Biomedical subjects

R D Badgaiyan

Publications and source records attributed to R D Badgaiyan.

At least 19 recordsLinked to original sources

PubMed2001

Priming within and across modalities: exploring the nature of rCBF increases and decreases.

Neuroimaging studies suggest that within-modality priming is associated with reduced regional cerebral blood flow (rCBF) in the extrastriate area, whereas cross-modality priming is associated with increased rCBF in prefrontal cortex. To characterize the nature of rCBF changes in within- and cross-modality priming, we conducted two neuroimaging experiments using positron emission tomography (PET). In experiment 1, rCBF changes in within-modality auditory priming on a word stem completion task were observed under same- and different-voice conditions. Both conditions were associated with decreased rCBF in extrastriate cortex. In the different-voice condition there were additional rCBF changes in the middle temporal gyrus and prefrontal cortex. Results suggest that the extrastriate involvement in within-modality priming is sensitive to a change in sensory modality of target stimuli between study and test, but not to a change in the feature of a stimulus within the same modality. In experiment 2, we studied cross-modality priming on a visual stem completion test after encoding under full- and divided-attention conditions. Increased rCBF in the anterior prefrontal cortex was observed in the full- but not in the divided-attention condition. Because explicit retrieval is compromised after encoding under the divided-attention condition, prefrontal involvement in cross-modality priming indicates recruitment of an aspect of explicit retrieval mechanism. The aspect of explicit retrieval that is most likely to be involved in cross-modality priming is the familiarity effect.

Adult↗

PubMed2000

Dissociation of response conflict, attentional selection, and expectancy with functional magnetic resonance imaging.

Two different attentional networks have been associated with visuospatial attention and conflict resolution. In most situations either one of the two networks is active or both are increased in activity together. By using functional magnetic resonance imaging and a flanker task, we show conditions in which one network (anterior attention system) is increased in activity whereas the other (visuospatial attention system) is reduced, showing that attentional conflict and selection are separate aspects of attention. Further, we distinguish between neural systems involved in different forms of conflict. Specifically, we dissociate patterns of activity in the basal ganglia and insula cortex during simple violations in expectancies (i.e., sudden changes in the frequency of an event) from patterns of activity in the anterior attention system specifically correlated with response conflict as evidenced by longer response latencies and more errors. These data provide a systems-level approach in understanding integrated attentional networks.

Adult↗

PubMed2000

Executive control, willed actions, and nonconscious processing.

Neuroimaging studies have identified a number of cortical areas involved in the executive control of conscious actions. The areas most frequently implicated are prefrontal and cingulate cortices. Evidence suggests that both of these areas may be essential for executive control of willed action. Prefrontal cortex, however, may be responsible for the initial processing. Executive control is usually discussed with reference to willed actions and is assumed to regulate complex cognitive responses. Although many implicit processes involve complex responses, it is not known whether these actions are also controlled by executive processes. Significantly, some implicit tasks like those involving motor sequence learning and cross-modality priming activate the same areas of prefrontal cortex that are implicated in the executive control of willed actions. It is, however, not clear whether a single executive process controls both implicit and explicit processes, or the implicit processes are regulated by a separate set of executive control having distinct neuroanatomical location and processing properties.

Animals↗

PubMed2000

Neuroanatomical organization of perceptual memory: an fMRI study of picture priming.

Neuroanatomical organization of perceptual representation in human memory system is unclear primarily because it has been studied using paradigms that have both, perceptual and conceptual components (e.g., word stem completion and word fragment completion). In the present experiment, functional magnetic resonance imaging (fMRI) technique was used to examine the pattern of cortical activation in a picture identification test in which subjects were asked to identify subliminally presented primed and novel pictures. This test is a modification of the word identification test that is considered a "pure" form of perceptual priming. Results indicate that perceptual priming is associated with reduced activation in the extrastriate cortex and that the memory for subliminally presented stimuli is processed by the same brain areas that process adequate stimuli. The activation pattern observed in picture identification test is different from that reported in the experiments of conceptual priming, suggesting that perceptual and conceptual representation of memory are supported by separate brain mechanisms.

Adult↗

PubMed2000

Neurotrophic factors attenuate alterations in spinal cord evoked potentials and edema formation following trauma to the rat spinal cord.

