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S Kapur

Publications and source records attributed to S Kapur.

At least 145 records · Page 8Linked to original sources
PubMed1995

The statistical power of [15O]-water PET activation studies of cognitive processes.

[15O]-Water positron emission tomography (PET) scanning is an important means of investigating the neural correlates of cognitive processes. This study analyses the statistical power of these experiments under usual experimental conditions. Eleven subjects were scanned repeatedly while they undertook an active-baseline task. Using an empirically derived estimate of variance, the statistical power to detect task-induced increases in regional cerebral blood flow was calculated for different values of magnitude of change, number of subjects and probability of Type I error. The results (a) provide an empirical basis for selecting the number of subjects for cognitive studies using [15O]-water PET; (b) illustrate the importance of considering the statistical power of the test, while making a physiological interpretation of the results; and (c) highlight the problems in concluding the non-involvement of a given brain region in a cognitive task, based solely on the results of a PET study.

Adult↗
PubMed1994

Novelty encoding networks in the human brain: positron emission tomography data.

Data from positron emission tomography (PET) studies showed novelty activations--higher regional cerebral blood flow associated with perceiving novel rather than familiar stimuli. Regions in the right 'expanded' limbic system--hippocampal formation, parahippocampal gyrus, retrosplenial cortex, thalamus, subcallosal area, the border between cortical areas 32 and 10, anterior and inferior cingulate cortex, putamen, and medial prefrontal cortex--showed such activations for complex pictures. Because novel information is usually encoded for storage in memory, these regions can be seen as constituting components of a visual/spatial novelty encoding network. Insular, opercular and temporal regions (e.g. area 37) showed novelty activations not only for visual pictures but also for auditorily presented sentences, and can be thought of as components of a transmodal novelty encoding network.

Auditory Pathways↗
PubMed1994

The role of the left prefrontal cortex in verbal processing: semantic processing or willed action?

This study was designed to test the various proposed explanations (semantic processing, willed action, production of a spoken response) for the unilateral activation of the left prefrontal cortex noted in PET studies of verbal processing. Twenty subjects underwent 15O-water PET scans while undertaking a lexical task (detecting the letter 'a' in visually presented words) and a semantic task (categorizing nouns into living/non-living). The semantic task resulted in a significant unilateral left dorsolateral prefrontal activation. This finding suggests that the left inferior prefrontal cortex is the anatomical region involved in 'working with meaning', and that the activation does not reflect willed action, is not task-specific and is not attributable to the requirements of a spoken response.

Adult↗
PubMed1994

Activation of specific cortical regions by apomorphine: an [15O]H2O PET study in humans.

The purpose of this study was to investigate the functional effects of apomorphine, a non-selective dopamine agonist, on regional neuronal activity using regional cerebral blood flow, measured using [15O]H2O and positron emission tomography (PET), as an index. Eight normal volunteers were scanned twice before and twice after receiving 10 micrograms/kg subcutaneous apomorphine. Apomorphine produced the expected side-effects and endocrine response. Analysis of the PET scans revealed that apomorphine increased regional cerebral blood flow (rCBF), presumably reflecting a change in neuronal activity, in the anterior cingulate, ventral motor cortex and the dorsolateral prefrontal cortex along with a decrease in rCBF in the retrosplenial cingulate region. These regions form a functional network of brain regions modulated by the dopaminergic system.

Adult↗
PubMed1994

Modulation of cortical neuronal activity by a serotonergic agent: a PET study in humans.

This study investigates the effect of a serotonergic agent, fenfluramine, on neuronal activity, as measured using [18F]fluorodeoxyglucose (FDG) uptake with positron emission tomography (PET) in humans. Eleven subjects each received oral fenfluramine and placebo, on two different occasions, followed by FDG PET scans. Our study shows that fenfluramine modulates ongoing neuronal activity in a regionally specific fashion with a relative increase in metabolism in the prefrontal cortex and a relative decrease in the occipital-temporal regions.

Adult↗
PubMed1994

Rhabdomyosarcoma of the clitoris.

Genitourinary rhabdomyosarcoma in females usually originates in the vagina or uterus, but rarely the vulva. The authors present a case of rhabdomyosarcoma originating in the clitoris. A 4-year-old with an alveolar rhabdomyosarcoma of the clitoris was treated with radical clitorectomy, radiation, and chemotherapy. Follow-up at 3 years showed no active disease.

Child, Preschool↗
PubMed1994

Relapse of acute lymphoblastic leukemia in the inferior rectus muscle of the eye.

