Dopamine modulates novelty seeking behavior during decision making

Individual associations of adolescent alcohol use disorder versus cannabis use disorder symptoms in neural prediction error signaling and the response to novelty

Two of the most commonly used illegal substances by adolescents are alcohol and cannabis. Alcohol use disorder (AUD) and cannabis use disorder (CUD) are associated with poorer decision-making in adolescents. In adolescents, level of AUD symptomatology has been negatively associated with striatal reward responsivity. However, little work has explored the relationship with striatal reward prediction error (RPE) representation and the extent to which any augmentation of RPE by novel stimuli is impacted. One-hundred fifty-one adolescents participated in the Novelty Task while undergoing functional magnetic resonance imaging (fMRI). In this task, participants learn to choose novel or non-novel stimuli to gain monetary reward. Level of AUD symptomatology was negatively associated with both optimal decision-making and BOLD response modulation by RPE within striatum and regions of prefrontal cortex. The neural alterations in RPE representation were particularly pronounced when participants were exploring novel stimuli. Level of CUD symptomatology moderated the relationship between novelty propensity and RPE representation within inferior parietal lobule and dorsomedial prefrontal cortex. These data expand on an emerging literature investigating individual associations of AUD symptomatology levels versus CUD symptomatology levels and RPE representation during reinforcement processing and provide insight on the role of neuro-computational processes underlying reinforcement learning/decision-making in adolescents.

Human complex exploration strategies are enriched by noradrenaline-modulated heuristics

An exploration-exploitation trade-off, the arbitration between sampling a lesser-known against a known rich option, is thought to be solved using computationally demanding exploration algorithms. Given known limitations in human cognitive resources, we hypothesised the presence of additional cheaper strategies. We examined for such heuristics in choice behaviour where we show this involves a value-free random exploration, that ignores all prior knowledge, and a novelty exploration that targets novel options alone. In a double-blind, placebo-controlled drug study, assessing contributions of dopamine (400 mg amisulpride) and noradrenaline (40 mg propranolol), we show that value-free random exploration is attenuated under the influence of propranolol, but not under amisulpride. Our findings demonstrate that humans deploy distinct computationally cheap exploration strategies and that value-free random exploration is under noradrenergic control.

Distinct roles for dopamine clearance mechanisms in regulating behavioral flexibility

Dopamine plays a crucial role in adaptive behavior, and dysfunctional dopamine is implicated in multiple psychiatric conditions characterized by inflexible or inconsistent choices. However, the precise relationship between dopamine and flexible decision making remains unclear. One reason is that, while many studies have focused on the activity of dopamine neurons, efficient dopamine signaling also relies on clearance mechanisms, notably the dopamine transporter (DAT), which predominates in striatum, and catechol-O-methyltransferase (COMT), which predominates in cortex. The exact locus, extent, and timescale of the effects of DAT and COMT are uncertain. Moreover, there is limited data on how acute disruption of either mechanism affects flexible decision making strategies mediated by cortico-striatal networks. To address these issues, we combined pharmacological modulation of DAT and COMT with electrochemistry and behavior in mice. DAT blockade, but not COMT inhibition, regulated sub-second dopamine release in the nucleus accumbens core, but surprisingly neither clearance mechanism affected evoked release in prelimbic cortex. This was not due to a lack of sensitivity, as both amphetamine and atomoxetine changed the kinetics of sub-second release. In a multi-step decision making task where mice had to respond to reversals in either reward probabilities or the choice sequence to reach the goal, DAT blockade selectively impaired, and COMT inhibition improved, performance after reward reversals, but neither manipulation affected the adaptation of choices after action-state transition reversals. Together, our data suggest that DAT and COMT shape specific aspects of behavioral flexibility by regulating different aspects of the kinetics of striatal and cortical dopamine, respectively.

The Effect of "Novelty Input" and "Novelty Output" on Boredom During Home Quarantine in the COVID-19 Pandemic: The Moderating Effects of Trait Creativity

Governments have adopted strict home quarantine measures during the COVID-19 pandemic. A monotonous, barren, and under-stimulating environment can cause state boredom, and people often deal with boredom via novelty-seeking behavior. Novelty-seeking behavior can be divided into "novelty input" and "novelty output." The former refers to obtaining novel information such as browsing the Web; the latter refers to engaging in creative behavior such as literary creation. This study explores the relationship between two types of novelty-seeking behavior and individual state boredom during home quarantine, along with the moderation effect of trait creativity. The study sample consists of 582 Chinese college students who were quarantined at home during the COVID-19 pandemic. Participants completed the Multidimensional State Boredom Scale, the Williams Creativity Aptitude Test, and self-compiled questionnaires of novelty input and novelty output. The results show that there is no significant relationship between novelty input or novelty output and boredom during the COVID-19 quarantine. Trait creativity is found to negatively moderate the relationship between the two means of novelty seeking and boredom. Specifically, novelty output negatively predicts the state boredom of individuals with high creativity, while novelty input positively predicts the state boredom of individuals with low creativity. Our findings suggest that different novelty-seeking behaviors may have different effects on the boredom level of individuals with high versus low creativity during quarantine. During a quarantine period, individuals should avoid excessively engaging in novelty input behaviors aimed at escaping boring situations.

Are adolescents more optimal decision-makers in novel environments? Examining the benefits of heightened exploration in a patch foraging paradigm

Adolescence is a period of heightened exploration relative to adulthood and childhood. This predisposition has been linked with negative behaviours related to risk-taking, including dangerous driving, substance misuse and risky sexual practices. However, recent models have argued that adolescents' heightened exploration serves a functional purpose within the lifespan, allowing adolescents to develop experiential knowledge of their surroundings. Yet, there is limited evidence that heightened exploration in adolescence is associated with positive outcomes. To address this, the present pre-registered study utilised a foraging paradigm with a sample of adolescents aged 16-17 (N = 68) and of adults aged 21 and above (N = 69). Participants completed a patch foraging task, which required them to choose between exploiting a known resource which gradually yields fewer rewards, and exploring a novel, unknown resource with a fresh distribution of rewards. Findings demonstrated that adolescents explored more than adults, which - in the context of the current task-represented more optimal patch foraging behaviour. These findings indicate that adolescents' heightened exploration can be beneficial, as they were able to effectively navigate unknown environments and accrue rewards more successfully than adults. This provides evidence that heightened exploration in adolescence, relative to adulthood, can lead to positive outcomes and contributes to our understanding of the role increased novelty-seeking plays at this point in the lifespan.

Neural circuitry of information seeking

Humans and animals navigate uncertain environments by seeking information about the future. Remarkably, we often seek information even when it has no instrumental value for aiding our decisions - as if the information is a source of value in its own right. In recent years, there has been a flourishing of research into these non-instrumental information preferences and their implementation in the brain. Individuals value information about uncertain future rewards, and do so for multiple reasons, including valuing resolution of uncertainty and overweighting desirable information. The brain motivates this information seeking by tapping into some of the same circuitry as primary rewards like food and water. However, it also employs cortex and basal ganglia circuitry that predicts and values information as distinct from primary reward. Uncovering how these circuits cooperate will be fundamental to understanding information seeking and motivated behavior as a whole, in our increasingly complex and information-rich world.