Influence of brain derived neurotrophic factor (BDNF) and insulin like growth factor-1 (IGF-1) on spinal cord injury induced disturbances in spinal cord conduction, edema formation and cellular stress response was examined in a rat model. Pretreatment with BDNF or IGF-1 significantly attenuated the loss of SCEP negative amplitude seen immediately after spinal cord injury. In these neurotrophins treated rats, upregulation of heat shock protein (HSP 72 kD) immunoreactivity, a measure of cellular stress response and spinal cord edema formation were considerably reduced 5 h after injury. These results suggest that neurotrophic factors improve spinal cord conduction after trauma and this beneficial effect of growth factors may be related with their ability to attenuate trauma induced cellular stress response, not reported earlier.

Animals↗

PubMed2000

Growth hormone attenuates alterations in spinal cord evoked potentials and cell injury following trauma to the rat spinal cord. An experimental study using topical application of rat growth hormone.

The influence of exogenous rat growth hormone on spinal cord injury induced alterations in spinal cord evoked potentials (SCEP) and edema formation was examined in a rat model. Repeated topical application of rat growth hormone (20microl of 1microg/ml solution) applied 30min before injury and at 0min (at the time of injury), 10min, 30min, 60min, 120min, 180min, and 240min, resulted in a marked preservation of SCEP amplitude after injury. In addition, the treated traumatised cord showed significantly less edema and cell changes. These observations suggest that growth hormone has the capacity to improve spinal cord conduction and attenuate edema formation and cell injury in the cord indicating a potential therapeutic implication of this peptide in spinal cord injuries.

Animals↗

PubMed1999

Visual word stem completion priming within and across modalities: a PET study.

Using positron emission tomography, we studied changes in the regional cerebral blood flow (rCBF) associated with cross modality (auditory to visual) and within modality visual priming in a word stem completion task. Compared to baseline completion performance and to within modality visual priming, cross modality priming was associated with increased rCBF in prefrontal cortex and decreased rCBF in the left angular gyrus. The results confirm and complement trends observed in a previous study concerning visual to auditory cross modality priming, and suggest that distinct cortical mechanisms may mediate within- and cross modality priming on the stem completion task. The findings are consistent with the neuropsychological data concerning auditory to visual cross modality priming, and indicate involvement of aspects of explicit retrieval and lexical processes in cross modality priming.

Acoustic Stimulation↗

PubMed1999

Auditory priming within and across modalities: evidence from positron emission tomography.

Previous neuroimaging studies of perceptual priming have reported priming-related decreases in the extrastriate cortex. However, because these experiments have used visual stimuli, it is unclear whether the observed decreases are associated specifically with some aspect of visual perceptual processing or with more general aspects of priming. We studied within- and cross-modality priming using an auditory word stem completion paradigm. Positron emission tomography (PET) images were obtained during stem completion and a fixation task. Within-modality auditory priming was associated with blood flow decreases in the extrastriate cortex (bilateral), medial/right anterior prefrontal cortex, right angular gyrus, and precuneus. In cross-modality priming, the study list was presented visually, and subjects completed auditory word stems. Cross-modality priming was associated with trends for blood flow decreases in the left angular gyrus and increases in the medial/right anterior prefrontal cortex. Results thus indicate that reduced activity in the extrastriate cortex accompanies within-modality priming in both visual and auditory modalities.

Acoustic Stimulation↗

PubMed1998

Mapping the cingulate cortex in response selection and monitoring.

Many cognitive tasks have activated areas of the cingulate cortex. These include error detection, divided attention, conflict, and word generation tasks. However, the exact area of the cingulate found to be active has differed. This could be due to difference in subjects, laboratories, data analysis, or task conditions. The current study uses two very different tasks known to activate the cingulate and compares data from the same subjects and same trials to see whether there are temporal and spatial distinctions in cingulate activations. The tasks chosen were generation of the use of a noun and feedback that an error was made in the time window required for generation. High-density electrical recording was used to trace the time course of cingulate activation in the difference waves between correct and error feedback and between generate and repeat. Both tasks produced activity that is consistent with cingulate activation. However, the two tasks produced activity in different areas. These data are consistent with the idea that differences in areas of the cingulate activated differ between cognitive tasks and are not merely due to subject and laboratory differences.

Adult↗

PubMed1998

Spinal cord evoked potentials and edema in the pathophysiology of rat spinal cord injury. Involvement of nitric oxide.

