Biomedical subjects

M S Mega

Publications and source records attributed to M S Mega.

31 records · Page 2Linked to original sources

PubMed1998

Cortical variability and asymmetry in normal aging and Alzheimer's disease.

The onset of Alzheimer's disease (AD) is accompanied by a complex and distributed pattern of neuroanatomic change, difficult to distinguish clinically from dynamic alterations in normal aging. Extreme variations in the sulcal patterns of the human cortex have made it difficult to identify diffuse and focal variations in cortical structure in neurodegenerative disease. We report the first comprehensive 3D statistical analysis of deep sulcal structure in vivo, in both normal aging and dementia. High-resolution 3D T1-weighted fast SPGR (spoiled GRASS) MRI volumes were acquired from 10 patients diagnosed with AD (NINCDS-ARDRA criteria; age: 71.9 +/- 10.7 years) and 10 normal subjects matched for age (72.9 +/- 5.6 years), gender, educational level and handedness. Scans were digitally transformed into Talairach stereotaxic space. To determine specific patterns of cortical variation in dementia patients, 3D average and probabilistic maps of primary deep sulci were developed for both normal and AD groups. Major sulci (including supracallosal, cingulate, marginal, parieto-occipital, anterior and posterior calcarine sulci, and Sylvian fissures) were modeled as complex systems of 3D surfaces using a multi-resolution parametric mesh approach. Variations and asymmetries in their extents, curvature, area and surface complexity were evaluated. Three-dimensional maps of anatomic variability, structural asymmetry and local atrophy indicated severe regionally selective fiber loss in AD. A midsagittal area loss of 24.5% at the corpus callosum's posterior midbody (P < 0.025) matched increases in structural variability in corresponding temporo-parietal projection areas. Confidence limits on 3D cortical variation, visualized in 3D, exhibited severe increases in AD from 2 to 4 mm at the callosum to a peak SD of 19.6 mm at the posterior left Sylvian fissure. Normal Sylvian fissure asymmetries (right higher than left; P < 0.0005), mapped for the first time in three dimensions, were accentuated in AD (P < 0.0002), and were greater in AD than in controls (P < 0.05). Severe AD-related increases in 3D variability and asymmetry may reflect disease-related disruption of the commissural system connecting bilateral temporal and parietal cortical zones, regions known to be at risk of early metabolic dysfunction, perfusion deficits and selective neuronal loss in AD.

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PubMed1998

Sulcal variability in the Alzheimer's brain: correlations with cognition.

We mapped the three dimensional (3D) extents and variability of selected sulci in the Alzheimer's brain and explored the relationship between sulcal pattern and patient's cognitive performance. High-resolution MRIs of 10 patients with probable Alzheimer's disease (AD) were linearly transformed into a standard "normalized" 3D atlas (known as the Talairach coordinate system) and, on each relevant slice, contours of the left and right Sylvian fissure, anterior and posterior calcarine, callosal, parietooccipital, and cingulate sulci and the floor of the temporal horn of the lateral ventricle were traced. These landmarks were chosen because of their relative invariant location across individuals and because they demarcate functional boundaries relevant in AD. The sulcal contours were resolved into two-dimensional surfaces that cut through a brain volume. All 10 patients' sulcal surfaces were averaged to determine their mean spatial locations in the Talairach coordinate system. The 3D spatial extents of each patient's sulci were compared with their disease severity based on neuropsychological performance. The 3D sulcal variability, within the "normalized" atlas space, ranged from 4.0 mm for the left callosal sulcus to 9.1 mm for the left Sylvian fissure. Significant correlations were found among the spatial extents for the posterior floor of the right temporal horn of the lateral ventricle (r = -0.89, p < 0.001 for vertical extent) and right anterior calcarine sulcus (r = -0.75, p < 0.01 for anterior-posterior extent) with copying ability of the Rey-Osterrieth Complex Figure; the right anterior calcarine also had a significant relationship (r = -0.72, p = 0.02 for anterior-posterior extent) with performance on the Block Design subtest from the Wechsler Adult Intelligence Scale-Revised. Verbal fluency performance measured by the Controlled Oral Word Association Test was significantly related to the left cingulate (r = 0.91, p < 0.001 for anterior-posterior extent, and r = -0.82, p < 0.01 for vertical extent) and right cingulate (r = -0.72, p < or = 0.02 for vertical extent) sulci. This exploratory study is the first to evaluate the relationship between 3D sulcal variability and cognition; our preliminary findings suggest that the 3D pattern of sulci in the AD brain is related to the severity of the disease as reflected by cognitive performance. In the Talairach brain atlas, sulcal variability, within an AD population, approaches 1 cm. This large variability requires correction when functional imaging data are transformed into the Talairach atlas space to "normalize" individual morphologic differences.

