Following treatment with oxytocin, the proportion of balls sent to the most cooperative character increased significantly, Sirigu and colleagues reported, with a mean score of 9 compared with 5.5 and 6.5 for the neutral and least cooperative characters.
After the game was over, the autism-spectrum patients were asked to rate their level of trust with the three characters and their preferences for them as playing partners. After placebo treatment, mean trust and preference scores for the three characters were nearly identical.
In the oxytocin condition, however, patients expressed substantially more trust and preference toward the most cooperative character relative to the least cooperative.
Sirigu and colleagues also repeated the ball-toss experiment, with oxytocin and the placebo control, with a second set of seven high-functioning autism-spectrum patients, this time without the monetary incentive. They reported that the results were essentially the same as when participants were paid for receiving the ball, with the same significant differences despite the smaller sample.
Participants also looked at photos of faces on a computer and asked to identify either the gender or whether the face was looking into the camera or away to one side. The focus of participants' gaze was recorded.
Mean time spent looking at the faces, as opposed to elsewhere, was about 20 to 30 percent greater following oxytocin treatment both in the gender identification and the facial-direction tasks.
Moreover, when participants were looking at the faces versus elsewhere, their attention was more focused on the subjects' eyes after oxytocin treatment by about 30 percent in the gender identification task and by 45 percent in the facial-direction task.
"We demonstrated that oxytocin can promote social approach and social comprehension in patients with autism," Sirigu and colleagues wrote. They suggested that the specific effect may be that the hormone reduces mistrust and fear associated with social interactions.
"Future research is necessary to investigate whether a long-term intake of oxytocin may improve real-life social functioning of these patients," they added.