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The moments that follow a perceptual decision can be as critical as the ones leading up to it. This thesis examines rapid olfactory decisions in mice and rapid changes of mind following an initial decision in humans. To study olfactory decisions, we trained mice to discriminate different odor concentrations in a novel head-fixed paradigm. Odor concentration is an important cue for localizing odor sources, from searching for food and mates to avoiding predators. However, little is known about how olfactory systems encode odor concentration. We found that mice could discriminate the different odor concentrations in as little as 80 ms after odorant inhalation. This is an unprecedented speed for olfaction and is fast even by the standards of other sensory modalities. We attribute this new insight into olfactory perception to our choice of motor output, accurate sniff measurement, and precise stimulus control. This result suggests that odor-based decisions can be very rapid and based on information over a very brief temporal window. To study changes of mind following an initial decision, humans made decisions about a noisy visual stimulus, which they indicated by moving a handle. Although they received no additional information after initiating their movement, their hand trajectories betrayed a change of mind on some trials. We modeled these changes of mind by extending the diffusion-to-bound model, originally developed to account for both the timing and accuracy of the initial decision. We propose that noisy evidence is accumulated over time until it reaches a criterion, or bound which determines the initial decision, and that the brain exploits information that is in the processing pipeline when the initial decision is made to subsequently either reverse or reaffirm the initial decision. Sensory and motor processing latencies ensure that not all of the information available from stimulus onset to movement initiation contributes to the initial decision. This model explains both the frequency of changes of mind, as well as their dependence on both task difficulty and whether the initial decision was accurate or erroneous.

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.

Decision making can be a complicated process involving perception of the present situation, past experience and knowledge necessary to foresee a better future. This cognitive process is one of the essential human ability that is required from everyday walk of life to making major life choices. Although it may seem ambiguous to translate such a primitive process into quantifiable science, the goal of this thesis is to break it down to signal processing and quantifying the thought process with prominence of EEG signal power variance. This paper will discuss the cognitive science, the signal processing of brain signals and how brain activity can be quantifiable through data analysis. An experiment is analyzed in this thesis to provide evidence that theta frequency band activity is associated with stress and stress is negatively correlated with concentration and problem solving, therefore hindering decision making skill. From the results of the experiment, it is seen that theta is negatively correlated to delta and beta frequency band activity, thus establishing the fact that stress affects internal focus while carrying out a task.

Do endocrine systems influence personality and social behavior? Although animal research has identified several hormone-behavior relationships and the mechanisms that give rise to them, much less is known about hormones and social functioning in humans. This dissertation used three large data sets to investigate whether testosterone and cortisol were related to variation in personality constructs (Study 1), leadership behaviors (Study 2), and economic decision making (Studies 3 and 4). Study 1 revealed that basal testosterone was negatively associated with conscientiousness, basal cortisol was negatively associated with extraversion but positively associated with social dominance orientation, and the interaction between testosterone and cortisol was associated with the implicit power motive. Study 2 found that the testosterone-cortisol interaction predicted leadership behaviors, and Study 3 showed that basal testosterone as well as change in cortisol predicted economic decisions in the Hawk-Dove Game. Finally, Study 4 demonstrated that aggression predicted decisions to punish unfair monetary offers in the Ultimatum and Third Party Punishment Games. Aggression was also related to women's changes in testosterone from before to after the games. Taken together, these studies provide important evidence that testosterone and cortisol are related to personality, leadership, and social decision making. More broadly, this dissertation lays the empirical foundation for further inquiry on the complex biological systems that regulate personality and social behavior.

When given a choice between getting a high reward that requires climbing a high ramp or pressing a lever multiple times, versus freely obtaining a low reward, healthy rats prefer the former, while rats with lesions to the anterior cingulate cortex (ACC) prefer the latter. We developed two novel effort tasks to examine if ACC mediates other types of physical effort (weight-lifting) as well as emotional effort (courage). We replicated previous findings on a modified version of the ramp-climbing task, showing that ACC lesions impair these decisions. Lesions of ACC did not impair weight-lifting effort, even when higher levels of effort were used and training on the task was eliminated. Initially, lesions of ACC did not impair courage effort. When the task effort was subsequently increased, rats with ACC lesions showed a failure to adapt to novelty throughout testing. This research indicated that not all effort is mediated by ACC. / xii, 177 leaves : ill. ; 29 cm