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PubMed1997

Mapping histology to metabolism: coregistration of stained whole-brain sections to premortem PET in Alzheimer's disease.

The association between [18F]fluorodeoxyglucose positron emission tomography (FDG-PET) counts obtained 8 h before death and neurofibrillary tangle (NFT) staining density in a patient with Alzheimer's disease (AD) was evaluated. In our patient FDG-PET counts were globally decreased with a greater focal deficit in the left medial temporal region independent of volume loss. After death, whole-brain sections derived from cryomacrotome sectioning were stained for NFTs by the Gallyas method and elastically warped into their native space enabling registration with premortem FDG-PET data. Gallyas staining density was localized to the paralimbic cortex of the basal forebrain, medial temporal, and orbital frontal regions. The poor correlation between NFT staining density and hypometabolism on FDG-PET implicates alternate mechanisms underlying the metabolic defect in AD.

Aged↗

PubMed1997

The limbic system: an anatomic, phylogenetic, and clinical perspective.

The limbic system is the border zone where psychiatry meets neurology. The authors provide a model of limbic function that combines phylogenetic, anatomic, functional, and clinical data to interpret diseases relevant to neuropsychiatry. They provide evidence supporting two major divisions in the limbic system: a paleocortical division with the amygdala and orbitofrontal cortex at its center, and an archicortical division with the hippocampus and cingulate cortex at its center. The implicit integration of affect, drives, and object associations is the function of the paleocortical limbic division; explicit sensory processing, encoding, and attentional control is the function of the archicortical limbic division. The two work in concert to integrate thought, feeling, and action. Understanding their development and organization informs us about how best to care for our patients.

Animals↗

PubMed1997

Akinetic mutism: disconnection of frontal-subcortical circuits.

Akinetic mutism may result from anterior cingulate lesions or a disconnection of the limbic connections projecting from the cingulate through subcortical circuits. Based on nonhuman primate primate tracer studies, ventral pallidal lesions should disrupt the anterior cingulate frontal-subcortical circuit. A patient developed a rigid akinetic mute state caused by bilateral lesions of the globus pallidus interna with ventral extension. The anatomic basis of the patient's clinical findings support a similarity in frontal-subcortical anatomy between humans and nonhuman primates. Isolated pallidal lesions are rare. Future studies should document whether ventral extension below the anterior commissure is associated with a loss of motivation.

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PubMed1996

The spectrum of behavioral changes in Alzheimer's disease.

We investigated the range of behavioral abnormalities in patients with Alzheimer's disease (AD) compared with normal age-matched control subjects. The range of behavioral disturbances manifested and the relationship between specific abnormalities with the level of cognitive impairment have not been established. Fifty consecutive outpatients with mild (n = 17), moderate (n = 20), and severe (n = 13) AD and 40 age-matched normal controls were evaluated for behavioral abnormalities occurring in the month preceding the interview. The caregivers of the patients and the spouses of the control subjects were interviewed with the Neuropsychiatric Inventory (NPI). The frequency and severity of the following 10 behaviors were assessed: delusions, hallucinations, agitation, dysphoria, anxiety, euphoria, apathy, disinhibition, irritability, and aberrant motor behavior. Correlations among these 10 behaviors and their relationship with cognitive impairment were also investigated. Eighty-eight percent of AD patients had measurable behavioral changes. All 10 behaviors were significantly increased in the AD patients compared with normal subjects. The most common behavior was apathy, which was exhibited by 72% of patients, followed by agitation (60%), anxiety (48%), irritability (42%), dysphoria and aberrant motor behavior (both 38%), disinhibition (36%), delusions (22%), and hallucinations (10%). Agitation, dysphoria, apathy, and aberrant motor behavior were significantly correlated wit cognitive impairment.

Aged↗

PubMed1996

Neuropsychiatric aspects of progressive supranuclear palsy.

