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Denson says that the dorsal anterior cingulate cortex switches you from autopilot mode into active attention mode. “So, take the same example,” he says. “You’re driving home, and now suddenly someone cuts you off and then flips you off for good measure. That dorsal anterior cingulate cortex is going to be active. It’s going to wake up and say, ‘Hey, I need some higher brain functions to come on board here and help me solve this problem.’ So, it wakes the brain up.”

This squares well with the explanation of annoyances being like halfalogues: they tend to be a disruption, and their unpredictability puts you in a heightened state of alertness. You can’t tune them out.

Denson believes that’s what happened in his experiment. The subjects came to the lab, like good college sophomores in psychology experiments are supposed to do. They expected to be treated in a certain way, and their minds were most likely focused entirely on other things. “And suddenly I’m treating them like kindergarteners. So the dorsal anterior cingulate cortex gets active.”

Denson also wanted to see whether the subjects who were the angriest by the end of the experiment were also the ones who had the most blood flowing to the dorsal anterior cingulate cortex. That’s what the mood-and-aggression questionnaires were all about. Indeed, he did see a correlation between the level of anger and blood flow to the dorsal anterior cingulate cortex, but this was a small study—only twenty people—so sweeping conclusions are premature.

The limbic system’s role in annoyance is probably a crucial one. Brain responses in the limbic system are only somewhat under our conscious control. You can learn that a particular dark cave doesn’t pose a danger, but you will always feel at least a tingle of apprehension when you enter one. You can learn to control your annoyance with someone or something, but somewhere deep down, the limbic system will still insist that the annoying wail of a baby’s cry is something you want to turn off if you possibly can.

The more “rational” part of the brain is usually associated with the cortex. The word rational is in quotes because numerous authors have shown that people can be counted on to behave irrationally. Maybe a better word is cognitive. It’s the part of the brain that considers the facts at hand, evaluates them, and then makes some decision—rational or not—on how to behave next. In Huntington’s patients, this part of the brain deteriorates, which may partly explain the emotional outbursts.

One way to find out the role of a particular part of the brain structure is to see how people behave without it. Occasionally, this happens: parts are essentially “removed” because of a stroke or some other brain injury. There are also many cases where brain areas are removed as a procedure in a medical therapy. Some neurosurgeons have removed part of a patient’s anterior cingulate cortex in order to treat psychiatric disorders such as major depression, schizophrenia, aggression, anxiety, and substance abuse. Cingulotomy, as it is technically known, has also been used on patients with chronic pain.

“Cingulotomy evolved as a better solution than frontal lobotomy,” says neuroscientist Ron Cohen of Brown University. “The idea was that rather than do the whole removal of the frontal cortex”—a procedure that brought about a rainbow of psychological changes—surgeons “would try to get this area that was more specifically tied into the emotional systems and pain systems and things like that.”

Most of the studies on patients who have undergone cingulotomy focus on whether their main symptoms were relieved. Cohen conducted one, however, that actually looked at the changes in emotional states in patients who elected to have the surgery.{49} The patients in this study were being treated for intractable pain. After the surgery, researchers gave them standard personality questionnaires and mood-measurement tools like the ones Denson used with his subjects.

Most of the patients did get relief from their pain following surgery, according to the authors. None experienced severe negative emotional side effects from their surgery. Yet there did appear to be personality changes. The families of many of the patients reported that after surgery, the patients tended to be perceived as being more relaxed or laid back. “In some cases,” the authors wrote, “These changes were described as mild apathy and a lack of initiative after surgery.” The patients themselves tended not to be aware of major personality changes, other than reporting less emotional tension, anger, and pain.

Howard Wilkinson performed the surgeries on the patients in Cohen’s study. He is a neurosurgeon at Massachusetts General Hospital in Boston. Wilkinson has performed numerous cingulotomies, mostly to control chronic pain. He says patients who have the surgery still feel pain, it simply doesn’t bother them as much. “A constant, chronic, ongoing irritation or pain fades away,” says Wilkinson, “and people are less annoyed by the pain.”

Wilkinson’s study didn’t look specifically at whether postoperative patients were less likely to be annoyed in general, “but they did seem calmer,” he says. “The emotional state seemed slightly flatter.”

This fits with Cohen’s ideas of the role of the cingulate as a gateway to annoyance. All of the disorders that cingulotomy is used to treat involve what Cohen calls an “obsessive, ruminative loop.” When the surgery works, Cohen says that it breaks the loop and allows people to live with, if not actually to ignore, the stimulus they are obsessing over, whether it’s something unpleasant, such as pain or fingernails on a blackboard, or even when it’s pleasant, like gambling or taking cocaine.

Of course, this “calmer” state makes it seem that it’s not only annoyances that cingulotomy patients are less bothered by. Still, when neuroscientists trace the pathways of annoyance in the brain, as they are certain someday to do, it’s likely that the anterior cingulate cortex will be an important part of the route.

Another way to get at how the brain processes annoyances is to look at patients with amnesia. Never mind the amnesia depicted in Hollywood movies, where the hero suddenly remembers he’s a super spy. This is genuine amnesia, where people can form no new memories at all.

One of the best-studied cases of amnesia was a patient known only by the initials H.M. while he was alive. Henry Gustav Molaison died in 2008 at the age of eighty-two. When he was a child, he was hit by a bicycle. The accident caused him to start having severe seizures. When he was twenty-seven, surgeons removed a portion of his brain as a way to bring the seizures under control. The operation was a success, but it left Molaison with a very unusual problem. He couldn’t form any new memories.

You could walk into a room where Molaison was sitting, introduce yourself to him, chat for a minute or two, leave the room, return a few minutes later, and he’d have no memory whatever of having met you. To make things even stranger, he remembered lots of details from his life before the surgery—just nothing new that happened.

It turns out that one portion of the surgical procedure involved removing a part of Molaison’s brain known as the hippocampus, as well as some nearby related brain structures. It’s a region that appears to be crucial for consolidating memory. It’s not as if Molaison had no memory at all. He could hold a conversation, which meant remembering what someone had just said to him, but storing that memory, remembering the conversation for more than a minute or two, is impossible without a hippocampus and its neighboring brain regions.

Since scientists identified Molaison’s problem, they have found many more patients with damage to this part of the brain who experience the same memory deficits. Yet the kinds of memories that are lost without a hippocampus are what psychologists call declarative memories, memories for things such as names, faces, facts, and figures. Declarative memories require a conscious, thinking brain.