Momentary shifts in mood, even those lasting just a matter of seconds, profoundly alter the brain's response to pleasurable experiences in people with bipolar disorder, finds a new study by UCL researchers. The research is published in the journal Biological Psychiatry Global Open Science.

Previous research shows that mood can make us experience events in more positive or negative light—irrespective of having bipolar disorder. When we are in a good mood, we are drawn to viewing things more favorably—causing the good mood to rollover and gain momentum.

Equally, when we are upset we get drawn into perceiving bad outcomes as even worse, causing us to remain upset or get even more upset.

This "momentum" in mood can bias how we perceive events and the decisions we make.

Co-lead author, Dr. Liam Mason (UCL Psychology & Language Sciences) said, "Imagine going to a new restaurant for the first time. If you happen to be in a fantastic mood, you're likely to perceive the experience as being even better than it actually is."

However, the new study found that people with bipolar disorder are more prone to this mood bias. The researchers have also discovered the connections in the brain that drive this mood bias effect.

For the new study, the researchers investigated what happens in the brains of people with bipolar disorder while playing a computerized Roulette game in which they experienced good and bad outcomes.

The researchers used a technique called functional Magnetic Resonance Imaging (fMRI) to scan the brains of 21 participants with bipolar disorder and 21 control participants while playing the game. This allowed them to track the neural responses of participants during moments of winning and losing. They measured the extent to which these "reward signals" in the brain were influenced by micro mood fluctuations over a matter of seconds.

To achieve this, the researchers used a computational model to quantify the mood momentum experienced by participants based on recent outcomes. They assessed whether, during periods of upward momentum (a series of wins), the brain was extra responsive to subsequent wins, and vice-versa for periods of negative momentum.

The team observed heightened neural activity in the anterior insula, an area of the brain linked to transient mood states, during periods of upward momentum in both control participants and participants diagnosed with bipolar disorder.

However, only participants with bipolar disorder exhibited a more pronounced influence of this momentum on their perception of subsequent wins and losses, as the researchers observed heightened activation in their striatum, a brain region that responds to pleasurable experiences.

Importantly, the researchers also highlighted that the amount of communication between these two regions—striatum and anterior insula—was reduced in participants with bipolar disorder.

Co-lead author Dr. Hestia Moningka (UCL Psychology & Language Sciences) said, "In the control group, insula and striatum are both firing up in union, suggesting that participants were better able to keep their 'mood in mind' when perceiving rewards in the task.

"Meanwhile, participants with bipolar disorder showed the opposite; when there was higher momentum, they were less able to set this aside from how exciting they found the rewards to be."

The researchers believe that these findings may help to explain why people with bipolar disorder can get stuck in a "vicious cycle" where their mood escalates, and sometimes causes them to take bigger risks than usual.

Dr. Moningka said, "We think these findings could help us one day move beyond existing interventions which aim to regulate mood often at the cost of dampening down exciting experiences.

"Instead, new interventions that help people with bipolar disorder to better decouple their mood from their perception and decisions is an avenue we are looking into."