BACKGROUND: Extramedullary involvement of acute lymphoblastic leukemia (ALL) in sites outside the central nervous system (CNS) or testes is rare and may signal a refractory form of leukemia. METHODS: The authors describe a child with ALL who experienced a relapse involving the inferior rectus muscle of the eye. This patient had been treated with a bone marrow transplant for previous bone marrow and ovarian relapse. RESULTS: The patients had a pre-B ALL with a t(1;19) chromosomal translocation and previously had experienced relapse during therapy. At the time of the muscle relapse, she had pancreatomegaly consistent with leukemic infiltration but no CNS or bone marrow disease. CONCLUSIONS: Relapse of ALL in unusual sites may indicate disease that is particularly difficult to eradicate. Factors in addition to age and leukocyte count at diagnosis determined risk. Additional research is needed to define these factors and develop more effective therapy.

Child, Preschool↗
PubMed1994

Neuroanatomical correlates of encoding in episodic memory: levels of processing effect.

Cognitive studies of memory processes demonstrate that memory for stimuli is a function of how they are encoded; stimuli processed semantically are better remembered than those processed in a perceptual or shallow fashion. This study investigates the neural correlates of this cognitive phenomenon. Twelve subjects performed two different cognitive tasks on a series of visually presented nouns. In one task, subjects detected the presence or absence of the letter a; in the other, subjects categorized each noun as living or nonliving. Positron emission tomography (PET) scans using 15O-labeled water were obtained during both tasks. Subjects showed substantially better recognition memory for nouns seen in the living/nonliving task, compared to nouns seen in the a-checking task. Comparison of the PET images between the two cognitive tasks revealed a significant activation in the left inferior prefrontal cortex (Brodmann's areas 45, 46, 47, and 10) in the semantic task as compared to the perceptual task. We propose that memory processes are subserved by a wide neurocognitive network and that encoding processes involve preferential activation of the structures in the left inferior prefrontal cortex.

Adult↗
PubMed1994

Neuroanatomical correlates of retrieval in episodic memory: auditory sentence recognition.

This study used positron emission tomography (PET) to investigate the neuroanatomical correlates of remembering previously experienced events. Twelve young healthy adults listened to "old" meaningful sentences which they had studied 24 hr previously. As a control task the subjects listened to comparable "new" sentences that they had never heard before. Regional cerebral blood flow associated with each task was measured by PET scans using 15O-labeled water. Comparison (old-sentence task minus new-sentence task) of the PET images revealed an extended strip of increased blood flow in the right dorsolateral prefrontal cortex (Brodmann's areas 10, 46, and 9) and the anterior portion of area 6. Other principal regions of increased blood flow were situated around the left anterior cingulate sulcus and bilaterally in the parietal lobes (areas 7 and 40). Major decreases in blood flow were situated bilaterally in the temporal lobes (areas 21, 22, 41, and 42). A high proportion of activity changes seemed to be located in the depths of cortical sulci. Increases in blood flow are seen as reflecting the operations of a widely distributed neuronal network involving prefrontal and parietal cortical regions that subserves the conscious recollection of previously experienced events. Decreases in blood flow in the temporal auditory areas are interpreted as reflecting auditory priming. The prevalence of sulcal blood-flow changes may reflect extensive cortical gyrification; it may also indicate that memory-related processes rely on the densely packed neuropil of sulcal regions.

Adult↗
PubMed1994

Hemispheric encoding/retrieval asymmetry in episodic memory: positron emission tomography findings.

Data are reviewed from positron emission tomography studies of encoding and retrieval processes in episodic memory. These data suggest a hemispheric encoding/retrieval asymmetry model of prefrontal involvement in encoding and retrieval of episodic memory. According to this model, the left and right prefrontal lobes are part of an extensive neuronal network that subserves episodic remembering, but the two prefrontal hemispheres play different roles. Left prefrontal cortical regions are differentially more involved in retrieval of information from semantic memory and in simultaneously encoding novel aspects of the retrieved information into episodic memory. Right prefrontal cortical regions, on the other hand, are differentially more involved in episodic memory retrieval.

Brain↗
PubMed1994

Developmental changes in angiotensin II receptor subtypes and AT1 receptor mRNA in rat kidney.

