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Biomedical subjects

R Duara

Publications and source records attributed to R Duara.

At least 91 records · Page 5Linked to original sources
PubMed1991

Cerebrocerebellar relationship during behavioral activation: a PET study.

The effect of behavioral activation on cerebral and cerebellar glucose metabolism was studied in normal subjects when performing either a verbal memory task or a tactile somatosensory task. Each subject was also studied in a resting state control condition, either 1 h earlier or later than the activation task. Compared to the resting state, both tasks produced asymmetrical metabolic activation, which was opposite in direction within the cerebral and cerebellar hemispheres. In both tasks, the difference of activation of CMRglc in the right and left hemispheres in the cerebellum was negatively correlated with that in the sensory-motor region. This apparently coupled metabolic activation of one cerebellum and areas within the opposite cerebral hemisphere represents the inverse of the crossed cerebellar diaschisis phenomenon commonly observed when a vascular lesion affects one cerebral hemisphere and hypometabolism occurs in the opposite cerebellum. Because these correlations were selective and concordant with known anatomical connections, and were found in two different tasks, they suggest strong functional connections between these specific brain regions.

Aged↗
PubMed1991

Positron emission tomographic studies during serial word-reading by normal and dyslexic adults.

Positron-emission tomography (PET) was used to study regional cerebral metabolic activity during oral reading in right-handed adult males with, and without a childhood and family history of developmental dyslexia. Significant group differences in normalized regional metabolic values were revealed in prefrontal cortex and in the lingual (inferior) region of the occipital lobe. Lingual values were bilaterally higher for dyslexic than normal readers. In contrast to the asymmetry observed in prefrontal and lingual regions in nondyslexic subjects during reading, the dyslexic pattern was more symmetric. These results demonstrate that individuals who suffered from familial developmental dyslexia as children, activate different brain regions during reading as adults, as compared to individuals without such childhood history.

Adult↗
PubMed1991

Metabolic asymmetries in asymptomatic HIV-1 seropositive subjects: relationship to disease onset and MRI findings.

Fifteen male homosexual subjects (mean age 31.6 +/- 7.2 yr) who were asymptomatic, but HIV-1 seropositive (HIV+) were compared to 15 male age-matched HIV-1 seronegative (HIV-) subjects using resting PET/FDG studies and MR scans. Mean cerebral metabolic rates for glucose (mg/100 g/min) in the HIV+ and HIV- subjects were 7.7 +/- 1.7 and 7.0 +/- 2.1, (p = 0.44), respectively. An index of regional metabolic asymmetry for the whole brain was 5.8% +/- 3.2% in the HIV+ and 2.7% +/- 2.3% in the HIV- (p = 0.002), and the difference was most prominent in the prefrontal area. Significant asymmetries were found in 10/15 HIV+ subjects, primarily in prefrontal (7/15) and premotor (4/15) regions. MRI scans showed no abnormalities on clinical or quantitative evaluation in HIV+ subjects. Upon follow-up of HIV+ subjects over 18-40 mo, seven became symptomatic, of which two died. There was no relationship between the presence of PET scan abnormalities and earlier onset of symptomatic disease.

Adult↗
PubMed1990

Frontal hypermetabolism and thalamic hypometabolism in a patient with abnormal orienting and retrosplenial amnesia.

A patient with verbal amnesia and a propensity to direct his attention to the right following a retrosplenial area lesion was studied with positron emission tomography using [F-18] fluorodeoxyglucose. These studies showed that the left thalamus was hypometabolic, and the anterior 2/3 of the left hemisphere was hypermetabolic when compared with the right. There were no significant differences seen in the medial temporal lobes. Based on this study, it is posited that interruption of hippocampal input into the anterior thalamus was responsible for the amnesia, and the left frontal hyperactivity was associated with the propensity to attend contralaterally.

Adult↗
PubMed1990

MR signal abnormalities in memory disorder and dementia.

