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Biomedical subjects

S M Rao

Publications and source records attributed to S M Rao.

At least 19 recordsLinked to original sources
PubMed2003

Prevalence of renovascular abnormality in patients undergoing cardiac catheterization.

OBJECTIVE: To determine the prevalence of renal artery disease and to correlate the underlying risk factors like age, sex, diabetes, hypertension, urea and creatinine in patients who have undergone angiogram for cardiovascular diseases. METHODS: Retrospective analysis of the reports of angiogram of patients who have undergone cardiac catheterization in Vijaya Heart Foundation for cardiovascular diseases. RESULTS: The prevalence of renovascular stenosis is 12.4%. Prevalence of hypertension and diabetes in the group of patients with renovascular stenosis compared with group having coronary artery disease is not statistically significant (p > 0.8). Univariate and multivariate logistic identified age, diabetes, hypertension and urea as independent predicators of renal artery stenosis; while variables like sex and serum creatinine were not associated. CONCLUSION: High prevalence of unsuspected renovascular abnormalities is found in patients who undergo angiography for cardiovascular disease. Factors like age, diabetes, hypertension and urea could be clinical predicators of renal artery stenosis. Hence renal arteries should be visualized routinely in patients undergoing coronary angiogram for cardiovascular disease.

Adolescent↗
PubMed2001

Somatotopic organization of the medial wall of the cerebral hemispheres: a 3 Tesla fMRI study.

Somatotopic organization of the human medial wall of the cerebral hemispheres was studied using functional MRI conducted at high field strength (3 T) with fine spatial resolution ( approximately 2 mm). Healthy subjects performed paced, repetitive movements of the fingers and toes. Within the supplementary motor area (SMA), two regions were identified: finger movements activated a region rostral and superior to that for toe movements. Two activation foci were also identified in the cingulate motor area: toe movements activated a region rostral and ventral to that activated by finger movements. All foci were located between the anterior and posterior commissures. Our results confirm previous human and non-human primate studies regarding the rostral-caudal organization of the SMA and CMA. The dorsal-ventral organization of the CMA, however, appears to be divergent from results derived from cortical stimulation studies conducted in non-human primates.

Adult↗
PubMed2001

Can medial temporal lobe regions distinguish true from false? An event-related functional MRI study of veridical and illusory recognition memory.

To investigate the types of memory traces recovered by the medial temporal lobe (MTL), neural activity during veridical and illusory recognition was measured with the use of functional MRI (fMRI). Twelve healthy young adults watched a videotape segment in which two speakers alternatively presented lists of associated words, and then the subjects performed a recognition test including words presented in the study lists (True items), new words closely related to studied words (False items), and new unrelated words (New items). The main finding was a dissociation between two MTL regions: whereas the hippocampus was similarly activated for True and False items, suggesting the recovery of semantic information, the parahippocampal gyrus was more activated for True than for False items, suggesting the recovery of perceptual information. The study also yielded a dissociation between two prefrontal cortex (PFC) regions: whereas bilateral dorsolateral PFC was more activated for True and False items than for New items, possibly reflecting monitoring of retrieved information, left ventrolateral PFC was more activated for New than for True and False items, possibly reflecting semantic processing. Precuneus and lateral parietal regions were more activated for True and False than for New items. Orbitofrontal cortex and cerebellar regions were more activated for False than for True items. In conclusion, the results suggest that activity in anterior MTL regions does not distinguish True from False, whereas activity in posterior MTL regions does.

Behavior↗
PubMed2001

The evolution of brain activation during temporal processing.

Timing is crucial to many aspects of human performance. To better understand its neural underpinnings, we used event-related fMRI to examine the time course of activation associated with different components of a time perception task. We distinguished systems associated with encoding time intervals from those related to comparing intervals and implementing a response. Activation in the basal ganglia occurred early, and was uniquely associated with encoding time intervals, whereas cerebellar activation unfolded late, suggesting an involvement in processes other than explicit timing. Early cortical activation associated with encoding of time intervals was observed in the right inferior parietal cortex and bilateral premotor cortex, implicating these systems in attention and temporary maintenance of intervals. Late activation in the right dorsolateral prefrontal cortex emerged during comparison of time intervals. Our results illustrate a dynamic network of cortical-subcortical activation associated with different components of temporal information processing.