Dopaminergic modulation of the exploration/exploitation trade-off in human decision-making

Involvement of dopamine in regulating exploration during decision-making has long been hypothesized, but direct causal evidence in humans is still lacking. Here, we use a combination of computational modeling, pharmacological intervention and functional magnetic resonance imaging to address this issue. Thirty-one healthy male participants performed a restless four-armed bandit task in a within-subjects design under three drug conditions: 150 mg of the dopamine precursor L-dopa, 2 mg of the D2 receptor antagonist haloperidol, and placebo. Choices were best explained by an extension of an established Bayesian learning model accounting for perseveration, directed exploration and random exploration. Modeling revealed attenuated directed exploration under L-dopa, while neural signatures of exploration, exploitation and prediction error were unaffected. Instead, L-dopa attenuated neural representations of overall uncertainty in insula and dorsal anterior cingulate cortex. Our results highlight the computational role of these regions in exploration and suggest that dopamine modulates how this circuit tracks accumulating uncertainty during decision-making.

Noradrenergic But Not Dopaminergic Neurons Signal Task State Changes and Predict Reengagement After a Failure

The two catecholamines, noradrenaline and dopamine, have been shown to play comparable roles in behavior. Both noradrenergic and dopaminergic neurons respond to cues predicting reward availability and novelty. However, even though both are thought to be involved in motivating actions, their roles in motivation have seldom been directly compared. We therefore examined the activity of putative noradrenergic neurons in the locus coeruleus and putative midbrain dopaminergic neurons in monkeys cued to perform effortful actions for rewards. The activity in both regions correlated with engagement with a presented option. By contrast, only noradrenaline neurons were also (i) predictive of engagement in a subsequent trial following a failure to engage and (ii) more strongly activated in nonrepeated trials, when cues indicated a new task condition. This suggests that while both catecholaminergic neurons are involved in promoting action, noradrenergic neurons are sensitive to task state changes, and their influence on behavior extends beyond the immediately rewarded action.

Dynamic resource allocation during reinforcement learning accounts for ramping and phasic dopamine activity

For an animal to learn about its environment with limited motor and cognitive resources, it should focus its resources on potentially important stimuli. However, too narrow focus is disadvantageous for adaptation to environmental changes. Midbrain dopamine neurons are excited by potentially important stimuli, such as reward-predicting or novel stimuli, and allocate resources to these stimuli by modulating how an animal approaches, exploits, explores, and attends. The current study examined the theoretical possibility that dopamine activity reflects the dynamic allocation of resources for learning. Dopamine activity may transition between two patterns: (1) phasic responses to cues and rewards, and (2) ramping activity arising as the agent approaches the reward. Phasic excitation has been explained by prediction errors generated by experimentally inserted cues. However, when and why dopamine activity transitions between the two patterns remain unknown. By parsimoniously modifying a standard temporal difference (TD) learning model to accommodate a mixed presentation of both experimental and environmental stimuli, we simulated dopamine transitions and compared them with experimental data from four different studies. The results suggested that dopamine transitions from ramping to phasic patterns as the agent focuses its resources on a small number of reward-predicting stimuli, thus leading to task dimensionality reduction. The opposite occurs when the agent re-distributes its resources to adapt to environmental changes, resulting in task dimensionality expansion. This research elucidates the role of dopamine in a broader context, providing a potential explanation for the diverse repertoire of dopamine activity that cannot be explained solely by prediction error.

Primate Orbitofrontal Cortex Codes Information Relevant for Managing Explore-Exploit Tradeoffs

Reinforcement learning (RL) refers to the behavioral process of learning to obtain reward and avoid punishment. An important component of RL is managing explore-exploit tradeoffs, which refers to the problem of choosing between exploiting options with known values and exploring unfamiliar options. We examined correlates of this tradeoff, as well as other RL related variables, in orbitofrontal cortex (OFC) while three male monkeys performed a three-armed bandit learning task. During the task, novel choice options periodically replaced familiar options. The values of the novel options were unknown, and the monkeys had to explore them to see if they were better than other currently available options. The identity of the chosen stimulus and the reward outcome were strongly encoded in the responses of single OFC neurons. These two variables define the states and state transitions in our model that are relevant to decision-making. The chosen value of the option and the relative value of exploring that option were encoded at intermediate levels. We also found that OFC value coding was stimulus specific, as opposed to coding value independent of the identity of the option. The location of the option and the value of the current environment were encoded at low levels. Therefore, we found encoding of the variables relevant to learning and managing explore-exploit tradeoffs in OFC. These results are consistent with findings in the ventral striatum and amygdala and show that this monosynaptically connected network plays an important role in learning based on the immediate and future consequences of choices.SIGNIFICANCE STATEMENT Orbitofrontal cortex (OFC) has been implicated in representing the expected values of choices. Here we extend these results and show that OFC also encodes information relevant to managing explore-exploit tradeoffs. Specifically, OFC encodes an exploration bonus, which characterizes the relative value of exploring novel choice options. OFC also strongly encodes the identity of the chosen stimulus, and reward outcomes, which are necessary for computing the value of novel and familiar options.

A Curiosity-Based Learning Method for Spiking Neural Networks

Spiking Neural Networks (SNNs) have shown favorable performance recently. Nonetheless, the time-consuming computation on neuron level and complex optimization limit their real-time application. Curiosity has shown great performance in brain learning, which helps biological brains grasp new knowledge efficiently and actively. Inspired by this leaning mechanism, we propose a curiosity-based SNN (CBSNN) model, which contains four main learning processes. Firstly, the network is trained with biologically plausible plasticity principles to get the novelty estimations of all samples in only one epoch; secondly, the CBSNN begins to repeatedly learn the samples whose novelty estimations exceed the novelty threshold and dynamically update the novelty estimations of samples according to the learning results in five epochs; thirdly, in order to avoid the overfitting of the novel samples and forgetting of the learned samples, CBSNN retrains all samples in one epoch; finally, step two and step three are periodically taken until network convergence. Compared with the state-of-the-art Voltage-driven Plasticity-centric SNN (VPSNN) under standard architecture, our model achieves a higher accuracy of 98.55% with only 54.95% of its computation cost on the MNIST hand-written digit recognition dataset. Similar conclusion can also be found out in other datasets, i.e., Iris, NETtalk, Fashion-MNIST, and CIFAR-10, respectively. More experiments and analysis further prove that such curiosity-based learning theory is helpful in improving the efficiency of SNNs. As far as we know, this is the first practical combination of the curiosity mechanism and SNN, and these improvements will make the realistic application of SNNs possible on more specific tasks within the von Neumann framework.

Gambling Phenotypes in Online Sports Betting

BACKGROUND AND OBJECTIVES

The Internet provides easy access to multiple types of gambling and has led to changes in betting habits. A severe rise in problematic gambling has been predicted among all sectors of the population, and studies are required to assess the emerging phenotypes related to the new structures of gambling activities. This study aimed to explore the existence of latent classes associated with gambling habits among treatment-seeking gamblers due to Online Sports Betting (OSB).

METHOD

Initial sample included n = 4,516 patients consecutively admitted for treatment in a hospital unit specialized in behavioral addictions. Two-step clustering analysis was used within the subsample of n = 323 patients who reported problems related with OSB, within a set of indicators including sociodemographics, psychopathological distress, personality, and severity of the gambling activity.