MR imaging of the brain, performed in 86 normal subjects and 113 patients with objective memory disorder or dementia, demonstrated white- and gray-matter areas of high signal intensity on long TR images (short and long TE). Hyperintensities were analyzed with respect to size (on a scale of 0-3) and location: lesions were periventricular, subcortical, or cortical. The patients with memory disorder and dementia were categorized as having probable/possible Alzheimer disease, a combination of Alzheimer disease and multiinfarct cognitive disorder, or multiinfarct cognitive disorder alone on the basis of clinically determined Hachinski ischemic scores. Significant correlations were found between age and scores for periventricular lesions (r = .40, p less than .0005) and subcortical lesions (r = .39, p less than .0005) in normal subjects. Correlations were also found between the Hachinski ischemic score and scores for periventricular lesions (r = .21, p less than .01), subcortical lesions (r = .27, p less than .0002), and cortical lesions (r = .32, p less than .0005) in subjects with memory disorder/dementia. Comparing multiinfarct cognitive disorder, Alzheimer disease, and normal groups, the mean scores for periventricular lesions were 12.0 +/- 4.6, 7.6 +/- 4.8, and 3.4 +/- 2.6, while mean scores for subcortical lesions were 10.8 +/- 12.2, 4.1 +/- 6.4, and 0.8 +/- 1.2, respectively. Periventricular lesions were present in 99-100% of patients with Alzheimer disease and multiinfarct cognitive disorder. On the other hand, subcortical lesions, which were identified in 100% of patients with multiinfarct cognitive disorder, were present in only about half of the patients with Alzheimer disease. Thus, scores for both periventricular and subcortical lesions are positively correlated with age and risk factors for cerebrovascular disease and also are significantly increased in the presence of objective memory disorder or dementia. These results imply that in the subject groups considered here, elderly patients with vascular dementia are most likely to have severe white-matter abnormalities on MR scans. The score for subcortical lesions appears to be more helpful than the score for periventricular lesions in distinguishing vascular dementia from Alzheimer disease and normal aging, so that a patient with prominent subcortical white-matter abnormalities is more likely to have a diagnosis of vascular than degenerative dementia.

Adult↗
PubMed1990

[Cerebral white matter bundle alterations in patients with dementia of Alzheimer type and patients with multi-infarct dementia--magnetic resonance imaging study].

The widths of the anterior white matter bundle (AWM) and the interhemispheric (AWM-TER) and intrahemispheric (AWM-TRA) bundles at the level of the foramen of Monro on horizontal inversion recovery MRI scans were measured in 17 patients with dementia of Alzheimer type (DAT), 16 patients with multi-infarct dementia (MID) and 47 age-matched normal subjects (NOR). The area of the corpus callosum (CC) on midsagittal spin-echo MRI scans was also measured in 12 DAT, 11 MID and 36 NOR. The Mini-mental score in patients with DAT was 20.8 +/- 5.9, which was not significantly different from that of 22.9 +/- 5.4 in patients with MID. The width of AWM was not significantly decreased in either DAT or MID compared with NOR. However, the width of AWM-TER in DAT and MID showed a significant decrease from that in NOR. The width of AWM-TRA was decreased significantly only in DAT. Compared with NOR, the area of the CC in DAT and MID was decreased by 7.0% (p less than 0.05) and 6.5%, respectively. The white matter bundle has an important role in the connectivity of the brain. Although loss of white matter occurs in both DAT and MID, the change appears more diffuse in DAT than MID.

Aged↗
PubMed1989

Asymmetric somatosensory activation with right- vs left-hand stimulation: a positron emission tomographic study.

Metabolic activation of the right and left somatosensory cortices (SSC) in response to an active sensorimotor task (palpation and sorting of mah jongg tiles) was studied in 16 right-handed normal volunteers using positron emission tomography (PET) and a double-injection [18F]fluorodeoxyglucose strategy. In 8 subjects with right-hand stimulation, cerebral metabolic rate for glucose (CMRglc) in the contralateral SSC increased by 16.7 +/- 5.1% (mean +/- S.D.); the increase in the ipsilateral SSC was 4.8 +/- 3.2%. In contrast, in the 8 subjects with left-hand stimulation, the contralateral increase was 12.0 +/- 2.9% and the ipsilateral increase was 5.9 +/- 1.5%. Thus, contralateral SSC activation was significantly higher with stimulation of the right hand, while the ipsilateral/contralateral symmetry of activation was greater when the left hand was stimulated.

Adult↗
PubMed1989

Predominant left hemisphere metabolic dysfunction in dementia.

Thirty-one patients with probable Alzheimer's disease and 11 patients with memory disorders, attributable to multiple cerebral infarctions, were studied using 18-F-fluorodeoxyglucose-positron emission tomography scans. Asymmetry in cerebral glucose metabolism within these diagnostic groups was assessed by comparison with the metabolic rates obtained in age-equivalent healthy control subjects. A significantly greater number of individuals in both patient groups exhibited predominant left rather than right hemisphere hypometabolism. In addition, for patients with Alzheimer's disease, the degree of asymmetry was not related to either the severity or duration of dementia. These findings could be explained by greater susceptibility of the left hemisphere to degenerative or ischemic brain disease, by a specific sampling effect, or most likely, by greater metabolic deficits resulting from left rather than right hemisphere impairment.

Brain↗
PubMed1989

A new scale for the assessment of functional status in Alzheimer's disease and related disorders.

