Robert Burton is the former chief of neurology at the University of California at San Francisco-Mt. Zion hospital. He recently wrote a book, On Being Certain, that explored the neuroscience behind the feeling of certainty, or why we are so convinced we’re right even when we’re wrong. He and Jonah Lehrer, the editor of Mind Matters, discussed the science of certainty.

LEHRER: What first got you interested in studying the mental state of certainty?

BURTON: A personal confession: I have always been puzzled by those who seem utterly confident in their knowledge. Perhaps this is a constitutional defect on my part, but I seldom have the sense of knowing unequivocally that I am right. Consequently I have looked upon those who ooze self-confidence and certainty with a combination of envy and suspicion. At a professional level, I have long wondered why so many physicians will recommend unproven, even risky therapies simply because they "know" that these treatments work.

It is easy to be cynical and suspect the worst of motives, from greed to ignorance, but I have known many first-rate, highly concerned and seemingly well motivated physicians who, nevertheless, operate based upon gut feelings and personal beliefs even in the face of contrary scientific evidence. After years of rumination, it gradually dawned on me that there may be an underlying biological component to such behavior.

LEHRER: In your book, you compare the "feeling of certainty" that accompanies things such as religious fundamentalism to the feeling that occurs when we have a word on the-tip-of-our-tongue. Could you explain?

BURTON: There are two separate aspects of a thought, namely the actual thought, and an independent involuntary assessment of the accuracy of that thought.

To get a feeling for this separation, look at the Muller-Lyer optical illusion.

Even when we consciously know and can accurately determine that these two horizontal lines are the same length, we experience the simultaneous disquieting sensation that this thought—the lines are of equal length—is not correct. This isn't a feeling that we can easily overcome through logic and reason; it simply happens to us.

This sensation is a manifestation of a separate category of mental activity—-unconscious calculations as to the accuracy of any given thought. On the positive side, such feelings can vary from a modest sense of being right, such as understanding that Christmas falls on December 25, to a profound a-ha, "Eureka" or sense of a spiritual epiphany. William James referred to the latter—the mystical experience—as "felt knowledge," a mental sensation that isn't a thought, but feels like a thought.

Once we realize that the brain has very powerful inbuilt involuntary mechanisms for assessing unconscious cognitive activity, it is easy to see how it can send into consciousness a message that we know something that we can't presently recall—the modest tip-of-the-tongue feeling. At the other end of the spectrum would be the profound "feeling of knowing" that accompanies unconsciously held beliefs—a major component of the unshakeable attachment to fundamentalist beliefs—both religious and otherwise—such as belief in UFOs or false memories. 

LEHRER: Why do you think that the feeling of certainty feels so good?

BURTON: Stick brain electrodes in rat pleasure centers (the mesolimbic dopamine system primarily located in the upper brain stem). The rats continuously press the bar, to the exclusion of food and water, until they drop. In humans the same areas are activated with cocaine, amphetamines, alcohol, nicotine and gambling—to mention just a few behaviors to which one can become easily addicted.