Dopaminergic modulation of probabilistic reasoning and overconfidence in errors: a double-blind study

INTRODUCTION

Reasoning biases such as jumping to conclusions (JTC) and overconfidence in errors have been well replicated in patients with delusions. However, their relation to dopaminergic activity, central to pathophysiologic models of psychosis, has not yet been investigated. This study aimed to examine the effects of a dopaminergic agonist (L-dopa) and a dopaminergic antagonist (haloperidol) on the JTC bias and overconfidence in errors after single-dose administration in healthy individuals.

METHODS

The study used a randomized, double-blind, placebo-controlled, 3-way crossover design. Participants were 36 healthy individuals aged 18-36 years. The variables of interest were draws to decision and probability threshold to decision on a computerized variant of the beads task and the number of high-confident incorrect responses on a visual memory task.

RESULTS

There were no significant effects of substance on draws to decision and probability threshold to decision. A significant effect emerged for high-confident incorrect responses in the memory task; pairwise comparisons indicated a significant reduction of the number of high-confident incorrect responses after administration of haloperidol vs l-dopa and placebo.

CONCLUSIONS

This is the first study to investigate the direct effects of dopaminergic drugs on reasoning biases. The JTC bias and overconfidence in errors showed a differential pattern of dopaminergic modulation, suggesting that they represent different facets of reasoning abnormalities that interact with each other to produce delusions in susceptible individuals.

Effects of dopaminergic modulation on automatic semantic priming: a double-blind study

BACKGROUND

Enhanced automatic spreading of activation in the semantic network has been suggested to underlie formal thought disorder in patients with schizophrenia, but it is not clear how this relates to the dopaminergic dysfunction implicated in the disorder. Previous studies on dopaminergic modulation of priming in healthy volunteers have focused on controlled rather than automatic processes. The present study aimed to examine the effects of both a dopaminergic agonist and a dopaminergic antagonist on semantic priming while minimizing the contribution of controlled processes.

METHODS

We investigated the effects of levodopa (L-Dopa; 100 mg), haloperidol (2 mg) and placebo on priming in healthy participants within a randomized, double-blind, crossover design. We used a pronunciation priming task with word triplets; the middle word was an ambiguous word, whereas the first word of the triplet served to provide either a congruent, incongruent or unbiased context for the target word. Two stimulus onset asynchronies (SOA) were used: 150 ms and 750 ms.

RESULTS

The study involved 34 participants. At an SOA of 150 ms, L-Dopa accelerated responses to incongruent targets and subordinate targets of ambiguous words, whereas haloperidol was associated with faster responses in congruent contexts and dominant targets. At an SOA of 750 ms, haloperidol accelerated responses to subordinate targets.

LIMITATIONS

Modulations in the relative magnitude of priming according to substance and condition rather than absolute priming were assessed.

CONCLUSION

Effects of L-Dopa on automatic priming processes appear to be different than those on controlled processes. Our results are consistent with those of studies on semantic priming and the effects on antipsychotics in patients with schizophrenia.

[Demographic aging in Germany and the need for care in private households: a regional perspective]

"In the Federal Republic of Germany there are regional differences in the ageing process. As a result the increase of people needing care and attention differs regionally, too. The authors deal with the following questions: Which particular regions will be most affected by the ageing process and to which extent? How is the proportion of people needing care and those providing it in private households affected by this? To which extent can private households cope with the demands of nursing elderly people at home?" The focus is on the period 1992 to 2010. (SUMMARY IN ENG)