Fatores como o tempo de espera ou o risco a ser enfrentado por uma recompensa maior têm um efeito importante e, por vezes, paradoxal no processo de tomada de decisão. O Capítulo I apresenta uma discussão teórica sobre a tomada de decisão mediada por esses dois fatores, bem como sua interligação com o conceito de impulsividade e o Transtorno de Déficit de Atenção e Hiperatividade (TDAH). O Capítulo II oferece uma aplicação desses conceitos em um modelo animal do espectro da Síndrome Alcoólica Fetal, condição que apresenta algumas características semelhantes ao TDAH. Utilizando ratos expostos ao álcool no período pré-natal, duas tarefas de tomada de decisão mediada por tempo ou probabilidade foram usadas para testar se esses animais apresentam diferenças em seus padrões de escolha. Não foram encontradas diferenças significativas entre grupos controle e experimentais. Futuros estudos com outros protocolos, espécies e/ou linhagens são desejáveis. / Factors such as the time to wait, or the risk to be faced for a bigger reward have an important and, sometimes, paradoxical effect on the decision making process. Chapter I presents a theoretical discussion about decision making mediated by these two factors, as well as how they relate to the concept of impulsivity and the Attention-Deficit Hyperactivity Disorder (ADHD). Chapter II offers a practical application of these concepts in an animal model of the spectrum of Fetal Alcohol Syndrome, a condition that presents some similar characterstics in comparison to ADHD. Using rats prenatally exposed to ethanol, two decision making tasks, mediated by time or probability, were used to test if these animals show any difference in their patterns of choice. No significant differences were found between control and experimental groups. Future studies with other protocols, species and/or strains are desirable.

Fatores como o tempo de espera ou o risco a ser enfrentado por uma recompensa maior têm um efeito importante e, por vezes, paradoxal no processo de tomada de decisão. O Capítulo I apresenta uma discussão teórica sobre a tomada de decisão mediada por esses dois fatores, bem como sua interligação com o conceito de impulsividade e o Transtorno de Déficit de Atenção e Hiperatividade (TDAH). O Capítulo II oferece uma aplicação desses conceitos em um modelo animal do espectro da Síndrome Alcoólica Fetal, condição que apresenta algumas características semelhantes ao TDAH. Utilizando ratos expostos ao álcool no período pré-natal, duas tarefas de tomada de decisão mediada por tempo ou probabilidade foram usadas para testar se esses animais apresentam diferenças em seus padrões de escolha. Não foram encontradas diferenças significativas entre grupos controle e experimentais. Futuros estudos com outros protocolos, espécies e/ou linhagens são desejáveis. / Factors such as the time to wait, or the risk to be faced for a bigger reward have an important and, sometimes, paradoxical effect on the decision making process. Chapter I presents a theoretical discussion about decision making mediated by these two factors, as well as how they relate to the concept of impulsivity and the Attention-Deficit Hyperactivity Disorder (ADHD). Chapter II offers a practical application of these concepts in an animal model of the spectrum of Fetal Alcohol Syndrome, a condition that presents some similar characterstics in comparison to ADHD. Using rats prenatally exposed to ethanol, two decision making tasks, mediated by time or probability, were used to test if these animals show any difference in their patterns of choice. No significant differences were found between control and experimental groups. Future studies with other protocols, species and/or strains are desirable.

Fatores como o tempo de espera ou o risco a ser enfrentado por uma recompensa maior têm um efeito importante e, por vezes, paradoxal no processo de tomada de decisão. O Capítulo I apresenta uma discussão teórica sobre a tomada de decisão mediada por esses dois fatores, bem como sua interligação com o conceito de impulsividade e o Transtorno de Déficit de Atenção e Hiperatividade (TDAH). O Capítulo II oferece uma aplicação desses conceitos em um modelo animal do espectro da Síndrome Alcoólica Fetal, condição que apresenta algumas características semelhantes ao TDAH. Utilizando ratos expostos ao álcool no período pré-natal, duas tarefas de tomada de decisão mediada por tempo ou probabilidade foram usadas para testar se esses animais apresentam diferenças em seus padrões de escolha. Não foram encontradas diferenças significativas entre grupos controle e experimentais. Futuros estudos com outros protocolos, espécies e/ou linhagens são desejáveis. / Factors such as the time to wait, or the risk to be faced for a bigger reward have an important and, sometimes, paradoxical effect on the decision making process. Chapter I presents a theoretical discussion about decision making mediated by these two factors, as well as how they relate to the concept of impulsivity and the Attention-Deficit Hyperactivity Disorder (ADHD). Chapter II offers a practical application of these concepts in an animal model of the spectrum of Fetal Alcohol Syndrome, a condition that presents some similar characterstics in comparison to ADHD. Using rats prenatally exposed to ethanol, two decision making tasks, mediated by time or probability, were used to test if these animals show any difference in their patterns of choice. No significant differences were found between control and experimental groups. Future studies with other protocols, species and/or strains are desirable.

