Mapping Choice-Making in the Brain

March 2003 - Someone who says "I'm of two minds about this" is not just procrastinating. Research conducted by Kip Smith, using Positive Emission Tomography (a brain imaging technique), shows that the reason why people often can't make up their minds may be due to the brain using different areas in the decision-making process.

"We're of at least two minds," Smith said. "This research shows the brain is not a single entity. There is not a single executive decision-making mechanism there."

Smith's research produced neuroimages of the parts of the brain used in different types of choices. Smith found evidence for two systems used to make decisions in the brain: deliberative and emotional. Deliberative systems, also referred to as calculation areas, utilize parts of the brain related to mathematics and rational decisions. Emotional systems utilize older, more primal parts of the brain.

Smith considers that individual behavior is affected by attitudes about payoffs, such as gains and losses, as well as beliefs about outcomes, such as risk and ambiguity. During his experiments, participants' brain activities were measured by positron emission tomography. The research demonstrated a relationship between brain activity and observed choices. Smith's results allowed him to create images of the parts of the brain used for risk, ambiguity, gains and losses with decision making in the experiment.

Smith said some of the results were surprising. "We thought that risky losses would be processed by the part of the brain that responds to fear, but they were dealt with in a fairly rational manner," he said. Also, the deliberative areas of the brain did not show high usage with decisions relating to risky gains. "It could be that the emotional areas overwhelm the calculation areas. The results are correlational, because it's not a completely controlled experiment."

Smith's results were published in the June 2002 issue of Management Science in the article "Neuronal Substrates for Choice under Ambiguity, Risk, Gains and Losses." The paper was co-authored by John Dickhaut, University of Minnesota; Kevin McCabe, George Mason University; and Jose V. Pardo, Veterans Affairs Medical Center and the University of Minnesota. A second paper, "The Impact of the Certainty Context on the Process of Choice," is forthcoming in the Proceedings of the National Academy of Sciences. Dickhaut, McCabe and Pardo, as well as Aldo Rustichini, University of Minnesota, and Jennifer C. Nagode, Veterans Affairs Medical Center and the University of Minnesota, co-authored the second paper.

Positive Emission Tomography

Positron Emission Tomography, or PET is a procedure designed to produces images of the body's biological processes. Conventional imaging (x-rays, CT scans, etc) show the body's anatomy whereas PET reveals the metabolic function of an organ or tissue.

Typically, a patient or experimental subject is given an intravenous injection of FDG, a glucose analog labeled with radioactive fluorine and asked to lie still for 45-60 minutes while the isotope is distributed throughout the body and absorbed by the cells. Then, the subject lies on a table called a scanning bed and is moved slowly through a scanner which detects the distribution of the injected tracer. The scanner can create a three-dimensional image of the tracer's distribution when analyzed by a computer.