Adult↗
PubMed2000

Practice-related functional activation changes in a working memory task.

The effects of practice on the functional anatomy of a visuospatial working memory (VSWM) task were studied using functional Magnetic Resonance Imaging (fMRI). Functional imaging was conducted as subjects completed a moderate (Experiment 1) or extensive (Experiment 2) amount of practice on a delayed-match-to-sample task. While improvement in task performance was seen with practice, the task's dependence upon VSWM did not change. Activations in frontal (inferior, middle, and precentral gyri and superior frontal sulcus), parietal (intra-parietal sulcus, inferior parietal lobule, and precuneus) and cingulate (anterior and posterior) regions were observed as were bilateral insular and occipital activations. With the exception of the posterior cingulate, practice produced activation decreases in these regions, thus providing little evidence for a re-organization of the functional neuroanatomy. Fewer regions passing statistical criteria were observed at the end of practice relative to early in practice. Regions that were lost were mostly posterior (occipital and precuneus) but also included the left middle frontal gyrus, left precentral gyrus, and right insula suggesting that a more precise VSWM functional map can be observed once processes specific to encountering a novel task are removed. Little further activation changes were observed after extensive practice. These results suggest, minimally, that practice effects should be considered so as to avoid incorrectly attributing functional activation to a cognitive process of interest. Further, these data show that the dynamics of functional change can be tracked while a task is being learned and as an important cognitive process becomes more skilled.

Adult↗
PubMed2000

Neural systems underlying the recognition of familiar and newly learned faces.

Memory for famous faces can be used to examine the neural systems underlying retrieval from long-term memory. To date, there have been a limited number of functional neuroimaging investigations examining famous face recognition. In this study, we compared recognition of famous faces to recognition of newly learned faces. Whole-brain, event-related functional magnetic resonance imaging was used to image regional changes in neural activity in 11 subjects during the encoding of unfamiliar faces and during familiarity judgments for: (1) newly learned faces, (2) unfamiliar face distractors, and (3) famous faces. Image analyses were restricted to correct recognition trials. Recognition accuracy and response time to famous and recently learned faces were equivalent. Recognition of famous faces was associated with a widespread network of bilateral brain activations involving the prefrontal, lateral temporal, and mesial temporal (hippocampal and parahippocampal regions) regions compared to recognition of recently encoded faces or unfamiliar faces seen for the first time. Findings are discussed in relation to current proposals concerning the neural regions thought to participate in long-term memory retrieval and, more specifically, in relation to retrieval of information from the person identity semantic system.

Adult↗
PubMed2000

Oxidant stress and essential fatty acids in patients with risk and established ARDS.

Oxygen free radicals are important mediators of both physiological and pathological events. In acute lung injury, the activated lymphocytes stimulate tumor necrosis factor (TNF) and other cytokines. These lymphokines augment free radical generation by polymorphonuclear leukocytes (PMNLs), macrophages and other cells which may ultimately produce acute respiratory distress syndrome (ARDS). This is supported by our results presented here in that there is a significant increase in lipid peroxidation products in patients with established ARDS. The amount of lipid peroxidation was significantly higher in the established ARDS group compared to patients who are at risk for ARDS. Nitric oxide concentrations were significantly decreased in established ARDS compared to the control and those who are at risk for ARDS. Fatty acid analysis of the plasma phospholipid fraction revealed a significant decreased in linoleic acid, gamma-linolenic acid, dihomo-gamma-linolenic acid and arachidonic acid levels of n-6 series and alpha-linolenic acid, eicosapentaenoic acid, docosa-hexanenoic acid of n-3 series. Patients who are at risk for ARDS have decreased levels of gamma-linolenic acid of the n-6 series, alpha-linolenic acid and eicosapentaenoic acid of the n-3 series. These results suggest that lipid peroxides and alteration in essential fatty acid metabolism may have a role in the pathogenesis of ARDS.

Arachidonic Acid↗
PubMed2000

Specialized neural systems underlying representations of sequential movements.

