Author name cluster

Marnie E. Shaw

Possible papers associated with this exact author name in Arrow. This page groups case-insensitive exact name matches and is not a full identity disambiguation profile.

7 papers

1 author row

YNIMG Journal 2020 Journal Article

Objectively measured physical activity is associated with dorsolateral prefrontal cortex volume in older adults

Joseph M. Northey
Ben Rattray
Kate L. Pumpa
Disa J. Pryor
Mark A. Fraser
Marnie E. Shaw
Kaarin J. Anstey
Nicolas Cherbuin

Background Epidemiological studies suggest physical activity (PA) can slow or prevent both cognitive decline and age-related atrophy in frontal and hippocampal gray matter volumes. However, much of this evidence is based on self-reported measures of PA. Methods PA was measured objectively with a SenseWear™ Armband to examine the cross-sectional associations between the duration of light, moderate and vigorous intensity PA with gray matter volume in the dorsolateral prefrontal cortex (DLPFC) and hippocampus in 167 (female: 43%) cognitively healthy older adults aged 73 to 78. Results The duration of objective moderate to vigorous intensity physical activity (MVPA) was associated with a greater volume of the right DLPFC (β = 0. 16; p = 0. 04). In addition, objective moderate-intensity PA alone was also associated with greater volume of the left (β = 0. 17; p = 0. 03) and right (β = 0. 19; p = 0. 01) DLPFC after controlling for covariates and adjustment for multiple comparisons. In contrast, there were no significant associations between light- or vigorous-intensity PA and gray matter volumes (all p > 0. 05). No associations between PA and cognitive performance were detected, and self-reported PA was not associated with any of the outcomes investigated. Conclusions These findings suggest that an intensity-dependent relationship may exist, whereby a greater duration of MVPA, perhaps driven by moderate-intensity PA, is associated with preserved gray matter volume in frontal regions of the brain. Future research should investigate the mechanisms of this dose-effect and determine whether greater brain volumes associated with objective PA convey protective effects against cognitive decline.

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YNIMG Journal 2015 Journal Article

A systematic review and meta-analysis of longitudinal hippocampal atrophy in healthy human ageing

Mark A. Fraser
Marnie E. Shaw
Nicolas Cherbuin

Introduction This review aimed to produce hippocampal atrophy rate estimates from healthy ageing studies as well as control samples from observational studies across the adult lifespan which can be used as benchmarks to evaluate abnormal changes in pathological conditions. Methods The review followed PRISMA guidelines. PUBMED (to February 2014) was searched for longitudinal MRI studies reporting hippocampal atrophy or volume change in cognitively healthy individuals. Titles were screened and non-English, duplicate or irrelevant entries were excluded. Remaining record abstracts were reviewed to identify studies for full text retrieval. Full text was retrieved and screened against inclusion/exclusion criteria. Bibliographies and previous reviews were examined to identify additional studies. Data were summarised using meta-analysis and age, segmentation technique and study type were tested as potential moderators using meta-regression. It was hypothesised that population studies would produce higher atrophy rates than clinical observational studies. Results The systematic search identified 4410 entries and 119 studies were retrieved with 58 failing selection or quality criteria, 30 were excluded as multiple reports and 3 studies were unsuitable for meta-analysis. The remaining 28 studies were included in the meta-analysis, n=3422, 44. 65% male, 11, 735person-years of follow-up, mean age was 24. 50 to 83years. Mean total hippocampal atrophy for the entire sample was 0. 85% per year (95% CI 0. 63, 1. 07). Age based atrophy rates were 0. 38% per year (CI 0. 14, 0. 62) for studies with mean age <55years (n=413), 0. 98% (CI 0. 27, 1. 70) for 55 to <70years (n=426), and 1. 12% (CI 0. 86, 1. 38) for ≥70years (n=2583). Meta-regression indicated age was associated with increased atrophy rates of 0. 0263% (CI 0. 0146, 0. 0379) per year and automated segmentation approaches were associated with a reduced atrophy rate of −0. 466% (CI −0. 841, −0. 090). Population studies were not associated with a significant effect on atrophy. Analyses of 11 studies separately measuring left and right hippocampal atrophy (n=1142) provided little evidence of laterality effects. While no study separately reported atrophy by gender, a number tested for gender effects and 2 studies reported higher atrophy in males. Conclusions Hippocampal atrophy rates increase with age with the largest increases occurring from midlife onwards. Manual segmentation approaches result in higher measured atrophy rates.

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YNIMG Journal 2013 Journal Article

How anatomical asymmetry of human auditory cortex can lead to a rightward bias in auditory evoked fields

Marnie E. Shaw
Matti S. Hämäläinen
Alexander Gutschalk

Auditory evoked fields and potentials, such as the N1 or the 40-Hz steady state response, are often stronger in the right compared to the left auditory cortex. Here we investigated whether a greater degree of cortical folding in left auditory cortex could result in increased MEG signal cancelation and a subsequent bias in MEG auditory signals toward the right hemisphere. Signal cancelation, due to non-uniformity of the orientations of underlying neural currents, affects MEG and EEG signals generated by any neuronal activity of reasonable spatial extent. We simulated MEG signals in patches of auditory cortex in seventeen subjects, and measured the relationships between underlying activity distribution, cortical non-uniformity, signal cancelation and resulting (fitted) dipole strength and position. Our results suggest that the cancelation of MEG signals from auditory cortex is asymmetric, due to underlying anatomy, and this asymmetry may result in a rightward bias in measurable dipole amplitudes. The effect was significant across all auditory areas tested, with the exception of planum temporale. Importantly, we also show how the rightward bias could be partially or completely offset by increased cortical area, and therefore increased cortical activity, on the left side. We suggest that auditory researchers are aware of the impact of cancelation and its resulting rightward bias in signal strength from auditory cortex. These findings are important for studies seeking functional hemispheric specialization in the auditory cortex with MEG as well as for integration of MEG with other imaging modalities.

