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Exploring the neural, neurochemical and molecular basis of impulsivity and risky decision making, particularly as these cognitive traits relate to addiction disorders. Most of the work we do uses rat models of cognitive behaviour, but we are starting to translate our findings into human subjects.
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Graduate Student Supervision
Doctoral Student Supervision (Jan 2008 - May 2019)
Choosing adaptively among candidate actions requires a cost-benefit analysis, inwhich potential rewards are considered against the costs required to obtain them.One cost frequently encountered by humans is the cost of cognitive effort, inwhich executive processes spanning attention, working memory, reasoning, andthe like are taxed. This form of effort is in contrast to the physical effort costs thathave generally been the focus of the cost/benefit decision-making literature. Thisthesis reviews the currently available literature investigating the brain regions andneurotransmitter systems guiding these respective forms of decision making, andthen carries out a set of experiments to further characterize the neurobiologyguiding cognitive effort allocation. These experiments utilize an animal model ofdecision making known as the rodent Cognitive Effort Task (rCET), in whichsubjects decide whether to exert more attention in pursuit of larger rewards, or toobtain smaller reward for comparatively less attentional demand. In experiment1, I use chemogenetics to downregulate cholinergic neurons of the basalforebrain as rats perform the rCET, to determine whether this neuronalpopulation is responsible for the previously ascribed role of acetylcholine inregulating decision making with cognitive effort costs. Experiments 2 and 3 usestandard inactivation techniques to investigate striatal and orbitofrontal cortexcontributions to this form of decision making, and Experiment 4 uses adisconnection procedure to assess whether BLA- ACC signaling regulates willingness to apply cognitive effort. Collectively, the current findings complementexisting work in the domain of physical effort allocation, and support the notionthat these two forms of effort-based decision making are mediated by distinct,albeit overlapping circuitries. While this work fundamentally contributes to anunderstanding of how organisms navigate their environment, it also has practicalutility. Indeed, work with the rCET and related cognitive effort paradigms mayhelp identify behavioural or pharmacological therapies that can boost cognitivewillingness. Alternatively, information gained may shed light on the aberrantprocesses underlying a blunted desire to achieve lucrative outcomes, asobserved in disorders like depression, schizophrenia, and Parkinson’s Disease.
Addiction is a chronic relapsing psychiatric disorder affecting millions worldwide. Despite years of research investigating the etiology and phenomenology of substance abuse, there is no cure. Determining factors which promote the addictive phenotype may help to discover new therapeutics. Several clinical studies have shown addicts demonstrate poor cost/benefit decision making as measured by validated tasks such as the Iowa Gambling Task (IGT), a cognitive deficit maintained during periods of abstinence and associated with relapse risk. However, it is unclear whether disadvantageous choice precedes or is the consequence of drug abuse. Furthermore, dopaminergic signalling, actively recruited by drugs of abuse, has also been implicated in decision-making biases, and may contribute to choice deficits after drug exposure. The experiments here explored the role of disadvantageous choice in addiction susceptibility using rodent analogues of the IGT, the rat gambling task (rGT) and cued rat gambling task (crGT). These paradigms require the animal to choose between four different nose poke options which are associated with sugar wins, probabilities of winning, and timeouts. The crGT also includes salient reward-paired cues to enhance risky decision making. The first two experiments assessed whether baseline risk-preference on the rGT and crGT affected drug seeking as measured by cocaine self-administration, and whether drug exposure affected task performance. The third study examined the influence of task experience on the locomotor response to cocaine and responding for conditioned reinforcement, two dopamine-dependent behavioural assays associated with addiction risk. Basal and cocaine-induced nucleus accumbens dopamine release was also assessed using microdialysis after task training. The final study used chemogenetics to reduce nucleus accumbens dopamine to investigate the role of dopaminergic tone in choice biases. Our results show poor decision making precedes drug exposure, and is uniquely susceptible to drug-induced cognitive deficits. crGT rats showed greater drug seeking and sensitivity to cocaine-induced choice impairments, a phenotype linked to basal accumbal dopamine efflux. Finally, by reducing accumbens dopamine, animals showed marked reductions in risky choice. These data support the conclusion that poor decision making may serve as a cognitive endophenotype for addiction via aberrant dopaminergic signaling within the mesostriatal network.
No abstract available.
