Paradoxical dopaminergic drug effects in extraversion: dose- and time-dependent effects of sulpiride on EEG theta activity

Disentangling periodic and aperiodic resting EEG correlates of personality

Previous studies of resting electroencephalography (EEG) correlates of personality traits have conflated periodic and aperiodic sources of EEG signals. Because these are associated with different underlying neural dynamics, disentangling them can avoid measurement confounds and clarify findings. In a large sample (n = 300), we investigated how disentangling these activities impacts findings related to two research programs within personality neuroscience. In Study 1 we examined associations between Extraversion and two putative markers of reward sensitivity-Left Frontal Alpha asymmetry (LFA) and Frontal-Posterior Theta (FPT). In Study 2 we used machine learning to predict personality trait scores from resting EEG. In both studies, power within each EEG frequency bin was quantified as both total power and separate contributions of periodic and aperiodic activity. In Study 1, total power LFA and FPT correlated negatively with Extraversion (r ∼ -0.14), but there was no relation when LFA and FPT were derived only from periodic activity. In Study 2, all Big Five traits could be decoded from periodic power (r ∼ 0.20), and Agreeableness could also be decoded from total power and from aperiodic indices. Taken together, these results show how separation of periodic and aperiodic activity in resting EEG may clarify findings in personality neuroscience. Disentangling these signals allows for more reliable findings relating to periodic EEG markers of personality, and highlights novel aperiodic markers to be explored in future research.

The D1/D2-like receptor antagonist flupentixol and the D2-like receptor antagonist L-741626 decrease operant responding for nicotine and food and locomotor activity in male and female rats

BACKGROUND

The reinforcing properties of nicotine play a critical role in smoking and vaping. There is a need for treatments that decrease the reinforcing properties of nicotine and thereby improve smoking and vaping rates. Dopamine plays a role in the reinforcing properties of nicotine, but little is known about the role of dopamine D2-like receptors in nicotine intake and whether there are sex differences in the effects of dopaminergic drugs on nicotine intake.

AIM

The goal of the present studies was to investigate the effects of the D1/D2-like receptor antagonist flupentixol and the D2-like receptor antagonist L-741626 on nicotine self-administration in male and female rats.

METHODS

The effects of flupentixol and L-741626 on operant responding for nicotine and food and locomotor activity in a small open field were investigated.

RESULTS

There were no sex differences in baseline nicotine intake. The D1/D2-like receptor antagonist flupentixol and the D2-like receptor antagonist L-741626 decreased operant responding for nicotine. Blockade of D1/D2-like receptors and blockade of D2-like receptors also decreased operant responding for food and decreased locomotor activity. Flupentixol induced a greater decrease in operant responding for food in males than females. However, in the other tests, there were no sex differences in the effects of the dopamine receptor antagonists.

CONCLUSIONS

Blockade of D1/D2-like receptors with flupentixol and D2-like receptors with L-741626 decreases nicotine and food intake in rats of both sexes. These compounds also decrease locomotor activity which might be indicative of a sedative effect.

Does openness/intellect predict sensitivity to the reward value of information?

A recent theory proposes that the personality trait openness/intellect is underpinned by differential sensitivity to the reward value of information. This theory draws on evidence that midbrain dopamine neurons respond to unpredicted information gain, mirroring their responses to unpredicted primary rewards. Using a choice task modelled on this seminal work (Experiment 1, N = 139, 69% female), we examined the relation between openness/intellect and willingness to pay for non-instrumental information (i.e., information with no secondary utility). We also assessed whether any such relation was moderated by the dopamine D2 receptor antagonist sulpiride (Experiment 2, N = 164, 100% male). Unexpectedly, most measures of openness/intellect were unrelated to costly information preference in both experiments, and some predicted a decreased willingness to incur a cost for information. In Experiment 2, this cost-dependent association between openness/intellect and information valuation appeared in the placebo condition but not under sulpiride. In addition, participants were more willing to pay for moderately costly information under sulpiride compared to placebo, consistent with a dopaminergic basis to information valuation. Potential refinements to the information valuation theory of openness/intellect are discussed in the light of these and other emerging findings.