RESULTS

The prevalence of OSB as a main type of gambling problem in the study was 7.2% (95% confidence interval: 6.4 to 7.9%). Two latent clusters were identified, with differences in sociodemographics and clinical status. Cluster 1 (n = 247, 76.5%) grouped patients that were more affected due to the OSB behaviors, and it was characterized by non-married patients, lower socioeconomic position index, higher comorbidity with other substance related addictions, younger age, and early onset of the gambling activity, as well as higher debts due to the OSB, higher psychopathological distress, and a more dysfunctional personality profile. Cluster 2 (n = 76, 23.5%) grouped patients that were less affected by OSB, mostly married (or living with a stable partner), with higher social position levels, older age and older onset of the gambling activity, as well as a more functional psychopathological and personality profile.

CONCLUSION

The increasing understanding of latent classes underlying OSB phenotypes is essential in guiding the development of reliable screening tools to identify individuals highly vulnerable to addictive behaviors among Internet gamblers, as well as in planning prevention and treatment initiatives focused on the precise profiles of these patients.

Frontostriatal and Dopamine Markers of Individual Differences in Reinforcement Learning: A Multi-modal Investigation

Prior studies have shown that dopamine (DA) functioning in frontostriatal circuits supports reinforcement learning (RL), as phasic DA activity in ventral striatum signals unexpected reward and may drive coordinated activity of striatal and orbitofrontal regions that support updating of action plans. However, the nature of DA functioning in RL is complex, in particular regarding the role of DA clearance in RL behavior. Here, in a multi-modal neuroimaging study with healthy adults, we took an individual differences approach to the examination of RL behavior and DA clearance mechanisms in frontostriatal learning networks. We predicted that better RL would be associated with decreased striatal DA transporter (DAT) availability and increased intrinsic functional connectivity among DA-rich frontostriatal regions. In support of these predictions, individual differences in RL behavior were related to DAT binding potential in ventral striatum and resting-state functional connectivity between ventral striatum and orbitofrontal cortex. Critically, DAT binding potential had an indirect effect on reinforcement learning behavior through frontostriatal connectivity, suggesting potential causal relationships across levels of neurocognitive functioning. These data suggest that individual differences in DA clearance and frontostriatal coordination may serve as markers for RL, and suggest directions for research on psychopathologies characterized by altered RL.

Resynthesizing behavior through phylogenetic refinement

This article proposes that biologically plausible theories of behavior can be constructed by following a method of "phylogenetic refinement," whereby they are progressively elaborated from simple to complex according to phylogenetic data on the sequence of changes that occurred over the course of evolution. It is argued that sufficient data exist to make this approach possible, and that the result can more effectively delineate the true biological categories of neurophysiological mechanisms than do approaches based on definitions of putative functions inherited from psychological traditions. As an example, the approach is used to sketch a theoretical framework of how basic feedback control of interaction with the world was elaborated during vertebrate evolution, to give rise to the functional architecture of the mammalian brain. The results provide a conceptual taxonomy of mechanisms that naturally map to neurophysiological and neuroanatomical data and that offer a context for defining putative functions that, it is argued, are better grounded in biology than are some of the traditional concepts of cognitive science.

Subcortical Substrates of Explore-Exploit Decisions in Primates

The explore-exploit dilemma refers to the challenge of deciding when to forego immediate rewards and explore new opportunities that could lead to greater rewards in the future. While motivational neural circuits facilitate learning based on past choices and outcomes, it is unclear whether they also support computations relevant for deciding when to explore. We recorded neural activity in the amygdala and ventral striatum of rhesus macaques as they solved a task that required them to balance novelty-driven exploration with exploitation of what they had already learned. Using a partially observable Markov decision process (POMDP) model to quantify explore-exploit trade-offs, we identified that the ventral striatum and amygdala differ in how they represent the immediate value of exploitative choices and the future value of exploratory choices. These findings show that subcortical motivational circuits are important in guiding explore-exploit decisions.

A neurocomputational account of reward and novelty processing and effects of psychostimulants in attention deficit hyperactivity disorder

Computational models of reinforcement learning have helped dissect discrete components of reward-related function and characterize neurocognitive deficits in psychiatric illnesses. Stimulus novelty biases decision-making, even when unrelated to choice outcome, acting as if possessing intrinsic reward value to guide decisions toward uncertain options. Heightened novelty seeking is characteristic of attention deficit hyperactivity disorder, yet how this influences reward-related decision-making is computationally encoded, or is altered by stimulant medication, is currently uncertain. Here we used an established reinforcement-learning task to model effects of novelty on reward-related behaviour during functional MRI in 30 adults with attention deficit hyperactivity disorder and 30 age-, sex- and IQ-matched control subjects. Each participant was tested on two separate occasions, once ON and once OFF stimulant medication. OFF medication, patients with attention deficit hyperactivity disorder showed significantly impaired task performance (P = 0.027), and greater selection of novel options (P = 0.004). Moreover, persistence in selecting novel options predicted impaired task performance (P = 0.025). These behavioural deficits were accompanied by a significantly lower learning rate (P = 0.011) and heightened novelty signalling within the substantia nigra/ventral tegmental area (family-wise error corrected P < 0.05). Compared to effects in controls, stimulant medication improved attention deficit hyperactivity disorder participants' overall task performance (P = 0.011), increased reward-learning rates (P = 0.046) and enhanced their ability to differentiate optimal from non-optimal novel choices (P = 0.032). It also reduced substantia nigra/ventral tegmental area responses to novelty. Preliminary cross-sectional evidence additionally suggested an association between long-term stimulant treatment and a reduction in the rewarding value of novelty. These data suggest that aberrant substantia nigra/ventral tegmental area novelty processing plays an important role in the suboptimal reward-related decision-making characteristic of attention deficit hyperactivity disorder. Compared to effects in controls, abnormalities in novelty processing and reward-related learning were improved by stimulant medication, suggesting that they may be disorder-specific targets for the pharmacological management of attention deficit hyperactivity disorder symptoms.

Abdominal vagal deafferentation alters affective behaviors in rats

BACKGROUND

There is growing evidence for a role of abnormal gut-brain signaling in disorders involving altered mood and affect, including depression. Studies using vagus nerve stimulation (VNS) suggest that the disruption of vagal afferent signaling may contribute to these abnormalities. To test this hypothesis, we used a rat model of subdiaphragmatic vagal deafferentation (SDA), the most complete and selective vagal deafferentation method existing to date, to study the consequences of complete disconnection of abdominal vagal afferents on affective behaviors.

METHODS

SDA- and Sham-operated male rats were subjected to several tests that are commonly used in preclinical rodent models to assess the presence of anhedonic behavior, namely the novel object-induced exploration test, the novelty-suppressed eating test, and the sucrose preference test. In addition, we compared SDA and Sham rats in a social interaction test and the forced swim test to assess sociability and behavioral despair, respectively.

RESULTS

Compared to Sham controls, SDA rats consistently displayed signs of anhedonic behavior in all test settings used. SDA rats also showed increased immobility and reduced swimming in the forced swim test, whereas they did not differ from Sham controls with regards to social approach behavior.

LIMITATIONS

This study was conducted in male rats only. Hence, possible sex-specific effects of SDA on affective behaviors remained unexamined.

CONCLUSIONS

Our findings demonstrate that hedonic behavior and behavioral despair are subject to visceral modulation through abdominal vagal afferents. These data are compatible with preclinical models and clinical trials showing beneficial effects of VNS on depression-like and affective behaviors.

Dopamine manipulations drive changes in information sampling in healthy volunteers

BACKGROUND

Information sampling is the cognitive process of accumulating information before committing to a decision. Patients across numerous disorders show decreased information sampling relative to controls.

AIMS

Here, we used the Beads and the Best Choice Tasks to study the role of dopamine signaling in information sampling.

