On the promising side, the small study, published Monday in The Proceedings of the National Academy of Sciences, found that the hormone, given as an inhalant, generated increased activity in parts of the brain involved in social connection. This suggests not only that oxytocin can stimulate social brain areas, but also that in children with autism these brain regions are not irrevocably damaged but are plastic enough to be influenced.

The limitations could include a finding that oxytocin prompted greater brain activity in children with the least severe autism. Some experts said that this could imply that oxytocin may work primarily in less-impaired people, but others said it might simply suggest that different doses are needed.

“Here we have a really clear demonstration that oxytocin is affecting brain activity in people with autism,” said Dr. Linmarie Sikich, director of the Adolescent and School-Age Psychiatric Intervention Research Program at the University of North Carolina, who was not involved in the study. “What this shows is that the brains of people with autism aren’t incapable of responding in a more typical social way.”

Nonetheless, said Dr. Sikich, who will be leading a large federally funded trial of 300 children to evaluate behavioral effects of daily oxytocin for six or 12 months, “there’s still a big gap in knowing how much it will really change overall functioning and how to best use it.”

In the new study, conducted by the Yale Child Study Center, 17 children, ages 8 to 16, all with mild autism, got a spray of oxytocin or a placebo (researchers did not know which, and in another session each child received the other substance). The children were placed in a functional magnetic resonance imaging machine, an f.M.R.I., and given a well-established test of social-emotional perception: matching emotions to photographs of people’s eyes. They took a similar test involving objects, choosing if photos of fragments of vehicles corresponded to cars, trucks, and so on.