Thesis (Ph.D.)--Kent State University, 2007. / Title from PDF t.p. (viewed Jan. 16, 2007) Advisor: Chet C. Sherwood. Includes bibliographical references (p. 165-198)

Proefschrift Rijksuniversiteit Groningen. / Met lit.opg. - Met samenvatting in het Nederlands.

<p>Animals must continuously move through the environment in pursuit of the goals required to maintain homeostasis. In vertebrates, this is accomplished through an ever-changing pattern of muscle contraction in a multipurpose body, and coordinated by a hierarchy of neural circuits acting in parallel. At the lower levels of this hierarchy, spinal circuits control muscle force and length. One level above that, brainstem, midbrain and cortical circuits control various aspects of body configuration as well as a number of self-contained motor functions including locomotion and orientation. A still-higher level of organization is controlled by the basal ganglia, a set of subcortical nuclei that appear to be responsible for continuously orchestrating the extent and direction of various motor programs and body configurations for the sake of controlling a still higher level of perceptual variable, such as proximity to food. In this way, the basal ganglia orchestrate the performance of motor functions to achieve a single goal in the same way that a conductor orchestrates the performance of musicians in a symphony to achieve a single song. </p><p>Despite the continuous and graded nature of animal behavior, researchers have traditionally studied the basal ganglia in the context of highly controlled experimental tasks or neglected to record continuous measures of behavioral outputs. To address this gap, the following experiments were designed investigate role of the basal ganglia in continuously modulating unconstrained goal directed movements. In the first set of experiments (chapter 2), mice stood on a small covered perch which was continuously tipped left and right along the roll plane while neural activity was recorded wirelessly. During each recording session, mice were exposed to slow and fast speeds of postural disturbance. Pressure pads were mounted in the left and right floor of the perch to monitor mouse movement. In both putative dopamine and GABA neurons, we found two basic patterns of neural activity; one class of cell increased firing with tip to the left and decreased with tip to the right while the other class decreased firing with tip to the left and increased with tip to right. This correlation between neural firing rate and instantaneous postural disturbance is continuous and very high. The correlation is seen for both slow and fast disturbances. The majority of cells recorded fell into one of these two categories. Pressure pad readout, as expected, revealed paw forces on the left pad to increase with tilt to the left and decrease with tilt to the right while the opposite pattern was observed on the right pad. These results show continuous and graded modulation of activity in the substantia nigra during performance of an ongoing motor task and suggest that BG outputs, rather than monolithically disinhibiting brainstem motor structures, instead coordinate behavior by continuously specifying desired states of lower systems. </p><p>In the second set of experiments (chapter 3), we employed continuous motion tracking of the head in parallel with neural recording from the substantia nigra pars reticulata during a simple goal-directed task. In this study, mice were water deprived and then positioned on a perch equipped with a movable drinking spout. During each session, mice performed a simple reward-guided task in which sucrose solution was delivered in small quantities after the presentation a cue. The purpose of this task was to elicit voluntary head movements and to investigate the relationship between these continuous movements and the activity of GABA output neurons. A typical reward-directed behavior involved the movement of the whole head and body to collect the sucrose solution following its delivery. However, movements during each individual trial were unique. For all movements, the majority of GABA cells were found to either positively or negatively correlate with either X or Y axis head position