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YNIMG Journal 2005 Journal Article

How reliable are fMRI–EEG studies of epilepsy? A nonparametric approach to analysis validation and optimization

Anthony B. Waites
Marnie E. Shaw
Regula S. Briellmann
Angelo Labate
David F. Abbott
Graeme D. Jackson

Simultaneously acquired functional magnetic resonance imaging (fMRI) and electroencephalography (EEG) data hold great promise for localizing the spatial source of epileptiform events detected in the EEG trace. Despite a number of studies applying this method, there has been no independent and systematic validation of the approach. The present study uses a nonparametric method to show that interictal discharges lead to a blood oxygen level dependent (BOLD) response that is significantly different to that obtained by examining random ‘events’. We also use this approach to examine the optimization of analysis strategy for detecting these BOLD responses. Two patients with frequent epileptiform events and a healthy control were studied. The fMRI data for each patient were analyzed using a model derived from the timings of the epileptiform events detected on EEG during fMRI scanning. Twenty sets of random pseudoevents were used to generate a null distribution representing the level of chance correlation between the EEG events and fMRI data. The same pseudoevents were applied to control data. We demonstrate that it is possible to detect blood oxygen level-dependent (BOLD) changes related to interictal discharges with specific and independent knowledge about the reliability of this activation. Biologically generated events complicate the fMRI–EEG experiment. Our proposed validation examines whether identified events have an associated BOLD response beyond chance and allows optimization of analysis strategies. This is an important step beyond standard analysis. It informs clinical interpretation because it permits assessment of the reliability of the connection between interictal EEG events and the BOLD response to those events.

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YNIMG Journal 2003 Journal Article

Evaluating subject specific preprocessing choices in multisubject fMRI data sets using data-driven performance metrics

Marnie E. Shaw
Stephen C. Strother
Maria Gavrilescu
Katherine Podzebenko
Anthony Waites
John Watson
Jon Anderson
Graeme Jackson

This study investigated the possible benefit of subject specific optimization of preprocessing strategies in functional magnetic resonance imaging (fMRI) experiments. The optimization was performed using the data-driven performance metrics developed recently [Neuroimage 15 (2002), 747]. We applied numerous preprocessing strategies and a multivariate statistical analysis to each of the 20 subjects in our two example fMRI data sets. We found that the optimal preprocessing strategy varied, in general, from subject to subject. For example, in one data set, optimum smoothing levels varied from 16 mm (4 subjects), 10 mm (5 subjects), to no smoothing at all (1 subject). This strongly suggests that group-specific preprocessing schemes may not give optimum results. For both studies, optimizing the preprocessing for each subject resulted in an increased number of suprathresholded voxels in within-subject analyses. Furthermore, we demonstrated that we were able to aggregate the optimized data with a random effects group analysis, resulting in improved sensitivity in one study and the detection of interesting, previously undetected results in the other.

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YNIMG Journal 2002 Journal Article

Abnormal Functional Connectivity in Posttraumatic Stress Disorder

Marnie E. Shaw
Stephen C. Strother
Alexander C. McFarlane
Philip Morris
Jon Anderson
C.Richard Clark
Gary F. Egan

This study investigated the efficacy of a combined multivariate/resampling procedure for the analysis of PET activation studies. The covariance-based multivariate analysis was used to investigate distributed brain systems in posttraumatic stress disorder (PTSD) patients and matched controls during performance of a working memory task. The results were compared to univariate results obtained in an earlier study. We also examined whether the PTSD patients demonstrated a breakdown in functional connectivity that may be associated with working memory difficulties often experienced by these patients. A resampling procedure was used specifically to test the reliability of measured between-group effects, to avoid mistaken inference on the basis of random intersubject differences. Significant and reproducible differences in network connectivity were obtained for the two groups. The functional connectivity pattern of the patient group was characterized by relatively more activation in the bilateral inferior parietal lobes and the left precentral gyrus than the control group, and less activation in the inferior medial frontal lobe, bilateral middle frontal gyri and right inferior temporal gyrus. The resampling procedure provided direct evidence that working memory updating was abnormal in PTSD patients relative to matched controls. This work focuses on the need to identify extended brain networks (in addition to regionally specific changes) for the full characterization of brain responses in neuroimaging experiments. Our multivariate analysis explicitly measures the reliability of the patterns of functional connectivity we obtain and demonstrates the potential of such analyses for the study of brain network dysfunction in psychopathology.

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YNIMG Journal 2002 Journal Article

Simulation of the Effects of Global Normalization Procedures in Functional MRI

Maria Gavrilescu
Marnie E. Shaw
Geoffrey W. Stuart
Peter Eckersley
Imants D. Svalbe
Gary F. Egan

We report on differences in sensitivity and false-positive rate across five methods of global normalization using resting-state fMRI data embedded with simulated activation. These methods were grand mean session scaling, proportional scaling, ANCOVA, a masking method, and an orthogonalization method. We found that global normalization by proportional scaling and ANCOVA decreased the sensitivity of the statistical analysis and induced artifactual deactivation even when the correlation between the global signal and the experimental paradigm was relatively low. The masking method and the orthogonalization method performed better from this perspective but are both restricted to certain experimental conditions. Based on the results of these simulations, we offer practical guidelines for the choice of global normalization method least likely to bias the experimental results.

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