Schizophrenia dampens volition

By medwireNews Reporters

Patients with schizophrenia and negative symptoms are less likely than mentally healthy people to increase their efforts for higher levels of reward, research shows.

In addition, these individuals are less motivated to engage in higher levels of effort for the receipt of uncertain rewards.

Writing in Biological Psychiatry, James Gold (University of Maryland School of Medicine, Baltimore, USA) and colleagues say these motivational impairments of schizophrenia might be associated with abnormalities in estimating the cost of effortful behavior.

In the study, the group evaluated effort-cost decision-making in 44 patients with schizophrenia and 36 age- and gender-matched controls. The participants performed a computerized task that examined the effects of reward value and probability on making high- and low-effort decisions.

They had a choice between two response alternatives: an easy option with a lower reward and a more difficult option with a higher reward. In each trial, the easy alternative required 20 button presses to pop an on-screen balloon, a task that paid US$ 1 (€ 0.7). The more effortful task required 100 button presses to pop the balloon and paid between $ 3 and $ 7 (€ 2.2-5.2).

In half the trials, the payoff was certain (100%), whereas in the other half of trials the payoff was uncertain (50%).

During the 100% probability trials, schizophrenia patients were less likely than control individuals to select the high-effort response alternative. Interestingly, these individuals were less likely to select the high-effort response when the payoff was highest ($ 6 or $ 7).

"Furthermore, these impairments in effort-cost computations were greatest among patients with elevated negative symptoms," report Gold and colleagues.

In the 50% probability condition, the schizophrenic patients were also less likely to select the high-effort options.

Overall, the schizophrenic patients required more time to complete the tasks than controls, but there was no difference in the time required between patients with positive and negative symptoms.

All patients were on stable doses of antipsychotic medication, but medication dose had no effect on the patients' decision making. This suggests that altered effort-cost computations in schizophrenia are not a consequence of antipsychotic treatment-induced dopaminergic blockade, say the researchers.

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