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Background: The valuation of risks and the speed with which decisions are made and acted upon are important characteristics of everyone’s personality. These characteristics exist along a continuum that ranges from weak to strong expressions of impulsivity. In certain situations it is crucial to decide and react quickly. Yet these qualities can prove disadvantageous if they are expressed excessively and persistently. Self-reports, such as the Barratt Impulsiveness Scale, inquire long-term patterns of behavior to assess the level of trait impulsivity. Experimental paradigms, on the other hand, quantify specific impulsive facets, which depend rather on the current environment and state of the individual. These paradigms include decision-making tasks that capture impulsive facets such as the attitudes towards delays, risks and losses. Research indicates that these attitudes are governed by a valuation network of cortical and subcortical brain regions along with several neurotransmitters. Within this intricate network, frontostriatal circuits innervated by dopamine were identified as an important locus of control. Although a wealth of studies have subsequently examined the influence of the dopaminergic system on impulsive choice, the regulatory mechanisms remain largely unclear. This may originate from the interrelations within the valuation network but also from the complexity of the dopaminergic system itself. Seminal investigations have shown that this complicated interplay may be partly explained by an underlying inverted U-shaped function, which describes an optimal level of dopamine, flanked by increasing impulsivity in the context of sub- and supraoptimal signaling. Research Question: This work aimed to shed more light on the inverted-U theory by characterizing the contribution of dopaminergic signaling to trait and decisional impulsivity, and by clarifying whether the manipulation of decisional impulsivity through boosting striatal dopamine via L-DOPA depends on baseline signaling. We hypothesized that individuals with optimal striatal dopaminergic signaling as measured by [18F]DOPA positron emission tomography would feature low trait impulsivity as assessed with the Barratt Impulsiveness Scale. By contrast, individuals with suboptimal signaling were hypothesized to exhibit stronger trait impulsivity corresponding to higher scores on the Barratt Impulsiveness Scale. Assuming an inverted U-shaped function, we predicted that the dopamine precursor L-DOPA would reduce impulsive decisions in the latter but overdose individuals with an already optimal signaling and thus make their choice behavior more impulsive. Materials and Methods: The present studies combined trait and choice measures of impulsivity with the investigation of the dopaminergic system by positron emission tomography and a pharmacological manipulation. In a double-blind, randomized, placebo-controlled, counter-balanced, repeated measures design, 87 healthy adults completed a computerized decision-making test battery. The battery includes four tasks, each of which captures one distinct dimension of impulsive choice: a delay discounting task quantifies delay discounting, a probability discounting for gains task quantifies risk-seeking for gains, a probability discounting for losses task quantifies risk-seeking for losses and a mixed gambles task quantifies loss aversion. In order to test for baseline-dependent L-DOPA effects on these dimensions, we controlled for trait impulsivity (a suggested proxy for central dopamine) as assessed with the Barratt Impulsiveness Scale (N = 87) and striatal dopamine as measured by [18F]DOPA positron emission tomography (in 60 of the 87 participants). Results: Our findings highlight the complex role of dopamine in impulsivity and the heterogeneity of its underlying biology. Participants who scored relatively high on the Barratt Impulsiveness Scale appeared to benefit from L-DOPA, indicated by a decrease in delay discounting, risk-seeking for gains and loss aversion. Participants with low levels of impulsive personality traits as assessed with the