Unbroken Brain: A Revolutionary New Way of Understanding Addiction

by Maia Szalavitz

our understanding of how humans bond chemically began with research on the sex lives of two types of obscure field mice. One kind, the prairie vole, belongs to the select five percent of mammal species that are monogamous, meaning that they form long-term sexual and child-rearing bonds with members of the opposite sex (though, as in humans, this bonding doesn’t rule out sexual infidelity). Another type, known as the montane vole, hooks up but never settles down. Montane voles mate promiscuously and the males don’t parent. When Carter and her colleagues realized that the key difference between these animals was their mating patterns, they recognized that studying their brains could potentially reveal how monogamy is represented anatomically. And after the researchers peeked inside the voles’ brains, these anatomical distinctions became clear. The two species’ dopamine systems are wired quite differently. In female prairie voles, the pleasure and desire circuitry contain large numbers of receptors for a hormone called oxytocin. In male prairie voles, this circuitry has many receptors for both oxytocin and another hormone called vasopressin. But in montane voles, it’s another story. Both male and female montane voles have far fewer of these respective receptors in the relevant regions.