Administering the Neuropsychiatric Inventory (NPI), we examined the behavioral symptoms of 22 patients with progressive supranuclear palsy (PSP), 50 patients with Alzheimer's disease, and 40 controls. PSP patients exhibited apathy (91%), disinhibition (36%), dysphoria (18%) and anxiety (18%), but rarely (< 9%) irritability, abnormal motor behaviors, or agitation. Apathy in PSP was significantly associated with executive dysfunction. The presence of high apathy and low agitation and anxiety scale scores correctly identified the PSP patients 85% of the time. Evaluating the behavioral abnormalities of patients with neurodegenerative disorders will aid diagnosis and facilitate management.

Aged↗

PubMed1996

Dementia with Lewy bodies: reliability and validity of clinical and pathologic criteria.

Clinical criteria for dementia with Lewy bodies (DLB) have been proposed, but their formulation, reliability, and validity require further study. Pathologic criteria for DLB are also undergoing evolution. Two studies were conducted with the goal of identifying the components of these evolving criteria that may benefit from further refinement; one study evaluated the components of the clinical criteria and another study operationalized the pathologic criteria for DLB. Twenty-four patients with a premorbid diagnosis of probable or possible Alzheimer's disease (AD) (n = 18), Parkinson's disease (PD) (n = 5), or progressive supranuclear palsy (PSP) (n = 1) were studied. Inter-rater reliability and validity of the clinical criteria were determined by a retrospective chart review, done by five neurologists, and a blinded pathologic evaluation. The Consortium on dementia with Lewy bodies (CDLB) pathologic criteria were operationalized to compare past criteria and test the validity of the evolving clinical criteria on the dementia patients. Three or more cortical fields (at 250 x magnification) with many (four or more) Lewy bodies (LBs) on ubiquitin immunoreactive sections were required to meet the CDLB neocortical score of > 6. Fifteen of the AD patients had at least one LB in a cortical section, four had many LBs, while three had no LBs; all patients with movement disorder had at least one LB in a cortical section. The sensitivity/specificity ratio of the CDLB probable DLB clinical criteria based upon many LBs being present was 75%/79%. Reformulated clinical criteria that require the presence of extrapyramidal signs significantly predicted those patients with many LBs versus those with few or no LBs (chi 2 = 5.48, p = 0.02) and increased clinical specificity to 100%. This preliminary study identifies components of the evolving clinical and pathologic criteria for DLB that require further refinement.

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PubMed1995

Alien hand syndrome: interhemispheric motor disconnection due to a lesion in the midbody of the corpus callosum.

The neuroanatomic substrate of the alien hand syndrome has remained controversial due to the noncircumscribed nature of cerebral injuries present in most cases. There have been few cases studied in which damage was restricted to portions of the body of the callosum, and most of those involved surgical callosotomy for tumors or epilepsy. We report the case of a woman with a transient alien hand syndrome caused by a stroke limited to the middle and posterior portions of the body of the corpus callosum. This case provides supportive evidence for damage to the midbody of the corpus callosum as the anatomic basis of nondominant alien hand syndrome and conforms to a model of interhemispheric motor disconnection as the essential component of this unusual behavioral syndrome. This disconnection can occur with injuries involving interhemispheric premotor and motor fibers traveling in the midportion of the callosum in individuals with left hemisphere dominance for motor activities.

Aged↗

PubMed1994

Frontal-subcortical circuits and neuropsychiatric disorders.

Five parallel anatomic circuits link regions of the frontal cortex to the striatum, globus pallidus/substantia nigra, and thalamus. The circuits originate in the supplementary motor area, frontal eye fields, dorsolateral prefrontal region, lateral orbito-frontal area, and anterior cingulate cortex. Open loop structures that provide input to or receive output from specific circuits share functions, cytoarchitectural features, and phylogenetic histories with the relevant circuits. The circuits mediate motor and oculomotor function as well as executive functions, socially responsive behavior, and motivation. Neuropsychiatric disorders of frontal-subcortical circuits include impaired executive function, disinhibition, and apathy; indicative mood disorders include depression, mania, and lability. Transmitters, modulators, receptor subtypes, and second messengers within the circuits provide a chemoarchitecture that can inform pharmacotherapy.

Brain↗

PubMed1994

Subcortical aphasia: the core profile of capsulostriatal infarction.

