The Neuroscience of the Seven Deadly Sins

Techniques such as functional magnetic resonance imaging (fMRI), which highlights metabolically active areas of the brain, now allow us to view the biology of bad intentions.

The most enjoyable sins engage the brain’s reward circuitry, including evolutionarily ancient regions such as the nucleus accumbens and hypothalamus; located deep in the brain, they provide us such fundamental feelings as pain, pleasure, reward, and punishment.

More disagreeable forms of sin such as wrath and envy enlist the dorsal anterior cingulate cortex. This area, buried in the front of the brain, is often called the brain’s conflict detector, coming online when you are confronted with contradictory information or even simply when you feel pain.

The more social sins (pride, envy, lust, wrath) recruit the medial prefrontal cortex. Found just behind the forehead, this region helps shape the awareness of self.

No understanding of temptation is complete without considering restraint, and neuroscience illuminates this process as well. As we struggle to resist, inhibitory cognitive control networks involving the front of the brain activate to squelch naughty impulses by tempering their appeal.

Meanwhile, research suggests that regions such as the caudate—partly responsible for body movement and coordination—suppress the physical impulse.

It seems to be the same whether you feel a spark of lechery, a surge of jealousy, or the desire to pop somebody in the mouth: The two sides battle it out, the devilish reward system versus the angelic brain regions that hold us in check.

It might be too strong to claim that evolution has wired us for sin, but excessive indulgence in lust or greed could certainly put you ahead of your competitors.

There is no sin centre in the brain, no single node of fiendishness that we might be able to shut down with drugs or electrodes. With the advent of modern imaging techniques that peer into the brain as it functions, though, we at least gain some perspective on our bad habits. At the same time, we can indulge in another wickedly gratifying pastime: As other people misbehave, we can sit back and watch.

In the annals of sin, weaknesses of the flesh—lust, gluttony, sloth—are considered second-tier offenses, less odious than the “spiritual” sins of envy and pride.

That’s good news, since these yearnings are notoriously difficult to suppress.

Watching pornography calls upon brain regions associated with reward, sensory interpretation, and visual processing. It enlists the amygdala and the hypothalamus, which deal with emotional information; it also stimulates the reward processing ventral striatum, probably due to the satisfying nature of watching erotic stimuli. All said, the most notable thing about lust is that it sets nearly the whole brain buzzing.

These responses are so unique and distinctive that, in the context of an experiment, it is possible to determine whether a man is aroused just by looking at an fMRI brain scan. “These are huge effects,” Safron says. “You’re looking at the difference between something that elicits intense desire and something that does not.” (Women show a less spectacular response, Safron says, and it is unclear exactly why.).

If lechery is all-consuming, how do we ever manage to control it? As with other powerful impulses, we try to shut down arousal by calling upon the right superior frontal gyrus and right anterior cingulate gyrus, according to research led by Mario Beauregard. He and others propose that these brain areas form a conscious self regulatory system. This network provides us with the evolutionarily unprecedented ability to control our own neural processing—a feat achieved by no other creature.

Today it is difficult to regard overeating as a sin, considering the overwhelming evidence of the powerful role of physiology in appetite. Physician Gene-Jack Wang has studied the brains of overeaters since 1999, when he and colleague Nora Volkow originally observed that obesity and drug addiction alter the same brain circuits.

These pathways, which rely on the neurotransmitter dopamine, are often referred to as the reward system, but they are also involved in motivation, attention, decision making, and other complex functions. In their studies, Wang and Volkow found that both drug addicts and obese people are less sensitive to dopamine’s rewarding effects. Being relatively numb to the pleasure and motivation signal may make them more likely to chase after a stronger thrill: more food or a bump of cocaine. Excessive stimulation further desensitizes dopaminergic neurons, and the compulsion snowballs.

In some of his experiments, Wang asks his volunteers to come hungry. He then torments them, asking them to describe their favorite food in detail while he heats it up in a microwave so that its aroma wafts through the room. When they go into a positron-emission tomography (PET) scanner, Wang sees the motivation regions of their brains go wild. Parts of the orbital frontal cortex, which is implicated in decision making, also light up.