Gambling is an enjoyable and innocuous past-time for many, but for some it can become a maladaptive compulsion akin to drug or alcohol addiction. Despite increasing recognition that the phenomenological process underlying both substance and behavioural addictions may be similar, treatment options for problem gambling remain limited, and of questionable efficacy. Animal models offer an invaluable opportunity to not only study the underlying neurobiology of disorders such as gambling, but may also facilitate the development of novel pharmacotherapies. To that end we have developed a rodent slot machine task (rSMT) that suggests rats share key behavioural features with human gamblers. The dopamine D₂-like receptor family is critically involved in modulating animals’ performance on the rSMT. Specifically, the D₄ receptor appears to contribute to animals’ attributions of salience to game-related stimuli. D₄ receptors are principally located within prefrontal cortical regions and consequently represent an intriguing target for modulating higher order cognitive processes. In addition to systemic pharmacology, we have demonstrated that disruption of neural regions that are relatively rich in D₄ receptors, such as the anterior cingulate and insular cortex, impact animals’ ability to accurately respond to reward-related stimuli on the rSMT; further emphasising a role for these receptors in gambling-related decision making.Additionally, we have used the rSMT to try and model iatrogenic gambling observed in patients with Parkinson’s disease (PD). This form of compulsive gambling arises de-novo in a small but significant sub-set of patients following adjunctive therapy with D₂-like agonists. Chronic administration of a D₂/₃ receptor agonist galvanized performance on the rSMT, a finding that could be considered translationally analogous to the compulsive play exhibited by some PD patients. These alterations in performance were accompanied by an increase in the transcription factor pCREB in the nucleus accumbens. Administration of the β-adrenoreceptor blocker propranolol, which putatively attenuates this increase in pCREB, ameliorates the compulsive-like task engagement. Ultimately, gambling is a heterogeneous disorder that is unlikely to have a single underlying aetiology. However, these data indicate that aberrant dopaminergic signalling within the D2-like receptor family may underlie at least some of the cognitive perturbations observed in problem gambling.
Amotivational states and insufficient recruitment of mental effort have been observed in a variety of clinical populations, including depression, traumatic brain injury, post-traumatic stress disorder, and attention-deficit/hyperactivity disorder. Previous animal models of effort-based decision making have utilized physical costs whereas human studies of effort have been primarily cognitive in nature, and it is unclear whether the two types of effortful decision making are underpinned by the same neurobiological processes. We therefore validated a novel rat Cognitive Effort Task (rCET) based on the five-choice serial reaction-time task, a well-established measure of attention and impulsivity. Within each rCET trial, rats were given the choice between an easy or hard visuospatial discrimination, and successful hard trials were rewarded with double the number of sugar pellets. Similar to previous human studies, stable individual variation in choice behaviour was observed, with “workers” choosing hard trials significantly more than their “slacker” counterparts. We used a variety of pharmacological agents as well as temporary inactivation of select brain regions, and showed that the effects of these manipulations often interacted with animals’ baseline preferences. Amphetamine and caffeine caused workers to “slack off”, whereas slackers “worked harder” under amphetamine but not caffeine. Dopamine antagonism had no discernible effects on animals’ choice, contrary to the physical-effort literature. The cholinergic drug nicotine decreased slackers’ willingness to expend effort, whereas scopolamine more substantially decreased workers’ choice of the high-effort option. Temporary inactivation of the basolateral amygdala caused workers to slack off and slackers to work harder, whereas anterior cingulate and medial prefrontal cortex inactivations caused all animals to slack off. In sum, we have shown for the first time that rats are differentially sensitive to cognitive effort when making decisions, independent of other processes such as impulsivity, and these baseline differences appear to be reflected by differences in underlying neurobiology. Further, we demonstrate that mental and physical effort are in part dissociable, both behaviourally and in terms of neurochemistry and neural circuitry. Such findings could inform our understanding of the neurobiological basis of decision making as well as impairments in effort-based decision making, and may contribute to novel therapeutic interventions.
The Iowa Gambling Task (IGT) is a commonly used clinical test of decision-making. During the IGT, subjects choose between options associated with gains and losses. We have developed a novel rat gambling task (rGT), during which subjects are required to maximize their earnings within a 30 min session. Animals choose between four options, each associated with a different number of sucrose pellets, probability of receiving reward, and the magnitude and possibility of experiencing a punishing time-out period during which reward cannot be earned. Persistent choice of the larger reward options results in greater loss—as these options are associated with more frequent and longer time-out periods—resulting in less reward earned per unit time. Therefore, similar to the IGT, subjects are required to choose from the smaller reward options to maximize long-term gains. Results from Experiment 1 demonstrated that rats learn to choose most often from the best option by incorporating multiple factors into making their decisions. Therefore, the rGT may be a useful tool to study the biological basis of decision-making. Following pharmacological challenges with amphetamine and receptor-specific serotonergic and dopaminergic agents, data from Experiments 1 and 2 demonstrated that both neurotransmitters play important roles in modulating decision-making preferences. Furthermore, results from Experiment 2 suggested that amphetamine’s ability to alter decision-making may not be caused by increased dopamine release. Additionally, animals reared in an enriched environment or in isolation were slower to learn the optimal strategy, but only isolation-reared rats chose more often from the disadvantageous options. Experiment 3 determined that lesions of either orbitofrontal cortex (OFC) or basolateral amygdala (BLA) impaired acquisition of the rGT. However, if these lesions occurred after training on the rGT, only rats with BLA lesions chose disadvantageously. These results indicated that the BLA—but not the OFC—is involved in maintaining an optimal strategy on the rGT, yet both regions are required during task acquisition. Experiment 4 used a contralateral disconnection lesion procedure to determine that the connectivity between the OFC and BLA was important in learning the optimal strategy, as well as updating decision-making preferences following reward devaluation.