The Selective Dopamine D2 Blocker Sulpiride Modulates the Relationship Between Agentic Extraversion and Executive Functions

Initial studies suggest that agentic extraversion and executive functions (EF) are associated, because they share influences of individual differences in the dopamine (DA) system. However, it is unclear whether previously reported associations are specific to certain EFs (e.g., to updating or shifting) or due to shared variance among EF tasks. We investigated the DA-related relationship between agentic extraversion and two EF tasks in a placebo-controlled between-group design with the DA D2 receptor blocker sulpiride (200 mg) in 92 female volunteers. Our goals were to investigate whether (1) there is an association between agentic extraversion and EFs measured with two different tasks (3-back and switching), (2) this association is sensitive to a pharmacological manipulation of DA, and (3) the effects can be ascribed to shared or specific task variance. We observed the expected interaction between drug condition and agentic extraversion for both tasks in a multivariate multiple linear regression model, which supports the DA theory of extraversion. Subsequent univariate analyses revealed a highly similar interaction effect between drug condition and agentic extraversion on two of three performance measures and this effect was somewhat attenuated when we controlled for shared task variance. This pattern matches the interpretation that the association between agentic extraversion and both tasks is partly due to DA-based processes shared among the tasks. Our results, although limited by the low reliability of the switching task, suggest that variance components and measurement difficulties of EF tasks should be considered when investigating personality-related individual differences in EFs.

Methylphenidate boosts choices of mental labor over leisure depending on striatal dopamine synthesis capacity

The cognitive enhancing effects of methylphenidate are well established, but the mechanisms remain unclear. We recently demonstrated that methylphenidate boosts cognitive motivation by enhancing the weight on the benefits of a cognitive task in a manner that depended on striatal dopamine. Here, we considered the complementary hypothesis that methylphenidate might also act by changing the weight on the opportunity cost of a cognitive task, that is, the cost of foregoing alternative opportunity. To this end, 50 healthy participants (25 women) completed a novel cognitive effort-discounting task that required choices between task and leisure. They were tested on methylphenidate, placebo, as well as the selective D2-receptor agent sulpiride, the latter to strengthen inference about dopamine receptor selectivity of methylphenidate's effects. Furthermore, they also underwent an [18F]DOPA PET scan to quantify striatal dopamine synthesis capacity. Methylphenidate boosted choices of cognitive effort over leisure across the group, and this effect was greatest in participants with more striatal dopamine synthesis capacity. The effects of sulpiride did not reach significance. This study strengthens the motivational account of methylphenidate's effects on cognition, and suggests that methylphenidate reduces the cost of mental labor by increasing striatal dopamine.

From Description to Explanation: Integrating Across Multiple Levels of Analysis to Inform Neuroscientific Accounts of Dimensional Personality Pathology

Dimensional approaches to psychiatric nosology are rapidly transforming the way researchers and clinicians conceptualize personality pathology, leading to a growing interest in describing how individuals differ from one another. Yet, in order to successfully prevent and treat personality pathology, it is also necessary to explain the sources of these individual differences. The emerging field of personality neuroscience is well-positioned to guide the transition from description to explanation within personality pathology research. However, establishing comprehensive, mechanistic accounts of personality pathology will require personality neuroscientists to move beyond atheoretical studies that link trait differences to neural correlates without considering the algorithmic processes that are carried out by those correlates. We highlight some of the dangers we see in overpopulating personality neuroscience with brain-trait associational studies and offer a series of recommendations for personality neuroscientists seeking to build explanatory theories of personality pathology.

