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Dive into the research topics where Elizabeth A. Bowman is active.

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Featured researches published by Elizabeth A. Bowman.


Visual Neuroscience | 2005

Contrast response of temporally sparse dichoptic multifocal visual evoked potentials

Ted Maddess; Andrew C. James; Elizabeth A. Bowman

Temporally sparse stimuli have been found to produce larger multifocal visual evoked potentials than rapid contrast-reversal stimuli. We compared the contrast-response functions of conventional contrast-reversing (CR) stimuli and three grades of temporally sparse stimuli, examining both the changes in response amplitude and signal-to-noise ratio (SNR). All stimuli were presented dichoptically to normal adult human subjects. One stimulus variant, the slowest pattern pulse, had interleaved monocular and binocular stimuli. Response amplitudes and SNRs were similar for all stimuli at contrast 0.4 but grew faster with increasing contrast for the sparser stimuli. The best sparse stimulus provided an SNR improvement that corresponded to a recording time improvement of 2.6 times relative to that required for contrast reversing stimuli. Multiple regression of log-transformed response metrics characterized the contrast-response functions by fitting power-law relationships. The exponents for the two sparsest stimuli were significantly larger (P < 0.001) than for the CR stimuli, as were the mean response amplitudes and signal-to-noise ratios for these stimuli. The contrast-dependent response enhancement is discussed with respect to the possible influences of rapid retinal contrast gain control, or intracortical and cortico-geniculate feedback.


American Journal of Neuroradiology | 2011

Size and shape of the corpus callosum in adult Niemann-Pick type C reflects state and trait illness variables.

Mark Walterfang; Michael Fahey; Larry A. Abel; Michael Fietz; Amanda G. Wood; Elizabeth A. Bowman; David C. Reutens; Dennis Velakoulis

BACKGROUND AND PURPOSE: Variable alterations to the structure of the corpus callosum have been described in adults with NPC, a neurometabolic disorder known to result in both white and gray matter pathology. This study sought to examine the structure of the callosum in a group of adult patients with NPC and compared callosal structure with a group of matched controls, and to relate callosal structure with state and trait illness variables. MATERIALS AND METHODS: Nine adult patients with NPC were matched to control subjects (n = 26) on age and sex. The corpus callosum was segmented from the midsagittal section of T1-weighted images on all subjects, and total area, length, bending angle, and mean thickness were calculated. In addition, 39 regional thickness measures were derived by using a previously published method. All measures were compared between groups, and analyzed alongside symptom measures, biochemical parameters, and ocular-motor measures. RESULTS: The callosal area and mean thickness were significantly reduced in the patient group, and regional thickness differences were greatest in the genu, posterior body, isthmus, and anterior splenium. Global callosal measures correlated significantly with duration of illness and symptom score, and at trend level with degree of filipin staining. Measures of reflexive saccadic peak velocity and gain, and self-paced saccades, correlated strongly with total callosal area. CONCLUSIONS: Callosal structure and size reflect both state and trait markers in adult NPC, and they may be useful biomarkers to index both white and gray matter changes that reflect illness severity and progression.


European Journal of Neurology | 2011

Pontine-to-midbrain ratio indexes ocular-motor function and illness stage in adult Niemann-Pick disease type C.

Mark Walterfang; Matthew D. Macfarlane; Jeffrey Chee Leong Looi; Larry A. Abel; Elizabeth A. Bowman; Michael Fahey; Patricia Desmond; Dennis Velakoulis

Background and purpose:  Niemann–Pick disease type C (NPC) is a progressive neurovisceral disorder associated with dystonia, ataxia and a characteristic gaze palsy. Neuropathological studies have demonstrated brainstem atrophy associated with neuronal inclusions and loss, and neurofibrillary tangles, although it is not known whether this pathology can be detected in vivo or how these changes relate to illness variables, particularly ocular‐motor changes. Our aim was to utilize a method for brainstem atrophy, validated in progressive supranuclear palsy (PSP), in a group of adult patients with NPC, and explore its relationship to illness variables and ocular‐motor functioning.


