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Humans exhibit a number of suboptimal behaviours in the wake of a loss. For example, gamblers often ‘chase' their losses in an attempt to break even. Similarly, investors tend to hold on to losing stocks too long in the hope that the declining share price might make a recovery. However, the neural mechanisms that instantiate such behaviour are poorly understood. I begin the introductory chapter with a basic historical overview of fundamental economic concepts, interleaving intersecting ideas from psychology and neuroscience. This leads to a more in-depth exploration of the notion that loss-related behavioural biases might provide insight into the neural mechanisms that underlie risky choice. From this, I argue that rats represent a viable animal model of risky decision- making for neuroeconomic research. The original research presented in Chapters 2 – 5 pave the way toward advancing our current understanding of loss-related biases in behaviour with rat models of risky decision-making. By employing insight from psychology and economics, I developed two models of rat behaviour that can be used to study the neural substrates of loss valuation. I presented the experimental paradigms in Chapters 2 and 5, while demonstrating novel loss-related correlations between the midbrain dopamine system and observed loss behaviour in Chapters 3 and 4. The results presented in Chapter 5 demonstrate that rats are capable of producing behavioural patterns akin to loss aversion and the disposition effect. This work has also highlighted a number of areas for future research. In Chapter 6, I explore potential theoretical implications of the results discussed in previous chapters. In summary, this thesis uses experimental risky decision-making tasks in rats to advance our current knowledge of the ways in which concepts such as loss aversion critically influence our internal representation of value.

Repetitive presentation of any non-significant stimulus to an animal results in a decrement in the animal's response to that stimulus. This phenomenon, termed habituation, is distinguishable from fatigue and receptor adaptation in that it is long-lasting and in that the habituation is fairly specific to the repeated stimulus. The prevailing view of habituation is that it, like learning in general, results from an increase in the efficacy of neural transmission, but, unlike learning, this increased efficacy primarily affects inhibitory interneurons (e.g., Soko1ov, 1960; Hernandez-Peon, 1960; Jouvet, 1961). Within this broad framework, disagreements exist regarding the source of the inhibitory influences. [...]

The ascending cholinergic and serotonergic projections are central to cortical activation and normal behavior. The objective of this thesis was to determine whether unilaterally damaging both of these systems would disrupt the production of skilled movements on the contralateral side of the body. Rats received unilateral damage to either the ascending cholinergic, or serotonergic, or both projections. The respective lesions reduced neocortical leveles of acetylcholine and serotonin as assessed by acetylcholinesterase reactivity and immunohistochemical staining for serotonin. Subjects were assessed on a battery of sensorimotor tasks sensitive to neocortical integrity. The cholinergic lesion produced mild deficits on some taks but damage to both together did not abolish skilled movement. The impairments are decreased in relation to the severe effects of bilateral lesions. The results show that the sensorimotor cortex remains functional following deafferentation of both cholinergic and serotonergic afferents. / vii, 166 leaves : ill. ; 28 cm.

This thesis examines the behavioral, structural, cellular, and epigenetic changes observed in offspring exposed to different prenatal stressors. A number of questions were answered in this thesis that contribute to a basic understanding of the mechanisms by which early experiences alter long-term outcomes. These include: 1) What epigenetic modifications are associated with prenatal stress? 2) What are the structural and cellular changes in the brains of offspring that correspond to prenatal stress exposure? 3) How do these epigenetic and structural changes manifest as behavioral changes? And 4) What are the consequences of varying the level of prenatal stress?The key findings were that not all prenatal stress is the same. Variations to the intensity and nature of the stress dramatically alter offspring outcomes. Second, prenatal stress produces changes at many levels and these changes can be functionally related. Expression changes were identified in genes involved in altering dendritic morphology, which in turn modifies behaviour. For the first time, a comprehensive examination of brain plasticity occurred following prenatal stress. Additionally, this thesis demonstrated that brain changes related to prenatal stress are age-dependent and sex-dependent. The effects of prenatal stress on the pre-weaning brain are dramatically different than those observed in adulthood. Also, the sex of the offspring significantly influences neuroanatomical and epigenetic modifications. This finding is of critical importance because a majority of prenatal stress research is conducted on male offspring only. Taken together these discoveries emphasize that perturbations to development during the prenatal period produce persistent changes in the structure and functioning of the brain that will influence all subsequent experiences / xx, 201 leaves ; 29 cm

Stress is thought to be antithetical to play. However, this thesis shows that mild stress (e.g., social deprivation) enhances rough-and-tumble play, as opposed to other social behaviors, in adolescent rats. Social deprivation results in both higher levels of corticosterone (a stress hormone) and higher levels of play. When non-socially deprived rats were injected with ACTH (a precursor to corticosterone), the frequency of play was elevated to levels comparable to that seen when juveniles were socially deprived. Moreover, corticosterone was reduced by the opportunity to play, but not when given social contact (but no play) or solitary exercise (i.e. a running wheel). Therefore, this thesis provides evidence that play is not only enhanced by mild stress, but that it is used by animals to reduce stress. / vi, 70 leaves ; 29 cm.