METHODS

Participants were given placebo, amisulpride, or ropinirole in each session, in a double-blind cross-over design.

RESULTS

We found that ropinirole (agonist) increased the number of beads drawn in the Beads Task specifically when participants faced a loss, and decreased the rank of the chosen option in the Best Choice Task.

CONCLUSIONS

These effects are likely driven by a combination of effects at presynaptic D₂ receptors, which affect dopamine release, and post-synaptic D₂ receptors. Increased D₂ relative to D₁ receptor activation in the striatum leads to increased sampling in the loss condition in the Beads Task. It also leads to choice of a poorer ranked option in the Best Choice Task. Decreased D₂ relative to D₁ receptor activation leads to decreased sampling in the Beads Task in the loss condition.

Dopamine blockade impairs the exploration-exploitation trade-off in rats

In a volatile environment where rewards are uncertain, successful performance requires a delicate balance between exploitation of the best option and exploration of alternative choices. It has theoretically been proposed that dopamine contributes to the control of this exploration-exploitation trade-off, specifically that the higher the level of tonic dopamine, the more exploitation is favored. We demonstrate here that there is a formal relationship between the rescaling of dopamine positive reward prediction errors and the exploration-exploitation trade-off in simple non-stationary multi-armed bandit tasks. We further show in rats performing such a task that systemically antagonizing dopamine receptors greatly increases the number of random choices without affecting learning capacities. Simulations and comparison of a set of different computational models (an extended Q-learning model, a directed exploration model, and a meta-learning model) fitted on each individual confirm that, independently of the model, decreasing dopaminergic activity does not affect learning rate but is equivalent to an increase in random exploration rate. This study shows that dopamine could adapt the exploration-exploitation trade-off in decision-making when facing changing environmental contingencies.

An investigation of the single and combined effects of hypogravity and ionizing radiation on brain monoamine metabolism and rats' behavior

BACKGROUND

Ionizing radiation and hypogravity can cause central nervous system (CNS) dysfunctions. This is a key limiting factor for deep space missions. Up until now, the mechanisms through which they affect the neural tissue are not completely understood.

OBJECTIVES

We studied how the combination of hypogravity (antiorthostatic suspension model, AS) and ionizing radiations (γ-quanta and ¹H⁺ together, R) affects the CNS.

METHODS

We applied separately and in combination AS and R to determine the influence of these factors on behavior and metabolism of monoamines in Wistar rat's brain.

RESULTS

We found out that R has a slight effect on both the behavior and metabolism of monoamines. However, when applied in combination with AS the former was able to reduce the negative effects of the latter. The combined effect of ionizing radiation and hypogravity led to the recovery of locomotor activity, orientation and exploratory behavior, and long-term context memory impaired under the impact of hypogravity only. These changes came together with an increase in the serotonin and dopamine turnover in all of the brain structures that were studied.

CONCLUSIONS

We received the first evidence of interferential interaction between the effects of ionizing radiation and hypogravity factors with regard to a behavior and monoamine turnover in the brain. Further studies with heavy nuclei at relevant doses (<0.5 Gy) are needed.

Ventral striatal dopamine transporter availability is associated with lower trait motor impulsivity in healthy adults

Impulsivity is a transdiagnostic feature of a range of externalizing psychiatric disorders. Preclinical work links reduced ventral striatal dopamine transporter (DAT) availability with heightened impulsivity and novelty seeking. However, there is a lack of human data investigating the relationship between DAT availability, particularly in subregions of the striatum, and the personality traits of impulsivity and novelty seeking. Here we collected PET measures of DAT availability (BP_ND) using the tracer ¹⁸F-FE-PE2I in 47 healthy adult subjects and examined relations between BP_ND in striatum, including its subregions: caudate, putamen, and ventral striatum (VS), and trait impulsivity (Barratt Impulsiveness Scale: BIS-11) and novelty seeking (Tridimensional Personality Questionnaire: TPQ-NS), controlling for age and sex. DAT BP_ND in each striatal subregion showed nominal negative associations with total BIS-11 but not TPQ-NS. At the subscale level, VS DAT BP_ND was significantly associated with BIS-11 motor impulsivity (e.g., taking actions without thinking) after correction for multiple comparisons. VS DAT BP_ND explained 13.2% of the variance in motor impulsivity. Our data demonstrate that DAT availability in VS is negatively related to impulsivity and suggest a particular influence of DAT regulation of dopamine signaling in VS on acting without deliberation (BIS motor impulsivity). While needing replication, these data converge with models of ventral striatal functions that emphasize its role as a key interface linking motivation to action.

My Reflections on Understanding Animal Emotions for Improving the Life of Animals in Zoos

Scientists are often reluctant to attribute emotions to nonhuman animals that are similar to human emotions. When the author published her early studies, reviewers prohibited the word fear. Fearful behavior had to be described as agitated. The core emotional systems described by Panksepp may provide a useful framework for people who work hands-on with animals. The core systems are fear, rage, panic (separation distress), seek, lust, nurture, and play. Some scientists who deny that animals have real emotions often fail to review important areas of the literature. The areas that are sometimes left out are the effects of psychiatric medications on animals and genetic influences on differences in animal behavior. In both people and animals, genetics has an influence on both fearfulness and novelty seeking. Visualizing the seven core emotional systems as separate volume controls on a music mixing board may help zoo professionals determine the motivation of both normal and abnormal behavior. It may also help them to design more effective environmental enrichments.

Individual differences in exploration and persistence: Grit and beliefs about ability and reward

The tradeoff between knowing when to seek greater rewards (exploration), and knowing when to settle (exploitation), is critical to success. One dispositional factor that may modulate this tradeoff is "grit." Gritty individuals tend to persist in the face of difficulty and consequently experience greater life success. It is possible that they may also experience a greater tendency to explore in a reward task. However, although most exploration/exploitation tasks manipulate beliefs about the presence/magnitude of rewards in the environment, the belief of one's ability to actually achieve a reward is also critical. As such, we investigated whether individuals higher in grit were more likely to explore, and how beliefs about the magnitude/presence of rewards, and the perceived ability to achieve a reward, modulated their exploration tendencies. Over two experiments, participants completed 4 different exploration/persistence tasks: two that tapped into participant beliefs about the presence/magnitude of rewards, and two that tapped into participant beliefs about their ability to achieve a reward. Participants also completed measures of dispositional grit (Experiment 1a and 1b), conscientiousness (Experiment 1b), and working memory (Experiment 1a and 1b). In both experiments, we found a relationship between the two "belief of rewards" tasks, as well as between the two "belief of ability" tasks, but performance was unrelated across the two types of task. We also found that dispositional grit was strongly associated with greater exploration, but only on the "belief of ability" tasks. Finally, in Experiment 1b we showed that conscientiousness better predicted exploration on the "belief of ability" tasks than grit, suggesting that it is not grittiness per se that is associated with exploration. Overall, our findings showed that individuals high in grit/conscientiousness are more likely to explore, but only when there is a known reward available that they believe they have the ability to achieve.

Temperament and Character Inventory in Bipolar Disorder versus Healthy Controls and Modulatory Effects of 3 Key Functional Gene Variants

BACKGROUND

Bipolar disorder (BD) has been associated with temperamental and personality traits, although the relationship is still to be fully elucidated. Several studies investigated the genetic basis of temperament and character, identifying catechol-O-methyltransferase (COMT), brain derived neurotrophic factor (BDNF), and serotonin transporter (5-HTT) gene variants as strong candidates.

