We already know that mood affects the way we judge and perceive things — and it’s generally considered to be negative. Studies have found that bad or sad moods can affect our judgement and reasoning, with clinical depression even having an impact on perception of time.
But a new study suggests that mood, and extreme changes in mood, may actually be “an evolutionary relic that may have been advantageous for early humans”.
The study, conducted by a team at UCL and published in Trends in Cognitive Science, found that mood influences our perception of reward outcomes “such that outcomes are perceived as better when one is in a good mood relative to when one is in a bad mood”. This change in mood leads to a subsequent change in behaviour — and thus allows us to adapt to fast moving environmental factors.
The research used the example of a trader. On experiencing unexpected gains on the stock market, the trader’s mood would improve. This positive upswing would subsequently lead to the trader making more risks — meaning they would be able to adapt to a fast-moving stock market.
As people learn from these mood-based experiences, their expectations come to reflect the reward, or punishment, associated with each event. This, researchers say, allows learning to account for the impact of environmental factors.
“This effect of mood should be useful whenever different sources of reward are interconnected or possess an underlying momentum,” said Eran Eldar, co-author of the study. “That may often be the case in the natural as well as in the modern world, as successes in acquiring skills, material resources, social status, and even mating partners may all affect one another.”
Positive and negative moods maximise their utility by existing only until expectations match change in rewards — explaining why satisfaction with a situation returns to a baseline level even after significant changes in environment, such as a bereavement or the receipt of a large amount of money.
Researchers hope their findings will help better explain the provenance of mood disorders such as depression or bipolar. They believe that mood can often be a “self-fulfilling prophecy”, as experience related moods cause a person to perceive subsequent events more negatively — potentially leading to a depressive episode.
“We think that this novel approach may help reveal what predisposes particular individuals to bipolar disorder and depression,” Eldar says.
The findings do not yet account for the biological or genetic factors that are associated with mood disorders.