The possibility that nitric oxide is somehow involved in the early bioelectrical disturbances following spinal cord injury in relation to the later pathophysiology of the spinal cord was examined in a rat model of spinal cord trauma. A focal trauma to the rat spinal cord was produced by an incision of the right dorsal horn of the T 10-11 segments under urethane anaesthesia. The spinal cord evoked potentials (SCEP) were recorded using epidural electrodes placed over the T9 and T12 segments of the cord following supramaximal stimulation of the right tibial and sural nerves in the hind leg. Trauma to the spinal cord significantly attenuated the SCEP amplitude (about 60%) immediately after injury which persisted up to 1 h. However, a significant increase in SCEP latency was seen at the end of 5 h after trauma. These spinal cord segments exhibited profound upregulation of neuronal nitric oxide synthase (NOS) immunoreactivity, and the development of edema and cell injury. Pretreatment with a serotonin synthesis inhibitor drug p-chlorophenylalanine (p-CPA) or an anxiolytic drug diazepam significantly attenuated the decrease in SCEP amplitude, upregulation of NOS, edema and cell injury. On the other hand, no significant reduction in SCEP amplitude, NOS immunolabelling, edema or cell changes were seen after injury in rats pretreated with L-NAME. These observations suggest that nitric oxide is somehow involved in the early disturbances of SCEP and contribute to the later pathophysiology of spinal cord injury.

Animals↗

PubMed1997

Time course of cortical activations in implicit and explicit recall.

The distinction between implicit and explicit retrieval of learned material is central to recent thinking about the neural systems underlying memory. Word stem completion is one task in which subjects can be instructed either to make a deliberate recall (explicit instruction) or to be told to complete the stem with any appropriate word (implicit instruction). Positron emission tomography (PET) studies have indicated that during implicit retrieval, there is reduced blood flow in right posterior areas, whereas some tasks of explicit retrieval involve frontal and hippocampal activation. However, there is no information about the timing of these activations or how implicit and explicit retrieval might be related. We used word stem completion tasks similar to those used in the PET studies, but used high-density electrical recording designed to allow localization of the regions involved in the tasks and to provide temporal information. We found reduced activity for primed words in right posterior cortex corresponding to previous PET results. The reduction occurred within the first 200 msec after input, suggesting early interaction with the information stored in this area. Similar reductions observed during explicit recall of the previously presented words indicate that priming is similar under implicit and explicit conditions. In addition, when priming was not an adequate basis for response, then frontal areas were active. Retrieval of unprimed words under implicit instruction elicited right frontal activation, whereas explicit retrieval activated frontal areas bilaterally. Left frontal and hippocampal activations appear to occur only when the retrieval involved use of the words from the list studied previously.

Adult↗

PubMed1996

Priming reduces input activity in right posterior cortex during stem completion.

A recent positron emission tomography (PET) study showed reduced blood flow in the right posterior cortex for primed words during a stem completion task, suggesting reduction in processing demand in this area for primed tasks. The time course of this attenuation was studied using event-related potentials (ERPs) in 40 normal subjects. As compared to the unprimed stems, primed stems elicited significantly less positive ERP in the right posterior channels between 60 and 200 ms after presentation of the stem. The results, while confirming the PET findings, implicate involvement of right posterior cortex in bottom-up processing of primed stimuli. In addition to right posterior channels, the primed stems also had attenuated positivity in the right frontal channels after 250 ms of stem presentation, indicating reduced requirement for explicit recall process.

Adult↗

PubMed1995

Centrally infused anions alter body temperature in conscious rats.

Central anionic influences on the regulation of body temperature were studied in 42 conscious male rats. The animals were divided into seven equal groups and were given intraventricular infusions of either chloride or bicarbonate solution of sodium, calcium, or potassium. Infusions were made in the unanesthetized and unrestrained animals through stainless steel cannulae, chronically implanted into the anteroventral part of third ventricle. Control rats received intraventricular infusions of artificial cerebrospinal fluid. All of the chloride solutions, irrespective of the associated cations, elicited hyperthermia, whereas bicarbonates had hypothermic effect. Responses of chloride and bicarbonate solutions varied significantly (p < 0.001). There was, however, cationic modification of the anionic responses. Thus, sodium ions manifested hyperthermic modifications, accentuating hyperthermia of chloride and attenuating hypothermic effect of bicarbonate. Calcium and potassium ions exerted hypothermic modulation. The results suggest that anionic concentration of intraventricular CSF is crucial for central regulation of body temperature in unanesthetized conscious rats. The cations probably have only modulatory influences.

