In the manic stage, the patient often feels intense excitement and irritability, which can trigger unpredictable risky behavior. Work, family, and social life all can be impaired by this risk-taking.
Professor Wael El-Deredy of Manchester University, UK, and colleagues investigated the neuroscience behind this risky behavior. They engaged 20 individuals with bipolar disorder but not taking antipsychotic medication and 20 without bipolar disorder.
They measured with fMRI these individuals’ brain activity while playing a game of roulette. Participants were encouraged to make both safe and risky gambles in the game.
This showed “a dominance of the brain’s pleasure center” among those with bipolar disorder, say the team. This area, the nucleus accumbens, drives us to seek out and pursue rewards, they explain, and is not under conscious control. Healthy participants had a less strongly activated nucleus accumbens than those with bipolar disorder.
There were also differences in the prefrontal cortex, a more recently developed part of the brain which allows us to make conscious decisions. The team describe the prefrontal cortex as “much like the conductor of an orchestra.”
They say it gives us the ability to coordinate our various drives and impulses, such as quelling our urges when faced with risky decisions, allowing people to make decisions that are less immediately rewarding but better in the long run.
Participants with bipolar disorder showed greater neural activity for risky gambles, whereas the non-bipolar roulette players were guided by their prefrontal cortex toward safer gambles.
The study is published in the journal Brain. These findings will help to design, evaluate, and monitor therapies for bipolar disorder, the team believes. They now plan to work on psychological therapies that help people engage with their value systems and have greater regulation over their pursuit of goals.
“The greater buzz that people with bipolar disorder get from reward is a double-edged sword,” said El-Deredy.
“On the one hand, it helps people strive toward their goals and ambitions, which may contribute to the success enjoyed by many people with this diagnosis. However, it comes at a cost: these same people may be swayed more by immediate rewards when making decisions and less by the long-term consequences of these actions.”
Co-author Professor Richard Bentall pointed out that this study shows how the new tools of neuroscience, such as advances in fMRI, can be used to better understand the psychological mechanisms that lead to a psychiatric disorder.
Impulsivity and risky decision-making is also characteristic of some other disorders including substance dependence, attention deficit hyperactivity disorder, and pathological gambling.
The team say their findings suggest that in bipolar disorder, and potentially other disorders characterized by impulsivity, the weighting of signals in an area called the ventromedial prefrontal cortex “may be biased towards the ventral striatal contribution, and away from the dorsolateral signal.”
The outcome of this bias is that “lower-order, strongly desired outcomes are favoured above and beyond those that fit with the long-term goal.”
A tendency toward hyperactivation of ventral striatum appears to take place both during anticipation and experience of rewards, among participants with bipolar disorder.
“When immediate rewards are likely to be available, this group have a greater drive to obtain them,” the researchers explain, because rewards have “a greater hedonic impact” and are “more enticing.”
This process may be part of the link between mania and increases in impulsive and unrestrained reward-seeking behavior. Hence, “bipolar disorder cannot be reduced to affective instability alone,” believes the team.
“Our findings have implications for clinical intervention,” they add. For example, psychotherapeutic interventions might be aided by specifically focusing on problems with goal regulation.
In addition, the brain pathways involved could suggest targets for new pharmacological treatments. “In particular, interventions that bolster dorsolateral prefrontal cortex-mediated cognitive control may be an important direction for future research,” they conclude.
Commenting on the study, Professor Peter Kinderman of Liverpool University said, “This excellent study is yet another example of how psychologists are piecing together the picture of why people experience mental health problems.
“Researchers here found that some people are more strongly motivated to take risks to pursue their goals, feel somewhat more of an emotional ‘high,’ but are also somewhat more likely to experience the distressing mood swings that lead to a diagnosis of bipolar disorder.
“That makes a lot of sense, could point the way to effective therapies, but also helps to make sense of mental health problems; too often seen as inexplicable ‘illnesses.'”
El-Deredy, W. et al. Decision-making and trait impulsivity in bipolar disorder are associated with reduced prefrontal regulation of striatal reward valuation. Brain, 9 July 2014 http://brain.oxfordjournals.org/content/137/8/2346