Download Vanderbilt neuroscientists identify “oops center” in the brain

Vanderbilt neuroscientists identify “oops center” in the brain
David F. Salisbury
December 14, 2000
Have you ever wondered what’s going on in your head when you say, “Oops!”
Neuroscientists at Vanderbilt University have come up with an answer. They have shown that a
set of neurons in a specific region of the brain reacts when you realize that you have made a
mistake.
The finding, reported in the Dec. 14 issue of the journal Nature, was made by post-doctoral
fellows Veit Stuphorn and Tracy L. Taylor—now an assistant professor at Dalhousie University—
and Professor of Psychology Jeffrey D. Schall.
The researchers propose that this region is part of an “executive system” that has evolved within
the brain in order to control its own activity as it makes decisions, corrects errors and overrides
habitual responses. Although cognitive psychologists generally agree that such a supervisory
system must exist, this is one the first studies to reveal its workings at such a fundamental level.
“The work is very important because it shows the cellular basis of self-control,” says Sohee Park,
associate professor of psychology at Vanderbilt. “It gets at really basic questions of psychology
and philosophy like the origin of thought and free will.” It also has important implications for the
understanding of schizophrenia, obsessive-compulsive disorder and psychopathic behavior, she
adds.
Schall’s group specializes in the study of the brain’s control of eye movement. The study they
report is based on an elegantly simple task: deciding whether or not to shift one’s gaze. The
researchers sat macaque monkeys in front of a computer screen. An eye-tracking system
monitored where they were looking. A spot appeared in the center of the screen. When the
monkey’s gaze was fixed on the spot, the spot disappeared and another spot appeared on the
periphery of its vision. If the monkey shifted its gaze to the new spot, it was rewarded with a drink
of juice. During some of the trials, the central spot reappeared during the time the monkey was
preparing to shift its gaze to the peripheral spot. In these cases, the monkey was rewarded when
it cancelled the eye movement it was planning and kept its vision fixed on the central target.
As the monkeys were performing these tasks, the researchers were monitoring the activity of
neurons in part of the macaque’s brain called the supplementary eye field. This structure is
located in the frontal lobe of the brain and is part of the supplementary motor area that was
discovered in the 1940s by neurosurgeons exploring the brains of epileptic patients. Previous
research by Schall and others had shown that an area nearby, called the frontal eye field,
exercised direct control over eye movements. The researchers knew the supplementary eye field
also had some involvement in the control of eye movements and they were attempting to discover
the role that it plays.
Schall and his colleagues found that the supplementary eye field exhibited a much different
pattern of neuron activity than the frontal eye field. “It appears that the neurons in the secondary
eye field are monitoring eye movement, not controlling it,” Schall summarizes. He and his
colleagues report finding three distinct types of neurons in the area. One type acts when the
monkey realizes that it has made the correct decision and will be rewarded. Similar “reward” or
reinforcement neurons have been reported in other parts of the brain. The second type, which
they have dubbed the “oops” or error neurons, reacts when the monkey realizes that it has made
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Vanderbilt neuroscientists identify “oops center” in the brain
a mistake and will not receive a reward. The third type responds when the brain has received two
conflicting instructions.
These findings shed new light on an ongoing debate over the interpretation of similar research
performed with human subjects using electroencephalograms (EEG) and fMRI, a remote sensing
technique that measures levels of brain activity.
Michael Coles and coworkers at the University of Illinois discovered an EEG signal that occurred
when human subjects made errors. They called this the “blunder blip” and attributed it to the
brain’s error-recognition response. Then Jonathan Cohen at Princeton University conducted a
series of fMRI experiments that mapped brain activity when human subjects were put in situations
where they are likely to make mistakes. When they realize that they have made an error, Cohen
found that the supplementary motor area and an adjacent area called the anterior cingulate
cortex both become active. But Cohen’s group also recorded activity in these areas when the
person judged correctly. So he concluded that this activity can’t just be about errors and has
proposed that it signals when the brain is coping with conflicting impulses.
“Our results suggest that both interpretations are partially right,” Schall says. Different groups of
neurons are responding to both errors and conflicts.”
Gordon Logan developed the “countermanding paradigm” that provides the basis for Schall’s
study. “I was interested in impulse control. To what extent are impulses automatic and how well
can people control them,” says Logan, who recently joined the psychology department at
Vanderbilt as a Centennial professor.
But there is a basic difficulty in studying this subject. When a person is asked to stop a behavior
and they do stop, there is no behavior to measure. To get around this difficulty, Logan decided to
study what happens when people are asked to start then stop doing something in rapid
succession. In this situation he reasoned that two neurological processes—“go” and “stop”—must
be racing with each other. Based on this conception, he developed a mathematical model that
estimates the probability that a subject will stop a behavior in a given circumstance.
“I’m amazed at how successfully Schall has used this method and the quality of the data that he
has gotten from it,” says Logan.
There is an interesting parallel between Schall’s findings and a study of children with Attention
Deficit Hyperactivity Disorder (ADHD) that he was involved with in Toronto, Logan points out: “We
found that the children with ADHD were slower to respond to stop signals than normal children.
Interestingly, Ritalin, one of the drugs used to treat this condition, also improved their stopping
ability.”
Park, who studies schizophrenia, describes an even more striking clinical connection. In eyetracking experiments, she has found that 80 percent of schizophrenia patients and about half of
their healthy, first-degree relatives have difficulties in the executive control of eye movements.
Park, Logan and Schall plan to collaborate with Herbert Meltzer, professor of psychiatry and
pharmacology at Vanderbilt and an expert on the treatment of schizophrenia, on a series of
parallel studies with monkeys and people to test the efficacy of anti-schizophrenia drugs like
clozapine.
The research was supported by the National Institute of Mental Health and the National Sciences
and Engineering Research Council of Canada.
- VU For additional information:
Schall Laboratory web site
http://www.vanderbilt.edu/VVRC/VRGroups/SchallLab/Schall VVRC Home Page.htm
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