The ease by which movements are combined into skilled actions depends on many factors, including the complexity of movement sequences. Complexity can be defined by the surface structure of a sequence, including motoric properties such as the types of effectors, and by the abstract or sequence-specific structure, which is apparent in the relations amongst movements, such as repetitions. It is not known whether different neural systems support the cognitive and the sensorimotor processes underlying different structural properties of sequential actions. We investigated this question using whole-brain functional magnetic resonance imaging (fMRI) in healthy adults as they performed sequences of five key presses involving up to three fingers. The structure of sequences was defined by two factors that independently lengthen the time to plan sequences before movement: the number of different fingers (1-3; surface structure) and the number of finger transitions (0-4; sequence-specific structure). The results showed that systems involved in visual processing (extrastriate cortex) and the preparation of sensory aspects of movement (rostral inferior parietal and ventral premotor cortex (PMv)) correlated with both properties of sequence structure. The number of different fingers positively correlated with activation intensity in the cerebellum and superior parietal cortex (anterior), systems associated with sensorimotor, and kinematic representations of movement, respectively. The number of finger transitions correlated with activation in systems previously associated with sequence-specific processing, including the inferior parietal and the dorsal premotor cortex (PMd), and in interconnecting superior temporal-middle frontal gyrus networks. Different patterns of activation in the left and right inferior parietal cortex were associated with different sequences, consistent with the speculation that sequences are encoded using different mnemonics, depending on the sequence-specific structure. In contrast, PMd activation correlated positively with increases in the number of transitions, consistent with the role of this area in the retrieval or preparation of abstract action plans. These findings suggest that the surface and the sequence-specific structure of sequential movements can be distinguished by distinct distributed systems that support their underlying mental operations.

Adolescent↗
PubMed2000

Neural mechanisms of visual attention: object-based selection of a region in space.

Objects play an important role in guiding spatial attention through a cluttered visual environment. We used event-related functional magnetic resonance imaging (ER-fMRI) to measure brain activity during cued discrimination tasks requiring subjects to orient attention either to a region bounded by an object (object-based spatial attention) or to an unbounded region of space (location-based spatial attention) in anticipation of an upcoming target. Comparison between the two tasks revealed greater activation when attention selected a region bounded by an object. This activation was strongly lateralized to the left hemisphere and formed a widely distributed network including (a) attentional structures in parietal and temporal cortex and thalamus, (b) ventral-stream object processing structures in occipital, inferior-temporal, and parahippocampal cortex, and (c) control structures in medial- and dorsolateral-prefrontal cortex. These results suggest that object-based spatial selection is achieved by imposing additional constraints over and above those processes already operating to achieve selection of an unbounded region. In addition, ER-fMRI methodology allowed a comparison of validly versus invalidly cued trials, thereby delineating brain structures involved in the reorientation of attention after its initial deployment proved incorrect. All areas of activation that differentiated between these two trial types resulted from greater activity during the invalid trials. This outcome suggests that all brain areas involved in attentional orienting and task performance in response to valid cues are also involved on invalid trials. During invalid trials, additional brain regions are recruited when a perceiver recovers from invalid cueing and reorients attention to a target appearing at an uncued location. Activated brain areas specific to attentional reorientation were strongly right-lateralized and included posterior temporal and inferior parietal regions previously implicated in visual attention processes, as well as prefrontal regions that likely subserve control processes, particularly related to inhibition of inappropriate responding.

Adult↗
PubMed2000

Effects of methylphenidate on functional MRI blood-oxygen-level-dependent contrast.

OBJECTIVE: The authors' goal was to determine potential hemodynamic consequences of methylphenidate on functional magnetic resonance imaging (MRI) blood-oxygen-level-dependent (BOLD) contrast. METHOD: BOLD and perfusion changes were recorded from the motor cortex of six healthy subjects while they performed flexion-extension movements of the right index finger (finger tapping) at varying rates before and after oral methylphenidate administration. RESULTS: Functional MRI signals increased monotonically with faster movement rates. Subjects' heart rates increased modestly after methylphenidate administration, but no changes in finger tapping performance or functional MRI signals were observed. CONCLUSIONS: Methylphenidate does not alter BOLD neural-hemodynamic coupling. Consequently, functional MRI can be used to map neural systems that subserve cognitive operations (e.g., attention and executive processes) in subjects taking methylphenidate.