The changes in angiotensin II receptor subtypes, type 1 (AT1) and type 2 (AT2) binding, and AT1 mRNA levels during development were studied in the rat kidney using autoradiographic and in situ hybridization techniques. Autoradiographic analysis of 125I-[Sar1,Ile8]Ang II binding to slide-mounted kidney sections from 2 and 5 day-old rats discerned AT2 binding sites associated with advancing tubules and ampullae of the ureteric bud, and in the metanephric mass in the nephrogenic zone of the cortex. AT1 binding was present in the metanephric mass and immature glomeruli on days 2, 5 and 7 after birth. Differentiating and mature kidneys of 14-day, 21-day and 14-week old adult rats had solely AT1 receptor binding over glomeruli in renal cortex and in the inner stripe of the outer medulla. AT1 mRNA was expressed discretely as early as 2 days of age in the immature glomeruli and in a diffuse radiating pattern in the renal cortex. In the medulla, AT1 receptor mRNA expression appeared discretely on day 7 and reached peak levels on day 21 in the inner stripe of the outer medulla. The data indicate that AT1 receptor mRNA is developmentally regulated in rat kidney and its expression in the cortex precedes that of AT1 receptor ligand binding. The temporal pattern of expression of binding for both receptor subtypes suggests that while AT2 receptors may be involved in cell proliferation and early differentiation of the nephron, AT1 receptors have a dual role, early in nephron differentiation and later in development in renal function.

Animals↗
PubMed1994

Absence of residual effects after physiological stimulation of the visual and motor cortex: an [15O]-H2O PET study in humans.

Cognitive experiments using positron emission tomography (PET) with [15O]-H2O require multiple scans done at 10 to 12 min intervals. Momose and colleagues reported that regional cerebral blood flow changes in response to visual stimulation do not return to baseline even 15 min after the stimulation. If confirmed, this fact would have important implications for the design and interpretation of PET cognitive studies. The purpose of this study was to determine the temporal course of residual effects following visual and motor stimulation. Six healthy volunteers undertook six scans each. Two scans were done to establish a baseline, one to observe the task induced activation, and three scans to investigate the residual effects at varying intervals after the task. The data were analysed using both statistical parametric mapping and a region of interest analysis. The visual and motor task produced robust activations bilaterally in the occipital cortex and in the contralateral primary motor cortex. There was no evidence for a statistically significant residue effect at any of the three intervals studied (30 s, 3 and 6 min). Our results refute the findings of Momose and colleagues and suggest that the 10-min interscan interval is more than adequate to re-establish a resting baseline.

Adult↗
PubMed1994

Clinical aspects of the MASA syndrome in a large family, including expressing females.

We have evaluated, both clinically and by linkage analysis, a large family with 22 known affected males with the MASA syndrome (McKusick 303300). Clinical findings varied widely amongst the affected family members, with some appearing initially to have the MASA syndrome and others to have X-linked hydrocephalus (HSAS) (McKusick 307000). Important findings included the presence of adducted thumbs in two obligate carriers, learning problems or mild mental retardation in three females, two of whom were obligate carriers, and hydrocephalus with neonatal death in three females born to obligate carriers. X-inactivation analysis in lymphocytes from the two women with adducted thumbs revealed preferential inactivation of one X chromosome, suggesting that nonrandom X-inactivation may be responsible for clinical expression in females. The presence of HSAS in some individuals of this family and the MASA syndrome in others further supports the hypothesis that these two conditions are the result of a mutation in the same gene.

Child, Preschool↗
PubMed1994

Diphallus and associated anomalies with balanced autosomal chromosomal translocation.

We report a sporadic case of complete diphallus with multiple other anomalies in a premature newborn. Chromosomal analysis at the 500 band level showed an apparently balanced reciprocal translocation 46,XY, t(1;14)(p36.3;q24.3). The mother has a normal karyotype, but the father was not available for chromosomal analysis. The significance of this balanced chromosomal rearrangement and the possibility that the chromosomal breakpoints contribute to deregulation of mesodermal development is discussed.

Abnormalities, Multiple↗
PubMed1994

Elucidation of biochemical basis of the antidepressant action of electroconvulsive therapy by human studies.

A variety of direct and indirect human studies indicate that electroconvulsive therapy (ECT) enhances transmission in a number of key transmitter systems in the brain. These include the noradrenergic system, the serotonergic system, and the GABAergic and dopaminergic systems. On the other hand, ECT probably reduces cholinergic transmission. The enhanced transmission effects have been related to the antidepressant effect of ECT, whereas the cholinergic effect has been attributed to its effects on memory and cognition as well as depression. This paper will briefly review the research methodologies and results from clinical studies of neurotransmitter effects of ECT. Promising future directions of research will be indicated.

Biogenic Monoamines↗