Attention in the Brain Under Conditions of Sub-Optimal Alertness: Neurobiological Effects and Individual Differences

Sleep deprivation (SD) is a prevalent problem in modern society, and one that can have serious adverse consequences for health and safety. Critically, even short periods of SD can lead to relatively large decrements in attention, which may in turn cause an individual to neglect important environmental stimuli. In this thesis, I report the results of three experiments designed to investigate the neural bases of attentional declines under conditions of sleep loss and mental fatigue. In two experiments using arterial spin labeled fMRI, a technique that enables the quantification of absolute levels of cerebral blood flow (CBF), it was found that CBF patterns in the resting brain differed significantly based on arousal levels (Study #1) and prior cognitive workload (Study #2). These findings are a departure from prior neuroimaging studies, which have typically taken neural activity during non-task periods as static and inseparable baseline. In a test of sustained attention, performance declines were observed both following SD (Study #1) and when performing the task for an extended period of time while well-rested (Study #2). These decrements were primarily mediated by hypoactivation in a fronto-parietal attentional circuit. Furthermore, resting baseline levels of cerebral blood flow in the thalamus and prefrontal cortex before the start of the task were predictive of interindividual differences in subsequent performance decline (Study #2). In Study #3, an experiment using standard BOLD fMRI, it was found that performance declines in a test of selective attention following SD were accompanied by reduced functional connectivity between top-down control areas and regions of ventral visual cortex, as well as reductions in activation to targets in object-selective areas. Taken together, these results further our understanding of the neural basis of attention under conditions when this system is taxed beyond its normal limits

Catalytic asymmetric synthesis of highly substituted pyrrolizidines

A catalytic asymmetric double (1,3)-dipolar cycloaddition reaction has been developed. Using a chiral silver catalyst, enantioenriched pyrrolizidines can be prepared in one flask from inexpensive, commercially available starting materials. The pyrrolizidine products contain a variety of substitution patterns and as many as six stereogenic centers

Order effects: a randomised study of three major cancer-specific quality of life instruments

BACKGROUND: In methodological studies and outcomes research, questionnaires often comprise several health-related quality of life (HRQoL) measures. Previous psychological studies have suggested that changing the sequential order of measurement scales within a questionnaire could alter the pattern of responses. Yet, information on the presence or absence of order effects on the assessment of HRQoL in cancer patients is limited. METHODS: An incomplete block design was used in this study of 1277 cancer patients. Each patient filled out a questionnaire package that contained two of the three major cancer-specific HRQoL instruments, namely the Functional Assessment of Cancer Therapy – General, the European Organization for the Research and Treatment of Cancer Core Quality of Life Questionnaire and the Functional Living Index – Cancer. Within a questionnaire package the sequential order of the instruments contained were randomised. Measurement properties of the instruments, including the number of missing values, mean HRQoL scores, known-groups validity and internal consistency were compared between samples of different presentation orders. RESULTS: No effect of presentation order on the four properties aforementioned was found. CONCLUSION: Presentation order is unlikely to alter the responses to these HRQoL instruments administered in cancer patients when any two of them are used together

The relative eye size, visual cells, cone mosaic and retinal tapetum in the spotted barb Puntius binotatus (Valenciennes, 1842)

The relative eye size, types of visual cell and mosaic, and the existence of retinal tapetum in the eyes of the spotted barb Puntius binotatus were determined to gain baseline information on its visual capability. The P. binotatus acquired relatively larger eye size than the other similar sized freshwater fish species with its retina being contained both cone and rod visual cells (cone ellipsoid to outer nuclei ratio = 1: 5.7). Three types of cone were identified (double-, central single- and corner single- cones), arranging in the square mosaic, and the retinal tapetum was determined to be existed. These results evidenced that the P. binotatus has good visual capability as it possessed both the photopic and scotopic visions. Vision can be the primary sense for the P. binotatus. Further study is needed to gain more information on the vision of this species.