Assessment of the functional competencies of patients with dementia is typically conducted in an indirect manner. Psychological tests of cognition or descriptions by relatives or other caregivers are often used to make judgments as to the patient's ability to adapt to the demands of the environment. However, these methods have built-in biases. The need for direct assessment of functional status was addressed by developing a standardized operational procedure to examine areas of functional competence which may become impaired in Alzheimer's disease and other related memory disorders. The resulting instrument has high interrater and test-retest reliabilities. Convergent validity is evidenced by significant correlations between the scale and established measures of functional status. Patients with Alzheimer's disease exhibited deficits in functional capacities relative to age-equivalent normal controls and to elderly patients with a primary major depression.

Activities of Daily Living↗
PubMed1989

Sensitivity and specificity of positron emission tomography and magnetic resonance imaging studies in Alzheimer's disease and multi-infarct dementia.

Positron emission tomographic (PET) scans using [18F]-fluorodeoxyglucose and magnetic resonance imaging (MRI) scans were quantitatively analyzed for metabolic and structural abnormalities in normal subjects and patients classified as having Alzheimer's disease (AD), mixed dementia and multi-infarct dementia (MID) according to Hachinski ischemic scores. MRI-detected abnormalities in the periventricular white matter and in subcortical locations increased in incidence with age in normals and increased markedly in AD and especially in MID. Upper limits for the severity of these white matter lesions could be defined only for normal young and elderly subjects, but not for AD, mixed or MID patients. PET scan abnormalities occurred in about 90% of demented patients and in 54% of elderly and 34% of young normals. There was no characteristic pattern of abnormality that distinguished MID from AD patients. It is concluded that PET and MRI studies in demented patients are useful ancillary tests especially in evaluating the mild, questionably demented subject and for assessing the functional impact of structural disease.

Aged↗
PubMed1989

[Cerebral white matter bundle measurements by magnetic resonance imaging].

The width of the anterior whole white matter bundle (AWM), interhemispheric (AWM-TER), and intrahemispheric (AWM-TRA) components at the level of the foramen of Monro on horizontal inversion recovery (IR) magnetic resonance (MR) scans were measured in 32 healthy males. The mean age of subjects were 54.4 +/- 18.8, ranged 25 to 83 years old. MR scans were performed using a 0.5 Tesla superconductive magnet, with inversion time of 400 msec, repetition time of 2.1 sec and echo time of 35 msec. The slice thickness was 10mm. Horizontal maximum internal skull diameter (HISD) at the same level was also measured and normalized values of AWM, AWM-TER, AWM-TRA were calculated by dividing the width of AWM, AWM-TER, AWM-TRA by the width of HISD. When absolute values of each AWM width were compared between right and left sides, there were no differences in AWM and AWM-TER. However, AWM-TRA of the right side was significantly wider than that of the left side (t = 4.28, p less than 0.001). The width of AWM was not correlated with age, but the width of AWM-TER showed a significant decline in the left (r = -0.36, p = 0.04) and non-significant trend to decline in the right side (r = -0.33, p = 0.07). The width of AWM-TRA of the left side was tended to decrease with age. Normalized values of AWM, AWM-TER, AWM-TRA showed a similar results as that of the absolute values. The measurement of the white matter bundle width provide some insights into the connectivity of the brain.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1989

[Size of the corpus callosum in normal subjects and patients with Alzheimer's disease--magnetic resonance imaging study].

The area of the corpus callosum (CC) on midsagittal spin-echo sequence magnetic resonance (MR) scans was measured in 64 normal subjects and 12 patients with Alzheimer's disease (AD). The normal subjects consisted of 32 males and 32 females, aged 25 to 83 years old. There was no significant age difference between males and females. Fifty-five out of 64 subjects were right-handed (RH) and 9 were left-handed or ambidextrous (NRH). Among patients with AD, 5 were males and 7 were females, aged 53 to 79 years old. Diagnosis of AD was performed mainly based on clinical history, magnetic resonance image (MRI) and positron emission tomographic findings. The outline of the CC on midsagittal MR film was traced and the total callosal sectional area (CCT) as well as the anterior half (CCA), posterior half (CCP) and posterior 5th or splenium (CCS) area measurements were performed using a planimeter. In either normal males or females, the CCA showed a significant negative correlation with age, but the CCP and the CCS did not correlate with age. Total CC (CCT) area was 691.2 +/- 91.0 sq. mm for the whole group and no difference was found between males and females. When the CC area was normalized with respect to the midsagittal area of the supratentorial portion of the brain (MSB), females were found to have a larger CC than males. No portion of the CC area was significantly different between RH and NRH subjects in absolute or normalized measures.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1989

Two behavioral states studied in a single PET/FDG procedure: error analysis.

