PEERING AT FEELINGS:
To see how and where the brain generates emotions, University of Wisconsin researchers are draping subjects in a n elaborate headdress that registers shifting electrical impulses from 128 sites in the brain's cortex.
A woman in her early twenties sits alone in a small, windowless room at the University of Wisconsin's Health Emotions Research Institute in Madison. A bundle of spaghetti-thin wires draped over her head contains sensors that register the electrical activity of 128 brain sites as she watches photographic images flash by on a computer screen. A plump mushroom pops up for a few seconds, followed by a mangled body in a wrecked car and then a blooming rose.
Meanwhile, in a separate room, grad student Chris Larson watches the woman on a video screen and records the shifting pattern of electrical impulses in her brain. When a photo of a naked man and woman prompts a noticeable blip, Larson smiles. "Erotic pictures are the best," she says, for eliciting strong positive responses.
The electric charges Larson is most closely observing come from the woman’s prefrontal cortex, just behind her forehead. This palm-sized section of gray matter determines both our general outlook on life and whether we respond positively or negatively to events and experiences. “Animals do a lot of things instinctively,” says psychiatrist Ned Kalin, director of the institute. “But people—and probably monkeys—have the ability to think 20 steps into the future: ‘In the end I’m going to feel great, because I worked hard to get there,’ or ‘I’m going to get a lot of credit for this.’ It’s the prefrontal cortex that brings those emotions into play and guides us in our behavior. If we didn’t have a sense of what would be wonderful or awful in the future, we would behave very haphazardly.”
Brain imaging has revealed that positive and negative emotions are polarized on opposite sides of the prefrontal cortex. The right side governs a physiological loop that produces negative, inhibiting feelings, while the left commands a loop for positive, outward-reaching emotions. Research now suggests that a person’s natural temperament—optimistic, pessimistic, extroverted, or introverted—may depend on which side of the prefrontal cortex is more active. In one study of 10-month-old infants who were briefly separated from their mothers, researchers found that babies who cried had a dominant right prefrontal cortex, and that those who calmly explored the area where they had been abandoned had a more active left cortex.
“Emotion is the glue that holds a personality together, yet until now it’s been hard to measure,” says neuroscientist Richard Davidson.
Some asymmetry in the prefrontal cortex is normal, but in people who are depressed, the balance tips way over to the dark right side. Initially, scientists figured the system goes out of whack because of an overactive right cortex. Now some suggest the problem also stems from an underpowered left cortex. The deficit appears to be twofold. The left cortex seems to falter in mustering and maintaining positive feelings in response to outside stimuli as well as in dampening the outpouring of negative feelings in response to negative stimuli that are generated by another part of the brain: the amygdala. This almond-shaped structure behind the ear is Fear Central, the neural processing station that sends out warnings of perceived danger and threat. Scientists suspect that the left cortex normally shuts down the amygdala’s alarm signal, firing off a sort of “message received.” Without a robust left cortex, they theorize, the amygdala runs unchecked, flooding a person with fear that leads to helplessness and despair.
The primary purpose of Larson’s blitz of images is to test how long it takes the young woman viewing the photos to tamp down her fear. As she looks at a bloody photo, she is also subjected to a brief burst of loud white noise delivered through a pair of earphones. Startled, she blinks rapidly for a half second or so—a normal startle response. “People who are still having eye blinks two-and-a-half seconds after the picture goes off are more right frontal,” Larson says. They apparently lack the biological wattage to shut down their startle response, and they are more prone to depression. She theorizes that the same individuals may have trouble managing other negative emotions, such as anger, fear, or sadness. Ultimately, an inability to rein in negative mental responses could aggravate physical problems like high blood pressure and heart disease.
Sensors register brain impulses while a series of photos—some attractive, others repellent—flash by on a computer screen. This can show which side of the subject’s prefrontal cortex is more active. A person who takes more than a few seconds to tamp down reaction to a negative image is more right-dominant and may be more prone to fear, sadness, and depression.
University of Wisconsin researchers are in the vanguard of exploring the uncharted frontier that neuroscientist Richard Davidson has dubbed affective neuroscience—the study of how emotion is generated by the brain. “Emotion is the glue that holds a personality together,” says Davidson, a principal investigator at the institute. “Yet until now it’s been relegated to second-tier status as a subject of scientific study because it has been hard to measure.” Extraordinary improvements in brain-imaging technology during the past five years are the key. Davidson and Kalin use magnetic resonance imaging (mri), positron emission tomography (pet), and electrical sensing techniques to scour pockets of the brain where emotions dwell, then develop detailed schematics of the neural circuitry among them. By mapping how the brain generates and processes emotions, they hope to discover ways people might use the power of their own minds to overcome the crippling impact of fear or depression, and maybe even improve their physical health as well.
“This is the Holy Grail of human health research,” says Kalin.
Sustained emotional stress is known to damage the brain, and scientists wonder how it might affect the right and left prefrontal cortex, particularly in young children whose brains are still developing. “Severe stress affects the size of the structures in the brain, causes cell death, and affects the number of connections between brain cells,” observes Kalin. “Early in life the brain is much more vulnerable to these insults.” Studies with young rats, monkeys, and other mammals reveal that emotionally stressful events can flood the brain with cortisol, which Kalin calls “the master stress hormone. In low doses it alerts us and organizes our behavior so we make sure we protect ourselves.” But in high doses, “it leaves us stressed out, inattentive, disorganized, and depressed.” Early sustained cortisol exposure also damages the hippocampus, a part of the brain that regulates mood and memory.
And what kind of stress causes the most damage? “A car wreck is bad,” Kalin says, “but it’s not as bad as be-ing neglected, isolated, or ostracized by your peers. Deprivation—lack of love, comfort, security—can have big-time effects.” Research from the University of Minnesota has shown that children age 2 and up who lack secure attachments to their mothers have higher rushes of cortisol during even mildly stressful events, such as getting a vaccination shot, than do youngsters with strong parental bonds.
Full text of this article appears in Discover magazine.
The HealthEmotions Web site is www.healthemotions.org.