vector components. These correlations were very high, and not due to averaging artifacts as trial-by-trial correlation between movement and neural activity can be clearly observed. These correlations were also independent of the presence of a reward. These data show for the first time a continuous and quantitative relationship between basal ganglia output and body posture. It is hypothesized that these signals represent reference signals sent to downstream postural and orientation controllers. In this case a baseline level of GABA activity would represent neutral reference position, and changes in activity above and below this level represent increased or decreased reference positions. </p><p>In the third set of experiments (chapter 4), we recorded from dopamine neurons in the substantia nigra pars compacta during the same task as in chapter 3. The purpose of this task was to investigate the correlation between dopamine activity and movement kinematics during goal-directed behavior. Animals were found to produce movements at the onset of the cue and also at reward delivery. Dopamine-classified cells show phasic firing or pausing at the onset of each of these movements. When compared to head movement kinematics, these patterns of neural activity correlate highly with different vector components of head acceleration and velocity; up, down, left and right. Importantly, these correlations are continuous and exist throughout the entire recording session. These correlations are also independent of the presence of reward. To test the ‘causality’ of these observed patterns, we also employed optogenetics to stimulate substantia nigra dopamine neurons expressing channel rhodopsin 2 (Chr2) while head movements were recorded and quantified. We found that stimulation of ChR2-expressing animals could elicit head movement while stimulation of control animals had no effect. Combined, these data suggest that dopamine is responsible for controlling the velocity of transitions between different body postures.</p> / Dissertation

An abstract of the thesis of Casie S. Bass, for the Masters of Science degree in Animal Science, presented on April 7, 2010 at Southern Illinois University Carbondale. TITLE: CABERGOLINE EFFECTS ON MARE ESTROUS BEHAVIOR, CYCLICITY, AND ENDOCRINE PROFILES MAJOR PROFESSOR: DR. SHERYL S. KING Adding to the seasonal reproductive perplexity in the mare, many researchers support the idea that multiple controllers may "drive" this event, including both hormonal and neural regulators. Evidence supports the theory that dopamine can exert direct action on the equine ovary independent of prolactin (Jeffcoate, 1993; King et al., 2005). Operating on the hypothesis that dopamine causes direct inhibitory actions within the mare ovary, the present investigation was designed to examine the ovarian, hormonal, and reproductive behavior responses to longterm stimulation of dopamine D2 receptors on the cycling ovary. We hypothesized that the dopamine agonist, cabergoline, would induce a autumnal transitional-like ovarian function in summer cycling mares. More specifically, cabergoline-treated mares would express decreased circulating prolactin, decreased luteal progesterone levels, slowed follicular growth leading to longer estrous cycles, an increased incidence of luteolytic failure resulting in spontaneous prolonged corpora lutea, and possibly a decrease in the intensity of estrous behavior. Cabergoline, a dopamine agonist, was administered orally to cycling mares during the peak breeding season. Reproductive behavior, ovarian and cervical activity, and endocrine profiles were assessed. Results from the present study demonstrated a suppression of prolactin after cabergoline administration, a unique ambivalent effect that dopamine appears to exert on sexual behavior, and a possible suppression-effect during diestrous follicle development in the mare.