A low dosage of the dopamine D2-receptor antagonist sulpiride affects effort allocation for reward regardless of trait extraversion

Dopamine (DA) is known to be involved in various aspects of reward processing and goal-directed behavior. The present preregistered study aims at directly accessing the causal influence of DA activity on reward motivation in humans, while also accounting for trait extraversion. Therefore, we examined the effect of a single dose of the DA D2 receptor antagonist sulpiride (200 mg) on effort allocation in a modified version of the Effort-Expenditure for Reward Task (EEfRT). Based on its presumably DA increasing action, we expected the low dose of sulpiride to increase participants' willingness to allocate effort during the modified EEfRT relative to placebo, especially in trials with low probability of reward attainment. Further, we expected a moderating effect of trait extraversion on the effects of sulpiride. Two hundred and three healthy male participants were tested in a randomized, double-blind between-subjects design. Contrary to our expectations, sulpiride reduced the average number of clicks within the modified EEfRT and did not interact with reward attributes, suggesting a more global and not reward-specific effect of sulpiride. Furthermore, trait extraversion did not moderate the effect of sulpiride. Our results provide initial support for the validity of the modified version of the EEfRT, suggesting a possible inhibiting effect of a low dose of sulpiride on approach motivation regardless of trait extraversion. However, given the mixed pattern of findings and the possible confounding role of motoric abilities, further studies examining these effects are clearly warranted.

Enhancing Clinical Trials Through Synergistic Gamma Power Analysis

While the etiology of many neuropsychiatric disorders remains unknown, increasing evidence suggests that aberrant sensory processing plays a central role. For this class of disorders, which are characterized by affective, cognitive, and behavioral symptoms, electroencephalography remains the dominant tool for providing insight into the physiological and molecular underpinnings of the disease state and predicting the effectiveness of investigational new drugs. Within the spectrum of electrical activity present in the CNS, high-frequency oscillations in the gamma band are frequently altered in these patient populations. Measurement of gamma oscillation can be further classified into baseline and evoked, each of which offers a specific commentary on disease state. Baseline gamma analysis provides a surrogate of pharmacodynamics and predicting the time course effects of clinical candidate drugs, while alterations in evoked (time-locked) gamma power may serve as a disease biomarker and have utility in assessing patient response to new drugs. Together, these techniques offer complimentary methods of analysis for discrete realms of clinical and translational medicine. In terms of drug development, comprehensive analysis containing aspects of both baseline and evoked gamma oscillations may prove more useful in establishing better workflow and more accurate criteria for the testing of investigational new drugs.

Effects of Pharmacotherapy Treatment on Patient-Reported Outcomes in a Narcolepsy and Idiopathic Hypersomnia Cohort

STUDY OBJECTIVE

We aimed to evaluate the association between patient-reported outcomes (PROs) and treatment regimen/standardized dose (STD), a measure of drug burden, in patients with narcolepsy type 1 (NT1)/type 2 (NT2) and idiopathic hypersomnia (IH).

METHODS

Patients age 18 years or older with NT1/NT2 and IH with baseline and ≥ 6-month follow-up during 2008-2010 were included. Changes in PROs (Epworth Sleepiness Scale [ESS], Fatigue Severity Scale [FSS], Patient Health Questionnaire 9 [PHQ-9], total sleep time [TST]) by diagnosis, treatment regimen (monotherapy versus polytherapy, sodium oxybate [SO] use), and STD were assessed by t tests and univariable/multivariable linear regressions, adjusting for patient characteristics.

RESULTS

A total of 92 patients (26 [28.3%] NT1, 27 [29.3%] NT2, 39 [42.4%] IH) were included (age 43.8 ± 14.8 years; 66 [71.7%] female). Baseline PROs suggested excessive daytime sleepiness (ESS 14.2 ± 5.2 [74% patients > 10]), significant fatigue (FSS 47.5 ± 12.9), and mild depression (PHQ-9 9.0 [4.0, 14.0] [49.4% ≥ 10]). At follow-up, ESS and PHQ-9 improved significantly overall and within diagnostic, monotherapy/polytherapy, and SO use groups (all P < .01). FSS improved significantly overall (P = .016), but improvements were not significant for IH, monotherapy, polytherapy, and non-SO using groups. In multivariable models, PRO changes were not significantly different between groups, but baseline STD was associated with worsening PHQ-9 across PHQ-9 change models, and ESS worsened with increasing STD at follow-up (P = .056).