American Journal of Neuroradiology | 2013

Subcortical Volumetric Reductions in Adult Niemann-Pick Disease Type C: A Cross-Sectional Study

Mark Walterfang; Brian Patenaude; Larry A. Abel; Hans Kluenemann; Elizabeth A. Bowman; Michael Fahey; Patricia Desmond; Wendy Kelso; Dennis Velakoulis

BACKGROUND AND PURPOSE: Voxel-based analysis has suggested that deep gray matter rather than cortical regions is initially affected in adult Niemann-Pick type C. We sought to examine a range of deep gray matter structures in adults with NPC and relate these to clinical variables. MATERIALS AND METHODS: Ten adult patients with NPC (18–49 years of age) were compared with 27 age- and sex-matched controls, and subcortical structures were automatically segmented from normalized T1-weighted MR images. Absolute volumes (in cubic millimeters) were generated for a range of deep gray matter structures and were compared between groups and correlated with illness variables. RESULTS: Most structures were smaller in patients with NPC compared with controls. The thalamus, hippocampus, and striatum showed the greatest and most significant reductions, and left hippocampal volume correlated with symptom score and cognition. Vertex analysis of the thalamus, hippocampus, and caudate implicated regions involved in memory, executive function, and motor control. CONCLUSIONS: Thalamic and hippocampal reductions may underpin the memory and executive deficits seen in adult NPC. Volume losses in other subcortical regions may also be involved in the characteristic range of motor, psychiatric, and cognitive deficits seen in the disease.


Journal of Neurology | 2015

Longitudinal changes in cerebellar and subcortical volumes in adult-onset Niemann–Pick disease type C patients treated with miglustat

Elizabeth A. Bowman; Mark Walterfang; Larry A. Abel; Patricia Desmond; Michael Fahey; Dennis Velakoulis

Niemann–Pick disease type C (NPC) is a rare neurovisceral disorder resulting in impaired intracellular lipid trafficking. The only disease-modifying treatment available to date is miglustat, an iminosugar inhibiting the accumulation of lipid by-products in neurons. This study explored how changes in cerebellar grey and white matter volumes, and in subcortical volumes, related to patient treatment status and disability and ataxia ratings. Nine adult-onset NPC patients and 17 matched controls underwent T1-weighted MRI. One patient was not receiving miglustat, and pre-treatment data were available for a further patient. Semi-automated cerebellar and subcortical segmentation was undertaken, and the rates of change in putamen, hippocampal, thalamic and caudal volumes, and grey and white matter cerebellar volumes, were compared to rates of change in Iturriaga disability score, Brief Ataxia Rating Scale (BARS), and horizontal saccadic gain. Untreated NPC patients appeared to lose cerebellar grey and white matter, bilateral thalamic volume, and right caudate volume faster than treated patients. Cerebellar grey matter volume loss and volume loss in the left thalamus were significantly correlated with Iturriaga disability scale changes. Change in both cerebellar grey and white matter was correlated with decrease in horizontal saccadic gain, but not with change in BARS. This is the first study to examine longitudinal treatment effects of miglustat on cerebellar and subcortical volumes in patients with adult-onset NPC, and is evidence that miglustat may have a protective effect on cerebellar and subcortical structure and function.


PLOS ONE | 2012

Saccadic eye movement characteristics in adult Niemann-Pick Type C disease: relationships with disease severity and brain structural measures.

Larry A. Abel; Elizabeth A. Bowman; Dennis Velakoulis; Michael Fahey; Patricia Desmond; Matthew D. Macfarlane; Jeffrey Chee Leong Looi; Christopher L. Adamson; Mark Walterfang

Niemann-Pick Type C disease (NPC) is a rare genetic disorder of lipid metabolism. A parameter related to horizontal saccadic peak velocity was one of the primary outcome measures in the clinical trial assessing miglustat as a treatment for NPC. Neuropathology is widespread in NPC, however, and could be expected to affect other saccadic parameters. We compared horizontal saccadic velocity, latency, gain, antisaccade error percentage and self-paced saccade generation in 9 adult NPC patients to data from 10 age-matched controls. These saccadic measures were correlated with appropriate MRI-derived brain structural measures (e.g., dorsolateral prefrontal cortex, frontal eye fields, supplemental eye fields, parietal eye fields, pons, midbrain and cerebellar vermis) and with measures of disease severity and duration. The best discriminators between groups were reflexive saccade gain and the two volitional saccade measures. Gain was also the strongest correlate with disease severity and duration. Most of the saccadic measures showed strongly significant correlations with neurophysiologically appropriate brain regions. While our patient sample is small, the apparent specificity of these relationships suggests that as new diagnostic methods and treatments become available for NPC, a broader range of saccadic measures may be useful tools for the assessment of disease progression and treatment efficacy.