Adult↗
PubMed1999

Importance of factor VIIa Gla-domain residue Arg-36 for recognition of the macromolecular substrate factor X Gla-domain.

Macromolecular substrate docking with coagulation enzyme-cofactor complexes involves multiple contacts distant from the enzyme's catalytic cleft. Here we characterize the binding of the Gla-domain of macromolecular substrate coagulation factor X to the complex of tissue factor (TF) and VIIa. Site-directed mutagenesis of charged residue side chains in the VIIa Gla-domain identified Arg-36 as being important for macromolecular substrate docking. Ala substitution for Arg-36 resulted in an increased KM and a decreased rate of X activation. X with a truncated Gla-domain was activated by mutant and wild-type VIIa at indistinguishable rates, demonstrating that Arg-36 interactions require a properly folded Gla-domain of the macromolecular substrate. VIIa Arg-36 was also required for effective docking of the X Gla-domain in the absence of phospholipid, demonstrating that the Gla-domain of VIIa participates in protein-protein interactions with X. In the absence of TF, the mutant VIIa had essentially normal function, indicating that the cofactor positions VIIa's Gla-domain for optimal macromolecular substrate docking. Computational docking suggests multiple charge complementary contacts of the X Gla-domain with TF.VIIa. A prominent interaction is made by the functionally important X residue Gla-14 with the center of the extended docking site created by residues in the carboxyl module of TF and the contiguous VIIa Gla-domain. These data demonstrate the functional importance of interactions of the Gla-domains of enzyme and substrate, and begin to elucidate the molecular details of the ternary TF.VIIa.X complex.

1-Carboxyglutamic Acid↗
PubMed1999

Mapping of semantic, phonological, and orthographic verbal working memory in normal adults with functional magnetic resonance imaging.

Twelve neurologically normal participants (4 men and 8 women) performed semantic, phonological, and orthographic working memory tasks and a control task during functional magnetic resonance imaging. Divergent regions of the posterior left hemisphere used for decoding and storage of information emerged in each working memory versus control task comparison. These regions were consistent with previous literature on processing mechanisms for semantic, phonological, and orthographic information. Further, working memory versus control task differences extended into the left frontal lobe, including premotor cortex, and even into subcortical structures. Findings were consistent with R. C. Martin and C. Romani's (1994) contention that different forms of verbal working memory exist and further suggest that a reconceptualization of premotor cortex functions is needed.

Adolescent↗
PubMed1999

Stress and course of disease in multiple sclerosis.

In this prospective study, 96 healthy controls and 101 multiple sclerosis patients were followed up for as many as 6 years, and self-reported stressful events and health status were assessed. The authors evaluated (a) whether patients reported more stressful life events than healthy controls and (b) the bidirectional relationship between stress and functional deterioration among patients. Healthy controls reported more life events than patients, Odds ratio (OR) = 1.13, p < .0001; and this relationship was attributable to healthy controls' reporting more neutral/positive events than patients. A bidirectional relationship was confirmed between stress and illness: there was an increased risk of disease progression when rate of reported stressful events was higher, OR = 1.13, p < .0003, and an increased risk of reported stressful events when rate of disease progression was higher, OR = 2.13, p < .0001. There were no differences in reported stress by level of baseline disability. The authors concluded that multiple sclerosis patients demonstrate a vicious cycle between stress and disease progression.

Adaptation, Psychological↗
PubMed1999

Language processing is strongly left lateralized in both sexes. Evidence from functional MRI.

Functional MRI (fMRI) was used to examine gender effects on brain activation during a language comprehension task. A large number of subjects (50 women and 50 men) was studied to maximize the statistical power to detect subtle differences between the sexes. To estimate the specificity of findings related to sex differences, parallel analyses were performed on two groups of randomly assigned subjects. Men and women showed very similar, strongly left lateralized activation patterns. Voxel-wise tests for group differences in overall activation patterns demonstrated no significant differences between women and men. In further analyses, group differences were examined by region of interest and by hemisphere. No differences were found between the sexes in lateralization of activity in any region of interest or in intrahemispheric cortical activation patterns. These data argue against substantive differences between men and women in the large-scale neural organization of language processes.