nÃo hà / O etanol tem influÃncia sobre diversos sistemas de neurotransmissores. VÃrios estudos tÃm relatado a interaÃÃo entre a via dopaminÃrgica e colinÃrgica e a interaÃÃo delas isoladamente com os efeitos do etanol. O bloqueador colinÃrgico atropina, que à um alcalÃide muito utilizado no caso de intoxicaÃÃes colinÃrgica e comprometimento cardÃaco e o haloperidol, à neurolÃptico, antagonista das vias dopaminÃrgicas, principalmente pelo bloqueio do receptor D2, utilizado no tratamento da esquizofrenia, tanto na fase aguda como crÃnica, psicoses e episÃdios manÃacos psicÃticos sÃo fÃrmacos utilizados para o estudo desses sistemas. Este trabalho objetivou estudar os efeitos comportamentais e neuroquÃmicas produzidos em corpo estriado induzidos pelo tratamento subcrÃnico com etanol na presenÃa e ausÃncia de atropina ou haloperidol. Foram utilizados camundongos Swiss, fÃmeas, com peso variando entre 25 â 30g. Os animais foram tratados com Ãgua destilada (controle), etanol (1 ou 3g/kg, v.o) ou prà tratados com haloperidol (0,5mg/kg, i.p) ou atropina (0,5mg/kg, i.p), essa aplicaÃÃo foi feita trinta minutos antes da administraÃÃo do etanol ou Ãgua destilada diariamente durante sete dias.Trinta minutos apÃs a Ãltima administraÃÃo das drogas por via intraperitoneal ou sessenta minutos apÃs a Ãltima administraÃÃo por via oral, os animais foram submetidos aos testes comportamentais de campo aberto e rota rod (atividade locomotora), placa perfurada e plus maze (atividade de ansiedade) e, posteriormente, sacrificados com dissecaÃÃo do corpo estriado para determinaÃÃo dos nÃveis de monoaminas (norepinefrina, dopamina e seu metabÃlico Ãcido 3, 4-dihidroxifenilacÃtico) e a atividade da acetilcolinesterase. O etanol apresentou efeito estimulante na menor dose e depressor na maior dose, principalmente nos testes de atividade locomotora. Quando associado à maior dose, o haloperidol apresentou, na maioria das vezes o efeito potencializador do etanol, jà a atropina apenas em alguns testes mostrou uma tendÃncia de reversÃo desse efeito apenas associado ao etanol na menor dose, embora nÃo observado em todos os paramentos avaliados. AlÃm disso, o efeito produziu um discreto aumento nos nÃveis de dopamina no corpo estriado, porÃm quando associado aos bloqueadores, houve reduÃÃo desses nÃveis, sendo mais acentuada quando essa associaÃÃo foi feita com o etanol na maior dose. Na avaliaÃÃo da atividade da enzima acetilcolinesterase, todas as substÃncias utilizadas associadas ou nÃo, provocaram a reduÃÃo de mais de 60% na atividade desta enzima, sendo mais evidente na administraÃÃo isolada de atropina, ou seja, as administraÃÃes que apresentaram reduÃÃo significativa da concentraÃÃo de DA, apresentaram tambÃm a atividade da AchE reduzida, evidenciando a interaÃÃo desses dois sistemas, sugerindo-os como possÃveis alvos de aÃÃo no desenvolvimento de medicamento que coadjuvem no tratamento do alcoolismo / Ethanol is an agent with nonspecific action, which may interfere in various neurotransmitter systems. Atropine is an alkaloid with blocking action of the cholinergic system, used in cholinergic intoxication and other with cardiac involvement. The neuroleptic, haloperidol, is an antagonist of dopaminergic pathways, mainly by blocking the D2 receptor, used in the treatment of schizophrenia in both acute and chronic psychoses and maniac psychotic episodes. Several studies have reported the interaction between the dopaminergic and cholinergic pathway and their interaction separately with the ethanol. This study investigated the behavioral and neurochemical effects produced in the striatum induced by subchronic treatment with ethanol in presence and absence of atropine or haloperidol. Swiss mice were used, females, weighing between 25 - 30g. The animals were treated with distilled water (control), ethanol (1 or 3g/kg, po) or pre-treated with haloperidol (0.5 mg / kg, ip) or atropine (0.5 mg / kg, ip), this application was thirty minutes before administration of ethanol or distilled water daily for seven days. Thirty minutes after the last drug administration intraperitoneally or sixty minutes after the last oral administration, the animals were subjected to behavioral tests of open field and track rod (locomotors activity), hole board and plus maze (anxiety activity) and then sacrificed with dissection of the striatum for determination of monoamines (norepinephrine, dopamine and its metabolic acid 3, 4-dihydroxyphenylacetic) or the concentration of acetylcholinesterase. Ethanol showed a stimulating effect in depressing the