In this article, Sharot et. al. tries to explain why it is that some of us are so optimistic and could it be a bad thing? The article focuses on the events in which people do not take the necessary precaution they need to in order to protect themselves, that being the underestimation of future negative events, and why they were adamant about not changing (Sharot et. al.). So the way the experiment was conducted was Sharot et. al. took participants and told them to estimate the probability that an event would happen to them and then measured their brain activity. There was a total of eighty events that were "tested" all of which were adverse life events such as house hold accident, adultery, owing a large amount of debt, etc. They then combined a learning task with fMRI. This allowed Sharot et. al. to identify how blood oxygen level-dependent (BOLD) signals track estimation error in response to whether the information given lead to optimism or pessimism (Sharot et. al). To determine estimation error, they used the equation: estimation error = estimation - probability presented. They also used questionnaires to see if people changed their beliefs of an event based off of some kind of emotional arousal, how bad an event is, if they were familiar with the event, or if they have encountered such an event before.
Their results were that there was this region of the brain, right inferior frontal gyrus, in which showed a reduction for neural coding of undesirable error regarding the future for people who were optimistic. They also found that the reason there was this asymmetry in people changing their beliefs was due to a reduced expression of an error signal in the region implicated in processing undesirable error regarding the future (Sharot et. al.). The questionnaire that was administered showed that people didn't change their beliefs due to the severity of the event, if it is familiar or not, or if they have encountered it or not. The BOLD signal tracking showed that people with the largest optimistic update bias failed to show any undesirable error meaning the relationship between undesirable error and BOLD signaling was close to zero, where as people who did not show a selective updating in belief showed a strong relationship between undesirable error and BOLD signaling.
So it didn't matter whether how bad the future event was going to be, whether it was familiar or not, or if it has been encountered before but due a lack of not being able to code and process this undesirable error regarding the future. So really being optimistic or being optimistic even after information has disproved your belief isn't in your absolute control because if your brain fails to code and process it you can't really do much about it. Though you possibly could in theory but that raises questions for another time.
Sharot, Tali, Christoph W. Korn, and Raymond J. Dolan. "How Unrealistic Optimism Is Maintained in the Face of Reality." Nature Neuroscience. Nature America, Inc., 9 Oct. 2011. Web. 3 Dec. 2011.