Chubby cheeks, big bright eyes—the characteristics of a baby’s face are thought to provoke nurturing and affectionate behavior in adults. New research suggests that a reward area of the brain initiates this response.

Neuroscientist Morten L. Kringelbach of the University of Oxford and his colleagues asked 12 adults, nine of whom were childless, to complete a computer task while infant and adult faces—comparable in expression and attractiveness—flashed onto the screen. The researchers captured the participants’ neural responses with magnetoencephalography, an imaging technique that directly detects brain activity in milliseconds. (In contrast, the imaging workhorse fMRI measures changes in blood flow, an indirect indication of brain activity, in seconds.)

Although the volunteers ultimately processed the faces using the brain regions that normally handle such a task, all the participants showed an early, distinct response to the infant faces alone. Within one seventh of a second, a spike in activity occurred in the medial orbitofrontal cortex, an area above the eye sockets linked to the detection of rewarding stimuli. This activity appears to “tag” infant faces as special, Kringelbach says.

The study offers clues as to why parents with postpartum depression are less responsive to their infants, Kringelbach adds. He speculates that depressed moms are “not getting this special signal” from the medial orbitofrontal cortex because of its connection to another brain area that is implicated in depression.