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Background: Healthy individuals show subtle orienting bias, a phenomenon known as pseudoneglect, reflected in a tendency to direct greater attention toward one hemispace. Accumulating evidence indicates that this bias is an individual trait, and attention is preferentially directed contralaterally to the hemisphere with higher dopamine signaling. Administration of methylphenidate (MPH), a dopamine transporter inhibitor, was shown to normalize aberrant spatial attention bias in psychiatric and neurological patients, suggesting that the reduced orienting bias following administration of MPH reflects an asymmetric effect of the drug, increasing extracellular dopamine in the hemisphere with lower dopamine signaling., Aim: We predicted that, similarly to its effect on patients with brain pathology, MPH will reduce the orienting bias in healthy subjects., Methods: To test this hypothesis, we examined the behavioral effects of a single dose (20 mg) of MPH on orienting bias in 36 healthy subjects (18 females) in a randomized, double-blind placebo-controlled, within-subject design, using the greyscales task, which has been shown to detect subtle attentional biases in both patients and healthy individuals., Results/outcomes: Results demonstrate that healthy individuals vary in both direction and magnitude of spatial orienting bias and show reduced magnitude of orienting bias following MPH administration, regardless of the initial direction of asymmetry., Conclusions/interpretations: Our findings reveal, for the first time in healthy subjects, that MPH decreases spatial orienting bias in an asymmetric manner. Given the well-documented association between orienting bias and asymmetric dopamine signaling, these findings also suggest that MPH might exert a possible asymmetric neural effect in the healthy brain.

Impaired decision making in patients with borderline personality disorder (BPD) has been reported in several studies. Although methylphenidate (MPH) is known to ameliorate impaired decision making in patients with attention-deficit/hyperactivity disorder (ADHD), it has not yet been examined in patients with BPD. We therefore assessed the efficacy of a single dose of MPH on cognitive functions and decision making in patients with BPD. Twenty-two patients diagnosed with BPD participated in the study. The study was a randomized, double-blind placebo-controlled, random block order cross-over trial. Patients participated in two sessions and performed the Test of Variables of Attention, a digit-span test, and the computerized Iowa Gambling Task, after they had been administered either the MPH or a placebo. ADHD symptoms were assessed using the Adult ADHD Self-Report Scale-18. Lower scores on the inattention symptoms scale were associated with a greater improvement in decision making following the administration of MPH when compared with improvements in patients with higher ADHD scores [F(1,17)=5.63, P=0.030]. We conclude that MPH may improve decision making in patients with BPD, although this effect is mediated by the level of ADHD symptoms. Further studies are needed to assess whether a prolonged beneficial effect of MPH on decision making in patients with BPD might also be present in 'real life'.

In recent years the use of psychostimulants for cognitive enhancement in healthy individuals with no psychiatric disorders has been on the rise. However, it is still unclear whether psychostimulants improve certain cognitive functions at the cost of others, and how these psychostimulants interact with individual personality differences. In the current study, we investigated whether the effect of one common stimulant, methylphenidate (MPH), on creativity is associated with novelty seeking. Thirty-six healthy adults, without attention-deficit hyperactivity disorder (ADHD) symptomology, were assigned randomly in a double-blind fashion to receive MPH or placebo. We found that the effect of MPH on creativity was dependent on novelty-seeking (NS) personality characteristics of the participants. MPH increased creativity in individuals with lower NS, while it reduced creativity levels in individuals with high NS. These findings highlight the role of the dopaminergic system in creativity, and indicate that among healthy individuals NS can be seen as a predictor of the effect of MPH on creativity.

Methylphenidate affects state-anxiety in ADHD patients. The current study examines the effect of Methylphenidate on state-anxiety in healthy subjects. In a cross-over, randomized, controlled, double-blind study, 36 healthy subjects received either Methylphenidate or placebo. As a group, no change in state-anxiety was detected with Methylphenidate. However, participants reporting higher anxiety levels experienced a significant and specific state-anxiety reduction following Methylphenidate. Moreover, a strong negative correlation was found between the initial-level of anxiety and net-change in state-anxiety. These changes were unrelated to self-perceived attention levels. Our results point to the state-dependent effects of Methylphenidate on anxiety., (Copyright © 2016 Elsevier Ireland Ltd. All rights reserved.)