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In the wake of several highly publicized cases in which teen taunting provoked either suicidal or violent behavior, we have to ask ourselves how social rejection, verbal abuse, and peer ridicule affect developing brains. Last week, I wrote about some of the effects of bullying and verbal abuse on teens. Now, a new piece of research on mice begs the question, Do negative social experiences change the developing brains of humans?
In the June issue of Physiology and Behavior, researchers at Rockefeller University report using mice to model the psychological effects of "social defeat" on the young. Yoav Litvin and his colleagues in Donald Pfaff's Laboratory of Neurobiology and Behavior set up a rough-and-tumble schoolyard scenario in which a young mouse is placed in a cage with a several larger, older mice. Mice are territorial. They don't cotton to newcomers, so the inevitable display of "who's the boss around here" ensues. The battle need not be lengthy or even violent, but the new arrival always ends up on the bottom of the social order.
In Litvin's world, the "socially defeated" mice are separated for a while and given some time to rest before being reintroduced to a different social environment--this time a nonthreatening one in which the mice are all the same size and age, and no dominance battles develop. How do the previously defeated mice respond? For one thing, they are more reluctant to socialize with their peers compared to nondefeated mice. They keep their distance and stay immobile. They also display the same sorts of "risk assessment" behaviors that fearful and anxious humans do, including hesitating, turning away, approaching cautiously, and withdrawing quickly.
When the researchers gave the animals certain anti-anxiety drugs that work in humans--drugs that block vasopressin receptors--the anxious behaviors of the socially defeated mice diminished in number. Vasopressin is a hormone. Its levels are known to run high in severely anxious rodents. In humans, it's associated with aggression, stress, and anxiety disorders.
When the researchers looked at the brains of the socially defeated animals, they found more receptors for vasopressin than normal mice have--particularly in the middle of the forebrain, a region known to be associated with emotion and social behavior. Receptors act like docking sites for hormone molecules. The more receptors the brain has, the more places the hormone has to latch on to nerve cells and affect their functioning. With a larger number of receptors, the defeated mice are, thus, more sensitive to vasopressin, so they respond more strongly to the hormone than other mice do. In this research project, the effect was found to be especially strong in the amygdala, a brain structure that some neuroscientists consider the seat of emotion.
"Changes in components of these systems have been implicated in human disorders, such as social phobias, depression, schizophrenia, and autism," the researchers say. They hope their research will point to methods for better control and treatment of anxiety disorders.
Furthermore, in my opinion, studies of this kind suggest that parents, teachers, school administrators, and communities need to stop "social battering" among children and teens before it starts. Acting in kind and accepting ways is a learned skill. We need to model it! We need to teach it directly! Children can learn to treat others with respect and, in the process, to respect themselves. If we teach our young people to behave with compassion toward one another, we can build better brains and better people.
For more information:
Yoav Litvin, Gen Murakami, and Donald W. Pfaff. Effects of chronic social defeat on behavioral and neural correlates of sociality: Vasopressin, oxytocin and the vasopressinergic V1b receptor. Physiology & Behavior, Volume 103, Issues 3-4, 1 June 2011, pages 393-403.
