norms—engaging in sexual transgressions and public nudity, shoplifting in front of store managers, eating out of the trash. It is common knowledge in the field of now that these behaviors are due to a problem of 'disinhibition' because of a deterioration of the cognitive control network in the lateral prefrontal cortex. Surely this is not the imp, though, but the shackles that normally keep him in check—remove the brake from a car and it will only move if you also apply the accelerator. So where is the gas coming from?

In a case that seems at first reminiscent of the man from the brain cutting, a wonderful piece in the Atlantic describes a man in 2007 who was arrested for child pornography. When he was caught, the man claimed that his desire came on suddenly and only recently. On the day before his sentencing, he went to the ER to see about a progressively worsening headache. A brain scan revealed a tumor in his orbitofrontal cortex (lying underneath the eyebrows). The tumor was removed without complication, and with it went his urge to view child . He began serving his time, and a year after his surgery, he felt the coming on again. He went immediately to the doctor, who found that a small piece of the original tumor that had been missed originally was growing again in the same place. After its removal, his urges once again vanished.

Interestingly, the tragic experimental treatment of mental illness called the frontal lobotomy actually targeted the orbitofrontal cortex. Using a sharp instrument reminiscent of an ice pick, Freeman and his colleagues performed tens of thousands of lobotomies, which entailed sticking the pick into the brain above the eyeball, and severing the connections between the orbitofrontal cortex and the rest of the brain. The problem was not that it did not remove violent tendencies, it often did. The problem was that it more often removed all tendencies: "these patients are not only no longer distressed by their mental conflicts but also seem to have little capacity for any emotional experiences—pleasurable or otherwise." Although the imp of the perverse may live in the orbitofrontal cortex, it seems that there also may dwell its less perverse cousins, those that motivate us to go camping with our friends, pursue a love interest, or apply to graduate school; to experience life.

So while the lateral prefrontal cortex provides a brake on behavior, it seems that medial prefrontal regions can supply the gas. Every day, these forces may keep behavior in balance—even if a dangerous impulse is there, the brake can keep it in check. But a strong impulse may over-ride even a working brake; and a weak brake might not be enough to keep even a mild impulse in check.

A final question might be, "Why do we never hear about pro-social, benevolent imps?" I would suggest that there may have been just as many of these cases—just as many tumors pressing on those particular imps, driving people to succumb to the fierce urgency of helping others. Who would question the motivations of a suddenly driven philanthropist? Wouldn't it be interesting if the slow press of different neural keys could accelerate us towards such deeply different impulses? How fervently we like to think of ourselves as the captains of our own fates, but how easily swayed our minds can be by that lump of cells within our skulls! There but for fully functional prefrontal cortical regions go we ...