lower dose and higher dose, especially in tests of locomotors activity. When associated with a higher dose, haloperidol showed, in most cases the potentiating effect of ethanol, since atropine in some tests only showed a tendency to reverse this effect only associated with ethanol at the lowest dose, although not observed in all parameters of evaluated. However, the effect produced a modest increase in the concentrations of dopamine in the striatum, but when associated with blockers, a reduction of these levels was more pronounced when the association was made with ethanol at the highest dose. In the evaluation of the enzyme acetylcholinesterase, all substances used, combined or not, reduced more than 60% levels this enzyme, being more evident in the administration of atropine alone, or the authorities which showed a significant reduction in the concentration of AD, also showed reduced AChE, showing the interaction of these two systems, suggesting them as possible targets of action of drug development which contribute to the treatment of alcoholism

CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel Superior / No presente trabalho, foi avaliado a interaÃÃo entre os sistemas dopaminÃrgico e colinÃrgico atravÃs do estudo dos efeitos comportamentais (campo aberto e catalepsia) e neuroquÃmicos (densidade de receptores dopaminÃrgicos (D1 e D2-sÃmile) e muscarÃnicos (M1+M2-sÃmile) em corpo estriado de rato. As seguintes drogas foram utilizadas: mazindol (agonista dopaminÃrgico indireto), apomorfina (agonista dopaminÃrgico D1-sÃmile e D2-sÃmile), pimozida (antagonista dopaminÃrgico D2-sÃmile), SCH 23390 (antagonista dopaminÃrgico D1-sÃmile), pilocarpina (agonista muscarÃnico M1-sÃmile), carbacol (agonista muscarÃnico M2-sÃmile), pirenzepina (antagonista muscarÃnico M1-sÃmile), atropina (antagonista muscarÃnico M1 e M2 nÃo seletivo), clozapina (neurolÃptico atÃpico). Os resultados mostraram que a pimozida e o carbacol, sozinhos ou associados, causaram um aumento da resposta catalÃptica e uma diminuiÃÃo da atividade locomotora. O mazindol tambÃm aumentou a atividade locomotora. Carbacol, nas menores doses, e o mazindol aumentaram a densidade de receptores D1-sÃmile. A pimozida e a atropina, isoladamente, aumentaram a densidade de receptores D1-sÃmile no corpo estriado enquanto que a atropina causou uma diminuiÃÃo dos receptores D2-sÃmile e uma upregulation dos receptores muscarÃnicos. O mazindol aumentou o binding de 3H-NMS no corpo estriado. O presente trabalho sugere, de maneira geral, que existe uma relaÃÃo entre os receptores muscarÃnicos M1 e M2 com os receptores dopaminÃrgicos D1 e D2, sendo que esta relaÃÃo pode ocorrer de maneira positiva ou negativa, dependendo da seletividade e da dose das drogas utilizadas / In the study, the interaction between the dopaminergic and cholinergic systems through the study of behavioral (open field and catalepsy) and neurochemical (density of dopaminergic receptor (D1 and D2-like) and muscarinic (M1+M2-like)) effect in striatum rat was evaluated. The following drugs were used: mazindol (indirect dopaminergic agonist), apomorphine (D1-like and D2-like dopaminergic agonist), pilocarpine (M1-like muscarnic aginist), carbachol (M-2like agonist muscarinc), pirenzepine (M1-like antagonist muscarinic), atropine (non-selective M1 and M2 antagonist muscarinic), clozapina(non-typical neuroleptic). The results showed that the pimozida and carbachol, alone or associated, caused increase in the cataleptic response and reduction in the motor activity. The mazindol also increased the motor activity. In small dosage, the carbachol and mazindol increased the density of D1-like receptors. Isolated, the pimozida and atropine increased the density of the D1-like receptors in striatum whereas the atropine caused a reduction of D2-like receptors and upregulation of muscarinic receptors. This work suggests a relationship, between muscarinc receptors M1 and M2 and dopaminergic receptors D1 and D2, and that this relationship can occur in a positive and negative manner, depending on the selectivity and the dose of the used drug

