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Biomedical subjects

B Horwitz

Publications and source records attributed to B Horwitz.

At least 19 recordsLinked to original sources
PubMed1992

Interregional correlations of resting cerebral glucose metabolism in old and young women.

A correlational analysis of normalized (regional to whole-brain) regional cerebral metabolic rates for glucose obtained in the 'resting' state (eyes covered, ears plugged) using [18F]fluorodeoxyglucose, demonstrated differences between old and young women in patterns of functional associations. Fifteen healthy young (age less than 40 years) and 17 healthy old women (age greater than 64 years) were scanned with a Scanditronix PC1024-7B tomograph. The brain was divided into 65 regions of interest. The old women had fewer and less positive correlations between pairs of metabolic ratios in the frontal and parietal cortices. The results suggest an age-related reduction in frontal and parietal functional interactions in the 'resting' state that is consistent with a prior correlation analysis using a low resolution ECAT II scanner on young and old men. Reduced functional interactions may reflect age-related cognitive changes.

Adult↗
PubMed1992

Gender differences in correlations of cerebral glucose metabolic rates in young normal adults.

Correlational analysis of normalized regional cerebral metabolic data obtained by positron emission tomography, in healthy subjects in the 'resting' state (eyes covered, ears plugged) using [18F]2-fluoro-2-deoxy-D-glucose, demonstrated gender differences in patterns of functional associations. Fifteen women and 18 men (less than 40 yr) were scanned with a Scanditronix PC1024-7B tomograph. The brain was divided into 65 regions of interest (ROIs). There were no differences between men and women in global or regional metabolic rates, or in metabolic right-left asymmetries. Although the total number of significant correlations did not differ between men and women, patterns differed: female correlations rF were most positive than male correlations rM more often than rM greater than rF; and most rF greater than rM cases involved left frontal and sensorimotor ROIs, whereas most rM greater than rF cases involved right sensorimotor and occipital ROIs. The findings demonstrate gender differences in the pattern of functional neocortical interactions at the 'resting' state.

Adult↗
PubMed1992

Age-related differences in volumes of subcortical nuclei, brain matter, and cerebrospinal fluid in healthy men as measured with magnetic resonance imaging.

Magnetic resonance imaging was used to determine the volumes of brain, subcortical gray matter nuclei, and the ventricular and sulcal cerebrospinal fluid in 27 healthy men. Subjects were divided into young (less than 35 years, n = 10) and old (greater than 60 years, n = 17) groups. Volumes were normalized as percent intracranial volume. Older subjects had significantly less brain mass and significantly larger ventricular and peripheral cerebrospinal fluid volumes than the younger men. The caudate and lenticular nuclei were significantly smaller in older than younger men. This significant difference remained when their volumes were expressed as a ratio of cerebral brain matter volume. This cross-sectional study demonstrates age-related atrophy and concurrent dilation of cerebrospinal fluid spaces in healthy subjects. Of brain regions affected, the caudate and lenticular nuclei are significantly more affected by healthy aging than is cerebral brain matter; this may account for some of the motor abnormalities in aging.

Adult↗
PubMed1992

Brain atrophy in hypertension. A volumetric magnetic resonance imaging study.

To determine whether hypertension, the predominant risk factor for stroke and vascular dementia, is associated with brain atrophy, magnetic resonance imaging (MRI) scans were performed to quantify brain volumes and cerebrospinal fluid spaces. Eighteen otherwise healthy, cognitively normal older hypertensive men (mean +/- SD age, 69 +/- 8 years, duration of hypertension 10-35 years) and 17 age-matched healthy, normotensive male control subjects were studied in a cross-sectional design. Axial proton-density image slices were analyzed using region-of-interest and segmentation analyses. The hypertensive subjects had significantly larger mean volumes of the right and left lateral ventricles (p less than 0.05, both absolute volume and volume normalized to intracranial volume) and a significantly smaller normalized mean left hemisphere brain volume (p less than 0.05) with a trend toward significance for a smaller normalized mean right hemisphere volume (p less than 0.09). Four hypertensive subjects and one healthy control subject were found to have severe periventricular hyperintensities on T2-weighted MRI images. When data for these subjects were removed from the analyses, the normalized lateral ventricle volumes remained significantly larger in the hypertensive group. Lateral ventricle enlargement was not related to age or use of diuretics in the hypertensive group nor to duration of hypertension between 10 and 24 years. Our findings suggest that long-standing hypertension results in structural changes in the brain. Longitudinal studies will determine whether MRI-associated changes are progressive and if such changes identify hypertensive subjects at increased risk for clinically apparent brain dysfunction.

