The manner in which the pupil size changes in response to distractions can reveal the brain's focus and how it processes distractions, found in a new study.
Duke University researchers have looked into monkeys' eyes for insight into how the brain processes distractions and they've found that changes to pupil size in response to distractors might predict how well the brain focuses on a goal.
The results may inform about the attention deficit hyperactivity disorder or other disorders in which mechanisms for maintaining attention go awry. The results could also inspire new ways to improve performance in school or on the job.
In the clinic, pupils might help diagnose or identify people at risk for mental illnesses, such as anxiety, or the effectiveness of potential therapies.
Michael Platt, director of the Duke Institute for Brain Sciences and the Center for Cognitive Neuroscience, said that where the eyes go and how much visual information gets in seems to tell a lot about what's going on inside the brain.
When humans are torn between paying attention to two different things, it triggers a "conflict" circuit in a brain region called the dorsal anterior cingulate cortex (dACC) which is part of a larger brain structure controlling rational thought and emotions.
Using a tiny sensor implanted in the dACCs of the monkeys, Platt's group was able to measure the electrical activity of single neurons. The team found a set of neurons that were active only when monkeys were completing the task and trying to override the distracting faces, but not when faced with either of the stimuli alone.
The more active the dACC neurons were, the better the monkeys were at tuning out the distracting faces in later trials. Even so, it was a difficult task.
The fight-or-flight response causes a release of the stress hormone noradrenaline, widens the pupils and allows a person to take in more information about their environment.
R. Becket Ebitz, a postdoctoral researcher at Stanford University, said that the dACC doesn't directly control pupil size, but it connects to another region of the brain that does. The dACC might well play a role in keeping people calm in the face of demands for their attention that might otherwise make them confused or stressed out.
The study is published in the journal Neuron.