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Biomedical subjects

V Prabhakaran

Publications and source records attributed to V Prabhakaran.

At least 19 recordsLinked to original sources
PubMed2006

Active epilepsy as an index of burden of neurocysticercosis in Vellore district, India.

OBJECTIVE: To determine the contribution of neurocysticercosis (NCC) to the causation of active epilepsy (AE) in a south Indian community. METHODS: We conducted a door-to-door survey of 50,617 people between the ages of 2 and 60 years in a rural (38,105 people) and urban setting (12,512 people) in the Vellore district of the south Indian state of Tamil Nadu to identify patients with AE. Patients with AE were investigated with a contrast-enhanced CT scan and serologic study using enzyme-linked immunotransfer blot (EITB) for cysticercal antibodies. RESULTS: We identified 194 patients with AE. The prevalence of AE was 3.83 per 1,000 people, with the prevalence in the urban clusters more than twice that in the rural clusters (6.23 vs 3.04 per 1,000) (p < 0.0001). A diagnosis of NCC was made in 46 (28.4%) of the 162 patients undergoing a CT scan, and EITB was positive in 21 (13%) patients. Overall, 55 (34%) patients were diagnosed with NCC (11 definitive NCC and 44 probable NCC). There was no significant difference in the prevalence of NCC causing AE in the urban (1.28 per 1,000) and rural (1.02 per 1,000) communities. CONCLUSIONS: NCC is the cause of nearly one-third of all cases of AE in both the urban and rural regions. Extrapolating our results to the country as a whole leads to an estimated disease burden of 1 million patients in India with AE attributable to NCC.

Adolescent↗
PubMed2004

Taenia solium metacestode glycoproteins as diagnostic antigens for solitary cysticercus granuloma in Indian patients.

Taenia solium metacestode glycoproteins specific for lentil lectin were evaluated as diagnostic antigens for solitary cysticercus granulomas in Indian patients, using both an ELISA and immunoblotting. In 250 patients suspected to have neurocysticercosis and subjected to a computerized tomography scan or magnetic resonance imaging, the proteins were diagnostic by the ELISA in 86 patients (80%) and by immunoblots in 67 (62%) of 107 patients with solitary cysticerus granuloma. Among 100 non-cysticercosis patients, the ELISA and immunoblot were negative in 94% and 97% respectively. No cross-reactions were observed with sera from patients with central nervous system tuberculosis. Proteins of </=18 kDa were the most diagnostic for solitary cysticercus granuloma.

Animals↗
PubMed2001

Rostrolateral prefrontal cortex involvement in relational integration during reasoning.

Patient and neuroimaging studies indicate that complex reasoning tasks are associated with the prefrontal cortex (PFC). In this study, we tested the hypothesis that the process of relational integration, or considering multiple relations simultaneously, is a component process of complex reasoning that selectively recruits PFC. We used fMRI to examine brain activation during 0-relational, 1-relational, and 2-relational problems adapted from the Raven's Progressive Matrices and hypothesized that PFC would be preferentially recruited by the 2-relational problem type. Event-related responses were modeled by convolving a canonical hemodynamic response function with the response time (RT) associated with each trial. The results across different analyses revealed the same pattern: PFC activation was specific to the comparison between 2- and 1-relational problems and was not observed in the comparison between 1- and 0-relational problems. Furthermore, the process of relational integration was specifically associated with bilateral rostrolateral PFC (RLPFC; lateral area 10) and right dorsolateral PFC (areas 9 and 46). Left RLPFC showed the greatest specificity by remaining preferentially recruited during 2-relational problems even after comparisons were restricted to trials matched for RT and accuracy. The link between RLPFC and the process of relational integration may be due to the associated process of manipulating self-generated information, a process that may characterize RLPFC function.

Adolescent↗
PubMed2001

Age differences in prefrontal cortical activity in working memory.

Working memory (WM) declines with advancing age. Brain imaging studies indicate that ventral prefrontal cortex (PFC) is active when information is retained in WM and that dorsal PFC is further activated for retention of large amounts of information. The authors examined the effect of aging on activation in specific PFC regions during WM performance. Six younger and 6 older adults performed a task in which, on each trial, they (a) encoded a 1- or 6-letter memory set, (b) maintained these letters over 5-s. and (c) determined whether or not a probe letter was part of the memory set. Comparisons of activation between the 1- and 6-letter conditions indicated age-equivalent ventral PFC activation. Younger adults showed greater dorsal PFC activation than older adults. Older adults showed greater rostral PFC activation than younger adults. Aging may affect dorsal PFC brain regions that are important for WM executive components.