Acoustic Stimulation↗
PubMed1999

Development of a multiple sclerosis functional composite as a clinical trial outcome measure.

The primary clinical outcome measure for evaluating multiple sclerosis in clinical trials has been Kurtzke's expanded disability status scale (EDSS). New therapies appear to favourably impact the course of multiple sclerosis and render continued use of placebo control groups more difficult. Consequently, future trials are likely to compare active treatment groups which will most probably require increased sample sizes in order to detect therapeutic efficacy. Because more responsive outcome measures will be needed for active arm comparison studies, the National Multiple Sclerosis Society's Advisory Committee on Clinical Trials of New Agents in Multiple Sclerosis appointed a Task Force that was charged with developing improved clinical outcome measures. This Task Force acquired contemporary clinical trial and historical multiple sclerosis data for meta-analyses of primary and secondary outcome assessments to provide a basis for recommending a new outcome measure. A composite measure encompassing the major clinical dimensions of arm, leg and cognitive function was identified and termed the multiple sclerosis functional composite (MSFC). The MSFC consists of three objective quantitative tests of neurological function which are easy to administer. Change in this MSFC over the first year of observation predicted subsequent change in the EDSS, suggesting that the MSFC is more sensitive to change than the EDSS. This paper provides details concerning the development and testing of the MSFC.

Clinical Trials as Topic↗
PubMed1999

Conceptual processing during the conscious resting state. A functional MRI study.

Localized, task-induced decreases in cerebral blood flow are a frequent finding in functional brain imaging research but remain poorly understood. One account of these phenomena postulates processes ongoing during conscious, resting states that are interrupted or inhibited by task performance. Psychological evidence suggests that conscious humans are engaged almost continuously in adaptive processes involving semantic knowledge retrieval, representation in awareness, and directed manipulation of represented knowledge for organization, problem-solving, and planning. If interruption of such 'conceptual' processes accounts for task-induced deactivation, tasks that also engage these conceptual processes should not cause deactivation. Furthermore, comparisons between conceptual and nonconceptual tasks should show activation during conceptual tasks of the same brain areas that are 'deactivated' relative to rest. To test this model, functional magnetic resonance imaging data were acquired during a resting state, a perceptual task, and a semantic retrieval task. A network of left-hemisphere polymodal cortical regions showed higher signal values during the resting state than during the perceptual task but equal values during the resting and semantic conditions. This result is consistent with the proposal that perceptual tasks interrupt processes ongoing during rest that involve many of the same brain areas engaged during semantic retrieval. As further evidence for this model, the same network of brain areas was activated in two direct comparisons between semantic and perceptual processing tasks. This same 'conceptual processing' network was also identified in several previous studies that contrasted semantic and perceptual tasks or resting and active states. The model proposed here offers a unified account of these findings and may help to explain several unanticipated results from prior studies of semantic processing.

Adolescent↗
PubMed1999

Neural basis of endogenous and exogenous spatial orienting. A functional MRI study.

Whole-brain functional magnetic resonance imaging (MRI) was used to examine the neural substrates of internally (endogenous) and externally (exogenous) induced covert shifts of attention. Thirteen normal subjects performed three orienting conditions: endogenous (location of peripheral target predicted by a central arrow 80% of the time), exogenous (peripheral target preceded by noninformative central cue). Behavioral results indicated faster reaction times (RTs) for valid than for invalid trials for the endogenous condition but slower RTs for valid than for invalid trials for the exogenous condition (inhibition of return). The spatial extent and intensity of activation was greatest for the endogenous condition, consistent with the hypothesis that endogenous orienting is more effortful (less automatic) than exogenous orienting. Overall, we did not observe distinctly separable neural systems associated with the endogenous and exogenous orienting conditions. Both exogenous and endogenous orienting, but not the control condition, activated bilateral parietal and dorsal premotor regions, including the frontal eye fields. These results suggest a specific role for these regions in preparatory responding to peripheral stimuli. The right dorsolateral prefrontal cortex (BA 46) was activated selectively by the endogenous condition. This finding suggests that voluntary, but not reflexive, shifts of attention engage working memory systems.

Adult↗