A healthy newborn might cry for up to two hours while colicky babies have been known to go uninterrupted for up to four hours. Either way, it's parents to the rescue.

But a small study of 18 adults conducted by the National Institutes of Health (NIH) indicates that only women's brains appear to be hard-wired to respond to these cries.

After asking men and women to let their minds wander, researchers played a recording of white noise interspersed with the sounds of an infant crying. Brain scans showed that the men's brains remained in the resting state. Meanwhile, brain activity in the women abruptly switched to an attentive mode upon hearing the infant cries.

Specifically, the dorsal medial prefrontal and posterior cingulate areas known to be involved in mind wandering ("stream of consciousness") were the regions recorded by functional magnetic resonance imaging (fMRI) and later studied for results.

"Determining whether these responses differ between men and women, by age, and by parental status, helps us understand instincts for caring for the very young," said study co-author Marc H. Bornstein, Ph.D., from the National Institute of Child Health and Human Development (NICHD).

Although brain activity patterns differed between men and women, there was no difference in the brain patterns between parents and nonparents.

The researchers also played the cries of infants who were later diagnosed with autism. Hearing these cries tended to interrupt the mind wandering of both men and women. An earlier study found that the cries of infants who develop ASD tend to be higher pitched than those of other infants and that the pauses between cries are shorter.

Dr. Bornstein collaborated with Nicola De Pisapia, Ph.D., Simona DeFalco, Ph.D., Paola Venuti, Ph.D., and Paola Rigo, all from the Observation, Diagnosis and Education Lab at the University of Trento, Italy, and Gianluca Esposito, Ph.D., of RIKEN Brain Science Institute, Japan. Findings from their study, sponsored by NICHD, appear in NeuroReport.

In an earlier study, researchers found that seeing images of infant faces appears to activate brain circuits that reflect preparation for movement and speech as well as feelings of reward. The distinct patterns of activity appeared in the brains of adults viewing an image of an infant face - even when the child is not theirs.

This pattern is specific to seeing human infants. The same activity did not appear when the participants looked at photos of adults or of animals, even baby animals.