Adult↗
PubMed1991

Dissociation of object and spatial visual processing pathways in human extrastriate cortex.

The existence and neuroanatomical locations of separate extrastriate visual pathways for object recognition and spatial localization were investigated in healthy young men. Regional cerebral blood flow was measured by positron emission tomography and bolus injections of H2(15)O, while subjects performed face matching, dot-location matching, or sensorimotor control tasks. Both visual matching tasks activated lateral occipital cortex. Face discrimination alone activated a region of occipitotemporal cortex that was anterior and inferior to the occipital area activated by both tasks. The spatial location task alone activated a region of lateral superior parietal cortex. Perisylvian and anterior temporal cortices were not activated by either task. These results demonstrate the existence of three functionally dissociable regions of human visual extrastriate cortex. The ventral and dorsal locations of the regions specialized for object recognition and spatial localization, respectively, suggest some homology between human and nonhuman primate extrastriate cortex, with displacement in human brain, possibly related to the evolution of phylogenetically newer cortical areas.

Adult↗
PubMed1991

Abnormal brain glucose metabolism in Alzheimer's disease, as measured by position emission tomography.

Resting glucose metabolism in the association neocortices, measured with positron emission tomography (PET), is disturbed early and throughout the course of Alzheimer's disease (AD), whereas resting metabolism in the primary sensory and motor neocortices is relatively spared. Neocortical metabolic asymmetries precede and predict appropriate deficits in neocortically-mediated cognitive functions in the initial course of disease, indicating that PET can be used for the early diagnosis and characterization of AD. Metabolic abnormalities of the neocortices in late-stage AD correlate with regional densities of neurofibrillary tangles but not of senile plaques post mortem, suggesting that tangle formation is important in disease pathogenesis. Despite demonstrating reduced resting glucose metabolism, visual association areas demonstrate equivalent (as percent baseline) blood flow responses in mildly-moderately demented AD patients and controls who are performing a face matching task. Thus, viability and integrity of this cortical circuitry is retained into the intermediate stages of the disease, and glucose delivery to the AD brain can be increased.

Alzheimer Disease↗
PubMed1991

Mapping the functional neuroanatomy of the intact human brain with brain work imaging.

The recent development of noninvasive methods for measuring local rates of energy metabolism or blood flow in the brain has made it possible to investigate functional neuroanatomy in healthy human subjects. The best of these methods, high resolution measurement of regional cerebral blood flow (rCBF) with positron emission tomography (PET), provides a precision of anatomical localization that far exceeds that attainable with human brain lesion studies. Moreover, the study of healthy subjects avoids possible confounding effects of brain lesions, such as compensatory reorganization of brain function. PET-rCBF studies have already identified several cortical areas involved in higher-order visual processing, indicating that functional neuroimaging may yield a map of human visual cortex analogous to maps that have been developed by vision research in nonhuman primates. PET-rCBF studies of imagery and language demonstrate the potential of functional neuroimaging to map regions of human cortex that perform functions that cannot be studied so easily in nonhuman primates or perform functions that humans do not share with other species.

Attention↗
PubMed1991

Cerebral metabolic pattern in obsessive-compulsive disorder: altered intercorrelations between regional rates of glucose utilization.

Correlations between normalized regional cerebral metabolic rates for glucose, determined by positron emission tomography with 18F-2-fluoro-2-deoxy-D-glucose, were used to investigate functional associations between pairs of brain regions in 18 adult patients with primary obsessive-compulsive disorder (OCD) of childhood-onset, as compared with 18 age- and sex-matched control subjects. The number of correlations that differed significantly between the two groups exceeded chance, although as many of these correlations were larger in the OCD group relative to controls as were smaller. The two regions that had the largest number of correlations that differed significantly between groups were a left hemisphere superior parietal region and the left hemisphere anterior medial temporal area (which includes principally the amygdala). Correlations involving the caudate nuclei did not differ between the two groups for the most part. Anterior limbic/paralimbic regions had correlations in the OCD group that were significantly larger with frontal areas than in controls, and correlations that were significantly smaller with posterior brain regions. This pattern was especially pronounced for the left hemisphere anterior medial temporal region. These results suggest that the correlation pattern in OCD is not characterized by an overall loss of functional integration but, rather, by functional reorganization.