There has been disagreement about the precise characteristics of "subcortical aphasia." We evaluated 14 patients with aphasia after subcortical lesions and controlled for duration, general anatomic site of lesions (capsulostriatal only), and etiology. The clinical profiles of the patients were quite similar, varying in severity in rough proportion to lesion size and varying in quality in proportion to anterior paraventricular extent. Large lesions were associated with impaired "executive" and "generative" language functions. Similar aphasia profiles in patients with deep frontal and paraventricular white matter lesions suggest that damage to a frontal-caudate functional system underlies a "core" aphasia profile in these patients.

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PubMedDate not supplied

Detection and mapping of abnormal brain structure with a probabilistic atlas of cortical surfaces.

PURPOSE: We have devised, implemented, and tested a technique for creating a comprehensive probabilistic atlas of the human cerebral cortex, based on high-dimensional fluid transformations. The goal of the atlas is to detect and quantify subtle and distributed patterns of deviation from normal cortical anatomy, in a 3D brain image from any given subject. METHOD: Given a 3D MR image of a new subject, a high-resolution surface representation of the cerebral cortex is automatically extracted. The algorithm then calculates a set of high-dimensional volumetric maps, fluidly deforming this surface into structural correspondence with other cortical surfaces, selected one by one from an anatomic image database. The family of volumetric warps so constructed encodes statistical properties of local anatomical variation across the cortical surface. Additional strategies are developed to fluidly deform the sulcal patterns of different subjects into structural correspondence. A probability space of random transformations, based on the theory of anisotropic Gaussian random fields, is then used to encode information on complex variations in gyral and sulcal topography from one individual to another. A complete system of 256(2) probability density functions is computed to reflect the observed variability in stereotaxic space of the points whose correspondences are found by the warping algorithm. Confidence limits in stereotaxic space are determined for cortical surface points in the new subject's brain. RESULTS: Color-coded probability maps are generated, which highlight and quantify regional patterns of deformity in the anatomy of new subjects. These maps indicate locally the probability of each anatomic point being as unusually situated, given the distributions of corresponding points in the scans of normal subjects. 3D MRI volumes are analyzed, from subjects with clinically determined Alzheimer disease and age-matched normal subjects. CONCLUSION: Applications of the random fluid-based probabilistic atlas include the transfer of multisubject 3D functional, vascular, and histologic maps onto a single anatomic template, the mapping of 3D atlases onto the scans of new subjects, and the rapid detection, quantification, and mapping of local shape changes in 3D medical images in disease and during normal or abnormal growth and development.

Aged↗

PubMedDate not supplied

Analyzing functional brain images in a probabilistic atlas: a validation of subvolume thresholding.

PURPOSE: The development of structural probabilistic brain atlases provides the framework for new analytic methods capable of combining anatomic information with the statistical mapping of functional brain data. Approaches for statistical mapping that utilize information about the anatomic variability and registration errors of a population within the Talairach atlas space will enhance our understanding of the interplay between human brain structure and function. METHOD: We present a subvolume thresholding (SVT) method for analyzing positron emission tomography (PET) and single photon emission CT data and determining separately the statistical significance of the effects of motor stimulation on brain perfusion. Incorporation of a priori anatomical information into the functional SVT model is achieved by selecting a proper anatomically partitioned probabilistic atlas for the data. We use a general Gaussian random field model to account for the intrinsic differences in intensity distribution across brain regions related to the physiology of brain activation, attenuation effects, dead time, and other corrections in PET imaging and data reconstruction. RESULTS: H2(15)O PET scans were acquired from six normal subjects under two different activation paradigms: left-hand and right-hand finger-tracking task with visual stimulus. Regional region-of-interest and local (voxel) group differences between the left and right motor tasks were obtained using nonparametric stochastic variance estimates. As expected from our simple finger movement paradigm, significant activation (z = 6.7) was identified in the left motor cortex for the right movement task and significant activation (z = 6.3) for the left movement task in the right motor cortex. CONCLUSION: We propose, test, and validate a probabilistic SVT method for mapping statistical variability between groups in subtraction paradigm studies of functional brain data. This method incorporates knowledge of, and controls for, anatomic variability contained in modern human brain probabilistic atlases in functional statistical mapping of the brain.

Adult↗