In the brains of obese people, the regions that regulate sensory information from the mouth and tongue are more active, suggesting that overweight people may experience the sensations of eating differently. Other research shows that their reward sensitivity is lower. The dorsolateral prefrontal cortex and other areas involved in inhibitory control are underactive; the heavier the person, the lower the activity there.

Mere laziness seems out of place among the deadly sins. It helps to know that this moral failing was originally conceived of as acedia, a term that suggested alienation and tedium, tinged with self-contempt. Acedia afflicted jaded monks who had grown weary of the cloistered life. Their sin was turning away from their moral obligations and toward selfish pursuits—a monastic form of ennui.

Today, paralyzing lassitude is often seen as a symptom of disease rather than of turpitude. Apathy is a classic sign of frontotemporal dementia. In this neurodegenerative disorder, the frontal lobes of the brain are slowly eaten away, causing social and mood changes as well as cognitive decline. Patients with such dementia often become increasingly withdrawn.

Sadness and listlessness are also hallmarks of major depression. With frontotemporal dementia the symptoms are caused by dead and dying cells; in depression the root cause is still unknown. In both conditions, the dorsolateral prefrontal cortex has an unusual pattern of activation.

Related to its ability to inhibit impulses, this region has a role in sustaining attention over the long haul. Abnormal function in the dorsolateral prefrontal cortex might be connected to the lethargy associated with both conditions. Conversely, activity in this area may keep a lid on negative emotions; in some studies, depression lifted with stimulation of that part of the brain.

Early theologians saw pride as the fundamental sin—the “queen of them all,” according to Pope Gregory the Great, who codified the list of seven deadly sins in the sixth century. Indeed, psychologists say that arrogance is second nature in Western society. Most of us perceive ourselves as slightly smarter, funnier, more talented, and better-looking than average.

These rose-colored glasses are important to mental health, functioning as a psychological immune system that protects us from despair. “Those who see themselves as they truly are—not so funny, a bad driver, overweight—have a greater chance of being diagnosed with clinical depression,” says Julian Paul Keenan.

For most of us, it takes less mental energy to puff ourselves up than to think critically about our own abilities. In one recent neuroimaging study, volunteers who imagined themselves winning a prize or trouncing an opponent showed less activation in brain regions associated with introspection and self-conscious thought than people induced to feel negative emotions such as embarrassment. We accept positive feedback about ourselves readily,

Pride gets its swagger from the self-related processing of the medial prefrontal cortex, which Keenan calls “a very interesting area of the brain, involved in all these wonderful human characteristics, from planning to abstract thinking to self-awareness.”

Using transcranial magnetic stimulation (TMS), in which a magnetic field applied to the scalp temporarily scrambles the signal in small areas of the brain, he was able to briefly shut off the medial prefrontal cortex in volunteers. With TMS switched on, his subjects’ normal, healthy arrogance melted away. “They saw themselves as they really were, without glossing over negative characteristics”.

Righteous humility has traditionally been depicted as the virtue that opposes pride, but the work of Keenan and others calls that into question. He is using TMS to disrupt deliberate self-deprecation—the type of unctuous, ingratiating behavior that seems humble but is actually disguised arrogance.

Patterns of brain activation during self-deprecation are fundamentally the same as those during selfdeceptive pride, Keenan is finding. “They’re in the same location and seem to serve the same purpose: putting oneself ahead in society."

Despite the enormous pool of potential research subjects, greed has not yet been systematically investigated in brain research. However, neuroscience does offer insight into a related phenomenon, the indignant outrage of the cheated.

Our hatred of unfairness runs deep, even trumping rational self-interest. In the lab, researchers frequently use the “ultimatum game” to test our responses to injustice. One of two partners is given a sum of money and told that he must offer some amount of his own choosing to his partner. If the partner rejects the offer, neither gets to keep any of the cash.

On a rational basis, the receiving partner should accept any nonzero offer, since getting some money is always better than getting none at all. But people’s sense of violation at unfairness is so strong that test subjects reject offers of 20 percent or less about half the time.

In response to unfair offers, the brain activates the pain detection process. It also engages the bilateral anterior insula, an area implicated in negative emotions such as anger, disgust, and social rejection. The overall picture that emerges from fMRI is that of a brain weighing an emotional response (the urge to punish the guy who is cheating you) against a logical response (the appeal of the cash).