Adult↗
PubMed1991

Functional interactions in the brain: use of correlations between regional metabolic rates.

Correlation coefficients between pairs of regional metabolic rates have been used to study patterns of functional associations among brain regions in humans and animals. An overview is provided concerning the additional information about brain functioning this type of analysis yields. A computer simulation model is presented for the purpose of giving a partial validation for correlational analysis. The model generates a set of simulated metabolic data upon which correlational analysis is performed. Because the underlying pattern of functional couplings in the model is known, these simulations demonstrate that the correlation coefficient between normalized metabolic rates is proportional to the strength of the functional coupling constant and that correlational analysis yields information on regional involvement in neural systems not evident in the pattern of absolute metabolic values.

Adult↗
PubMed1990

Longitudinal study of cerebral metabolic asymmetries and associated neuropsychological patterns in early dementia of the Alzheimer type.

Regional cerebral metabolic rates for glucose (rCMRglc), as measured with positron emission tomography, and neuropsychological function were studied longitudinally (range, 15 to 48 months) in 11 mildly impaired patients with dementia of the Alzheimer type (DAT) and compared with results from patients with moderate and severe DAT and from controls. At initial evaluation, association cortex metabolic asymmetries were greater in patients with DAT than in controls for all dementia severities and correlated significantly with neuropsychological discrepancies between visuospatial and language abilities in patients with moderate dementia. In mildly impaired patients, right-left metabolic asymmetries in the association cortices were directionally stable and became more pronounced over time. At initial evaluation, these patients had significant impairment, relative to controls, on tests of memory and attention to complex tasks but not on tests of language and visuospatial function. Memory, attention, language, and visuospatial impairments, however, all worsened significantly over time. In mildly impaired patients, correlations between right-left metabolic asymmetries and neuropsychological discrepancies were insignificant initially but were significant at last evaluation. These results demonstrate that heterogeneous nonmemory language and visuospatial impairments in early DAT are related to and predicted by the earlier-appearing distribution of metabolic reductions in the association neocortex.

Aged↗
PubMed1990

White matter hyperintensities in dementia of Alzheimer's type and in healthy subjects without cerebrovascular risk factors. A magnetic resonance imaging study.

T2-weighted (0.5 T) magnetic resonance images were used to study the prevalence of subcortical white matter hyperintensities (WMHIs) in 22 patients with dementia of Alzheimer's type (DAT), 20 age-matched older healthy control subjects, and 10 younger healthy control subjects. Exclusionary criteria for all groups included cerebrovascular risk factors. All subjects had Hachinski Ischemic Index scores of less than 2 and computed tomographic scans showing no infarct. The WMHIs were classified as periventricular WMHIs or deep WMHIs and graded 0 through 3 (0 indicated absent, and 3, severe). For the group with DAT and older control subjects, periventricular WMHIs and deep WMHIs were graded 2 or 3 in fewer than 17% and 27% of subjects, respectively, whereas in the younger control subjects, all ratings were grade 1 or less. Serum cholesterol and systolic blood pressure values, although within the normal range, were elevated significantly in older control subjects when compared with those in younger control subjects. No significant differences in WMHI ratings, blood pressure, cholesterol, or triglyceride levels were found between patients with DAT and age-matched control subjects. Systolic blood pressure levels correlated with the severity of periventricular WMHIs only in older control subjects. Age correlated with periventricular WMHIs and deep WMHIs within both the older control subjects and the patients with DAT. There was no significant correlation between WMHIs and the severity of dementia in the group with DAT. These results suggest that, in subjects screened for cerebrovascular risk factors, WMHIs are rare and occur with identical frequency in patients with DAT as in age-matched healthy control subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1990

Effect of gender on glucose utilization rates in healthy humans: a positron emission tomography study.

