From gamblers playing blackjack to investors picking stocks, humans make a wide range of decisions that require gauging risk versus reward. However, laboratory studies have not been able to unequivocally determine how the very basic information-processing "subcortical" regions of the brain function in processing risk and reward.
Now, Steven Quartz and colleagues at the California Institute of Technology have created a simple gambling task that, when performed by humans undergoing functional magnetic resonance imaging (fMRI) of their brains, distinguishes the "gambling" structures in the brain. Importantly, their findings tease apart the gambling function of these brain structures from their functions in learning, motivation, and assessment of the salience of a stimulus.
In their research article published in the August 3, 2006, issue of Neuron, published by Cell Press, the researchers said their findings and experimental method could help in understanding and perhaps treating aberrant risk-taking in disorders including gambling addiction, bipolar disorders, and schizophrenia.
In their experiments, the researchers asked subjects to choose two cards from a deck numbered one to ten. Before their choice, however, the subjects were asked to bet $1 on whether the first or second card would be higher. The fMRI imaging of the subjects' brains during the gambling task could show the researchers which areas of the brain activated during different parts of the task. In fMRI, harmless radio signals and magnetic fields are used to measure blood flow in brain regions, which reflects activity in those regions.
The researchers concentrated their analysis on the "anticipatory period" between the display of the first and second card, since it was then that the subjects were able to judge from the number on the card the risk of whether they were likely to win or lose their bet that the second card would be higher or lower.
Furthermore, the researchers divided that anticipatory period into two subperiods. During a one second period immediately after the first card was displayed, subjects were concentrating on expected reward, theorized the researchers; and in the following six seconds before the second card, they were assessing the risk revealed by the first card. The researchers based this approach on studies by other researchers of such processes in primates.
Quartz and colleagues found they could distinguish brain regions that specifically responded to either reward expectation or risk. Importantly, these areas showed activity that increased with the level of expected reward and perceived risk. The researchers found that the activation related to expected reward was immediate, while the activation related to risk was delayed.
These regions were part of the brain circuitry governed by the neurotransmitter dopamine that is also involved in learning, motivation, and salience. However, emphasized the researchers, the design of their gambling task and analysis of their data ruled out involvement of these functions, meaning that they had, indeed, isolated the "gambling" function of these regions.
Of the practical implications of their findings, the researchers wrote that "pathological behaviors ranging from addiction to gambling, as well as a variety of mental illnesses such as bipolar disorder and schizophrenia, are partially characterized by risk taking. To date, it is unknown whether such pathological decision making under risk is due to misperception of risk or disruptions in cognitive processes, such as learning, planning, and choice.
"For example, a bipolar subject during a manic episode may invest in a risky business proposition either because they misperceive the risk to be lower than it actually is, or because they accurately perceive the risk to be high but may have impaired learning, attentional, working memory, or choice processes."
Previous research approaches had not been able to distinguish the processes underlying such risky behavior, wrote the researchers. However, they wrote, "Since our task was designed to minimize the involvement of these high-level processes, in the future it may be utilized with clinical populations to determine whether alterations in risk perception accompany their changes in risky behavior. This may lead to a better understanding of the relative contributions of risk misperception versus cognitive impairments in these pathological cases, may suggest different treatment approaches, and may also gauge the impact on and the feedback from higher-level brain regions known to contribute to decision making."
The researchers include Kerstin Preuschoff, Peter Bossaerts, and Steven R. Quartz of the California Institute of Technology in Pasadena, CA. This work was supported by NSF Grant 0093757, the David and Lucile Packard Foundation, and the Gordon and Betty Moore Foundation.
Preuschoff et al.: "Neural Differentiation of Expected Reward and Risk in Human Subcortical Structures." Publishing in Neuron 51, 381--390, August 3, 2006 DOI 10.1016/j.neuron.2006.06.024 www.neuron.org
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