METHODS

In the GECO-BIP study, 125 BD patients and 173 HC were recruited. Subjects underwent to a detailed assessment and the temperament and character inventory 125 items (TCI) was administrated. Three functional genetic variants within key candidate genes (COMT rs4680, BDNF rs6265, and the serotonin-transporter-linked polymorphic region (5-HTTLPR)) were genotyped. Univariate and multivariate analyses were performed.

RESULTS

Compared to HC, BD patients showed higher scores in novelty seeking (NS; p = 0.001), harm avoidance (HA; p < 0.001), and self transcendence (St; p < 0.001), and lower scores in self directness (p < 0.001) and cooperativeness (p < 0.001) TCI dimensions. Concerning the genetic analyses, COMT rs4680 was associated with NS in the total sample (p = 0.007) and in the male subsample (p = 0.022). When performing the analysis in the HC and BD samples, the association was confirmed only in HC (p = 0.012), and in the HC male subgroup in particular (p = 0.004). BDNF rs6265 was associated with St in the BD group (p = 0.017).

CONCLUSION

COMT rs4680 may modulate NS in males in the general population. This effect was not detected in BD patients, probably because BD alters the neurobiological basis of some TCI dimensions. BDNF rs6265 seems to modulate St TCI dimension only in BD patients, possibly modulating the previously reported association between rs6265 and BD treatment response. Further studies are needed to confirm our findings.

Early Visual Foraging in Relationship to Familial Risk for Autism and Hyperactivity/Inattention

OBJECTIVE

Information foraging is atypical in both autism spectrum disorders (ASDs) and ADHD; however, while ASD is associated with restricted exploration and preference for sameness, ADHD is characterized by hyperactivity and increased novelty seeking. Here, we ask whether similar biases are present in visual foraging in younger siblings of children with a diagnosis of ASD with or without additional high levels of hyperactivity and inattention.

METHOD

Fifty-four low-risk controls (LR) and 50 high-risk siblings (HR) took part in an eye-tracking study at 8 and 14 months and at 3 years of age.

RESULTS

At 8 months, siblings of children with ASD and low levels of hyperactivity/inattention (HR/ASD-HI) were more likely to return to previously visited areas in the visual scene than were LR and siblings of children with ASD and high levels of hyperactivity/inattention (HR/ASD+HI).

CONCLUSION

We show that visual foraging is atypical in infants at-risk for ASD. We also reveal a paradoxical effect, in that additional family risk for ADHD core symptoms mitigates the effect of ASD risk on visual information foraging.

Novelty seeking is linked to openness and extraversion, and can lead to greater creative performance

OBJECTIVE

Novelty seeking (the tendency to explore things novel and unfamiliar) has been extensively researched in the clinical and health domains, but its effects on creative performance are largely unknown. We examined whether creativity-related personality traits (openness to experience and extraversion) are associated with novelty seeking, and whether novelty seeking is linked to, and facilitates, creativity.

METHOD

In Study 1a (N = 230; M_age  = 20; 64% females) and Study 1b (N = 421; M_age  = 19; 65% females), we measured extraversion, openness to experience, novelty seeking, and divergent thinking. To provide causal evidence for the relation between novelty seeking and creativity, in Study 2 (N = 147; M_age  = 27; 75% females), we manipulated people's motivation to seek novelty and then measured subsequent divergent thinking.

RESULTS

In Studies 1a and 1b, we demonstrated that trait novelty seeking is associated with openness and extraversion, on the one hand, and divergent thinking on the other. In Study 2, the novelty seeking manipulation led to greater divergent thinking.

CONCLUSIONS

We conclude that novelty seeking is linked to openness to experience and extraversion, and that it can lead to greater divergent thinking.

HIV-1 proteins dysregulate motivational processes and dopamine circuitry

Motivational alterations, such as apathy, in HIV-1+ individuals are associated with decreased performance on tasks involving frontal-subcortical circuitry. We used the HIV-1 transgenic (Tg) rat to assess effect of long-term HIV-1 protein exposure on motivated behavior using sucrose (1–30%, w/v) and cocaine (0.01–1.0 mg/kg/infusion) maintained responding with fixed-ratio (FR) and progressive-ratio (PR) schedules of reinforcement. For sucrose-reinforced responding, HIV-1 Tg rats displayed no change in EC₅₀ relative to controls, suggesting no change in sucrose reinforcement but had a downward shifted concentration-response curves, suggesting a decrease in response vigor. Cocaine-maintained responding was attenuated in HIV-1 Tg rats (FR1 0.33 mg/kg/infusion and PR 1.0 mg/kg/infusion). Dose-response tests (PR) revealed that HIV-1 Tg animals responded significantly less than F344 control rats and failed to earn significantly more infusions of cocaine as the unit dose increased. When choosing between cocaine and sucrose, control rats initially chose sucrose but with time shifted to a cocaine preference. In contrast, HIV-1 disrupted choice behaviors. DAT function was altered in the striatum of HIV-1 Tg rats; however, prior cocaine self-administration produced a unique effect on dopamine homeostasis in the HIV-1 Tg striatum. These findings of altered goal directed behaviors may determine neurobiological mechanisms of apathy in HIV-1+ patients.

Dopamine Modulates the Efficiency of Sensory Evidence Accumulation During Perceptual Decision Making

BACKGROUND

Perceptual decision making is the process through which available sensory information is gathered and processed to guide our choices. However, the neuropsychopharmacological basis of this important cognitive function is largely elusive. Yet, theoretical considerations suggest that the dopaminergic system may play an important role.

METHODS

In a double-blind, randomized, placebo-controlled study design, we examined the effect of methylphenidate in 2 dosages (0.25 mg/kg and 0.5 mg/kg body weight) in separate groups of healthy young adults. We used a moving dots task in which the coherency of the direction of moving dots stimuli was manipulated in 3 levels (5%, 15%, and 35%). Drift diffusion modelling was applied to behavioral data to capture subprocesses of perceptual decision making.

RESULTS

The findings show that only the drift rate (v), reflecting the efficiency of sensory evidence accumulation, but not the decision criterion threshold (a) or the duration of nondecisional processes (Ter), is affected by methylphenidate vs placebo administration. Compared with placebo, administering 0.25 mg/kg methylphenidate increased v, but only in the 35% coherence condition. Administering 0.5 mg/kg methylphenidate did not induce modulations.

CONCLUSIONS

The data suggest that dopamine selectively modulates the efficacy of evidence accumulation during perceptual decision making. This modulation depends on 2 factors: (1) the degree to which the dopaminergic system is modulated using methylphenidate (i.e., methylphenidate dosage) and (2) the signal-to-noise ratio of the visual information. Dopamine affects sensory evidence accumulation only when dopamine concentration is not shifted beyond an optimal level and the incoming information is less noisy.