Barratt Impulsiveness Scale, on the other hand, exhibited opposite changes in choice preference. Bearing in mind that trait impulsivity may be a behavioral expression of central dopamine, our results suggest an inverted U-shaped function in which impulsive decision-making arises from both sub- and supraoptimal dopaminergic activity. We found further support for an inverted U-shaped function when accounting for baseline dopamine as measured by [18F]DOPA positron emission tomography. Participants who had higher values on the Barratt Impulsiveness Scale featured low, presumably suboptimal, striatal dopamine signaling. After enhancing and possibly optimizing the basal signaling with L-DOPA, they discounted delays less and tended to less risk-seeking for gains and loss aversion. By contrast, participants with low trait impulsivity as assessed with the Barratt Impulsiveness Scale exhibited higher striatal dopamine, probably corresponding to optimal baseline activity as L-DOPA shifted their choice behavior in the opposite direction, thus indicating a dopamine overdose. The intake of L-DOPA had no influence on risk-seeking for losses, even when differences in trait impulsivity and basal levels of striatal dopamine were considered. Performance on tasks of the decision-making battery produced only few, weak intercorrelations, which implies that delay discounting, risk-seeking for gains, risk-seeking for losses and loss aversion represent dissociable aspects of choice. Conclusions: Our results endorse and extend previous findings that indicated an inverted U-shaped influence of dopamine on delay discounting and decisions under risk. Utilizing a battery of largely independent choice tasks, we were able to disentangle the effect of gains and losses on risky decisions. Whereas risk-seeking for gains seemed to depend on baseline dopamine signaling, we found no evidence for dopaminergic neurotransmission affecting risk-seeking for losses. Consistent with the literature, our data shows that self-reported trait impulsivity and experimentally measured decision-making dimensions are distinct phenomena within the multidimensional construct of impulsivity. Our analyses further revealed that choice measures were differentially related to dopaminergic activity, which suggests that they represent not merely descriptive distinctions but separable psychobiological decision-making processes. Since the regulation of choice probably spreads across neurotransmitter systems, more research on these systems is warranted. After identifying the precise mechanisms within each system, comprehensive studies of their interplay may ultimately uncover how impulsive decisions arise. Considering a series of studies that related steep delay discounting and excessive risk-seeking to poor health and mental illness, the acquired knowledge may also inform translational research on impulsivity-related maladies. / Hintergrund: Die Bewertung von Risiken und die Schnelligkeit mit der Entscheidungen getroffen und umgesetzt werden, sind wichtige Persönlichkeitsmerkmale eines jeden Menschen. Diese Merkmale existieren entlang eines Kontinuums, das von schwachen bis zu starken Ausprägungen von Impulsivität reicht. In bestimmten Situationen ist es entscheidend, schnell zu entscheiden und zu reagieren. Diese Eigenschaften können sich jedoch als nachteilig erweisen, wenn sie übermäßig und beharrlich zum Ausdruck gebracht werden. Selbstauskunftsberichte wie die Barratt-Impulsivitätsskala fragen nach überdauernden Verhaltensmustern, um den Grad impulsiver Persönlichkeit zu beurteilen. Experimentelle Paradigmen hingegen quantifizieren spezifische impulsive Facetten, die eher von der aktuellen Umwelt und Verfassung des Individuums abhängen. Zu diesen Paradigmen gehören Entscheidungsaufgaben, die impulsive Facetten wie die Einstellungen zu Verzögerungen, Risiken und Verlusten erfassen. Forschungsarbeiten legen nahe, dass diese Einstellungen von einem Bewertungsnetzwerk aus kortikalen und subkortikalen Hirnregionen zusammen mit mehreren Neurotransmittern gesteuert werden. Innerhalb dieses komplizierten Netzwerks wurden durch Dopamin innervierte frontostriatale