Functional MRI Helps Distinguish Belief, Disbelief, and Uncertainty

Susan Jeffrey

December 13, 2007

December 13, 2007 — A new study shows that belief, disbelief, and uncertainty may be distinguishable using functional neuroimaging. Researchers report that subjects challenged with statements that were true, false, or undecidable showed activation in distinct regions of the prefrontal and parietal cortices and the basal ganglia.

"These results suggest that the differences among belief, disbelief, and uncertainty may 1 day be distinguished reliably, in real time, by techniques of neuroimaging," the researchers, with first author Sam Harris, a graduate student from the University of California, Los Angeles (UCLA) Brain Mapping Center, conclude. "This would have obvious implications for the detection of deception, for the control of the placebo effect during the process of drug design, and for the study of any higher-cognitive phenomenon in which the differences among belief, disbelief, and uncertainty might be a relevant variable."

The study appeared online December 10 in advance of publication in the January 2008 issue of the Annals of Neurology. Senior author is Marc S. Cohen, PhD, from the Center for Cognitive Neuroscience at UCLA.

Potent Regulators of Emotion

The difference between believing and disbelieving a proposition is 1 of the most potent regulators of human behavior and emotion, the authors write. "When one accepts a statement as true, it becomes the basis for further thought and action; rejected as false, it remains a string of words."

The purpose of the present study was to see whether, using functional magnetic resonance imaging (fMRI), they could differentiate belief, disbelief, and uncertainty in 14 adult subjects. During each of 3 functional neuroimaging scans, subjects were asked to judge a variety of written statements as "true," indicating belief; "false," indicating disbelief; or "undecidable," indicating uncertainty. To characterize these concepts independently of the content of the statements, they included statements from a wide range of categories, including autobiographical, mathematical, geographical, religious, ethical, semantic, and factual statements.

When they contrasted the trials of belief vs disbelief, they found increased signals in the ventromedial prefrontal cortex (VMPFC), which is involved in linking factual knowledge with emotion. "The involvement of the VMPFC in belief processing suggests an anatomical link between the purely cognitive aspects of belief and human emotion and reward," they write.

Ethical belief followed a similar pattern of activation to mathematical belief, they noted, suggesting that the physiological difference between belief and disbelief is not related to content or emotional associations.

Contrasting disbelief with belief showed increased signals in the anterior insula, a brain region involved in the sensation of taste, perception of pain, and the feeling of disgust, the authors write. "Our results appear to make sense of the emotional tone of disbelief, placing it on a continuum with other modes of stimulus appraisal and rejection," the authors write.

Finally, uncertainty evoked a positive signal in the anterior cingulate cortex and a decreased signal in the caudate, a region of the basal ganglia that plays a role in motor action, they note. Because both belief and disbelief were associated with an increased signal in the caudate compared with uncertainty, the authors suggest that the basal ganglia may play a role in mediating the cognitive and behavioral differences between decision and indecision.

Truth is Beauty

Belief and disbelief differ from uncertainty in that both provide information that can subsequently inform behavior and emotion, the authors conclude. From this work, the mechanism underlying this difference appears to involve the anterior cingulate cortex and the caudate.

"Although many areas of higher cognition are likely involved in assessing the truth-value of linguistic propositions, the final acceptance of a statement as 'true' or its rejection as 'false' appears to rely on more primitive, hedonic processing in the medial prefrontal cortex and the anterior insula," they write. "Truth may be beauty, and beauty truth, in more than a metaphorical sense, and false propositions may actually disgust us."

In a statement from UCLA, first author Harris said what he finds interesting about these findings is the suggestion that a person's view of the world must pass through a "bottleneck" in regions of the brain generally understood to govern emotion, reward, and primal feelings like pain and disgust.

"While evaluating mathematical, ethical, or factual statements requires very different kinds of processing, accepting or rejecting these statements seems to rely upon a more primitive process that can be content-neutral," he said. "I think it has long been assumed that believing that '2 plus 2 equals 4' and believing that 'George Bush is president of the United States' have almost nothing in common as cognitive operations. But what they clearly have in common is that both representations of the world satisfy some process of truth-testing that we continually perform.

"I think this is yet another result, in a long line of results, that calls the popular opposition between reason and emotion into question," he concluded.

Ann Neurol. Published online December 10, 2007. Abstract


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