CONCLUSIONS

Significant improvements in sleep-related PROs were seen with pharmacotherapy use, regardless of diagnosis or treatment type, highlighting the importance of individualized prescribing decisions for this population.

Openness to experience predicts dopamine effects on divergent thinking

Individual differences in trait levels of openness to experience and creativity have been theoretically linked to dopamine function. However, empirical evidence for this assumption is scarce, especially for causal connections. The present study aims to directly assess the influence of dopamine activity on the established association between openness to experience and divergent thinking (i.e., an index of creativity). We hypothesized that manipulating dopamine activity alters the relationship between self-reported openness to experience and ideational fluency and flexibility. In a placebo-controlled between-subjects design, 193 healthy male volunteers completed four divergent thinking tasks after they received either the dopamine-receptor blocker sulpiride (200 mg) or a placebo. The data revealed an interaction such that openness to experience was more positively associated with divergent thinking in the dopamine blocker group (r = 0.304) than in the placebo group (r = −0.002). Specifically, highly open individuals in the dopamine blocker group reached the highest divergent thinking scores. Thus, sulpiride administration selectively affected divergent thinking as a function of trait levels of openness to experience. Although somewhat limited by the unexpected absence of the association between openness to experience and divergent thinking in the placebo group, the present study provides novel evidence for an association between dopamine activity and both openness to experience and divergent thinking.

Social context effects on error-related brain activity are dependent on interpersonal and achievement-related traits

Brain correlates of performance monitoring, such as the Error-Related Negativity (ERN), are considerably influenced by situational factors. For instance, errors committed during social interaction typically elicit enhanced ERNs. While individual differences in ERN magnitude have been implicated in a wide variety of psychopathologies, it remains unclear how individual dispositions may interact with situational incentives to influence performance monitoring. Here, we analysed how interpersonal (Affiliation) and achievement-related (Agency) traits moderated the effects of interpersonal competition and interpersonal cooperation on the ERN. For this purpose, electroencephalography was collected from 78 participants while they performed a Flanker Task either in a competitive or in a cooperative social context (i.e., between-subjects design). We found that competition predicted enhanced error-related activity patterns compared to cooperation. Furthermore, participants who scored high in Affiliation elicited enhanced error-related activity. Conversely, high Agency scores were associated with reduced error-related activity, but this was only observed in the competitive context. These results indicate that the brain's response to error commission is not only sensitive to social incentives. Rather, the activity of the evaluative system that produces error signals appears to be crucially determined by the personal relevance of the incentives present in the context in which performance is evaluated.

Laboratory-induced learned helplessness attenuates approach motivation as indexed by posterior versus frontal theta activity

Research suggests that midline posterior versus frontal electroencephalographic (EEG) theta activity (PFTA) may reflect a novel neurophysiological index of approach motivation. Elevated PFTA has been associated with approach-related tendencies both at rest and during laboratory tasks designed to enhance approach motivation. PFTA is sensitive to changes in dopamine signaling within the fronto-striatal neural circuit, which is centrally involved in approach motivation, reward processing, and goal-directed behavior. To date, however, no studies have examined PFTA during a laboratory task designed to reduce approach motivation or goal-directed behavior. Considerable animal and human research supports the hypothesis put forth by the learned helplessness theory that exposure to uncontrollable aversive stimuli decreases approach motivation by inducing a state of perceived uncontrollability. Accordingly, the present study examined the effect of perceived uncontrollability (i.e., learned helplessness) on PFTA. EEG data were collected from 74 participants (mean age = 19.21 years; 40 females) exposed to either Controllable (n = 26) or Uncontrollable (n = 25) aversive noise bursts, or a No-Noise Condition (n = 23). In line with prediction, individuals exposed to uncontrollable aversive noise bursts displayed a significant decrease in PFTA, reflecting reduced approach motivation, relative to both individuals exposed to controllable noise bursts or the No-Noise Condition. There was no relationship between perceived uncontrollability and frontal EEG alpha asymmetry, another commonly used neurophysiological index of approach motivation. Results have implications for understanding the neurophysiology of approach motivation and establishing PFTA as a neurophysiological index of approach-related tendencies.