Schaltkreise als wichtige Kontrollpunkte identifiziert. Obwohl nachfolgend eine Fülle von Studien den Einfluss des dopaminergen Systems auf impulsive Entscheidungen untersucht hat, bleiben die Regulationsmechanismen weitgehend unklar. Dies mag von den Wechselbeziehungen innerhalb des Bewertungsnetzwerks, aber auch von der Komplexität des dopaminergen Systems selbst herrühren. Bahnbrechende Untersuchungen haben gezeigt, dass dieses komplizierte Zusammenspiel teilweise durch eine zugrundeliegende umgekehrte U-Funktion erklärt werden könnte, die einen optimalen Dopamin-Spiegel flankiert von zunehmender Impulsivität bei sub- und supraoptimaler Signalgebung beschreibt. Fragestellung: Diese Arbeit zielte darauf ab, die umgekehrte U-Hypothese näher zu beleuchten, indem sie den Beitrag der dopaminergen Signalgebung zu Persönlichkeits- und Entscheidungsimpulsivität charakterisiert und klärt, ob die Manipulation der Entscheidungsimpulsivität durch Erhöhung des striatalen Dopamins mittels L-DOPA vom Baseline-Signal abhängt. Wir nahmen an, dass Individuen mit optimaler striataler dopaminerger Signalgebung, gemessen mit der 18F-DOPA Positronen-Emissions-Tomographie, eine geringe Persönlichkeitsimpulsivität aufweisen würden, die mit der Barratt-Impulsivitätsskala bewertet wurde. Bei Individuen mit suboptimaler Signalgebung vermuteten wir hingegen eine impulsivere Persönlichkeit, die höheren Werten auf der Barratt-Impulsivitätsskala entspricht. Unter Annahme einer umgekehrten U-Funktion prognostizierten wir, dass der Dopamin-Vorläufer L-DOPA bei letzteren impulsive Entscheidungen reduzieren würde, aber Individuen mit bereits optimaler Signalgebung überdosieren und somit deren Entscheidungsverhalten impulsiver machen würde. Material und Methoden: Die hier präsentierten Studien kombinierten Maße von Persönlichkeits- und Entscheidungsimpulsivität mit der Untersuchung des dopaminergen Systems mittels Positronen-Emissions-Tomographie und einer pharmakologischen Manipulation. In einem doppelblinden, randomisierten, placebokontrollierten, balancierten Messwiederholungsdesign absolvierten 87 gesunde Erwachsene eine computerbasierte Testbatterie zum Entscheidungsverhalten. Die Batterie umfasst vier Aufgaben, von denen jede eine bestimmte Dimension impulsiver Entscheidungsfindung erfasst: „Delay Discounting“ quantifiziert die Fähigkeit zum Belohnungsaufschub, „Probability Discounting for Gains“ quantifiziert das Risikoverhalten bei Gewinnen, „Probability Discounting for Losses“ quantifiziert das Risikoverhalten bei Verlusten und „Mixed Gambles“ quantifiziert die Verlustaversion. Um auf baseline-abhängige L-DOPA-Effekte bei diesen Dimensionen zu testen, kontrollierten wir für Persönlichkeitsimpulsivität (ein vorgeschlagener Proxy für zentrales Dopamin), die mit der Barratt-Impulsivitätsskala (N = 87) bewertet wurde, und für striatales Dopamin, das mit der 18F-DOPA Positronen-Emissions-Tomographie gemessen wurde (bei 60 der 87 Probanden und Probandinnen). Ergebnisse: Unsere Ergebnisse unterstreichen Dopamins komplexe Rolle in der Impulsivität und die Heterogenität der dieser zugrundeliegenden Biologie. Probanden und Probandinnen, die auf der Barratt-Impulsivitätsskala relativ hoch punkteten, schienen von L-DOPA zu profitieren, was sich in einer Abnahme der Abwertung von verzögerten Belohnungen, der Risikobereitschaft bei Gewinnen und der Verlustaversion zeigte. Probanden und Probandinnen mit einem geringen Grad an impulsiven Persönlichkeitszügen (bewertet mit der Barratt Impulsivitätsskala) zeigten dagegen entgegengesetzte Veränderungen in der Entscheidungspräferenz. In dem Bewusstsein, dass Persönlichkeitsimpulsivität ein Verhaltensausdruck zentralen Dopamins sein mag, suggerieren unsere Ergebnisse eine umgekehrte U-Funktion, bei der impulsives Entscheidungsverhalten sowohl aus sub- als auch supraoptimaler dopaminerger Aktivität erwächst. Wir fanden weiteren Anhalt für eine umgekehrte U-Funktion nach Berücksichtigung des Baseline-Dopamins, gemessen mit der 18F-DOPA Positronen-Emissions-Tomographie. Teilnehmer und Teilnehmerinnen mit höheren Werten auf der Barratt-Impulsivitätsskala wiesen eine niedrige, vermutlich