Molecular Genetics and Metabolism | 2013

Cerebellar volume correlates with saccadic gain and ataxia in adult Niemann-Pick type C.

Mark Walterfang; Larry A. Abel; Patricia Desmond; Michael Fahey; Elizabeth A. Bowman; Dennis Velakoulis

BACKGROUND AND PURPOSE Cerebellar Purkinje cells are known to be highly vulnerable to neuronal pathology in Niemann-Pick type C (NPC), a disease where widespread white matter changes have also been reported. We sought to determine the relationship between white and grey matter cerebellar changes and clinical variables in NPC. MATERIALS AND METHODS Ten adult patients with NPC were matched to control subjects (n=27) on age and gender. Patients were rated for symptom duration and severity, degree of ataxia, and were assessed for saccadic eye measures. Cerebellar white and grey matter volumes were automatically segmented using the Freesurfer software package. RESULTS NPC patients had a significant reduction in both grey and white matter volumes. Volume did not correlate with symptom duration or severity, but did correlate with saccadic gain and ataxia measures. CONCLUSIONS Both cerebellar grey and white matter volume decreases in adult NPC, and these changes are associated with impairments in saccadic gain and in motor control.


Archive | 2017

Longitudinal Changes in White Matter Fractional Anisotropy in Adult-Onset Niemann-Pick Disease Type C Patients Treated with Miglustat

Elizabeth A. Bowman; Dennis Velakoulis; Patricia Desmond; Mark Walterfang

Niemann-Pick disease type C (NPC) is a rare neurometabolic disorder resulting in impaired intracellular lipid trafficking. The only disease-modifying treatment currently available is miglustat, an iminosugar that inhibits the accumulation of lipid metabolites in neurons and other cells. This longitudinal diffusion tensor imaging (DTI) study examined how the rate of white matter change differed between treated and non-treated adult-onset NPC patient groups. Nine adult-onset NPC patients (seven undergoing treatment with miglustat, two not treated) underwent DTI neuroimaging. Rates of change in white matter structure as indexed by Tract-Based Spatial Statistics (TBSS) of fractional anisotropy were compared between treated and untreated patients. Treated patients were found to have a significantly slower rate of white matter change in the corticospinal tracts, the thalamic radiation and the inferior longitudinal fasciculus. This is further evidence that miglustat treatment may have a protective effect on white matter structure in the adult-onset form of the disease.


Archive | 2017

The Efficient Markets Hypothesis Does Not Hold When Securities Valuation Is Computationally Hard

Shireen Tang; Shijie Huang; Elizabeth A. Bowman; Nitin Yadav; Carsten Murawski; Peter Bossaerts

We study the Efficient Markets Hypothesis (EMH) in a setting where information heterogeneity emerges because securities valuation requires solving an NP-hard problem. We demonstrate experimentally that the quality of prices deteriorates substantially as computational complexity increases. Participants whose valuations are closer to true values earn more from trading. Participants improved their individual valuations by learning from market data, and their individual valuations on average were better than those reflected in market prices. These results are in sharp contrast with findings in experiments where correct valuation requires averaging of private information. They suggest that EMH only holds in very specific circumstances.


Neurology | 2009

Saccades in adult Niemann-Pick disease type C reflect frontal, brainstem, and biochemical deficits

Larry A. Abel; Mark Walterfang; Michael Fietz; Elizabeth A. Bowman; Dennis Velakoulis

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Andrew C. James

Australian National University

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Jeffrey Chee Leong Looi

Australian National University

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Matthew D. Macfarlane

Australian National University

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Michael Fietz

Boston Children's Hospital

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