The consequence of many psychiatric and neurodegenerative disorders, such as Parkinson's disease and schizophrenia, is an impairment in ‘executive functioning'; an umbrella term for several cognitive processes, including the focussing and shifting of attention and the inhibition of responding. The ability to form an ‘attentional set' involves learning to discriminate qualities of a multidimensional cue, and to subsequently learn which quality is relevant, and therefore predictive of reward. According to recent research, the subthalamic nucleus (STN) and possibly the adjacent zona incerta (ZI) may mediate the formation of attentional set. Dysregulation of the STN as a result of Parkinson's disease contributes to characteristic motor symptoms, and whilst deep-brain stimulation of this region may treat gross motor impairments, it may also impair cognition. The work in this thesis aimed to expand our understanding of the mechanisms of attentional set-formation, and the role of the STN in this process. This thesis evaluates new methods for examining set-formation in the attentional set-shifting task; rather than inferring this behaviour solely from the cost of shifting set, modifications to the task design in Chapters 3 & 4 explored several hypotheses designed to exploit a deficit in this behaviour. Chapter 6 revealed that inhibition of this region with designer receptors leads to a disruption in attentional selectivity, which compromises the ability to form an attentional set. This manifested as an inability to parse relevant information from irrelevant, and instead, animals learned the stimuli holistically. The findings in this thesis also suggested that reversal and attentional shifting processes do not operate independently, but rather in a hierarchy, and that consequently, the STN is a region that may be crucial in selecting appropriate responses during associative learning that leads to the formation of an attentional set.

Executive functions (EFs) are a set of cognitive operations, including working memory, inhibitory control and attention shifting, that underpin accurate, flexible and coordinated behaviour in many problem-solving contexts. While it seems likely that humans surpass nonhuman animals in EFs, previous research into the evolutionary origins of EFs is limited and lacks systematic comparisons of EFs in human and nonhuman animals. In this thesis, I aimed to overcome these limitations by developing a test battery to study EFs in our closest primate relative, the chimpanzee. Using an individual differences approach, I investigated the performance of 19 chimpanzees on several EF tasks and extracted two factors in an exploratory factor analysis accounting for 70.9 % of the variability. The two measures of working memory loaded onto one factor, suggesting that a common cognitive process underlay performance on both tasks. This factor could be clearly differentiated from a well-established measure of attention shifting, loading onto a second factor. In addition, the measures of inhibitory control did not contribute to a unique factor. Intriguingly, the emerging structure of separable EF processes, paralleled the EF structure suggested for human adults (Miyake et al, 2012). The subsequent comparison of a sub-sample of chimpanzees (n = 12; excluding aged individuals), pre-schoolers (n = 36) and undergraduates (n = 16) on two selected EF tests revealed impressive EF capacities of chimpanzees. Chimpanzees could deal with interference in working memory at levels comparable to four and five year-olds. Additionally, the ability of chimpanzees to shift attention was not significantly different from four year-olds; however, five- year-olds outperformed their primate relatives. My work suggests that important aspects of EFs are shared between humans and chimpanzees; while performance differences in EFs emerge late in human ontogeny. The implications of my results for theories on human cognitive evolution are discussed.

This study tested the hypothesis that daily physical activity improves the executive function and academic achievement of 9- to 11-year-old children. The quasi-experimental, pretest–posttest design included 60 eligible fourth and fifth grade students (51.7% female, 98% Hispanic; 10.26 years of age). Twenty-five students elected to participate in school day, zero-hour (1 hour before school starts) physical activity program for 8 weeks. The 35 students who did not sign up for the program served as the control group as masked data provided by the school. Standardized measures, Adele Diamond flanker task and the Wide Range Achievement Test 4, assessed executive function and academic achievement, respectively. Repeated-measures analysis of variance was used to determine differences between groups on executive function and academic achievement. There were no observable benefits from daily physical activity on executive function and academic achievement. Convenience sampling and voluntary attendance potentially limited the effect of exercise on performance.