The value of novelty in schizophrenia

Influential models of schizophrenia suggest that patients experience incoming stimuli as excessively novel and motivating, with important consequences for hallucinatory experience and delusional belief. However, whether schizophrenia patients exhibit excessive novelty value and whether this interferes with adaptive behaviour has not yet been formally tested. Here, we employed a three-armed bandit task to investigate this hypothesis. Schizophrenia patients and healthy controls were first familiarised with a group of images and then asked to repeatedly choose between familiar and unfamiliar images associated with different monetary reward probabilities. By fitting a reinforcement-learning model we were able to estimate the values attributed to familiar and unfamiliar images when first presented in the context of the decision-making task. In line with our hypothesis, we found increased preference for newly introduced images (irrespective of whether these were familiar or unfamiliar) in patients compared to healthy controls and this to correlate with severity of hallucinatory experience. In addition, we found a correlation between value assigned to novel images and task performance, suggesting that excessive novelty value may interfere with optimal learning in patients, putatively through the disruption of the mechanisms regulating exploration versus exploitation. Our results suggest excessive novelty value in patients, whereby even previously seen stimuli acquire higher value as the result of their exposure in a novel context - a form of 'hyper novelty' which may explain why patients are often attracted by familiar stimuli experienced as new.

Neural correlates of novelty and appropriateness processing in externally induced constraint relaxation

Novelty and appropriateness are considered the two fundamental features of creative thinking, including insight problem solving, which can be performed through chunk decomposition and constraint relaxation. Based on a previous study that separated the neural bases of novelty and appropriateness in chunk decomposition, in this study, we used event-related functional magnetic resonance imaging (fMRI) to further dissociate these mechanisms in constraint relaxation. Participants were guided to mentally represent the method of problem solving according to the externally provided solutions that were elaborately prepared in advance and systematically varied in their novelty and appropriateness for the given problem situation. The results showed that novelty processing was completed by the temporoparietal junction (TPJ) and regions in the executive system (dorsolateral prefrontal cortex [DLPFC]), whereas appropriateness processing was completed by the TPJ and regions in the episodic memory (hippocampus), emotion (amygdala), and reward systems (orbitofrontal cortex [OFC]). These results likely indicate that appropriateness processing can result in a more memorable and richer experience than novelty processing in constraint relaxation. The shared and distinct neural mechanisms of the features of novelty and appropriateness in constraint relaxation are discussed, enriching the representation of the change theory of insight.

Personality and Parkinson's disease: A meta-analysis

INTRODUCTION

Personality changes are considered pre-motor features of Parkinson's disease (PD). Cross-sectional studies revealed that PD patients were more introvert, apprehensive, and cautious than healthy subjects (HS), whereas other studies failed to disclose these behavioural traits. Some studies found mixed results concerning Novelty Seeking (NS) and Harm Avoidance (HA) profiles in PD patients. To better clarify the personality profile in PD we performed a meta-analysis on studies exploring such topic according to both Cloninger's Psychobiological Model (PM) and Big Five Model (BFM) METHODS: The meta-analysis included 17 studies evaluating the personality in PD patients compared with HS. The outcomes were the dimensions of the temperament and character of the PM and personality traits of BFM. Effect sizes from data reported in the primary studies were computed using Hedges'g unbiased approach. Heterogeneity among the studies and publication bias were assessed. Meta-regressions were conducted with age at evaluation, gender, schooling, and type of personality trait tools as moderators.

RESULTS

As for PM, PD patients scored higher on HA and lower on NS than HS. No difference was found on Reward Dependence, Perseverance/Persistence and on character level. As for BFM, higher levels of Neuroticism, but lower levels of Openness and Extraversion were associated with PD.

DISCUSSION

The personality profile in PD is characterized by high Neuroticism and HA, and by low Openness, Extraversion and NS. The personality profile delineated in the present study on PD patients seems to reflect the premorbid one and might contribute to development and persistence of affective disorders.

Finasteride inhibited brain dopaminergic system and open-field behaviors in adolescent male rats

AIMS

Finasteride inhibits the conversion of testosterone to dihydrotestosterone. Because androgen regulates dopaminergic system in the brain, it could be hypothesized that finasteride may inhibit dopaminergic system. The present study therefore investigates the effects of finasteride in adolescent and early developmental rats on dopaminergic system, including contents of dopamine and its metabolites (dihydroxy phenyl acetic acid and homovanillic acid) and tyrosine hydroxylase expressions both at gene and protein levels. Meanwhile, open-field behaviors of the rats are examined because of the regulatory effect of dopaminergic system on the behaviors.

METHODS

Open-field behaviors were evaluated by exploratory and motor behaviors. Dopamine and its metabolites were assayed by liquid chromatography-mass spectrometry. Tyrosine hydroxylase mRNA and protein expressions were determined by real-time qRT-PCR and western blot, respectively.

RESULTS

It was found that in adolescent male rats, administration of finasteride at doses of 25 and 50 mg/kg for 14 days dose dependently inhibited open-field behaviors, reduced contents of dopamine and its metabolites in frontal cortex, hippocampus, caudate putamen, nucleus accumbens, and down-regulated tyrosine hydroxylase mRNA and protein expressions in substantia nigra and ventral tegmental area. However, there was no significant change of these parameters in early developmental rats after finasteride treatment.

CONCLUSION

These results suggest that finasteride inhibits dopaminergic system and open-field behaviors in adolescent male rats by inhibiting the conversion of testosterone to dihydrotestosterone, and imply finasteride as a potential therapeutic option for neuropsychiatric disorders associated with hyperactivities of dopaminergic system and androgen.

The importance of nutrition in aiding recovery from substance use disorders: A review

BACKGROUND

Nutrition is a prerequisite for health; yet, there is no special nutritional assessment or guidance for drug and alcohol dependent individuals, despite the fact that their food consumption is often very limited, risking malnutrition. Further, the premise is examined that malnutrition may promote drug seeking and impede recovery from substance use disorders (SUD).

METHOD

A narrative review addressed the relationship between substance use disorders and nutrition, including evidence for malnutrition, as well as their impact on metabolism and appetite regulation. The implications of the biopsychology of addiction and appetite for understanding the role of nutrition in SUD were also considered.

RESULTS

The literature overwhelmingly finds that subjects with alcohol use disorder (AUD) and drug use disorder (DUD) typically suffer from nutrient deficiencies. These nutrient deficiencies may be complicit in the alcoholic myopathy, osteopenia and osteoporosis, and mood disorders including anxiety and depression, observed in AUD and DUD. These same individuals have also been found to have altered body composition and altered hormonal metabolic regulators. Additionally, brain processes fundamental for survival are stimulated both by food, particularly sweet foods, and by substances of abuse, with evidence supporting confusion (addiction transfer) when recovering from SUD between cravings for a substance and craving for food.

CONCLUSION

Poor nutritional status in AUD and DUD severely impacts their physical and psychological health, which may impede their ability to resist substances of abuse and recover their health. This review contributes to a better understanding of interventions that could best support individuals with substance use disorders.

(Reinforcement?) Learning to forage optimally

Foraging effectively is critical to the survival of all animals and this imperative is thought to have profoundly shaped brain evolution. Decisions made by foraging animals often approximate optimal strategies, but the learning and decision mechanisms generating these choices remain poorly understood. Recent work with laboratory foraging tasks in humans suggest their behaviour is poorly explained by model-free reinforcement learning, with simple heuristic strategies better describing behaviour in some tasks, and in others evidence of prospective prediction of the future state of the environment. We suggest that model-based average reward reinforcement learning may provide a common framework for understanding these apparently divergent foraging strategies.