Adult↗
PubMed2001

Neural substrates of mathematical reasoning: a functional magnetic resonance imaging study of neocortical activation during performance of the necessary arithmetic operations test.

Brain activation was examined using functional magnetic resonance imaging during mathematical problem solving in 7 young healthy participants. Problems were selected from the Necessary Arithmetic Operations Test (NAOT; R. B. Ekstrom, J. W. French, H. H. Harman, & D. Dermen, 1976). Participants solved 3 types of problems: 2-operation problems requiring mathematical reasoning and text processing, 1-operation problems requiring text processing but minimal mathematical reasoning, and 0-operation problems requiring minimal text processing and controlling sensorimotor demands of the NAOT problems. Two-operation problems yielded major activations in bilateral frontal regions similar to those found in other problem-solving tasks, indicating that the processes mediated by these regions subserve many forms of reasoning. Findings suggest a dissociation in mathematical problem solving between reasoning, mediated by frontal cortex, and text processing, mediated by temporal cortex.

Adult↗
PubMed2000

Hemispheric asymmetries and individual differences in visual concept learning as measured by functional MRI.

Dynamic changes in brain regions active while learning novel visual concepts were examined in humans using functional magnetic resonance imaging. Participants learned to distinguish between exemplars of two categories, formed as distortions of different unseen prototype stimuli. Regions of the right hemisphere (dorsolateral prefrontal and inferior parietal areas) were active early in learning and throughout task performance, whereas homologous portions of the left hemisphere were active only in later stages of learning. Left dorsolateral prefrontal activation was found only in participants who showed superior conceptual learning. Such a progression from initial right-hemisphere processing of specific instances to bilateral activity as left-hemisphere conceptual processes are recruited may underlie the development of many forms of visual knowledge.

Adult↗
PubMed2000

Integration of diverse information in working memory within the frontal lobe.

Ability to integrate diverse forms of information in current thought, or working memory, is essential for human reasoning and problem solving. We used functional imaging to identify brain regions preferentially involved in maintaining integrated versus unintegrated information in working memory. For equal amounts of verbal and spatial information, activation of prefrontal cortex was greater for maintaining integrated rather than unintegrated representations. Posterior brain regions showed the opposite pattern. These results demonstrate frontal-lobe specialization in maintaining working-memory representations that integrate verbal and spatial information. The role of prefrontal cortex in integrating multiple forms of information in working memory may underlie its unique contribution to high-level cognition that demands flexible mental representations.

Adult↗
PubMed2000

Time course of odorant-induced activation in the human primary olfactory cortex.

Paradoxically, attempts to visualize odorant-induced functional magnetic resonance imaging (fMRI) activation in the human have yielded activations in secondary olfactory regions but not in the primary olfactory cortex-piriform cortex. We show that odorant-induced activation in primary olfactory cortex was not previously made evident with fMRI because of the unique time course of activity in this region: in primary olfactory cortex, odorants induced a strong early transient increase in signal amplitude that then habituated within 30-40 s of odorant presence. This time course of activation seen here in the primary olfactory cortex of the human is almost identical to that recorded electrophysiologically in the piriform cortex of the rat. Mapping activation with analyses that are sensitive to both this transient increase in signal amplitude, and temporal-variance, enabled us to use fMRI to consistently visualize odorant-induced activation in the human primary olfactory cortex. The combination of continued accurate odorant detection at the behavioral level despite primary olfactory cortex habituation at the physiological level suggests that the functional neuroanatomy of the olfactory response may change throughout prolonged olfactory stimulation.

Adult↗
PubMed1999

Load-dependent roles of frontal brain regions in the maintenance of working memory.

Brain imaging studies have suggested a critical role for prefrontal cortex in working memory (WM) tasks that require both maintainenance and manipulation of information over time in delayed-response WM tasks. In the present study, functional magnetic resonance imaging (fMRI) was used to examine whether prefrontal areas are activated when only maintenance is required in a delayed-response WM task, without the overt requirement to manipulate the stored information. In two scans, six subjects performed WM tasks in which, on each trial, they (1) encoded 1, 3, or 6 to-be-remembered letters, (2) maintained these letters across a 5-second unfilled delay, and (3) determined whether a single probe letter was or was not part of the memory set. Activation of left caudal inferior frontal gyrus was observed, relative to the 1-letter task, when subjects were required to maintain 3 letters in WM. When subjects were required to maintain 6 letters in WM, additional prefrontal areas, most notably middle and superior frontal gyri, were activated bilaterally. Thus, increasing the amount of to-be-maintained information, without any overt manipulation requirement, resulted in the recruitment of wide-spread frontal-lobe regions. Inferior frontal gyrus activation was left-hemisphere dominant in both the 3- and 6-letter conditions, suggesting that such activation reflected material-specific verbal processes. Activation in middle and superior frontal gyri appeared only in the 6-letter condition and was right-hemisphere dominant, suggesting that such activation reflected material-independent executive processes.

