Certain images conjure up intense emotion: crying children, a bloody face, a snake rearing for a strike. When people take in pictures that hold deep meaning for them, they actually see the images more vividly. For them, emotion gives the world an extra burst of Technicolor and increases the odds that they will remember the scene.
But the amount of visual boost — called emotionally enhanced vividness — varies from person to person. Some of this variability is in our genes, a new study finds, suggesting that people really do see the world in different ways.
Many of us are familiar with the chemical messenger norepinephrine as a stress chemical. But it doesn’t just dictate whether we fight or flee, says Rebecca Todd, a cognitive neuroscientist at the University of British Columbia in Vancouver. Norepinephrine is also very important for emotional memory. “It’s important in the initial perception of emotional stimuli,” she explains. “It weighs down emotional memories so they burn brighter.”
Norepinephrine is produced in an area of the brain called the locus coeruleus. In an ideal system, the cells in this area produce norepinephrine in response to a signal such as stress. The norepinephrine signals pass to other areas of the brain, but some chemical messenger remains, binding to receptors called alpha2b adrenoreceptors on cells in the locus coeruleus. These adrenoreceptors act as a brake, stopping the production of norepinephrine before things get out of hand. The receptors are produced by the gene ADRA2b.
But a substantial proportion of Europeans and Africans have a variation on ADRA2b that deletes the alpha2b adrenoreceptor, possibly cutting some of the wires on the norepinephrine brakes. People with this deletion had stronger memories of emotionally charged events, a 2007 study found. Todd and graduate student Mana Ehlers wanted to see if this deletion might affect how people perceived emotional images.
For their study, they recruited 39 college students, 21 of whom had the ADRA2b deletion. While each participant was in an MRI machine, the researchers showed the students images overlaid with visual noise, which Todd compares to the snow on an old-fashioned TV set. First, the students were presented with a neutral image of lines overlaid with varying amounts of noise. Then, the students saw a second image with different noise. The students had to determine whether the second image had more or less noise than the first, a measure of how vividly they could see the image.
The second image was either emotionally charged or neutral. In the days of the Internet, it often seems like no image can get a rise out of our jaded minds, but spiders, rearing snakes and a little blood and gore are still pretty good examples of a negative image. On the opposite side, delicious desserts, puppies, and, it turns out, 1980s erotica served to produce a positive emotional jolt.
Participants saw all of the emotionally charged pictures more vividly than the neutral images. They consistently ranked the emotional pictures as having less noise than neutral pictures. But people with the ADRA2b deletion variant had higher levels of this visual boost than their peers.
For both groups, viewing emotional images increased activity in the lateral amygdala, an area of the brain involved in emotional processing. But people with the ADRA2b deletion had an extra input from an area called the ventromedial prefrontal cortex. This brain area is “related to emotional processing and internal emotional experience,” Ehlers explains. “It’s putting the emotional experience into context based on your own experiences. Our genetics, at least in part, determine whether we perceive emotions more strongly or more vividly.” Ehlers, Todd and their collaborators published their results April 22 in the Journal of Neuroscience.
This one deletion is probably just one part of how we experience emotional pictures. “We’re just looking at a very small piece of the puzzle,” says Todd. “The way people behave is this very complex interaction between gene and experience. [This variation] is operating in conjunction with a bunch of other genetic variations. It’s only one piece of the pie.”
Even with those caveats, the results show that a single gene deletion can change how we see the world, and how strongly good or bad images come bursting through the noise of everyday experience. “Certainly more neurotransmitters are involved, and of course to make our lives more complicated, they all interacting with one another and can be very nonspecific,” says Vladimir Miskovic, an affective neuroscientist at the State University of New York at Binghamton. But, he says the study is “really the first of its kind attempting to link some of these changes in how we perceive emotional stimuli to genetic variations. Any time you can chip away one part of that puzzle, it’s satisfying.”