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Reports from the Society for Neuroscience meeting on the moral disengagement of psychopaths, liars' decision making, a parasite that helps cats triumph over rats and how mother rats affect the behavioral development of their pups

WASHINGTON, D.C.— More than 30,000 neuroscientists from around the world gathered in Washington, D.C., November 15–19 for the annual meeting of the Society for Neuroscience. Presentations covered the science of nerves and brains on scales from molecules to societies. From among the first day’s presentations, Science News staffers report on the latest neural insights into psychopaths, liars and baby rats separated from their mothers, as well as new research on how a tiny parasite disrupts rats’ ingrained fear of cats and how a rat mother’s favoritism for outgoing pups influences developing social skills.

Morality askew in psychopaths’ brains
Psychopaths display a dangerous mix of impulsiveness, grandiose thinking, callousness toward others and manipulative skill. They also show neural responses related to moral insensitivity and a keen interest in moral violations, new studies find.

Researchers led by Kent Kiehl of the University of New Mexico in Albuquerque carted portable brain-scanning equipment to a New Mexico prison, where they recruited inmates who either did or did not qualify as psychopaths on an extensive questionnaire. Participants underwent scanning as they viewed images that depicted moral violations, such as a drunken driver or one man attacking another with a knife, or images that contained no moral violations, such as an angry driver.

Functional MRI scans showed reduced neural activity in 21 psychopathic inmates, relative to 21 non-psychopathic inmates, in brain regions linked to attaching emotional meaning to others’ acts and to reading others’ intentions in social situations, says study coauthor Alek Chakroff, a New Mexico graduate student in psychology. Psychopaths identified moral pictures and rated the severity of moral infractions as accurately as non-psychopaths did. These findings are consistent with the possibility that psychopaths intellectually evaluate the meaning of moral situations without experiencing any emotional reactions to those situations, Chakroff suggests.

In a second study, Kiehl’s group found that 25 psychopathic inmates displayed a signature neural electrical response a fraction of a second after viewing images of moral violations, indicating heightened attention to those images. A smaller version of this response appeared in non-psychopathic inmates. Moral violations draw psychopaths’ intense interest even before they have time to become consciously aware of what they’re seeing, Chakroff hypothesizes. —Bruce Bower

Parasite twists rats’ innate fear of cats…
In a dangerous game of cat and mouse, the most important player turns out to be a parasite. Researchers have known for some time that the parasite Toxoplasma gondii is a puppeteer that can force a rat to go against its own instincts and become attracted to the scent of cat urine. Now scientists have discovered the regions of a specific part of the rat brain called the amygdala involved in this parasite-imposed death wish.

Toxo can only reproduce in the gut of a cat, which poses a logistical nightmare for the rat-dwelling parasite. To get into the cat, Toxo tricks rats into acting recklessly in the presence of their feline predators. Up until now, researchers have known little about the brain regions involved in this behavioral switch. A team led by Patrick House at Stanford University reports that they have identified two distinct regions of the brain, one important for fear and the other responsible for attraction, that are activated in Toxo-infected rats after they smell cat odor.

“You see two pathways [the fear and the attraction pathways] light up,” explains House. Surprisingly, the attraction region of the rat brain is similarly activated when a male rat encounters a female, suggesting that Toxo may fool the rat into mistaking the smell of cat urine for the odor of a potential mate. Although the research is far from over, the findings give researchers new clues to the workings of Toxo’s mysterious mind control. —Laura Sanders

…while early separation from mother mutes it
Young rats separated from their mother at a crucial age are not appropriately afraid of dangerous situations later, shows a new study led by Yoav Litvin of the University of Hawaii at Manoa. The finding may hold implications for understanding why some people engage in high-risk activity. In the rat world, one of the highest-risk behaviors is sniffing around a hungry cat. Usually, when rats encounter a whiff of cat (or other threats), they freeze. But a rat pup that has been separated from its mother for the early part of its life doesn’t show the usual amount of fear. What’s more, these maternally deprived rats do not learn to freeze as quickly as a rat raised with plenty of maternal love.

The rats that showed this deficit were separated from their mothers for three hours a day from day two to day 13 of their lives, which the researchers think could be a critical period for development of a particular part of the brain, the hypothalamus, that is involved in fear conditioning. Steve Siviy of the University of Gettysburg College in Pennsylvania, who researches playful behavior in rats, likens these maternally deprived rats to kids who grow up in “crummy neighborhoods” whose mothers work two jobs. The researchers think that because these rats may expose themselves to more dangerous situations, they may set themselves up for a cycle of more emotional stress, not to mention bodily harm. —Laura Sanders

Deciding to lie, or not
Honest people don’t need to worry about being led into temptation, a new study suggests. To investigate whether honesty is an act of will or an inherent grace, Joshua Greene of Harvard University and colleagues scanned the brains of 25 people told they were participating in a study to see if a monetary reward made people better at predicting the future. Participants were prompted to predict the outcome of a coin toss. Sometimes they had to say this call out loud, sometimes were asked what they had guessed after the toss was completed. They were told they would win a set dollar amount when they predicted correctly. A control group of participants always said their prediction out loud, and thus had no opportunity to cheat.

As expected, the control group accurately predicted heads or tails about 50 percent of the time. The group that had the opportunity to cheat was “correct” about 66 percent of the time, with some participants “predicting” heads or tails with 90 percent accuracy. When these participants who tended to lie most actively chose not to lie, the brain scans showed significant activity in the prefrontal brain regions associated with decision making. Non-cheaters, who always told the truth, lacked this activity. The research team did wonder if these people “were really honest or just clueless,” says Greene. Post-experiment interviews confirmed that the honest people were aware of the opportunity to cheat. “When it comes to honesty, it seems to be more grace than will,” Greene says. —Rachel Ehrenberg

Moms favor outgoing pups, with consequences
Your mother probably does love your outgoing siblings more. A new study of rats shows that outgoing offspring got more attention from their mothers than did their more shy siblings.

Brothers and sisters have similar genes and grow up in a similar environment, but have differently personalities. Christina Ragan of Pennsylvania State University and her colleagues wanted to know if parental favoritism could affect personality. Previous research has shown that rat pups whose mothers licked them a lot were less susceptible to stress than pups from mothers that didn’t spend as much time grooming them. Ragan watched mother rats interact with their pups and counted how often each pup in a litter was licked in the first week of life. She found large differences in maternal attention, with the most-groomed pups in a litter getting two to three times more attention from mom than the least licked sibling, Ragan showed in a presentation at the neuroscience meeting.

Notably, usually the pups that got the most maternal attention sought it. Ragan found no connection between maternal attention and the amount of a stress hormone each pup produced. But she did find that pups that got the most attention from mom were also quicker to approach stranger rats. Pups that got less attention took longer to seek social contact with an unfamiliar rat. The difference between siblings evened out in adulthood. Ragan also saw that pups that actively sought attention from their mothers, but didn’t get it, hung back from interacting with rats they didn’t know. “Early interactions with mom can influence later social interactions,” she says. —Tina Hesman Saey

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