People, like animals, can interpret situations in either an optimistic or pessimistic way. If there is a 50% chance of rain, an optimist trusts their luck and cycles to work, while a pessimist grabs the car, an umbrella, and a raincoat.
What a new study, led by GIMM Group Leader Rui Oliveira and conducted in zebrafish, has now demonstrated is that this personality trait may have far more serious implications than simply getting wet or wasting fuel.
Published in Translational Psychiatry, a Nature Research journal, the study shows that this cognitive bias — the tendency to interpret ambiguous situations in an optimistic or pessimistic way — is stable over time in zebrafish and has a direct impact on the stress response. And consequently, on cancer progression.
“This study demonstrates how individual variation in susceptibility to diseases, such as cancer progression (melanoma), can be explained by cognitive biases that lead pessimistic individuals to perceive ambiguous stimuli as false alarm signals, overactivating their stress response with deleterious consequences for the organism,” explains Rui Oliveira.
In the first phase of the study, the researchers classified the animals based on their behavioral profiles. They observed that, unlike pessimists, optimistic zebrafish showed lower stress reactivity, better regulation of the neuroendocrine axis (HPI axis), and greater physiological resilience. A heightened stress response, in turn, is associated with a greater likelihood of developing diseases such as cancer.
Using a melanoma model in zebrafish, the authors observed that pessimistic fish developed tumors earlier and that these tumors progressed more rapidly. Optimistic fish, on the other hand, showed resistance to tumor progression — demonstrating that this psychological trait (optimism vs. pessimism) directly influences physical health.
To reach this conclusion, transgenic juveniles (genetically modified to develop melanoma) were classified as optimistic or pessimistic before the onset of tumors. Half of each group was exposed to chronic stress; the other half remained in control conditions, with tumor progression monitored weekly. The results were clear: even without stress exposure, pessimists developed tumors earlier and at a higher rate.
Chronic stress further accelerated cancer progression in optimists, but did not significantly alter outcomes in pessimists, who already had high incidence. Moreover, cellular proliferation markers showed higher tumor activity in pessimistic fish from the very beginning.
Taken together, these findings suggest that optimism functions as a kind of biological armor, providing physiological resilience and protection against stress-related diseases.
And you — do you see the glass half full or half empty?
