57 research outputs found
Revisiting Brain Atrophy and Its Relationship to Disability in Multiple Sclerosis
Brain atrophy is a well-accepted imaging biomarker of multiple sclerosis (MS) that partially correlates with both physical disability and cognitive impairment.Based on MRI scans of 60 MS cases and 37 healthy volunteers, we measured the volumes of white matter (WM) lesions, cortical gray matter (GM), cerebral WM, caudate nucleus, putamen, thalamus, ventricles, and brainstem using a validated and completely automated segmentation method. We correlated these volumes with the Expanded Disability Status Scale (EDSS), MS Severity Scale (MSSS), MS Functional Composite (MSFC), and quantitative measures of ankle strength and toe sensation. Normalized volumes of both cortical and subcortical GM structures were abnormally low in the MS group, whereas no abnormality was found in the volume of the cerebral WM. High physical disability was associated with low cerebral WM, thalamus, and brainstem volumes (partial correlation coefficients ~0.3-0.4) but not with low cortical GM volume. Thalamus volumes were inversely correlated with lesion load (r = -0.36, p<0.005).The GM is atrophic in MS. Although lower WM volume is associated with greater disability, as might be expected, WM volume was on average in the normal range. This paradoxical result might be explained by the presence of coexisting pathological processes, such as tissue damage and repair, that cause both atrophy and hypertrophy and that underlie the observed disability
Correlations between Diffusion Tensor Imaging (DTI) and Magnetic Resonance Spectroscopy (1H MRS) in schizophrenic patients and normal controls
<p>Abstract</p> <p>Background</p> <p>Evidence suggests that white matter integrity may play an underlying pathophysiological role in schizophrenia. N-acetylaspartate (NAA), as measured by Magnetic Resonance Spectroscopy (MRS), is a neuronal marker and is decreased in white matter lesions and regions of axonal loss. It has also been found to be reduced in the prefrontal and temporal regions in patients with schizophrenia. Diffusion Tensor Imaging (DTI) allows one to measure the orientations of axonal tracts as well as the coherence of axonal bundles. DTI is thus sensitive to demyelination and other structural abnormalities. DTI has also shown abnormalities in these regions.</p> <p>Methods</p> <p>MRS and DTI were obtained on 42 healthy subjects and 40 subjects with schizophrenia. The data was analyzed using regions of interests in the Dorso-Lateral Prefrontal white matter, Medial Temporal white matter and Occipital white matter using both imaging modalities.</p> <p>Results</p> <p>NAA was significantly reduced in the patient population in the Medial Temporal regions. DTI anisotropy indices were also reduced in the same Medial Temporal regions. NAA and DTI-anisotropy indices were also correlated in the left medial temporal region.</p> <p>Conclusion</p> <p>Our results implicate defects in the medial temporal white matter in patients with schizophrenia. Moreover, MRS and DTI are complementary modalities for the study of white matter disruptions in patients with schizophrenia.</p
Clinical correlates of grey matter pathology in multiple sclerosis
Traditionally, multiple sclerosis has been viewed as a disease predominantly affecting white matter. However, this view has lately been subject to numerous changes, as new evidence of anatomical and histological changes as well as of molecular targets within the grey matter has arisen. This advance was driven mainly by novel imaging techniques, however, these have not yet been implemented in routine clinical practice. The changes in the grey matter are related to physical and cognitive disability seen in individuals with multiple sclerosis. Furthermore, damage to several grey matter structures can be associated with impairment of specific functions. Therefore, we conclude that grey matter damage - global and regional - has the potential to become a marker of disease activity, complementary to the currently used magnetic resonance markers (global brain atrophy and T2 hyperintense lesions). Furthermore, it may improve the prediction of the future disease course and response to therapy in individual patients and may also become a reliable additional surrogate marker of treatment effect
Cortisol, cognition and the ageing prefrontal cortex
The structural and functional decline of the ageing human brain varies by brain
region, cognitive function and individual. The underlying biological mechanisms are
poorly understood. One potentially important mechanism is exposure to
glucocorticoids (GCs; cortisol in humans); GC production is increasingly varied with
age in humans, and chronic exposure to high levels is hypothesised to result in
cognitive decline via cerebral remodelling. However, studies of GC exposure in
humans are scarce and methodological differences confound cross-study comparison.
