BACKGROUND: Current research regarding the impact aging has on characteristics of sleep suggest that over the course of one’s lifespan, the quantity and quality of sleep declines. Sleep quality is a measure of the extent to which sleep is consolidated- the less number of brief awakenings one experiences during a period of sleep, the better. The extent to which degradation of sleep quality may impact overall health and increase susceptibility to age-related diseases is currently unknown, nor is the mechanism that mediates sleep fragmentation and consolidation understood. OBJECTIVE: The purpose of this study was to ascertain if the increased sleep fragmentation experienced with age is due to a decreased arousal threshold towards external stimuli. A decreased ability to inhibit sensory processes during sleep could potentially trigger a greater number of brief awakenings and negatively impact sleep quality. METHODS: Various age groups of inbred wild-type genotypes of Drosophila melanogaster had arousal threshold tested during the night using mechanical stimuli to see if the older flies were more likely to be woken up. Sleep characteristics at baseline and after the arousal assay were compared to observe any impacts aging has on the ability to recover from a mild sleep deprivation as such. RESULTS: I observed an increase in arousal threshold with age; older flies were less likely to be aroused by the presentation of the mechanical stimulus. Arousal threshold findings were consistent between sexes but not between genotypes. It was noted that the degree to which aging impacted arousal threshold was affected by the expected lifespan of a genotype. In terms of sleep characteristics measured outside of the arousal assay, I noticed an increase in quantity of sleep and decrease in activity as flies aged, including a greater reliance on day sleep. This was further reflected by a decrease in rebound sleep after the arousal assay was performed. More specific sleep architecture characteristics such as bout number and bout length were greatly impacted by both sex and genotype. CONCLUSION: Our results were greatly unexpected in comparison to previous studies, especially in regards to older flies having an increased arousal threshold and an increased quantity of sleep. This is not conclusive, however, as previous studies have shown that the saliency of the stimulus presented may prove important, especially when considering the internal state of the fly. Instead of solely focusing on if older flies are more or less easy to wake up with the application of an external stimulus, it may instead be beneficial to also consider their ability to discriminate between salient stimuli while quiescent.

Over the course of a typical night, sleep is comprised of multiple different stages that involve changes in brainwave patterns. Intracranial EEG (iEEG) is an invasive brain recording technique used in hospital settings in epileptic patients to determine the focus of their seizure activity. The intracranial data recorded allows one to directly observe the neural activity of deep brain structures such as the hippocampus and to detect single unit activity and local field potentials, thus providing a level of physiological detail normally available only in animal studies. In this thesis we employ intracranial data to advance our understanding of sleep neural dynamics in humans, and to this end its focus is in two areas : (1) developing a way of sleep scoring iEEG data and (2) investigating the neural dynamics of a particular waveform found during sleep, the sleep spindle, and its role in memory consolidation. Typically, iEEG recordings do not include electrooculogram or electromyogram recordings, which are normally needed for sleep scoring—especially for scoring rapid-eye movement (REM) sleep. We identified differences in alpha power between wake and REM sleep to develop a methodological way to reliably differentiate between wake and REM sleep states. We also wanted to investigate the neural dynamics involved with a particular brainwave seen during sleep, the sleep spindle, which is thought to be important for sleep-mediated memory consolidation. Historically, sleep spindles were thought to occur synchronously across the cortex, but recent findings using iEEG have identified that sleep spindles can also be local. We utilized intracranial EEG to confirm previous findings that iEEG can identify local sleep spindles. In addition to identifying local sleep spindles, we aimed to investigate the potential role that sleep spindles have on learning and memory using standard targeted memory reactivation paradigms for iii both procedural and declarative memories. We found that local sleep spindles occurred at a specific time following auditory stimulation for both procedural and declarative memories. This work has opened up the use of iEEG recordings to investigations of REM sleep dynamics and laid the groundwork for examining the role of local sleep spindles in memory consolidation. / Master of Science / During a night of sleep, our brain goes through different stages that exhibit changes in brainwave patterns. Intracranial EEG (iEEG) is an invasive brain recording technique used in hospital settings in epileptic patients to determine the focus of their seizure activity; this particular brain recording technique allows one to observe the brain activity of deep brain structures. By using iEEG data, we aimed to (1) develop a way of sleep scoring iEEG data and (2) investigate the neural dynamics of a particular waveform found during sleep, the sleep spindle, and its role in memory consolidation.  Electrooculograms (EOG) are used to record the electrical activity of eye movements, and electromyograms (EMG) are used to measure muscle activity. Both of these recording techniques, in addition to EEG, are needed for sleep scoring, especially rapid eye movement (REM) sleep. However, typical iEEG recordings do not have EOGs and EMGs applied to the patient. Using iEEG data, we were able to identify differences in a specific brainwave, the alpha rhythm, between wakeful brain activity and REM sleep brain activity. Furthermore, we were able to use this difference to reliably score REM sleep in iEEG data without the need for EOGs and EMGs.  We also wanted to investigate the brainwave changes in a particular waveform, the sleep spindle, that has been thought to be important for sleep-mediated memory consolidation. Previous research using typical EEG recordings showed that sleep spindles occur synchronously across the cortex, but recent findings using iEEG have identified that sleep spindles can also occur asynchronously across the cortex. We replicated previous research showing that these local sleep spindles are identifiable using iEEG recordings. In addition to identifying local sleep spindles, we investigated the potential role that sleep spindles have on learning and memory. To do so, we used standard targeted memory reactivation paradigms for two types of memory: declarative and procedural memory. We found that local sleep spindles occurred at a specific time following auditory stimulation for both procedural and declarative memories.  This work has opened up the use of iEEG recordings to investigations of REM sleep dynamics and laid the groundwork for examining the role of local sleep spindles in memory consolidation.