suboptimale, striatale Dopamin-Signalgebung auf. Nach Erhöhung und möglicherweise Optimierung der basalen Signalgebung mittels L-DOPA werteten diese Verzögerungen weniger ab und neigten zu weniger Risikobereitschaft bei Gewinnen und Verlustaversion. Im Gegensatz dazu wiesen Teilnehmer und Teilnehmerinnen mit geringer Persönlichkeitsimpulsivität (bestimmt mit der Barratt-Impulsivitätsskala) ein höheres striatales Dopamin auf. Dies entsprach wahrscheinlich einer optimalen Baseline-Aktivität, da L-DOPA deren Entscheidungsverhalten in die entgegengesetzte Richtung verlagerte, hinweisend auf eine Dopamin-Überdosierung. Die Einnahme von L-DOPA hatte keinen Einfluss auf das Risikoverhalten bei Verlusten, selbst wenn Unterschiede in der Persönlichkeitsimpulsivität und den Basalspiegeln von striatalem Dopamin berücksichtigt wurden. Die Performanz in den Aufgaben der Entscheidungsbatterie war nur wenig und schwach untereinander korreliert, was impliziert, dass „Delay Discounting“, „Probability Discounting for Gains“, „Probability Discounting for Losses“ und „Mixed Gambles“ separate Entscheidungsaspekte repräsentieren. Schlussfolgerungen: Unsere Ergebnisse bestätigen und erweitern bisherige Erkenntnisse, die nahelegten, dass der Belohnungsaufschub und Entscheidungen unter Risiken unter einem umgekehrt U-förmigen Einfluss Dopamins stehen. Mit einer Batterie von weitgehend unabhängigen Entscheidungsaufgaben konnten wir die Effekte von Gewinnen und Verlusten auf riskante Entscheidungen auftrennen. Während das Risikoverhalten bei Gewinnen vom Baseline-Dopamin-Signal abhängig zu sein schien, fanden wir keine Hinweise dafür, dass sich die dopaminerge Neurotransmission auf das Risikoverhalten bei Verlusten auswirkt. Übereinstimmend mit der Literatur zeigen unsere Daten, dass selbstberichtete Persönlichkeitsimpulsivität und experimentell gemessene Entscheidungsdimensionen unterschiedliche Phänomene innerhalb des mehrdimensionalen Konstrukts der Impulsivität sind. Unsere Analysen ergaben ferner, dass Entscheidungsmaße in unterschiedlicher Beziehung zu dopaminerger Aktivität standen. Dies legt nahe, dass diese nicht nur beschreibende Unterscheidungen, sondern separate psychobiologische Entscheidungsprozesse darstellen. Da die Regulierung von Entscheidungen wahrscheinlich mehrere Neurotransmittersysteme umfasst, ist die weitere Erforschung dieser Systeme gerechtfertigt. Nach Identifizierung der genauen Mechanismen innerhalb jedes Systems könnten umfassende Studien zu deren Zusammenwirken letztlich aufdecken, wie impulsive Entscheidungen entstehen. Angesichts einer Reihe von Studien, die eine geringe Fähigkeit zum Belohnungsaufschub und eine übermäßige Risikobereitschaft mit schlechter Gesundheit und psychischen Erkrankungen in Verbindung brachten, könnte das erworbene Wissen auch in die translationale Erforschung impulsivitätsassoziierter Krankheiten einfließen.

Systematic manipulations of the order in which questions are presented in hypothetical discounting tasks have shown that individual responses vary as a result of these manipulations. For example, Robles and Vargas (2007, 2008) and Robles, Vargas, and Bejarano (2009) demonstrated that individual discounting rates systematically change if questions are presented in a random, ascending, or descending order. The purpose of this study was to examine if specific sequential manipulations affected individual k values when using the Kirby, Petry, and Bickel (1999) 27-item Monetary Choice Questionnaire (MCQ). In a single session, participants (undergraduate students, N = 80), answered two MCQs. One of the MCQs was the standard Kirby et al. (1999) MCQ and the other was the MCQ with the question sequence altered systematically. Within-subject results suggest that individual k values are consistent when comparing k values from the two MCQs completed by each individual. In most cases, individual k values between MCQs did not vary substantially. Additionally, there was a statistically significant correlation between both MCQ administrations for each group. Results from this study indicate that k values obtained using the MCQ are reliable when question sequence is altered.