Furthermore, there has been little focus on the effects of GCs on the frontal lobes and
key white matter tracts in the ageing brain. This thesis therefore examines
relationships among cortisol levels, structural brain measures and cognitive
performance in 90 healthy, elderly community-dwelling males from the Lothian
Birth Cohort 1936. Salivary cortisol samples characterised diurnal (morning and
evening) and reactive profiles (before and after a cognitive test battery). Structural
variables comprised Diffusion Tensor Imaging measures of major brain tracts and a
novel manual parcellation method for the frontal lobes. The latter was based on a
systematic review of current manual methods in the context of putative function and
cytoarchitecture. Manual frontal lobe brain parcellation conferred greater spatial and
volumetric accuracy when compared to both single- and multi-atlas parcellation at
the lobar level. Cognitive ability was assessed via tests of general cognitive ability,
and neuropsychological tests thought to show differential sensitivity to the integrity
of frontal lobe sub-regions. The majority of, but not all frontal lobe test scores shared
considerable overlap with general cognitive ability, and cognitive scores correlated
most consistently with the volumes of the anterior cingulate. This is discussed in
light of the diverse connective profile of the cingulate and a need to integrate
information over more diffuse cognitive networks according to proposed de-differentiation
or compensation in ageing. Individuals with higher morning, evening
or pre-test cortisol levels showed consistently negative relationships with specific
regional volumes and tract integrity. Participants whose cortisol levels increased
between the start and end of cognitive testing showed selectively larger regional
volumes and lower tract diffusivity (correlation magnitudes <.44). The significant
relationships between cortisol levels and cognition indicated that flatter diurnal
slopes or higher pre-test levels related to poorer test performance. In contrast, higher
levels in the morning generally correlated with better scores (correlation magnitudes
<.25). Interpretation of all findings was moderated by sensitivity to type I error,
given the large number of comparisons conducted. Though there were limited
candidates for mediation analysis, cortisol-function relationships were partially
mediated by tract integrity (but not sub-regional frontal volumes) for memory and
post-error slowing. This thesis offers a novel perspective on the complex interplay
among glucocorticoids, cognition and the structure of the ageing brain. The findings
suggest some role for cortisol exposure in determining age-related decline in
complex cognition, mediated via brain structure
A Comparison of Neuroimaging Abnormalities in Multiple Sclerosis, Major Depression and Chronic Fatigue Syndrome (Myalgic Encephalomyelitis): is There a Common Cause?
Bigger is better! Hippocampal volume and declarative memory performance in healthy young men
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Computer simulation of low-frequency electromagnetic data acquisition
Computer simulation of low frequency electromagnetic (LFEM) digital data acquisition in the presence of natural field noise demonstrates several important limitations and considerations. Without the use of a remote reference noise removal scheme it is difficult to obtain an adequate ratio of signal to noise below 0.1 Hz for frequency domain processing and below 0.3 Hz base frequency for time domain processing for a typical source-receiver configuration. A digital high-pass filter substantially facilitates rejection of natural field noise above these frequencies but, at lower frequencies where much longer stacking times are required, it becomes ineffective. Use of a remote reference to subtract natural field noise extends these low-frequency limits a decade, but this technique is limited by the resolution and dynamic range of the instrumentation. Gathering data in short segments so that natural field drift can be offset for each segment allows a higher gain setting to minimize dynamic range problems
Technique for rapidly estimating resistivity of the Earth from transient electromagnetic soundings
Neural correlates of high and craving during cocaine self-administration using BOLD fMRI.
Modern theories of drug dependence hold the hedonic effects of drugtaking central to understanding the motivation for compulsive drug use. Previous neuroimaging studies have begun to identify brain regions associated with acute drug effects after passive delivery. In this study, a more naturalistic model of cocaine self-administration (SA) was employed in order to identify those sites associated with druginduced high and craving as measures of reward and motivation. Nontreatment seeking cocaine-dependent subjects chose both when and how often i.v. cocaine administration occurred within a medically supervised SA procedure. Both functional magnetic resonance imaging (fMRI) data and real-time behavioral ratings were acquired during the 1-h SA period. Drug-induced HIGH was found to correlate negatively with activity in limbic, paralimbic, and mesocortical regions including the nucleus accumbens (NAc), inferior frontal/orbitofrontal gyrus (OFC), and anterior cingulate (AC), while CRAVING correlated positively with activity in these regions. This study provides the first evidence in humans that changes in subjective state surrounding cocaine self-administration reflect neural activity of the endogenous reward system.
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