Adult↗
PubMed1999

Striatal activation during acquisition of a cognitive skill.

The striatum is thought to play an essential role in the acquisition of a wide range of motor, perceptual, and cognitive skills, but neuroimaging has not yet demonstrated striatal activation during nonmotor skill learning. Functional magnetic resonance imaging was performed while participants learned probabilistic classification, a cognitive task known to rely on procedural memory early in learning and declarative memory later in learning. Multiple brain regions were active during probabilistic classification compared with a perceptual-motor control task, including bilateral frontal cortices, occipital cortex, and the right caudate nucleus in the striatum. The left hippocampus was less active bilaterally during probabilistic classification than during the control task, and the time course of this hippocampal deactivation paralleled the expected involvement of medial temporal structures based on behavioral studies of amnesic patients. Findings provide initial evidence for the role of frontostriatal systems in normal cognitive skill learning.

Adult↗
PubMed1999

Blind smell: brain activation induced by an undetected air-borne chemical.

EEG and behavioural evidence suggests that air-borne chemicals can affect the nervous system without being consciously detected. EEG and behaviour, however, do not specify which brain structures are involved in chemical sensing that occurs below a threshold of conscious detection. Here we used functional MRI to localize brain activation induced by high and low concentrations of the air-borne compound oestra-1,3,5(10),16-tetraen-3yl acetate. Following presentations of both concentrations, eight of eight subjects reported verbally that they could not detect any odour (P = 0.004). Forced choice detection performed during the presentations revealed above-chance detection of the high concentration, but no better than chance detection of the low concentration compound. Both concentrations induced significant brain activation, primarily in the anterior medial thalamus and inferior frontal gyrus. Activation in the inferior frontal gyrus during the high concentration condition was significantly greater in the right than in the left hemisphere (P = 0.03). A trend towards greater thalamic activation was observed for the high concentration than the low concentration compound (P = 0.08). These findings localize human brain activation that was induced by an undetectable air-borne chemical (the low concentration compound).

Adult↗
PubMed1998

Odorant-induced and sniff-induced activation in the cerebellum of the human.

Functional magnetic resonance imaging was used to test whether odorants induce activation in the cerebellum of the human. The odorants vanillin and propionic acid both induced significant activation, primarily in the posterior lateral hemispheres. Activation was concentration-dependent, greater after stimulation with higher concentration odorants. By contrast, the action of sniffing nonodorized air induced significant activation in the anterior cerebellum, primarily in the central lobule. These findings demonstrate that the cerebellum plays a role in human olfaction. A hypothesis is proposed whereby the cerebellum maintains a feedback mechanism that regulates sniff volume in relation to odor concentration.

Adult↗
PubMed1998

Sniffing and smelling: separate subsystems in the human olfactory cortex.

The sensation and perception of smell (olfaction) are largely dependent on sniffing, which is an active stage of stimulus transport and therefore an integral component of mammalian olfaction. Electrophysiological data obtained from study of the hedgehog, rat, rabbit, dog and monkey indicate that sniffing (whether or not an odorant is present) induces an oscillation of activity in the olfactory bulb, driving the piriform cortex in the temporal lobe, in other words, the piriform is driven by the olfactory bulb at the frequency of sniffing. Here we use functional magnetic resonance imaging (fMRI) that is dependent on the level of oxygen in the blood to determine whether sniffing can induce activation in the piriform of humans, and whether this activation can be differentiated from activation induced by an odorant. We find that sniffing, whether odorant is present or absent, induces activation primarily in the piriform cortex of the temporal lobe and in the medial and posterior orbito-frontal gyri of the frontal lobe. The source of the sniff-induced activation is the somatosensory stimulation that is induced by air flow through the nostrils. In contrast, a smell, regardless of sniffing, induces activation mainly in the lateral and anterior orbito-frontal gyri of the frontal lobe. The dissociation between regions activated by olfactory exploration (sniffing) and regions activated by olfactory content (smell) shows a distinction in brain organization in terms of human olfaction.

Adult↗
PubMed1997

A method for functional magnetic resonance imaging of olfaction.