Sleep deprivation is defined as an individual sleeping less than 6 hours per night. It is a common behavior amongst individuals who live in industrialized nations.Along with industrialization, its prevalence is also expected to rise with age. Despite this, there has been a shift in recent years with sleep deprivation increasing in the youth, likely related to the increased use of technology during the nighttime. Sleep deprivation and chronic sleep disruption are behaviors commonly observed amongst patients suffering from neurological and psychiatric disorders, like Alzheimer’s disease, Parkinson’s disease, depression, and anxiety. Many of these patients suffer from sleep disorders like insomnia, hypersomnia, and rapid eye movement sleep behavior disorder. It has long been thought that lack of sleep was caused by these disorders, yet there may be evidence to support a bidirectional relation between the two. We searched the literature to determine if there is a link between sleep disorders and sleep deprivation causing the exacerbation of these neurological and psychiatric disorders. Some studies support this hypothesis, for example, linking β-amyloid plaque buildup to lack of sleep, therefore increasing the risk of Alzheimer’s disease among chronically sleep deprived individuals. In this presentation we will take a closer look into the possible reasons as to why poor sleep may negatively impact cognitive health.

The purpose of this study was to test the reliability and validity of the Verran and Snyder-Halpern (VSH) Sleep Scale on patients hospitalized in a coronary care unit (CCU) and to investigate the sleep characteristics of patients hospitalized in the CCU setting. Eighteen subjects aged 43 to 78 completed 30 nights of study using the VSH Sleep Scale. Results were compared to means from groups of healthy subjects and subjects hospitalized on general medical-surgical units. The VSH Sleep Scale demonstrated reliability in this group of CCU subjects. Factor analysis showed loadings on four factors rather than the theoretical three factors probably due to small sample size. The mean scores for this sample of CCU patients indicated their nighttime sleep was disturbed and ineffective. Significantly different sleep characteristics were demonstrated between CCU and healthy subjects. Comparisons between CCU and general medical-surgical subjects evidenced no differences in sleep characteristics.

Human Systems Integration Report / This study examined the effects of noise, temperature, humidity, motion and light on the sleep patterns of the crew of the HSV-2 SWIFT during Gulf of Mexico Exercise (GOMEX) 05-1. HSV-2 SWIFT was chosen for this study to examine crew sleep on an unconventional hull type manned with a small crew. Noise dosimeters, temperature and humidity monitors, actiwatches and questionnaires were used to quantify the data. With the exception of light, the independent variables did not have significant effect upon participant sleep. This is likely due to the limited range of the independent variables and the small number of participants in this study. There were two findings in this study; the relationship between the demographic variable sea time and participant sleep and the relationship between the independent variable light and participant sleep. Due to the limitations in the current study, it is recommended that further studies be conducted in more extreme operational environments. Additionally, studies such as the one discussed in this thesis, should be completed on different platforms to determine the differences in environmental factors that affect sleep between hull types so that the results can be applied to future vessel design.