Positron emission tomography (PET) was used with 18fluorodeoxyglucose to see if gender differences in resting cerebral glucose utilization could be detected. Thirty-two healthy subjects (15 women and 17 men; age range: 21-38 yr) were examined using a high-resolution PET scanner to determine the regional cerebral metabolic rate for glucose (CMRglc) in 65 gray matter regions of interest. Whole brain CMRglc did not differ significantly between the two genders, nor did any of the regional CMRglc values. Only 1 of 65 ratios of regional-to-whole brain CMRglc differed significantly between men and women, which is consistent with chance. These results indicate that there are no differences in resting regional cerebral glucose utilization between young men and women.

Adult↗
PubMed1990

Simulating functional interactions in the brain: a model for examining correlations between regional cerebral metabolic rates.

A computer simulation model was developed to investigate the use of interregional correlations of cerebral metabolic rates to analyze functional interactions in the brain. The model generates simulated metabolic data for individual brain regions in a specified number of subjects, where there are defined functional couplings amongst the regions. Random numbers provide the variability seen in measured metabolic data. Correlational analysis is performed on these simulated data sets. The parameters of the model can be chosen so that simulated and actual metabolic data are very similar. The model demonstrates that the change in the correlation coefficient between normalized metabolic data in two brain regions is related to the change in the strength of the functional association between the two regions. The model also is used to explore the relations between patterns of correlations and the underlying sets of functional couplings. The results indicate that correlational analysis provides more information about regional involvement in neural systems than does region-by-region comparisons of absolute metabolic rates.

Adult↗
PubMed1990

Cerebral metabolic pattern in young adult Down's syndrome subjects: altered intercorrelations between regional rates of glucose utilization.

Correlations between regional cerebral metabolic rates for glucose, determined by positron emission tomography with [18F]-2-fluoro-2-deoxy-D-glucose, have been used to indicate functional associations between pairs of brain regions. This method was applied to data from 14 healthy adult subjects with trisomy 21 Down's syndrome (age less than 34 years) and from 24 age-matched healthy controls. Correlations were obtained between ratios of regional-to-global resting glucose utilization. In comparison to age-matched controls, the Down's syndrome group had many smaller correlations for region-pairs within and between the frontal and parietal lobes; some correlations were large and negative in the Down's syndrome group, but large and positive in the controls. One region so affected was the inferior frontal gyrus that includes Broca's area. This result is consistent with the relatively greater language impairment in Down's syndrome subjects. The thalamus also had smaller correlations with temporal and occipital regions in the Down's syndrome group compared to controls. These results suggest that Down's syndrome is accompanied by a functional disruption of neural circuits associated with directed attention.

Adult↗
PubMed1990

A mathematical model for vasogenic brain edema.

A two-dimensional model of vasogenic brain edema was constructed using the FEM. The model incorporates the following physical parameters: cerebrovascular hydraulic conductivity, metabolic water production, tissue hydraulic conductivity and compliance, tissue and plasma osmotic and hydrostatic pressures, CSF hydrostatic pressure and absorption, intracerebral stress, and shift of brain tissue. These parameters, related by partial differential equations, were approximated numerically in time and space by the FEM. The results of computer simulation of brain edema by the FEM were compared with experimental data of cold injury brain edema in cats. Computer simulation predicted the observed changes in interstitial pressure, extension of edema, intracerebral stress distribution, and displacement.

Animals↗
PubMed1989

Replicated item level factor structure of the MMPI: racial and sexual differences.

Item-level factor studies of the MMPI date back to the work of Comrey (1957). Surprisingly, there are no extant studies of the items that clinicians use most in the course of daily MMPI interpretive reporting, namely, the 399 x 399 matrix that represents all of the items that comprise the traditional clinical and validity scales. Furthermore, there are no prior studies with adequate Ns that have examined the replicability of MMPI factor structure via available factor comparison techniques (Harman, 1976). In this study, 20,000 MMPIs were factored by the principal components method, followed by Varimax rotations of 6 through 25 factors. The coefficient of congruence was used to compare the factor structures of randomly divided subsamples, as well as males vs. females and Blacks vs. Whites. Differences in factor structure were found, and suggestions are made with regard to the significance of these findings in clinical and applied settings.

Adult↗