A method for generating olfactory stimuli for humans within a functional magnetic resonance imaging (fMRI) experimental design is described. The system incorporates a nasal-mask in which the change from odorant to no-odorant conditions occurs in less than 500 ms and is not accompanied by visual, auditory, tactile, or thermal cues. The mask provides an ordorant-free environment following prolonged ordorant presence. Specific imaging parameters that are conducive to the study of the human olfactory system are described. In a pilot study performed using these methods, the specific patterns of activation observed converged with published experimental and clinical findings.

Benzaldehydes↗
PubMed1997

Neural substrates of fluid reasoning: an fMRI study of neocortical activation during performance of the Raven's Progressive Matrices Test.

We examined brain activation, as measured by functional magnetic resonance imaging, during problem solving in seven young, healthy participants. Participants solved problems selected from the Raven's Progressive Matrices Test, a test known to predict performance on a wide range of reasoning tasks. In three conditions, participants solved problems requiring (1) analytic reasoning; (2) figural or visuospatial reasoning; or (3) simple pattern matching that served as a perceptual-motor control. Right frontal and bilateral parietal regions were activated more by figural than control problems. Bilateral frontal and left parietal, occipital, and temporal regions were activated more by analytic than figural problems. All of these regions were activated more by analytic than match problems. Many of these activations occurred in regions associated with working memory. Figural reasoning activated areas involved in spatial and object working memory. Analytic reasoning activated additional areas involved in verbal working memory and domain-independent associative and executive processes. These results suggest that fluid reasoning is mediated by a composite of working memory systems.

Adult↗
PubMed1995

Ethanol- and threonine-induced hypertension in rats: a common mechanism.

OBJECTIVE: To investigate the effects of oral L-threonine and ethanol, precursor of endogenous acetaldehyde, on systolic blood pressure, cystolic free calcium ([Ca2+]i) and vascular calcium uptake in Wistar-Kyoto (WKY) rats. METHODS: Twenty-four male WKY rats aged eight weeks were divided into four groups of six animals each. Animals were given either water or 5% ethanol, 8% L-threonine or 8% L-glycine in drinking water for 15 weeks, animals were sacrificed, aortic rings were incubated in physiological buffer containing 45Ca2+ and uptake was measured after 20 mins. ([Ca2+]i in platelets was measured with a fluorescence [Ca2+]i indicator, FURA-2. Tissues were processed for morphological investigation. RESULTS: After 15 weeks, systolic blood pressure, platelet [Ca2+]i and aortic calcium uptake were all significantly higher (P < 0.001) in rats given either threonine or ethanol than in control rats given water or glycine. Animals in threonine or ethanol group also showed smooth muscle cell hyperplasia, with some thickening of the wall and narrowing of the lumen in small arteries and arterioles of the kidney. Glycine treatment did not cause any of these changes in rats. CONCLUSION: These results suggest that acetaldehyde may be a common cause of both ethanol- and threonine-induced hypertension.

Animals↗
PubMed1995

N-acetyl cysteine attenuates ethanol induced hypertension in rats.

All known pathways of ethanol metabolism result in the production of acetaldehyde, a highly reactive compound. N-acetyl cysteine, an analogue of the dietary amino acid cysteine, binds acetaldehyde, thus preventing its damaging effect on physiological proteins. This study examined the effect of oral N-acetyl cysteine on the increased blood pressure, platelet cytosolic free calcium, blood acetaldehyde and adverse renal vascular changes induced by chronic ethanol treatment in rats. Twenty-four male Wistar-Kyoto (WKY) rats, age 7 weeks were divided into four groups of six animals each. Animals in group I were given water and group II 5% ethanol in water for the next 14 weeks. Animals in group III were given 5% ethanol + 1% N-acetyl cysteine for 4 weeks followed by 5% ethanol + 2% N-acetyl cysteine for the next 10 weeks. Animals in group IV were given 5% ethanol for 7 weeks; at that time ethanol was withdrawn and animals were placed on water with 2% N-acetyl cysteine for the next 7 weeks. After 14 weeks systolic blood pressure and platelet cytosolic free calcium were all significantly higher (p<0.001) in rats given ethanol as compared to rats in other groups. N-acetyl cysteine treatment, along with ethanol, significantly (p<0.001) attenuated the increased blood pressure and platelet cytosolic free calcium and adverse renal vascular changes. Discontinuation of ethanol treatment for 7 weeks along with N-acetyl cysteine supplementation also significantly lowered the blood pressure and platelet cytosolic free calcium and attenuated adverse renal vascular changes. There was no significant difference in aortic malonaldehyde among four groups. Increase in blood acetaldehyde with ethanol treatment was significantly attenuated with N-acetyl cysteine treatment. These results suggest that acetaldehyde may be the cause of ethanol-induced hypertension and elevated cytosolic free calcium and renal vascular changes.

Acetaldehyde↗