There is a surprising amount of truth in the old adage that “the eyes are the window to the soul.” We possess an innate ability to understand that the focus of someone else’s vision is the object of her attention. This ability is an important part of autism researcher Simon Baron-Cohen’s model for our specialized cognitive module devoted to social processing, and he has called the vast nonverbal sphere of social communication “the language of the eyes.”
Because of this ability, we’re also able to quickly trace others’ vision and lock onto whatever they are looking at. The neural substrate of this behavior, known as gaze following, might have less immediately apparent implications for the broader project of understanding what makes us human, but it is nevertheless a computationally interesting question. Now a study published in a recent issue of the Proceedings of the National Academy of the Sciences (the article is open access) has unified a deeper understanding of the mechanics of gaze following with a fundamental attribute of social cognition: neural mirroring.
Stephen Shephard, Jeffrey Klein, Robert Deaner, and Michael Platt examined gaze following behaviors in rhesus monkeys using a simple task. On each trial, the animals would look at a picture of another monkey on the screen placed in front of them. The monkey in this picture was looking either to the right or to the left. Then, the picture would disappear and a target would light up on one side of the screen, cuing the test subject to break fixation and look towards the target.
The test subjects performed the task with significantly shorter reaction times on trials when the monkey in the picture was looking towards the eventual location of the target than in those when it was looking in the other direction. To understand the neural processing at work here, the researchers recorded the activity of individual neurons in an region called the lateral intraparietal area (LIP), which is located high on the back side of the brain. This area is thought to encode spatial representations of visual attention, with individual neurons corresponding to discrete bits of the visual field.
Shephard and his colleagues recorded from neurons that were active directly before a monkey looked towards one of the targets, as these neurons encoded the impending shift in attention. Most importantly, they also found that these neurons became active earlier when the initial cue depicted the other monkey looking in the direction of the target’s eventual position. When this early activation was strongest, reaction times were shorter.
This pattern of activity is similar to that found in traditional mirror neurons, which fire both when a monkey performs specific hand and mouth actions and when it observes another monkey or a human experimenter performing the same actions. In humans, ethical constraints have thus far prevented single-cell research, but regional patterns of activity obtained using fMRI show mirroring both for observation of hand and mouth gestures, as in the monkey studies, and for emotions–leading to the suggestion that neural mirroring underlies our capacity for empathy and other social processing.
This study broadens the domain of mirror activity to a function that, at the behavioral level, we already know to be of great importance for our ability to understand other minds. When it comes to what others are thinking, we lack the privileged access that we have to our own thoughts. Yet, we intuitively understand that others possess a mind much like our own. The promise of understanding neural mirroring is that doing so will provide the simplest and most powerful explanation for this remarkable talent.
Shepherd, S., Klein, J., Deaner, R., & Platt, M. (2009). Mirroring of attention by neurons in macaque parietal cortex Proceedings of the National Academy of Sciences, 106 (23), 9489-9494 DOI: 10.1073/pnas.0900419106