When Lieberman increased the money being offered, he found that accepting a share that was larger but still unfair—say, $8 out of $23—was linked with increased activity in the ventrolateral prefrontal cortex and downregulation of the anterior insula, changes that are often seen during the regulation of negative feelings. People seemed to be swallowing their outrage to accept a reward that was inequitable but appealing.

Similarly, getting a fair offer—even if it was small in absolute terms—activated regions in the brain that are involved in automatic and intuitive reward processing.

Justice apparently feels good.

The sin of pride turned on its head, envy is the most social of the moral failures, sparked by the excruciating awareness of someone else’s supreme talent, stunning looks, or extremely expensive car. For that reason, it is also the least fun of the deadly sins; feeling jealous provides no dirty thrill.

Only one imaging study (conducted by Takahashi’s group in Japan) has probed the neural basis of envy. Volunteers in fMRI machines were asked to read three scenarios. In the first, “student A” was portrayed as similar to, but better than, the volunteer in every respect. “Student B” was depicted as equally successful but very different from the subject, and “student C” sounded pretty much like a loser.

Reading about the awe-inspiring student A activated the volunteers’ conflict-detecting brain region, perhaps responding to the gap between the default setting of self-aggrandizing pride and the ugly truth of someone else’s triumphs. This same region is enlisted when feeling pain, suggesting to Takahashi that envy is a kind of “social pain in the self.”

On the other hand, indulging in schadenfreude—delight in someone else’s downfall—can be downright bliss. Aquinas termed this “morose delectation” and condemned it as a failure to resist a passion. Indeed, Takahashi found that rejoicing in a rival’s defeat brings pleasure just as surely as envy does pain. In the second phase of his study, volunteers read about student A’s downfall, causing the ventral striatum to light up.

The striatum is part of the so-called reward system, which can be activated by such pleasures as money, food, or sex, Takahashi says. The stronger the activation of the brain’s conflict detector in the first study, the stronger the striatum response in the second.

It may not have been the original sin, but rage is certainly primordial: Much of the brain circuitry active during anger is very basic and very fast. In humans, anger also enlists the conflict-detecting dorsal anterior cingulate cortex, which immediately alerts other regions of the brain to pay attention. The more upset you get, the more it activates, according to Tom Denson, a psychologist at the University of New South Wales in Australia. In people with short fuses, this part of the brain seems to be primed to feel provocation and personal slights, Denson says.

Some of us are more easily enraged than others, but few are able to stifle rage completely. Instead we may convert overt hostility into angry brooding.

To investigate the difference between short fusers and brooders, Denson antagonized his volunteers, insulting them while he scanned their brains. “Within seconds you see differences,” he says.

The medial prefrontal cortex, associated with self-awareness and emotional regulation, quickly lit up in angry brooders. So did the hippocampus, involved in memory. As they fume, people repeatedly relive the insult in their minds. Denson found that the degree of hippocampal activation predicted how much people tended to ruminate.

Probing the underpinnings of vengeful behavior, a German group led by neuropsychologist Ulrike Krämer allowed people who had been provoked during an experiment to punish their antagonist with a blast of extremely annoying noise. While the subjects pondered how loud to set the volume, the dorsal striatum, part of the brain’s reward circuitry, lit up at the prospect of retaliation.

“We have this primitive brain that says, ‘Do it! Do it!’” Denson says. Similarly, people asked to imagine themselves engaging in aggressive behavior actively suppress activity in the prefrontal cortex, where social information is processed. By deliberately inhibiting our natural social response, we ready ourselves to strike out.

Historically, moralists have not paid much heed to the findings of science, and it is safe to say that all the brain-scans in the world probably will not persuade modern theologians to recalculate the wages of sin. Still, they might want to observe one recent finding from modern neuroimaging:

It turns out that acting virtuously does not really require a hair shirt. In fact, research suggests that it feels pretty good.

Jordan Grafman recently found that virtue literally is its own reward. Altruistic behavior sends reward-related brain systems into a pleasurable tizzy—even more so than the prospect of self-interested gain. “The big punch line is that all things being equal, your reward system fires off a lot more when you’re giving than when you’re taking,” says Grafman, who is chief of the cognitive neuroscience section at the National Institute of Neurological Disorders and Stroke. Call it the dirty little secret about being good: It might be even more fun than being wicked.