Dopamine reward-processing impaired in acute bipolar mania

Dopamine reward-processing impaired in acute bipolar mania

MedWire News: Bipolar patients in an acute manic phase of illness show impairments in dopamine neural networks related to reward processing, suggest the results of a functional magnetic resonance imaging (fMRI) study.
The findings provide a neurologic explanation for many of the symptoms frequently seen in acutely manic bipolar patients, such as poor decision-making, impulsiveness, excitability, and impaired learning.
Mania has been characterized as a disorder of abnormal goal pursuit regulation with elevated levels of achievement motivation and drive, Birgit Abler (University of Ulm, Germany) and co-workers explain.
The DSM-IV states that patients show excessive involvement in pleasurable activities that have a high potential for "painful consequences, eg, unrestrained buying sprees or foolish business investments."
In the early 1990s, researchers speculated that a dysregulation of reward-related neural networks mediating motivation and goal-directed behavior might account for these observations.
In the present study, the researchers tested these ideas by monitoring the brain activity of 12 acutely manic patients while they performed various reward games using fMRI.
They also assessed 12 mentally healthy subjects and 12 patients with schizophrenia as controls noting that "both patient groups were treated with comparable dosages of antipsychotic medication, providing the opportunity to disentangle the effects of medication and psychiatric diagnosis."
When presented with expectation of monetary awards, mentally healthy and schizophrenic subjects showed activation of dopaminergic brain areas, namely the ventral tegmentum. Manic bipolar patients, however, showed an entirely different pattern of brain activation.
Abler et al comment: "Such expectation signals are believed to help prepare for upcoming events and support decision making and planning processes.
"Dysfunctions of expectation signals could therefore help to explain the observation that manic patients tend to make suboptimal, often disadvantageous, decisions."
Further tests revealed that mentally healthy and schizophrenic subjects showed activation of dopaminergic nucleus accumbens regions when presented with a reward that was anticipated, but suppression of this region when an expected reward was omitted. By contrast, manic bipolar patients failed to show such a differentiation between receipt and omission of an anticipated reward.
The researchers say that this lack of "prediction error" could explain symptoms of impulsiveness, disinhibition, and impaired learning.
"Impulsivity was suggested to represent a core characteristic of the disorder responsible for symptoms like hyperactivation, excitability, and hasty decision making that could be related to striatal dysfunction as demonstrated here," they conclude.