Este trabalho tem como objetivo principal a utilização da técnica “bottom-up” para a construção de nanoestruturas de ouro por meio de técnicas voltamétricas sobre uma superfície de Carbono Vítreo. Estas estruturas foram caracterizadas por métodos microscópicos e voltamétricos. A dimensão crítica das nanoestruturas foi obtida por meio de uma curva Gausseana de distribuição de alturas e diâmetros, fornecendo um valor médio de 35 nm por 150 nm de diâmetro. As nanoestruturas obtidas foram modificadas pela deposição de uma camada automontada de cistamina (um tiól), resultando num substrato adequado para futuras aplicações como a imobilização de enzimas. Os comportamentos eletroquímicos da dopamina e do ácido ascórbico, sobre eletrodos de ouro, Carbono Vítreo e Nanoestruturado, foram avaliados para a caracterização das modificações dos eletrodos. A diferença dos potenciais de pico de oxidação do AA sobre eletrodos de Carbono Vítreo e de ouro, de cerca de 300 mV, possibilitou avaliar o recobrimento do Carbono Vítreo com nanoestruturas pela diminuição da corrente de pico. Já a dopamina foi utilizada neste trabalho para determinar a presença da camada automontada de cistamina sobre a superfície das nanoestruturas de ouro, uma vez que sua resposta voltamétrica mostra um deslocamento do potencial de pico quando realizada sobre Au e sobre Au modificado com a camada automontada. / The subject of this work is focused in the utilization of a “bottom-up” approach to develop an Au nanostructured electrodeposits on the glassy carbon surface by a voltammetric procedure. These Au nanostructures have been characterized either by microscopic and voltammetric techniques. The critical dimensions of nanostructures has been evaluated by a Gausean normal data distribution curve and presented, as results a mean height of 35 nm and a mean diameter of 150 nm. The Au nanostructures were further modified by the deposition of a cystamine (thiol) self-assembled monolayer, yielding a suitable substrate for enzyme immobilization, as a possible future application. The electrochemical behaviour of dopamine and ascorbic acid on gold, Glassy Carbon and nanostructures was studied aiming to characterize the modified electrode. The 300 mV shift in the oxidation peak potential for ascorbic acid on gold in relation to Glassy Carbon allows to calculate the nanostructure coverage factor by the peak current inhibition as 43%. Finally, dopamine was employed to detect the self assembled monolayer formation on the Au nanostructure through its voltammetric behaviour. The variation in the oxidation potential for DA on gold and self assembled monolayer was used as an indicator for such modification.

The persistence of memory over time is dependent on a variety of events between learning and remembering, one of which is sleep. Additionally, the strength of initial learning influences how well things will be remembered later on, and the way the sleeping brain processes information has been found to rely on some of these encoding factors. Given the extensive literature on the influence of dopamine on learning, we wanted to examine how two memory benefits thought to rely on dopamine – the novelty effect and the curiosity effect – may be impacted by periods of sleep or wakefulness. Three experiments were conducted: one in which novel scenes were viewed and associated information was recalled after wakefulness or sleep, one where subjects learned in the lab or at home, and one in which participants rated their curiosity for learning materials and were tested later after sleep or wakefulness (and in which eye blink rate (EBR) and PSG measures were observed). Our findings failed to replicate the novelty effect in the first two experiments, making our prediction regarding sleep difficult to assess. Though we replicated the curiosity effect in the third study, our predictions about sleep and slow wave sleep were not supported. However, N2 and REM were unexpectedly observed to play a role in this effect, a finding that deserves more assessment. Finally, EBR, an indirect measure of dopamine, was negatively associated with the curiosity effect due to a positive relationship with the retention of low curiosity stimuli. Future research should investigate this sensitive novelty effect in humans further and continue to examine EBR as a predictor of learning.