In a previous publication the theory, procedure, and results of a method were described for making two sequential measurements of cerebral metabolic rate for glucose (CMRglc), within a 2-hr period, using [18F]fluorodeoxyglucose. The error that is specific to this technique was estimated using computer simulations. CMRglc for the second state was sensitive to errors in (a) the values of the rate constants, (b) alignment of PET slices between the two scans, and (c) subtraction of one PET image from another. The root mean square of the average error from each error source was 6.4%, which gives the theoretical reliability of this method. The measured reproducibility, taken from our previous publication, was 4.2-6.2%, which is in good agreement with the present result. This method contributes a small additional error above that expected for two independent scans. However, independent scans done on different days are likely to be subject to larger physiological variations in CMRglc than would occur using this method.

Brain↗
PubMed1988

Hemispheric asymmetries, fourth ventricular size, and cerebellar morphology in autism.

Hemispheric asymmetries, fourth ventricular size, and cerebellar morphology were examined in 15 healthy men, aged 18 to 39 years, with documented childhood diagnoses of infantile autism, and in 20 healthy age- and sex-matched controls using computerized transverse axial tomography (CT). Nine patients were of approximately average intelligence, 3 showed specific language impairments, and 3 were mentally retarded. No significant group differences were seen in the distributions of frontal or posterior asymmetries of width or petalia. No subject showed evidence of cerebellar atrophy or an enlarged fourth ventricle. These results fail to support a hypothesis of unusual hemispheric asymmetry or macroscopic abnormalities of the posterior fossa in autism.

Adolescent↗
PubMed1988

Sensitivity of cerebral glucose metabolism to age, gender, brain volume, brain atrophy, and cerebrovascular risk factors.

In 76 normal volunteers studied by positron emission tomography, with [18F]fluorodeoxyglucose, CMRglu was significantly lower in the elderly as compared with young subjects and significantly higher in females relative to males. However, in 58 of these subjects who also had magnetic resonance imaging scans, age and gender were found to be unrelated to CMRglu, when the effects of brain volume and brain atrophy on CMRglu were partialed out using covariate analyses. Individually, brain volume was found to have a significant effect on CMRglu, explaining approximately 17% of the variability in CMRglu measures and brain atrophy explaining approximately 8% of the variance in CMRglu. Together these two measures accounted for approximately 21% of the variance. Cerebrovascular risk factors in normal subjects were not found to affect mean CMRglu or the variability of CMRglu measures. In this study almost 80% of the variance in CMRglu could not be explained by any of the factors that had been considered. This implies a lack of sensitivity of absolute values of global CMRglu to the mild effects of brain dysfunction. Although some of the unexplained variance is probably methodological in origin, physiological factors that are difficult to quantify, such as the state of arousal, are likely to be contributory as well.

Adult↗
PubMed1988

Cerebral metabolic effects of a verbal fluency test: a PET scan study.

Sixteen normal volunteers were studied with [F-18] fluorodeoxyglucose and positron emission tomography scans during behavioral activation with a verbal fluency test, and 35 age-matched controls were studied with resting-state scans. There was an overall increase of the cerebral glucose metabolic rate of 23.3% during verbal fluency activation, compared to the resting state, with the greatest activation in bilateral temporal and frontal lobes. A negative correlation between test performance scores and indices of metabolism was found in frontal, temporal, and parietal regions. Damage to the left frontal lobe maximally affects scores on verbal fluency tests, but performing the test activates a network of regions, of which the left frontal lobe is only one. Proficient performance in verbal fluency seems to require less metabolic activation than poor performance, perhaps because of the efficiency of cognitive strategies employed.

Adult↗
PubMed1988

Dyslexia subtypes: genetics, behavior, and brain imaging.

This study was designed to identify inherited subtypes of specific dyslexia and to characterize these types by a variety of studies. A previous linkage study in large three-generation families resulted in a LOD score of 3.24 at a 13% recombination frequency between dyslexia and normal variations for the short arm of chromosome 15. The odds for linkage with chromosome 15 markers are better than 1,000 to 1. We estimate that 30% of an extended series of families show linkage to chromosome 15 polymorphisms. Other linkages remain to be identified. PET scanning is being used to examine measures of regional cerebral glucose metabolism during two types of reading by (adult) dyslexics and normal readers. MRI is also being used to examine pertinent brain structures. Behavioral tests are also in progress. The long-term goals of this study are to develop specific genetic and other diagnostic techniques that can be used to test children before beginning school and to develop sufficient understanding of the abnormal brain function of each subtype so that specific and effective remedial programs can be developed.

Brain↗