People with remitted bipolar I disorder appear to show lower rather than higher activity in the ventral striatum in anticipation of monetary gains, compared with controls, results of a small study suggest. In addition, associations were found between positive urgency measure (PUM) and blunted activity in the nucleus accumbens in individuals with bipolar I.
“Together, these findings suggest that individuals with remitted bipolar disorder show blunted ventral striatal responses during anticipation of conventional rewards (e.g., money),” wrote lead author Sheri L. Johnson, PhD, and associates. The study was published in Neuroimage: Clinical.
Dr. Johnson’s team recruited the participants through advertisements online and in the community. Their study included 24 people with bipolar I (14 men; mean age, 36.22 years) and 24 controls without bipolar (13 men; mean age, 33.92 years), reported Dr. Johnson, of the University of California, Berkeley, and associates. The investigators used a version of the Monetary Incentive Delay Task to elicit neural and behavioral responses and their outcomes during fMRI.
Whole brain analyses found that, compared with the control group, those in the bipolar group “showed less activity for the gain anticipation contrast specifically in the ventral striatum (including the right [nucleus accumbens] and right globus pallidus), as well as less activity for the gain outcome contrast in the left occipital gyrus,” the investigators wrote.
PUM, a dimensional trait, was designed to assess tendencies to act “regrettably” or “impulsively” during states of positive emotion. PUM scores have been correlated with outcomes such as lower functioning in behavior, decreased quality of life, and worse outcomes in bipolar disorder. The investigators hoped that, by including PUM to help evaluate group differences, they could account for inconsistent findings regarding associations of neural imaging and reward responses.
“The current findings imply that, in individuals with bipolar disorder, individual differences in PUM may also help account for blunted [nucleus accumbens] during reward anticipation.”
The study’s sample size limited the power to detect small effects or interactions. The researchers felt, though, that the sample was well matched and adequately powered for the primary variables of interest.
The authors had no conflicts of interest to disclose. The study was funded by a grant from the National Institute of Mental Health.
SOURCE: Johnson SL et al. Neuroimage Clin. 2019. doi: 10.1016/j.nicl.2019.102018.