“I've calculated your chance of survival, but I don't think you'll like it.“ Marvin, “The Hitchhiker’s Guide to the Galaxy” (2005)

Marvin is a depressed and highly intelligent robot endowed with a human personality from the popular book and film “The Hitchhiker’s Guide to the Galaxy”. Poor Marvin is eternally sad due to being able to perform exact calculations and predictions about reality and in this way see the world in a completely unbiased way. His state perhaps resembles “depressive realism” which is what some researchers call the way in which people with depression display a less positive but unbiased and thus more realistic view on the self, the future and their sense of control. At the opposite end lies the so called “optimistic bias” observed in healthy people who seem to pay more attention to positive rather than negative information about themselves and the world. Optimistic bias has been used to explain social-economic phenomena such as financial bubbles and crises, unpreparedness for natural disasters, and risk-taking. Recent research has shown that this optimistic bias is absent in clinically depressed individuals. Scientists from the University College London and University of Zurich have now embarked on studies comparing how healthy and depressed individuals form their beliefs. One study by Garret et al. (2014) has been able to show that these two groups of people not only incorporate information about the world into their belief system in different ways but they have also investigated the possible neurobiological basis for this difference through functional MRI.

How did Garret et al. (2014) design their study?

The researchers wanted to look into how the two groups of people, depressed and non- depressed, make use of “good” and “bad” news. They asked the question: are people going to be rational and use good and bad news equally to update their beliefs about the world and their future? For this purpose, the participants were presented first with descriptions of various unfavourable events (burglary, accidents, etc) while they were lying inside of an MRI scanner. People were asked to imagine the event occurring and give their estimation of the probability of this event happening to them in real life. Afterwards, the participants were presented with the actual probability of this event occurring to people in their social environment. Sometimes the real probability came as “good news” when it was lower than the one given by the participant - that meant that the adversity has a lower chance of occurring than expected; and sometimes it came as “bad news” if the real probability was higher than expected. In order to test the extent to which the participants updated (changed) their beliefs regarding their chances of being faced with one of the calamities, in a third presentation of the event descriptions, the participants were asked to give their estimations again. Apart from this, the researchers were also interested in the brain activity at the time when participants faced their estimation error through seeing the real probability and had to update their beliefs.

And what did they find?

The researchers found that healthy people changed their beliefs (probability estimations) to a greater extent when they were presented with good news rather than bad news. So good news was more powerful in setting up their probability estimation at the final presentation of the events and bad news had lesser effect on their estimations. Depressed participants on the other hand didn’t show difference in the extent to which they were influenced by bad or good news - they incorporated these into their beliefs (probability estimations) equally. The people diagnosed with depression were more influenced by bad news than healthy people but by doing so they were also being less biased and more realistic. For example, if both a depressed and healthy individual thought that there is 23% chance of being burgled in their lifetime, on seeing that the chance is actually 39%, which comes as bad news, the depressed individual would potentially correct his/hers initial estimate of 23% to a greater extent than the healthy individual and this would be reflected in a more realistic final estimation of the probability for this event. There was no such difference in how depressed and healthy individuals approached good news. The researchers ruled out other possible explanations for the observed results by showing that the initial probability ratings, the memory of the events, the overall experience of such events throughout the participants’ life course and other possible confounding factors did not differ between the two groups. It is important to emphasise that depressed and healthy individuals did not have different initial beliefs about the world - their estimation errors did not differ. What was different about the two groups was the way they differentially updated their beliefs in response to good and bad news.

There were differences observed in how brain activity, as recorded by the functional MRI scanner “tracked” good and bad news. Firstly, it was observed that regions in the frontal and parietal lobes of the brains of depressed individuals tracked bad news with greater fidelity than the same regions in the healthy participants. Thus, in a way, bad news were better “coded” or represented in the brains of depressed individuals than in those of healthy individuals. Secondly, part of the frontal lobe called Inferior Frontal Gyrus (IFG) was identified as a region which is particularly “interested” in bad news for depressed participants - it became less active when bad news were presented. The bigger the difference between the participant’s belief and the reality, the less active this region became.

So what might this pattern of reduced activity in the IFG mean? Does the neuroimaging data from the study tell us anything about the mechanism by which depression makes people track bad news as faithfully as they track good news? It has been proposed that the answer lies in dopamine and the type of neurons found at the Inferior Frontal Gyrus and other related parts of the frontal cortex - neurons whose main neurotransmitter is dopamine. Dopamine has been shown to impair updating from bad news and a surge in dopamine through drug administration increases optimistic bias (Sharot et al., 2012). Furthermore, dysfunction of the dopamine system and reduced dopamine transmission are linked to depression (Dunlop & Nemeroff, 2007). It could be the case that diminished dopamine function in the brain regions involved in belief formation (such as IFG) prevents depressed individuals from discounting negative information about the world. Further exploration of how dopamine influences the brain networks involved in belief formation through tracking positive and negative information could shed light on how dopamine- based antidepressants affect cognition in depressed people. It could be that these drugs help in the reduction of the persistent maladaptive pessimistic beliefs which are one of the core symptoms of depression.

The adaptive bias

“...I’d far rather be happy than right any day.” (Slartibartfast, “Hitchhiker’s Guide to the Galaxy”, p. 200)

It looks like humans have evolved a bias for positive information in their perception of the world, or better said, we choose to ignore negative information. Why might we need this bias? After all, isn’t it better to anticipate the future and be prepared for it? And we can easily think of how lack of realism can affect financial, relationship-related and medical decisions. This has been most studied in the field of behavioural economics because the optimism bias can produce phenomena such as the housing price bubble which led to the global financial crisis of 2008. For the human mind, bad news is less informative than good news which can lead to “blindness” for the future. However, this irrationality might be a pre- requisite for mental health and for a positive outlook on life. Depression is a debilitating, life-threatening and costly condition and experimental data links it to lack of the optimistic bias. This points towards the adaptive value of the imbalance with which positive and negative information is treated. This would mean that having the ability to rationally calculate probabilities and expect the future like Marvin in the science fiction book would come at a price for us humans (and for human-like Marvin as well).

References:

Adams, D. (1979). The hitch hiker's guide to the galaxy. United Kingdom: Pan Books

Barber, G. (Producer) & Jennings, G. (Director).(2005). The Hitchhiker’s Guide to the Galaxy [motion picture]. United Kingdom

Dunlop, B. W., & Nemeroff, C. B. (2007). The role of dopamine in the pathophysiology of depression. Archives of general psychiatry, 64(3), 327-337.

Garrett, N., Sharot, T., Faulkner, P., Korn, C. W., Roiser, J. P., & Dolan, R. J. (2014). Losing the rose tinted glasses: neural substrates of unbiased belief updating in depression. Frontiers in Human Neuroscience, 8.

Sharot, T., Guitart-Masip, M., Korn, C. W., Chowdhury, R., & Dolan, R. J. (2012). How dopamine enhances an optimism bias in humans. Current Biology, 22(16), 1477-1481.

Image taken from: http://www.fribert.nu/marvin/marvin.html