Take away a certain hormone, and mice are left wondering, "Have I smelled you before?" Mice that lack oxytocin cannot remember one another's scent, researchers report in the July issue of Nature Genetics. The finding bolsters the theory that the brain stores "social memory" differently than other types of memory, and it may point to the biological roots of human disorders with a social component, such as autism.
Researchers have known for years that the hormone oxytocin helps animals from voles to humans bond to their comrades, their mates, and their offspring. For example, when injected in small doses into the brains of rats, oxytocin improves the animals' ability to recognize one another. When oxytocin is thwarted by chemicals that tie up its receptors in the brain, rats forget each other as soon as they're out of sniffing distance.
To find out the consequences of never having any oxytocin at all, a team of neuroscientists--Jim Winslow, Jennifer Ferguson, and colleagues at Emory University in Atlanta--experimented with mice that lack the gene for oxytocin. The researchers repeatedly put female mice into the cages of male mice. Normal males gave the newcomer a thorough sniffing, but the olfactory overtures tapered off with each subsequent visit by the same female as the two animals got acquainted. In contrast, the genetically modified males sniffed the visitor thoroughly each time, as if she remained forever a stranger. Yet despite their social ineptness, the modified mice remembered other things as well as their normal peers: They found their way through mazes, located food by its scent, and distinguished whiffs of lemon and chocolate.
The results parallel those from experiments with autistic children, says Deborah Fein, a psychologist at the University of Connecticut in Storrs. Two years ago, she reported that boys with autism have less oxytocin than other boys, and that autistic boys and girls do not remember faces as well as other children. The mouse experiments are "just what needs to be done," Fein says, although she cautions that a mouse lacking oxytocin "is a long way from being a comprehensive model of a human disorder."