Fluctuating ovarian hormones have been shown to affect decision-making processes in women. While emerging evidence suggests effects of endogenous ovarian hormones such as estradiol and progesterone on value-based decision-making in women, the impact of exogenous synthetic hormones, as in most oral contraceptives, is not clear. In a between-subjects design, we assessed measures of value-based decision-making in three groups of women aged 18 to 29 years, during (1) active oral contraceptive intake (N = 22), (2) the early follicular phase of the natural menstrual cycle (N = 20), and (3) the periovulatory phase of the natural menstrual cycle (N = 20). Estradiol, progesterone, testosterone, and sex-hormone binding globulin levels were assessed in all groups via blood samples. We used a test battery which measured different facets of value-based decision-making: delay discounting, risk-aversion, risk-seeking, and loss aversion. While hormonal levels did show the expected patterns for the three groups, there were no differences in value-based decision-making parameters. Consequently, Bayes factors showed conclusive evidence in support of the null hypothesis. We conclude that women on oral contraceptives show no differences in value-based decision-making compared to the early follicular and periovulatory natural menstrual cycle phases.

Decisions on measures reducing environmental damage or improving environmental impact are usually constrained by financial limitations. Eco-efficiency analysis has emerged as a practical decision support tool by integrating environmental and economic performance. Environmental impact, as well as economic revenues and expenses, are usually distributed over a certain time scale. The temporal distribution of economic data is frequently assessed by discounting while discounting of environmental impact is rather uncommon. The scope of this paper is to reveal if this assumed inconsistency is common in eco-efficiency assessment literature, what reasons and interrelations with indicators exist and what solutions are proposed. Therefore, a systematic literature review is conducted and 35 publications are assessed. Theoretical eco-efficiency definitions and applied eco-efficiency indicators, as well as applied environmental and economic assessment methods, are compared here, but it is revealed that none of the empirical literature findings applied or discussed environmental discounting. It was, however, found in methodical literature. It is concluded that the theoretical foundation for the application of discounting on environmental impact is still insufficient and that even the theoretical foundation of economic discounting in studies is often poor. Further research and, eventually, a practical framework for environmental discounting would be beneficial for better-founded, more “eco-efficient” decisions.

Doctor of Philosophy / Department of Psychology / Gary L. Brase / This research tested a general mediation model which proposes that individual differences (e.g., impulsivity, delay discounting, and time orientation) mediate the relationship between time perception (one’s subjective experience of the passage of time relative to actual time) and intertemporal behavior (decision-making involving tradeoffs between costs and rewards in both the present and the future). Study I did not find evidence to support the general mediation model and found that time perception was only weakly correlated with individual differences and intertemporal behavior (average r = .06) . Study II found tentative support for the proposed mediation model: individual differences in impulsivity fully mediated the relationship between time perception and intertemporal behavior in 4 separate mediation models. Three additional mediation models met the assumptions of mediation, demonstrating indirect effects significantly different from zero, but did not fully mediate the relationship between time perception and intertemporal behavior. In general, the mediation models explored in Study II (both fully and partially mediated) suggest that self-report impulsivity mediates the relationship between time perception and intertemporal health behaviors, like hours of sleep slept per night, sociosexual orientation, and frequency of eating breakfast. The findings from Study II suggest that how time is perceived influences intertemporal behavior indirectly by influencing impulsivity. Guidelines to aid future research linking time perception to individual differences and intertemporal behavior are provided.

Individuals experience risk ubiquitously, but measuring risk taking is difficult. The balloon analogue risk task (BART) was developed in order to assess risk taking through having subjects press a key that accrues reward but also risk losing all reward with each press. In humans, greater responding in this task is associated with other maladaptive risk taking behaviors. The present research modeled this relationship in pigeons due to their previously shown propensity towards risk taking behavior. Experiment 1 used an unsignaled balloon task in which losing could only occur after 5 pecks. Results showed below optimal performance with greater pecks associated with faster acquisition of risk taking in the suboptimal choice task and evidence of modulation by delay discounting measures. Experiment 2 signaled the number of pecks with colors and tested multiple hoppers as a reinforcement modality to increase performance. Results showed only signaling the number of pecks improved performance and was related to performance in the high risk BART task. Both the low and high risk variants were associated with slower suboptimal choice acquisition and again had evidence of modulation by delay discounting measures. Potential shared underlying mechanisms are discussed.