DURHAM, N.C. -- Duke University Medical Center researchers have discovered the brain region that automatically watches for patterns in sequences of events, even when the pattern emerges by random happenstance.
According to the scientists, such compulsive pattern-perception evolved to enable humans in the natural world to escape danger, for example by recognizing that a nearby twig snap and a growl signaled a looming predator. However, they said, in today's artificial world such pattern perception also gives rise to maladaptive superstitions such as the gambler's belief that a pair of dice is "due" to roll a seven.
In an article posted online April 8, 2002, in Nature Neuroscience, researchers Scott Huettel, Beau Mack and Gregory McCarthy reported experiments in which they asked subjects to watch simple random sequences of a circle or a square flash onto a screen. During the experiments, the scientists imaged the subjects' brains using a high-resolution functional MRI (fMRI) machine in the medical center's Brain Imaging and Analysis Center. The center is a joint facility of Duke and the University of North Carolina.
The analytical technique of fMRI works by using magnetic pulses that produce telltale changes in the molecules within brain tissues that are already under a powerful-but-harmless static magnetic field. Since even subtle differences in brain tissues cause them to react distinctively under the magnetic fields, the technique enables high-resolution mapping of the brain's regions. Specifically, fMRI detects increased blood flow to a particular region, and such increased flow is triggered by increased activity of the brain cells in that region.
In their experiments, Huettel and his colleagues concentrated on the prefrontal cortex, a brain region believed from previous studies to be involved in "working memory." Such working memory is the dynamic memory that people use to store information when engaged in moment-to-moment tasks.
"We simply asked the subjects to press a button in their left hand when they saw a circle, and the right hand for a square," said Huettel. "We purposely kept the experiment very simple.
"Then, in analyzing brain activity during those responses, we took advantage of the fact that when you present a large number of random events, some of the time there will be short patterns, like a series of circles or a sequence of alternating circles or squares," he said. "We concentrated on discovering whether the subjects' brain activity in the prefrontal cortex changed when these occasional patterns were violated, as when a square would appear after a series of circles, or an alternating circle-square pattern would be disrupted.
"And even though our subjects knew they were seeing random sequences, and they didn't behave in any explicit way when they saw these occasional patterns, their brains still reacted when the patterns were violated. So, their brains couldn't help but look for these patterns," said Huettel.
What's more, he said, in behavioral studies, the subjects generally showed increased reaction time to violations of longer patterns. This finding confirmed the fMRI results revealing that the subjects were, indeed, perceiving patterns in the sequences.
Also, he said, it required longer alternating circle-square sequences to produce a response on the fMRI scans than it did sequences of either circles or squares.
"The fact that there was no response until a relatively long alternating series seems to tell us that humans can pick up on simple repeating patterns rather quickly, but it takes longer to perceive more complex patterns," said Huettel. According to Huettel, the scientists' findings offer new insight into the role of the prefrontal cortex.
"These findings suggest that the prefrontal cortex is really actively and dynamically processing information about the environment," he said. "It's preparing the organism to change its behavior in response to something that's happening, not just passively rehearsing."
Further studies, said Huettel, will seek to map how the prefrontal cortex interacts with other areas of the brain in processing such information. According to Huettel, the scientists' findings reveal how brain functions that evolved to cope with the natural world might not be optimal in today's technological environment.
"Patterns in the modern world may be very different than those perhaps twenty thousand years ago," he said. "In a natural environment, almost all patterns are predictive, in that the world obeys physical laws. For example, when you hear a crash behind you, it's not something artificial; it means that a branch is falling, and you need to get out of the way. So, we evolved to look for these patterns, an ability that worked well in a natural environment, where these patterns mean something.
"But these causal relationships don't necessary hold in the technological world that can produce irregularities, and in which we look for patterns where none may exist," said Huettel. "A lot of superstitious behavior may arise from this expectation of patterns.
These superstitions may range from a perceived connection between washing the car and having it rain, to the belief that rolling dice without getting a seven means that a seven is due. Thus, brain processes that were perfectly adaptive in a natural environment become maladaptive in a technological environment," said Huettel.
The scientists' research was sponsored by the U.S. Department of Veterans Affairs and the National Institutes of Health. Huettel is an assistant professor of psychiatry; Mack is a Duke undergraduate, and McCarthy is a professor in radiology and psychology, a research career scientist at the VA medical center and director of the Brain Imaging and Analysis Center.