Do you think we can concentrate in noisy situations? I bet most of us would spontaneously answer “no” to this apparent simple question. Although we admit it is intuitively the best answer to give, this thesis aims to evidence that it is not always true and that, under certain circumstances, noise can be beneficial.<p><p>To appropriately discuss this question, it is necessary to answer others, such as: what is concentrating, paying attention? And, what is noise? Everyone has an idea of what attention is, and can give examples of situations in which it is required: school, work, driving, listening to our parents’ requests and so forth. But who could say that we can fully control attention like if we had a button to press, switching on and off according to the context? When we were little, my father used to say to my brothers and me: “Ok, you did not do this on purpose, but, please, pay attention to your attention”. Well, I can say now that it is not that easy and certainly not for everyone. In the population, around five percent of children and adults meet serious difficulties to pay attention. These people, more than others, often express their deficit with excessive distraction and/or hyperactivity as well as impulsivity. These multiple symptoms, for the individual who lives these behavioral excesses, represent an issue for his/her everyday-life: at school, at work, driving, trying to listen to his/her parents’ requests, etc.<p><p>Such symptoms refer to a syndrome called attention-deficit/hyperactivity disorder (ADHD). Although the definition of this syndrome has changed across the course of History, the first descriptions of ADHD go back to 1798. Since, a lot has been written about this disorder, which we do not fully understand yet. Beyond these simple words, “inattention, impulsivity, hyperactivity”, a consequent number of etiologies (environmental, genetic, psychosocial), subtypes, comorbidities, and outcomes reflect the enormous heterogeneity of the phenotypes that are found in this syndrome. The main treatment offered to individuals with ADHD is a psychostimulant drug called methylphenidate. This medication, acting mainly on dopaminergic brain functioning, has proven efficacy regarding ADHD symptoms. However, it has several limitations. For instance, its use remains controversial in the society; it causes side effects and around 30% of individuals with ADHD do not respond to this treatment. These mentioned limitations, among others, highlight the necessity to find alternative ways to reduce ADHD symptoms.<p><p>This is the main objective of this thesis. To do so, we will investigate a counterintuitive phenomenon. In certain situations, what can be called noise might improve cognition and, consequently, potentially reduce the symptoms associated with ADHD. As mentioned in the beginning of this preamble, one could think that everything unnecessary in our direct environment is a potential distraction. Intuitively, a sensible person would suggest that individuals prone to distraction, as those with ADHD, would benefit from a stimulation- free environment to improve attention and reduce impulsivity as well as hyperactivity. However, already in the 1970’s, authors such as Zentall (1975) developed a theory supported by empirical data, i.e. the optimal stimulation theory, showing that adding stimulation in the environment (with pictures, posters, music, colors, etc.) might improve symptoms of children with ADHD. Successively, many theories and findings were developed and related to the observation that the environmental context affects attention, hyperactivity and impulsivity. For instance, the delay aversion theory (Sonuga-Barke, Taylor, Sembi, & Smith, 1992) suggests that, as children with ADHD are motivated to discount delay, the inattentive, overactive and impulsive behaviors are the expression of such aversion when they cannot avoid the delay. Related to this theory, adding stimulation in the environment has evidenced hyperactivity and impulsive choice reduction (Antrop, Roeyers, Van Oost, & Buysse, 2000; Antrop et al. 2006). Another theory advocates that the ADHD-related symptoms are explained in terms of energetic dysfunction (Sergeant, 2000). For instance, children with ADHD would meet difficulties to adjust their internal state (e.g. their arousal) required for a task. Accordingly, Sergeant (2000) suggested that performance is influenced not only by cognitive capacity but also by environmentally determined levels of arousal and showed the extent to which variations in these energetic factors can be managed to ensure optimal performance. A recent theory, called the Moderate Brain Arousal model (Sikstrom & Soderlund, 2007), particularly caught our interest. This theory postulates that white noise has beneficial effect on cognition. The first study of these authors (Soderlund, Sikstrom, & Smart, 2007) supported their hypothesis, showing that children with ADHD improved their episodic memory performance when they were exposed to white noise. This is, to our knowledge, the first study that evidenced such improvement with white noise, considered as extra-task stimulation, in children with ADHD.