Such a model would enable scientists to better understand how processing of social attention works in the brain, and how it can go awry in such disorders as autism. Such basic studies, said the neurobiologists, could lead to better treatments for autism and better methods to teach autistic children.
The researchers, post-doctoral fellow Robert Deaner and Assistant Professor Michael Platt, reported their findings in the Sept. 16, 2003, issue of Current Biology. The research was supported by the National Institute of Mental Health and the National Eye Institute.
In their experiments, the researchers compared the eye movements of humans and rhesus macaque monkeys when they were shown images of monkeys looking either to the left or right.
The researchers would first concentrate the human or monkey test subjects' attention to the center of a computer screen by showing them a yellow square. The subjects would then be shown either another square or an image of a monkey looking either left or right. Immediately after that, the face would disappear and to the left or right on the screen a yellow square would flash. The researchers used a magnetic coil technique to measure with high accuracy and speed the eye movements of the subjects.
Explained Platt, "Our prediction was that if seeing a monkey looking in one direction or another actually changes where you're paying attention, then you should shift your gaze faster if the box appears in the direction in which that monkey face was looking and slower in the other direction. Which is exactly what we found with both humans and monkeys." Thus, he said, the subjects were "covertly" shifting their attention before obviously shifting their gaze. Although prior studies have shown that monkeys sometimes turn their head and eyes when they see another individual turn and look to the side, the study by Deaner and Platt provides the first evidence that monkeys reflexively and internally shift their attention where another individual is looking.
The subjects also provided other more subtle clues that their attention had reflexively shifted in the direction of the monkey-image gaze, said Platt. An instant after the monkey images appeared, the subjects showed infinitesimal, involuntary eye movements in the same direction the monkey image was looking, found Deaner and Platt.
Also importantly, said Platt, the shift in attention was very temporary, as would be expected if it were not immediately reinforced by something happening in the direction of the monkey-image gaze. The reflexive tendency to follow gaze is, indeed, powerful, said Platt.
"It's really striking when you're sitting there, and you look at these faces pop up," he said. "You feel yourself wanting to look in that same direction."
Platt said that the finding offers the promise of a manipulable animal model of "social attention" -- how the human brain assesses the goals and intentions of other humans and responds to them.
"It's been long known what parts of the human brain are involved in identifying and recognizing other individuals as well as those parts of the brain involved in shifting attention," said Platt. "And there have been new magnetic resonance imaging studies that show that both these parts of the brain respond to such social cues as gaze.
"But to get a real understanding of how this response is accomplished at a neuronal level, you need an animal model that you can manipulate physiologically," said Platt. "This is the first time it has been shown that such a cognitive ability corresponds so exquisitely in humans and monkeys."
Besides offering a basic understanding of the neural machinery of such social reflexes, said Platt, such a model could yield insights into such disorders as autism.
"Children with autism tend not to orient to other individuals," he said. "They don't tend to look other people in the eye, and in particular they show a strong deficit in shifting their attention where another individual is looking or paying attention."
Such deficits not only cause problems for autistic children in everyday social interactions, said Platt, but also in teaching them.
"When you're teaching another person, you often engage with them in 'joint attention,' where you establish attentive contact and undergo a give and take, as you both concentrate on something," said Platt. "You often don't see that capability in autistic individuals."
To understand the neural functions of such social processing, Platt and his colleagues are embarking on studies in which they will first study the responses of nerve cells in parts of the brain devoted to shifting attention to determine if social information influences patterns of brain activity there. In future studies, they plan to alter or disrupt neurons or structures in the social-processing regions of the monkeys' brains, and explore whether the resulting behaviors mimic the symptoms of autism.
Also, he said, the researchers can explore the environmental contribution to autism by studying the effects of manipulating the animals' social surroundings during their development.