Lesions of the subthalamic nucleus (STN) alleviate the cardinal signs of idiopathic as well as MPTP-induced Parkinson's disease in primates. For this reason, the STN is a target for clinical treatment of Parkinson's disease using deep brain stimulation. Despite its small size, the STN plays a vital role in the cortico-basal ganglia-thalamic network. However, the functional features of the STN have yet to be fully uncovered. The research presented in this thesis examines the functions of the STN by measuring behavioural changes resulting from STN lesions in rats performing executive abilities. In the first experiment, a ‘signal change' reaction time task was developed and the performance of humans and rats was compared. The main findings were that although humans and rats used different strategies in the task, the task did challenge the ability to inhibit unwanted responses. In the second and third experiments, the effects of bilateral lesions of the STN on performance of two variants of the ‘signal change' task were examined. Rats with the STN lesions were able to inhibit responses when under stimulus control, but were less able to inhibit responses that were not under stimulus control. In the final experiment, the effects of lesions of the STN on inhibitory control in a nonmotor, cognitive domain were examined. Rats with STN lesions were not impaired on reversal learning, suggesting intact inhibition of previously rewarded responses. The rats with STN lesions did show impairments in selective attention which resulted in an inability to form an attentional set. Together, these findings challenge the conventional view that the STN simply plays a global inhibitory role. Rather, the contribution of the STN to inhibitory control is more complex and neither the motor nor the cognitive effects of the lesions are easily explained simply as a failure of inhibition.

Individuals who have experienced a traumatic event and develop Post-Traumatic Stress Disorder (PTSD) frequently show deficits in both primarily “cool” and “hot” cognitive executive functions (e.g., traditional & emotional Stroop tasks, respectively) that can be impacted by high affective salience. Given the dimensional nature of psychopathology, questions remain about individuals within the general population who have experienced trauma but do not meet full criteria for PTSD and yet may manifest problems in these areas, especially areas of hot and cool executive functioning (EF). Thus, the current project was designed to assess hot and cool EF in a relatively large sample of individuals from the general population who have experienced trauma and currently demonstrate sub-clinical levels of post-traumatic symptoms. The Stroop task, Emotional Stroop task, and a novel modified Implicit Association Test were utilized to assess EF across a spectrum of individuals with varying traumatic histories and level of post-traumatic symptoms. Results suggest that a greater frequency of trauma experiences was moderately associated with worse performance on both hot and cool executive functioning measures. Specifically, females within the sample evidenced a close relationship between traumatic experiences, post-trauma symptoms, and executive functioning. Clinical and theoretical implications are discussed.

Executive control is a vital cognitive function that facilitates the focussing and shifting of attention, planning and working towards a goal, ignoring distractions, and flexibly responding to novel situations. Disruptions to executive control are seen in many psychiatric and neurodegenerative disorders, as well as healthy ageing, which can be profoundly detrimental. Despite having many effective and well-validated methodologies for detecting and quantifying these deficits, there are very few treatments — pharmacological or otherwise — for ameliorating executive dysfunction. This lack of progress can partly be blamed on difficulties associated with identifying drugs that enhance cognition in preclinical research. The work in this thesis aimed to expand our understanding of executive dysfunction — as well as the tasks that measure it — in rats. In results presented in chapter three, middle-aged rats demonstrated impaired reversal learning on the standard attentional set-shifting task, but this was treatable with a novel drug targeting the N-methyl-D-aspartate receptor. The age impairments seen in this experiment were similar to those previously found in young rats with orbital prefrontal cortex (OFC) lesions. The results of chapter four expanded on this similarity to show that, along with reversal deficits, young OFC-lesioned rats are impaired at forming attentional sets when tested on a modified task. In chapter five, another modified set-shifting task revealed that middle-aged rats also suffer from impaired set-formation, but their reversal learning impairments only manifest before attentional set has been formed — not after. Finally, in chapter six, the putative cognitive enhancer modafinil was found to exacerbate middle-aged rats' reversal learning deficit, but it also enhanced their subsequent ability to form attentional set. These experiments reveal that modifying the rat attentional set-shifting task can sometimes make it a more effective tool for testing cognitive enhancers in preclinical settings.

The role of executive functioning in substance dependence and addiction has received increased attention in recent years; however, the findings of empirical studies are at times contradictory and difficult to compare at face value. To address the current state of fragmentation and to delineate the current body of knowledge a systematic review of existing studies was conducted. The synthesis of the findings from these studies confirmed that lower neuropsychological performance scores of executive functioning are observed in substance dependent populations. Furthermore, the synthesis of the components of these studies provided a comprehensive overview and revealed a number of critical gaps in the current body of knowledge. The gaps include limitations concerning specific demographics of the samples studied (under-representation of females, adolescents, the elderly, individuals with limited education, and individuals from Africa, Oceania, Asia, Latin America and the Caribbean), as well as the scarce number of studies investigating specific substances; insufficient longitudinal studies; and the fragmentation of executive functioning as a theoretical construct. / Psychology / M.A. (Psychology)