A Primer on Foraging and the Explore/Exploit Trade-Off for Psychiatry Research

Foraging is a fundamental behavior, and many types of animals appear to have solved foraging problems using a shared set of mechanisms. Perhaps the most common foraging problem is the choice between exploiting a familiar option for a known reward and exploring unfamiliar options for unknown rewards-the so-called explore/exploit trade-off. This trade-off has been studied extensively in behavioral ecology and computational neuroscience, but is relatively new to the field of psychiatry. Explore/exploit paradigms can offer psychiatry research a new approach to studying motivation, outcome valuation, and effort-related processes, which are disrupted in many mental and emotional disorders. In addition, the explore/exploit trade-off encompasses elements of risk-taking and impulsivity-common behaviors in psychiatric disorders-and provides a novel framework for understanding these behaviors within an ecological context. Here we explain relevant concepts and some common paradigms used to measure explore/exploit decisions in the laboratory, review clinically relevant research on the neurobiology and neuroanatomy of explore/exploit decision making, and discuss how computational psychiatry can benefit from foraging theory.

Open-label versus double-blind placebo treatment in irritable bowel syndrome: study protocol for a randomized controlled trial

BACKGROUND

Placebo medications, by definition, are composed of inactive ingredients that have no physiological effect on symptoms. Nonetheless, administration of placebo in randomized controlled trials (RCTs) and in clinical settings has been demonstrated to have significant impact on many physical and psychological complaints. Until recently, conventional wisdom has suggested that patients must believe that placebo pills actually contain (or, at least, might possibly contain) active medication in order to elicit a response to placebo. However, several recent RCTs, including patients with irritable bowel syndrome (IBS), chronic low back pain, and episodic migraine, have demonstrated that individuals receiving open-label placebo (OLP) can still experience symptomatic improvement and benefit from honestly described placebo treatment.

METHODS AND DESIGN

This paper describes an innovative multidisciplinary trial design (n = 280) that attempts to replicate and expand upon an earlier IBS OLP study. The current study will compare OLP to double-blind placebo (DBP) administration which is made possible by including a nested, double-blind RCT comparing DBP and peppermint oil. The study also examines possible genetic and psychological predictors of OLP and seeks to better understand participants' experiences with OLP and DBP through a series of extensive interviews with a randomly selected subgroup.

DISCUSSION

OLP treatment is a novel strategy for ethically harnessing placebo effects. It has potential to re-frame theories of placebo and to influence how physicians can optimize watch-and-wait strategies for common, subjective symptoms. The current study aims to dramatically expand what we know about OLP by comparing, for the first time, OLP and DBP administration. Adopting a unique, multidisciplinary approach, the study also explores genetic, psychological and experiential dimensions of OLP. The paper ends with an extensive discussion of the "culture" of the trial as well as potential mechanisms of OLP and ethical implications.

TRIAL REGISTRATION

ClinicalTrials.gov, identifier: NCT02802241 . Registered on 14 June 2016.

Dopamine disruption increases cleanerfish cooperative investment in novel client partners

Social familiarization is a process of gaining knowledge that results from direct or indirect participation in social events. Cooperative exchanges are thought to be conditional upon familiarity with others. Indeed, individuals seem to prefer to engage with those that have previously interacted with them, which are more accurate predictors of reward than novel partners. On the other hand, highly social animals do seek novelty. Truth is that the physiological bases underlying how familiarity and novelty may affect cooperative decision-making are still rather obscure. Here, we provide the first experimental evidence that the level of the dopaminergic influence in cooperative exchanges is constrained to mechanisms of social familiarization and novelty in a cleanerfish, Labroides dimidiatus. Cleaners were tested against familiar and novel Ctenochaetus striatus surgeonfish (a common client species) in laboratorial conditions, and were found to spend more time providing physical contact (also referred to as tactile stimulation) to familiar fish clients. Cleaners use tactile stimulation as a way to reduce the risk of a non-rewarding outcome, a behavioural response that is even more pronounced when blocking dopamine (DA) D1 receptors. We discovered that the influence of DA disruption on cleaners' provision of physical contact was dependent on the level of familiarity with its partner, being highly exacerbated whenever the client is novel, and unnoticed when dealing with a familiar one. Our findings demonstrate that DA mediation influences the valuation of partner stimuli and the enhancing investment in novel partners, mechanisms that are similar to other vertebrates, including humans.

Cognitive Psychophysiological Substrates of Affective Temperaments

Affective temperaments are the subclinical manifestations or phenotypes of mood states and hypothetically represent one healthy end of the mood disorder spectrum. However, there is a scarcity of studies investigating the neurobiological basis of affective temperaments. One fundamental aspect of temperament is the behavioral reactivity to environmental stimuli, which can be effectively evaluated by use of cognitive event-related potentials (ERPs) reflecting the diversity of information processing. The aim of the present study is to explore the associations between P300 and the affective temperamental traits in healthy individuals. We recorded the P300 ERP waves using an auditory oddball paradigm in 50 medical student volunteers (23 females, 27 males). Participants' affective temperaments were evaluated using the Temperament Evaluation of Memphis, Pisa, Paris, and San Diego-auto questionnaire version (TEMPS-A). In bivariate analyses, depressive temperament score was significantly correlated with P300 latency ( r_s = 0.37, P < .01). In a multiple linear regression analysis, P300 latency showed a significant positive correlation with scores of depressive temperament (β = 0.40, P < .01) and a significant negative one with scores of cyclothymic temperament (β = -0.29, P = .03). Affective temperament scores were not associated with P300 amplitude and reaction times. These results indicate that affective temperaments are related to information processing in the brain. Depressive temperament may be characterized by decreased physiological arousal and slower information processing, while the opposite was observed for cyclothymic temperament.

Temperament and character traits in patients with tinnitus: a prospective case series with comparisons

OBJECTIVE

To describe the personality traits of temperament and character in patients with tinnitus and to identify differences in these traits associated with the severity of tinnitus.

STUDY DESIGN

Case series with comparisons.

SETTING

Tertiary referral centre.

PARTICIPANTS

From January to December 2014, one hundred and thirty-four adult patients with chronic subjective tinnitus completed psychoacoustic measurements of tinnitus and the Temperament and Character Inventory (TCI).

MEASUREMENTS

Personality traits were assessed by the TCI. The TCI assesses seven dimensions of personality traits and four temperaments 'novelty seeking, harm avoidance, reward dependence, persistence', as well as three characters 'self-directedness, cooperativeness, self-transcendence'.

MAIN OUTCOME MEASURES

The values of the TCI parameters in the tinnitus patients were compared with reference data from a non-institutional adult population, and associations between TCI parameter values and tinnitus severity were evaluated.

RESULTS

In terms of temperament, tinnitus patients had higher scores for 'harm avoidance', whereas scores for 'novelty seeking', 'reward dependence' and 'persistence' were significantly lower than the reference. In terms of character, lower 'cooperativeness' and 'self-transcendence' were identified in the subjects with tinnitus. The 'novelty seeking' score was inversely related to tinnitus severity (r = -0.285, P = 0.001), while other temperament and character traits did not show significant correlations.

CONCLUSIONS

There may be a connection between tinnitus and personality traits, especially in the case of 'novelty seeking', which is relatively constant over a lifetime. The TCI questionnaire may be useful in facilitating the application of personality traits to tailored counselling for tinnitus.