Master's Student Supervision (2010 - 2018)
The cholinergic system, encompassing the muscarinic and nicotinic receptor systems, plays a modulatory role in a variety of executive processes. However, its role in decision making is still unclear. Disorders characterized by disturbed muscarinic receptor functioning, such as schizophrenia, exhibit impaired performance on measures of real-world cost/benefit decision making, but whether this contributes to the choice deficits observed in the disorders is currently unknown. To address muscarinic receptor contributions to such processes, we investigated the effects of the broad-acting muscarinic receptor agonist oxotremorine (0.01, 0.03. 0.1 mg.kg) and antagonist scopolamine (0.01, 0.03, 0.1 mg.kg) on rodent Gambling Task (rGT) performance. Like the clinically administered Iowa Gambling Task (IGT), rodents must evaluate the costs and benefits of four nosepoke options that are each associated with the delivery of a different amount of reward, as well as different probabilities of receiving reward or a punishment time-out in which no reward can be earned. Rats quickly learn to select the advantageous options characterized by smaller rewards with lower penalties, and to avoid the large, high penalty reward options. Although systemic administration of oxotremorine had no effect, the highest dose of scopolamine impaired optimal performance by increasing choice of the option associated with the smallest reward and the lowest risk. This shift in choice is similar to that previously observed following administration of amphetamine, and suggests the drugs induce a hypersensitivity to loss. Given the functional connectivity of muscarinic and dopaminergic systems in the brain, and the antipsychotic-like profile of muscarinic agonists in amphetamine-induced animal models of schizophrenia, we then attempted to attenuate amphetamine’s choice impairments by prior administration of oxotremorine. Amphetamine (1.0 mg.kg) produced its characteristic choice impairments, despite pretreatment with oxotremorine. The results of this study suggest muscarinic receptor blockade can impair cost/benefit decision-making under conditions of risk and uncertainty, and prescribe a novel role to acetylcholine as a modulator of the decision process. Future work is required to pinpoint the mechanism driving amphetamine’s effect on the rGT, as cholinergic signaling through muscarinic receptors does not appear to be involved.
Background:Pathological gambling is a pervasive and destructive behavioral disorder in which individuals lose control over their gambling behavior, leading to severe personal, social and financial consequences. Current animal models of gambling behavior such as the rodent gambling task (rGT) are useful tools with which to evaluate choice behavior. However, they are limited in their insights into gambling behavior in that they mostly model dimensions of economic decision-making, but not the salient cues intrinsic to human gambling paradigms. Here, we developed a task called the cued rGT to examine the potential influence of salient win-associated cues on decision-making. Methods:16 male Long-Evans rats were tested on either the traditional or a cued version of the rGT. Once trained, they were treated with a number of dopaminergic compounds to delineate the role of this neurotransmitter in guiding choice behavior in both cued and uncued tasks.Results:Animals on the cued task showed a more disadvantageous choice preference at baseline than animals on the uncued task. Amphetamine caused a significant increase of a safe, certain option in both versions of the task, a result that is somewhat consistent with past findings. Quinpirole, a D2-like agonist, increased disadvantageous choice in the cued group but not the uncued group. There were no effects of eticlopride, a D₂-like antagonist, or selective D4 drugs on choice performance.Conclusions:Salient win-associated cues are sufficient to drive a shift towards disadvantageous choice preference. This effect appears to be mediated, at least in part, by D2-like receptors. These finding suggest the cued rGT is a valuable model with which to study how salient cues can invigorate maladaptive decision making, an important and understudied component of pathological gambling and substance use disorders.
The People’s Republic of China has increasingly been asserting its role as a responsible power in international affairs, emphasizing its engagement in and contribution to UN peacekeeping missions and its key role as a veto-yielding Security Council member. This thesis investigates that while China continues to champion a strong conception of state sovereignty in interstate relations, it has signaled a shift from an ideological insistence on non-interference toward a more pragmatic approach to humanitarian crises. This paper demonstrates how after 2005 China has managed to position itself in a ‘grey zone’ of uncertainty, that is to say that China’s dilemma is wanting to appear responsible on the international level but also wanting to adhere to safe principles such as non-interference and sovereignty. Therefore, it is my argument that China will never fully endorse R2P or any alternative norm that will justify foreign intervention in a sovereign state. While China continues to show support for alternative formulas for civilian protection, such as the Brazilian ‘Responsibility while Protecting’ (RwP), as well as develop its own version of R2P, ie. ‘Responsible Protection’ (RP), it is not to turn “words into deeds” but rather to keep up with appearances. China’s current position on responding to humanitarian crises is ambiguous. The principles behind RP represent a very useful conceptual approach to the issue of humanitarian protection, but the probability of implementing them is virtually non-existent. RP indicates that China has been more responsive to external criticisms in recent years, but does not fundamentally help to discern where China stands on responding to humanitarian crises. Because of RP’s tight criteria, China ensures that in practice no intervention can ever fully be justified, while appearing to advance more ‘responsible’ approaches to civilian protection as its great-power status and privileged position as a permanent member of the United Nations Security Council permit it to do so.