<p><p>The objective of this thesis is to investigate the potential beneficial effect of noise in individuals with and without ADHD regarding attentional and executive functioning. We will first review, in the first chapter of this Introduction, the general aspects of ADHD: definition criteria, prevalence, etiologies, treatments and outcomes. In the second chapter, we will present the main theories and findings related to this syndrome and to our main objective.<p>After the Introduction, we will describe the different experimental studies that we have carried out in the context of this thesis. Hereunder, we propose a short overview of these studies.<p>The first study of this thesis is a pilot study, aimed to validate the relevance to use event- related potentials (ERPs) in children with and without ADHD to further investigate noise effect. Accordingly, the second study investigated noise effect on behavioral and ERPs aspects in children with and without ADHD. To do so, children performed a visual cued Go/Nogo. They were also submitted to a neuropsychological assessment. Afterwards, in a third study, we used the same paradigm in adults with and without ADHD. Here, we also added a music condition to investigate another stimulation than noise.<p><p>In the fourth study, we decided to explore the effect of noise in a more ecological environment. To do so, we used a virtual reality tool that allowed to immerse the children in a virtual classroom environment. Children with and without ADHD were then assessed, being immersed in a classroom, with a continuous performance task (CPT) presented on the blackboard while several auditory and visual realistic distracters emerged during the test. Children performed the task with and without white noise exposure as well as a neuropsychological assessment. In the fifth study, we used the virtual classroom to investigate noise effect on interference control. Children with and without ADHD were submitted to a bimodal virtual reality Stroop (with auditory and visual target stimuli) and to a neuropsychological assessment. Finally, in a last study, we explored the effect of noise in consecutive young adults. Immersed in the virtual classroom, they were submitted to the CPT task with and without white noise. ADHD questionnaires and a neuropsychological assessment were also undertaken.<p><p>To end this thesis, we will discuss to what extent our studies allowed going one step further in the investigation of “on what, with whom, when and where” noise can be beneficial. We will discuss all our studies and results in the light of the theories and findings exposed in the Introduction. Finally, we will comment the clinical validation of these results.<p><p><p> / Doctorat en Sciences Psychologiques et de l'éducation / info:eu-repo/semantics/nonPublished

The placebo effect represents a fascinating example of how cognition can influence the physiology of the brain and body. The expectation of therapeutic benefit elicited by a placebo given in the guise of active medication has been proposed to be a form of reward expectation, and is associated with activation of brain reward circuitry. Prominent placebo effects occur in Parkinson’s disease (PD), where the expectation of symptom improvement stimulates dopamine release in the striatum. In the work described in this dissertation, positron emission tomography with [¹¹C] raclopride was used to investigate the relationship between the strength of expectation of benefit and the degree of dopamine release in PD, and how this relationship corresponds to current models of dopamine function in reward. Chapter 3 describes a pilot study conducted in patients who had undergone subthalamic nucleus deep-brain stimulation (STN-DBS) in which we examined how awareness of stimulator status (ON or OFF) affected synaptic dopamine levels compared to when subjects were blind. No difference was detected between conditions; however, it proved to be difficult to maintain blinding due to the profound effects of STN-DBS. Chapter 4 describes the development of the methodology for the analysis of high-resolution PET data, in which we utilized the combined efforts of neuroscience and imaging physics to optimize the analysis of [¹¹C] raclopride PET data. In Chapter 5, I describe the use of verbal instructions to manipulate patients’ expectations in order to investigate how the likelihood of receiving levodopa influenced dopamine release when the patients were in fact given placebo. Placebo-induced dopamine release was differentially modulated by expectation in the dorsal and ventral striatum: dopamine release in the putamen was related monotonically to expected reward value, whereas dopamine released in the ventral striatum reflected the uncertainty of benefit or the salience of the expectation. The placebo effect in PD therefore involves at least two related but separate mechanisms: the expectation of benefit itself, which is scaled to reflect the value of the drug to the patient and is mediated by nigrostriatal dopamine, and the uncertainty or salience of benefit that is mediated by mesolimbic dopamine. / Medicine, Faculty of / Graduate