In an experiment that had people with bipolar disorder playing roulette, brain scans revealed that the 'reward centers' of their brains were activated more than those of people without the psychiatric disorder formerly known as manic depression.
The research, published in the journal Brain, used functional MRI scans to monitor the response of a part of the brain known to be involved in reward and pleasure, the nucleus accumbens.
This center drives us to make decisions that bring satisfying short-term results, but was shown to be more active in response to risk-taking in the people with bipolar disorder, report the neuroscientists from the UK's universities of Manchester and Liverpool.
Prof. Wael El-Deredy, a cognitive neuroscientist from the University of Manchester, says there are upsides and downsides to this response for people living with bipolar. He says:
"The greater buzz that people with bipolar disorder get from reward is a double-edged sword.
On the one hand, it helps people strive towards 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."
The brains with bipolar disorder showed that another, less primitive area of the brain also gave a different response. The prefrontal cortex, highly developed in humans and associated with our ability to give conscious thought, was more effective at guiding the impulses of the study participants who did not have bipolar disorder, "towards safe gambles and away from risky ones."
This part of the brain for the control subjects was better able to temper desire for immediately rewarding decisions, in favor of maximizing overall results.
Prof. Richard Bentalla, an expert in psychology at the University of Liverpool, says: "This study shows how we can use the new tools of neuroscience to better understand the psychological mechanisms that lead to a psychiatric disorder which, until now, has been very difficult to understand."
Dr. Liam Mason, a psychologist from the Manchester team who now works at King's College London's Institute of Psychiatry, says the research revelations will inform the scientific pursuit of treatments.
"Understanding how the brain works to regulate the pursuit of goals will help us to design, evaluate and monitor better therapies for bipolar disorder," he says.
Risky pursuit of goals
Bipolar disorder results in disturbance of mood, and people with the diagnosis experience unpredictable episodes of depression and mania. The mania produces periods of intense excitement and irritability, often leading to very risky behavior.
The authors note:
"Bipolar disorder is characterized by marked difﬁculty in regulating the pursuit of goals, with the onset of manic and depressive episodes linked to the attainment and failure to obtain goals, respectively.
Although particularly elevated during mania, impulsivity represents a trait feature of the disorder and there is evidence of altered frontostriatal processing of reward prospects and outcomes across mood episodes."
The patients recruited to the study were in a euthymic phase, neither in an episode of depression or mania, and were not receiving antipsychotics, so that the medications would not affect the results.
The 20 people with bipolar disorder in remission were matched with 20 healthy control subjects of the same age, gender and level of education.
All participants were between 18 and 45 years of age, and had no current alcohol problem or recent substance use.
High and low stakes
The task being performed while functional MRI was used to evaluate brain activity involved three time phases to a roulette gamble:
The researchers used functional MRI scans to monitor the response of a part of the brain known to be involved in reward and pleasure, the nucleus accumbens.
This decision-making, and its resulting reward anticipation and receipt, was in response to two conditions of probability, and two levels of stake:
- Safe, high probability of reward (75%)
- Risky, low chance of reward (25%)
- Low stake of £3
- High stake of £9.
The safe or risky conditions were presented to participants at the beginning of each trial, and the magnitude of the stake was announced during the selection phase. The participants knew that they would be paid the actual winnings at the end.
There were 8 runs at the roulette game, of about 6 minutes each, giving a total of 272 trials for the participants. The probabilities and stakes were distributed equally in each run.
Results showed, for example, that during the anticipatory phase, the prefrontal cortex was more active across all the participants for "prospects that afforded a high probability of reward, and for prospects of larger magnitude." The authors say this is consistent with activity in that part of the brain for "aligning with the higher-order goal of maximizing rewards."
In the bipolar disorder group, however, the effect of probability was reduced, such that these patients "showed a smaller increase in prefrontal cortex activation" for high-probability prospects.
"Patients with bipolar disorder," the authors continue, "responded more strongly to gains but not losses, consistent with a stronger lower-order preference for rewards."