Youth with substance abuse histories exhibit dysfunctional representation of expected value during a passive avoidance task

Individuals with substance abuse (SA) histories show impairment in the computations necessary for decision-making, including expected value (EV) and prediction error (PE). Neuroimaging findings, however, have been inconsistent. Sixteen youth with (SApositive) and 29 youth without (SAnegative) substance abuse histories completed a passive avoidance task while undergoing functional MRI. The groups did not significantly differ on age, gender composition or IQ. Behavioral results indicated that SApositive youth showed significantly less learning than SAnegative youth over the task. SApositive youth show problems representing EV information when attempting to avoid sub-optimal choices in bilateral inferior frontal gyrus and striatum. Furthermore, SApositive youth showed a significantly increased differential response to reward versus punishment feedback modulated by PE in posterior cingulate cortex relative to SAnegative youth. Disrupted decision-making is likely to exacerbate SA as a failure to represent EV during the avoidance of sub-optimal choices is likely to increase the likelihood of SA. With respect to the representation of PE, future work will be needed to clarify the impact of different substances on the neural systems underpinning PE representation. Moreover, interaction of age/development and substance abuse on PE signaling will need to be explored.

Ethanol and Caffeine Effects on Social Interaction and Recognition in Mice: Involvement of Adenosine A2A and A1 Receptors

Ethanol and caffeine are frequently consumed in combination and have opposite effects on the adenosine system: ethanol metabolism leads to an increase in adenosine levels, while caffeine is a non-selective adenosine A1/A2A receptor antagonist. These receptors are highly expressed in striatum and olfactory tubercle, brain areas involved in exploration and social interaction in rodents. Ethanol modulates social interaction processes, but the role of adenosine in social behavior is still poorly understood. The present work was undertaken to study the impact of ethanol, caffeine and their combination on social behavior, and to explore the involvement of A1 and A2A receptors on those actions. Male CD1 mice were evaluated in a social interaction three-chamber paradigm, for preference of conspecific vs. object, and also for long-term recognition memory of familiar vs. novel conspecific. Ethanol showed a biphasic effect, with low doses (0.25 g/kg) increasing social contact and higher doses (1.0-1.5 g/kg) reducing social interaction. However, no dose changed social preference; mice always spent more time sniffing the conspecific than the object, independently of the ethanol dose. Ethanol, even at doses that did not change social exploration, produced amnestic effects on social recognition the following day. Caffeine reduced social contact (15.0-60.0 mg/kg), and even blocked social preference at higher doses (30.0-60.0 mg/kg). The A1 antagonist Cyclopentyltheophylline (CPT; 3-9 mg/kg) did not modify social contact or preference on its own, and the A2A antagonist MSX-3 (1.5-6 mg/kg) increased social interaction at all doses. Ethanol at intermediate doses (0.5-1.0 g/kg) was able to reverse the reduction in social exploration induced by caffeine (15.0-30.0 mg/kg). Although there was no interaction between ethanol and CPT or MSX-3 on social exploration in the first day, MSX-3 blocked the amnestic effects of ethanol observed on the following day. Thus, ethanol impairs the formation of social memories, and A2A adenosine antagonists can prevent the amnestic effects of ethanol, so that animals can recognize familiar conspecifics. On the other hand, ethanol can counteract the social withdrawal induced by caffeine, a non-selective adenosine A1/A2A receptor antagonist. These results show the complex set of interactions between ethanol and caffeine, some of which could be the result of the opposing effects they have in modulating the adenosine system.

Picture Novelty Influences Response Selection and Inhibition: The Role of the In-Group Bias and Task-Difficulty

The human visual system prioritizes processing of novel information, leading to faster detection of novel stimuli. Novelty facilitates conflict resolution through the enhanced early perceptual processing. However, the role of novel information processing during the conflict-related response selection and inhibition remains unclear. Here, we used a face-gender classification version of the Simon task and manipulated task-difficulty and novelty of task-relevant information. The novel quality of stimuli was made task-irrelevant, and an in-group bias was tightly controlled by manipulation of a gender of picture stimuli. We found that the in-group bias modulated the role of novelty in executive control. Novel opposite-sex stimuli facilitated response inhibition only when the task was not demanding. By contrast, novelty enhanced response selection irrespective of the in-group factor when task-difficulty was increased. These findings support the in-group bias mechanism of visual processing, in cases when attentional resources are not limited by a demanding task. The results are further discussed along the lines of the attentional load theory and neural mechanisms of response-inhibition and locomotor activity. In conclusion, our data showed that processing of novel information may enhance executive control through facilitated response selection and inhibition.

Influence of the Novelty-Seeking Endophenotype on the Rewarding Effects of Psychostimulant Drugs in Animal Models

Novelty seeking (NS), defined as a tendency to pursue novel and intense emotional sensations and experiences, is one of the most relevant individual factors predicting drug use among humans. High novelty seeking (HNS) individuals present an increased risk of drug use compared to low novelty seekers. The NS endophenotype may explain some of the differences observed among individuals exposed to drugs of abuse in adolescence. However, there is little research about the particular response of adolescents to drugs of abuse in function of this endophenotype, and the data that do exist are inconclusive. The present work reviews the literature regarding the influence of NS on psychostimulant reward, with particular focus on adolescent subjects. First, the different animal models of NS and the importance of this endophenotype in adolescence are discussed. Later, studies that have used the most common animal models of reward (self-administration, conditioned place preference paradigms) to evaluate how the NS trait influences the rewarding effects of psychostimulants are reviewed. Finally, possible explanations for the enhanced risk of developing substance dependence among HNS individuals are discussed. In conclusion, the studies referred to in this review show that the HNS trait is associated with: (1) increased initial sensitivity to the rewarding effects of psychostimulants, (2) a higher level of drug craving when the subject is exposed to the environmental cues associated with the drug, and (3) enhanced long-term vulnerability to relapse to drug consumption after prolonged abstinence.

Amygdala and Ventral Striatum Make Distinct Contributions to Reinforcement Learning

Reinforcement learning (RL) theories posit that dopaminergic signals are integrated within the striatum to associate choices with outcomes. Often overlooked is that the amygdala also receives dopaminergic input and is involved in Pavlovian processes that influence choice behavior. To determine the relative contributions of the ventral striatum (VS) and amygdala to appetitive RL, we tested rhesus macaques with VS or amygdala lesions on deterministic and stochastic versions of a two-arm bandit reversal learning task. When learning was characterized with an RL model relative to controls, amygdala lesions caused general decreases in learning from positive feedback and choice consistency. By comparison, VS lesions only affected learning in the stochastic task. Moreover, the VS lesions hastened the monkeys' choice reaction times, which emphasized a speed-accuracy trade-off that accounted for errors in deterministic learning. These results update standard accounts of RL by emphasizing distinct contributions of the amygdala and VS to RL.

Models of neuromodulation for computational psychiatry

Psychiatry faces fundamental challenges: based on a syndrome-based nosology, it presently lacks clinical tests to infer on disease processes that cause symptoms of individual patients and must resort to trial-and-error treatment strategies. These challenges have fueled the recent emergence of a novel field-computational psychiatry-that strives for mathematical models of disease processes at physiological and computational (information processing) levels. This review is motivated by one particular goal of computational psychiatry: the development of 'computational assays' that can be applied to behavioral or neuroimaging data from individual patients and support differential diagnosis and guiding patient-specific treatment. Because the majority of available pharmacotherapeutic approaches in psychiatry target neuromodulatory transmitters, models that infer (patho)physiological and (patho)computational actions of different neuromodulatory transmitters are of central interest for computational psychiatry. This article reviews the (many) outstanding questions on the computational roles of neuromodulators (dopamine, acetylcholine, serotonin, and noradrenaline), outlines available evidence, and discusses promises and pitfalls in translating these findings to clinical applications. WIREs Cogn Sci 2017, 8:e1420. doi: 10.1002/wcs.1420 For further resources related to this article, please visit the WIREs website.