published_or_final_version / Orthopaedic Surgery / Doctoral / Doctor of Philosophy

No description available.

This masters thesis examines the hemispheric activation pattern of the cognitive processes involved in a complex mental rotations test (MRT) (Vandenberg and Kuse, 1978) using Steady-State Probe Topography (SSPT) (Silberstein et al, 1990) as a method to index brain activity. The Steady State Visually Evoked Potential (SSVEP) was recorded from 64 electrode sites using a multichannel electrode helmet, and elicited by a 13 Hz sinusoidal visual flicker, whilst the subjects were performing a visual vigilance Baseline task and the MRT. Forty-one right handed subjects (twenty male and twenty-one female) were used. In the MRT the subjects were required to choose the two figures which correctly matched the criterion figure in the centre. The figures were three-dimensional objects represented in two-dimensions on a computer screen. A significant finding of this study was that when all the subjects were considered as one group, no noticeable lateralization in cerebral activation associated with mental rotation was evident. When analyzing the results for the subjects, partitioned into two groups according to gender, evidence was found suggesting that the cortical processing associated with mental rotation may be more localized bilaterally in the males than the females. However, no noticeable lateralization effects for mental rotation were found in the males or females, and hence no gender differences in hemispheric lateralization was evident. An important finding was the emergence of gender differences in hemispheric lateralization in subsets of subjects performing with higher spatial ability. A left hemisphere lateralization for mental rotation was associated with the Best Performance Male group. The Best Performance Female group showed the opposite effect, where a right hemisphere lateralization was associated with better performance on the task. The lateralization effect appeared to be stronger in the Best Performance Males than the Best Performance Females. An important conclusion from this study is that when examining for hemispheric lateralization effects in mental rotation, and possibly other visual-spatial tasks, not only gender effects need to be considered, but the level of spatial ability in the comparison groups needs also to be taken into account.

Thesis (Ph. D.)--York University, 1997. Graduate Programme in Psychology. / Typescript. Includes bibliographical references (leaves 93-99). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL:http://wwwlib.umi.com/cr/yorku/fullcit?pNQ22895.

Thesis (Ph. D.)--University of California, San Diego, 2003. / Vita. Includes bibliographical references (leaves 297-313).

Thesis (Ph. D.)--University of California, San Diego and San Diego State University, 2003. / Vita. Includes bibliographical references.

published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

No description available.

Transcutaneous electrical nerve stimulation (TENS) is a simple, non-invasive technique used in the control of chronic pain. Despite the success of TENS and its continued use for over twenty years, some patients either fail to respond or show only a partial response. Furthermore some patients respond initially to TENS but then become tolerant to its analgesic effects. The reasons for poor response to TENS are unknown; different clinics report widely differing success rates, and information on long-term efficacy is sparse. Furthermore, TENS is still administered on an empirical basis in which the patient determines by trial and error the most appropriate stimulator settings (i. e. electrical characteristics of TENS) to treat his or her particular pain. It is impossible to predict whether an individual patient will respond to TENS or which stimulator settings will be optimal. In an attempt to elucidate these problems, the clinical, electrophysiological, neuropharmacological, psychological and sociological factors that influence the analgesic effects and clinical efficacy of TENS have been examined in this thesis. Three clinical studies were performed. The first (Study 2.1) reviewed the use of TENS since its introduction to Newcastle Pain Relief Clinic in 1979. It was found that 1582 patients have been given a trial of TENS of which 927 (58.6%) continue to use a stimulator on a long-term basis (Study 2.1). The clinical use of TENS by 179 of these patients was examined in-depth (Study 2.2). Although previous literature suggests that TENS is most efficacious for pains of neurogenic (neuropathic) origin, it was found that any type of pain may respond. No relationships were found to exist between the electrical characteristics of TENS (i. e. stimulator settings) used by patients during TENS treatment and the cause and site of pain. However, patients utilised specific pulse frequencies and patterns and consistently used these settings on subsequent treatment sessions (Study 2.3). These clinical studies showed that in this population, 41.4% of patients failed to respond to TENS and half using TENS on a long-term basis achieved less than 50% relief of pain. Thus, a systematic investigation to determine optimal electrical characteristics of TENS was performed. Three experiments were undertaken to examine separately the analgesic effects of different electrical characteristics of TENS (pulse frequency, pulse pattern and stimulation mode) on cold-pressor pain in healthy subjects. The effects of a range of Long Abstract pulse frequencies (10Hz to 160Hz) applied to produce a 'strong but comfortable' electrical paraesthesia within the painful site were measured (Exp. 3.1). It was found that frequencies between 20-80Hz were most effective. However, no differential effects were observed between a range of pulse patterns (continuous, burst, modulation, random; Exp. 3.2). When TENS was applied in burst mode at an intensity sufficient to produce phasic muscle twitches at a site distant yet myotomally related to the site of pain (acupuncture-like TENS) a powerful analgesic effect was observed during and post-stimulation (Exp. 3.3). It is suggested that continuous mode stimulation at 80Hz, producing a 'strong but comfortable' electrical paraesthesia within the painful site, should be the primary TENS treatment choice in the clinic but that in selected cases AL-TENS may be more effective. A number of improvements in stimulator design are suggested. Further experiments were aimed at elucidating the mechanism of TENS effects by investigating the influence of TENS on electrophysiological and neuropharmacological variables. It was found that TENS reduced peak-to-peak amplitudes of the late waveform components (N1P2) of somatosensory evoked potentials (Exp. 4.1) and increased alpha, beta and theta activity of spontaneous EEG in healthy subjects (Exp. 4.2) and/or pain patients (Exp. 4.3). As TENS produced changes in SEPs elicited from non-painful stimuli, and also changes in spontaneous EEG in pain-free subjects, it is suggested that the effects of TENS may be due in part to changes in sensory processing at several levels in the nervous system which may not specific for the perception of pain. The surprising finding that TENS increased peripheral circulating met-enkephalin in chronic pain patients was attributed to a stress-like release although this observation remains to be confirmed using a larger population sample (Exp. 5.1). The results of these experiments suggest that baseline electrophysiological and neuropharmacological variables may be important determinants of individual response to TENS. Thus, a prospective investigation was undertaken on 29 patients who were undergoing a trial of TENS to control chronic pain, in an attempt to identify predictors of patient response. Patient response to TENS was related to baseline SEP amplitudes and spontaneous EEG but was not related to biochemical, psycho-social, personality or pain related factors (Exp. 6.1). Thus, patients with small peak-to-peak amplitudes of the SEP, and low power spectrum of spontaneous EEG showed poor response to TENS (Exp. 6.1). It is suggested that an individual's intrinsic central response pattern to external stimuli may influence response to TENS.

Thesis (Ph. D.)--University of California, San Diego, 2007. / Title from first page of PDF file (viewed October 5, 2007). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references.