Ph.D., Faculty of Science, University of the Witwatersrand, 2011 / Mole rats are a unique family of the rodent order and are known for a subterranean lifestyle, reduced eye size, regressed visual system and unusual patterns of circadian rhythmicity (co-existence of rhythmic and arrhythmic chronotypes within a species has been documented). Such dramatic changes especially that of phenotype, may lead to the prediction of significant differences in organisation of the brain and physiology, therefore these unusual phenotypic features form the core rationale providing the impetus for the present series of studies. Neuroanatomical examination of the mole rat brain for immunohistochemical markers of the cholinergic, catecholaminergic, serotonergic, orexinergic, and histaminergic systems revealed neuronal organisation that was remarkably similar to those previously reported in other rodents and mammals, despite the notable differences in lifestyle and phenotype. These results indicate a strong phylogenetic constraint acting at the systems level of neuronal organisation. The study of sleep and wake in rhythmic and arrhythmic chronotypes of a species of mole rat indicated the arrhythmic chronotype spent more time awake with a longer average duration of a waking episode and less time in sleep with a shorter average duration of a SWS episode. While remaining somewhat similar between mole rat chronotypes, total sleep time in the mole rats was significantly reduced in comparison to other rodents. These results also indicate independence of circadian rhythmicity and sleep homeostasis and possible alteration of specific genes involved in the sleep-wake cycle of the mole rats examined. Stereological assessment of absolute numbers of orexinergic neurons revealed that the arrrhythmic chronotype tends to have more orexinergic neurons per gram of body mass that the rhythmic chronotype, leading to the conclusion that enhanced vigilance and peripheral metabolism of the arrhythmic chronotype may underlie this difference. Immunohistochemical identification of nuclei involved with the sleep-wake cycle, showed no difference in the distribution of these nuclei between circadian chronotypes and no major differences when compared to other rodents. Some interesting and potentially functionally important homogeneities were observed in the distribution of GABAergic interneurons within the pontine region. Furthermore differential orexinergic terminal network densities were observed between chronotypes within the arcuate nucleus and the intergeniculate leaflet. Therefore despite unusual features in lifestyle and phenotype, the organisation of the mole rat brain remains remarkably similar to other rodents; however, distinctions of circadian chronotype consistently produced subtle differences in both the anatomy and physiology of these rodents.

Thesis (M.Sc.)--University of the Witwatersrand, Faculty of Science, 2013 / Unable to load abstract.

Yu, Xinting. / Thesis Ph.D. Chinese University of Hong Kong 2014. / Includes bibliographical references (leaves 188-207). / Abstracts also in Chinese; appendixes in Chinese. / Title from PDF title page (viewed on 14, September, 2016). / Yu, Xinting.

Currently, sleep staging is accomplished is by clinical polysomnography (PSG). By extracting features from different combinations of electroencephalogram (EEG), electrooculogram (EOG) and electromyogram (EMG) signals, this study uses neural network to perform sleep staging. A whole night and complete sleep stage contains wake stage, rapid eye movement (REM) stage, stage 1, stage 2, and slow wave sleep (SWS) stage. This project focuses on the classification of wake stage and light-sleep (stage 1 and 2). These three stages are classified by a two-step process. At first, wake stage and light-sleep are divided into two parts. Second, light sleep is divided into stage 1 and stage 2. For a fixed number of channels, this work identifies the best combination of signal channels. In addition, by simultaneously considering the Neighboring epochs Rule classifier, this work also introduces an empirical rule to improve the classification accuracy. Among the tested databases which contain two Medicine center and sixteen sets of different signal channels, the best results are obtained from the group of patients with the low average RDI value. They include the group that has a mean 15% SWS and the group that uses CPAP. As a whole, the combinative features of four channels are better results of classification. For our best results, the sensitivity and PPV of wake and stage 2 varies from 85%~88%, and those of stage 1 are respective 44.84% and 53.61%. And the total classification of sleep staging is 84.59%. Apparently, the research has satisfactory results on sleep staging. Keywords: Sleep Medicine, Sleep stage, Neural Networks

published_or_final_version / Medicine / Master / Doctor of Medicine