Animals↗

PubMed1991

Dipsogenic and feeding influences of intraventricularly infused anionic choline solutions.

Chloride and bicarbonate solutions of choline were infused into the anteroventral part of the third ventricle of two different groups of rats through chronically implanted stainless steel cannulae. Dipsogenic and feeding responses elicited by these solutions were studied by observations taken at half hour intervals up to two h and then, after 24 h of infusions. Results were compared with the control response evoked by similar infusion of artificial cerebrospinal fluid (aCSF). Food and water intakes were recorded in different groups (n = 18 each) of rats. Dipsogenic response elicited by choline chloride solution in the observation taken 24 h after infusion, however, was higher only as compared to the control. Dipsogenic effect of bicarbonate solution was not significantly different from the control in the first two observations (30 and 60 min), but in the later observations (90, 120 min and 24 h), it was significantly higher. None of the choline solutions significantly alter feeding response within 2 h of infusions. However, in the observation taken 24 h after infusion, the response evoked by choline chloride was greater than that elicited by aCSF. The results support our earlier observation that chloride concentration of third ventricular CSF significantly influences water and food consumption. Intraventricularly administered choline also appears to have positive influence on these behaviors.

Animals↗

PubMed1990

Alterations of ventricular pH alter water intake and food consumption in rats.

The pH of third ventricular CSF was altered by infusing acidic or alkaline solution of artificial cerebrospinal fluid (aCSF) through chronically implanted stainless steel cannula. In two separate group of rats (n = 18 each) water and food consumptions were recorded 30 min, 1 hr, and 24 hr after intraventricular infusions of the modified aCSF solutions having pH 6.0, 8.0 and 7.4 (control). On raising the CSF pH, water intake increased in all three observations. Feeding was not affected in the observations taken after 30 min and 1 hr, but significantly reduced food consumption was observed 24 hr after the infusions. Lowering of pH had no effect either on dipsogenic or feeding response. The CSF pH correlated positively with drinking in all three observations. Since dipsogenic and feeding responses are centrally regulated by ion sensitive cells, it may be presumed that altered CSF pH influenced the activities of the sensors by altering ionic conductance across their membranes.

Acetates↗

PubMed1989

Third ventricular chloride infusions enhance drinking in water deprived rats.

The influence of intraventricularly infused anions on drinking was studied in 54 water deprived male rats, divided in 9 equal groups. Stainless steel cannulae were chronically implanted into the anteroventral part of the third ventricle (AV3V) and the animals were water deprived for 24 hr prior to the infusions. Control group (n = 6) was given 10 microliters of artificial cerebrospinal fluid. The rats of the remaining 8 groups received similar quantity of equiosmolar chloride or bicarbonate solution of either sodium, potassium, calcium or barium. Cumulative quantity of water consumed in 30 min, 1 hr, and 24 hr after the infusion was recorded. All the chloride solutions, irrespective of the associated cation, enhanced drinking. Effects of the bicarbonates were relatively weak and transient. Dipsogenic effects of the solutions depended on their anionic composition. Thus, chlorides of all the cations elicited greater drinking than their bicarbonates. Responses of the similar anionic solutions were comparable. It appears that intraventricularly infused chloride ions stimulate drinking in water deprived rats.

Animals↗

PubMed1989

Lithium chloride SCN injection alters the circadian rhythm of food intake.

Effect of lithium injections through chronically implanted cannulae into the bilateral suprachiasmatic nuclei (SCN) on the circadian rhythm of food intake was investigated in the rat. It was observed that the circadian rhythm was disrupted by injections of lithium at the beginning of the light as well as the dark phase of the LD cycle. In either case the percentage of the food consumed during the 12-hr light period increased while that during the dark period decreased without any significant change in the total daily intake. Disruptions in the circadian rhythm of food intake failed to show any dose-response relation. Injections of saline into the SCN or lithium into the nearby SCN area did not produce a disruption of the circadian rhythm of food intake.

Animals↗

PubMed1987

Intracerebroventricular chloride infusion enhances water intake in rats.

Central anionic influences on dipsogenic response was studied in 54 euhydrated rats. Quantity of water consumed following third ventricular infusions of equimolar hypertonic chloride and bicarbonate solutions of sodium, potassium, calcium, and barium was compared. Control group (n = 6) was given artificial cerebrospinal fluid infusion while rats of the remaining 8 groups (n = 6 each) received one of the test solutions. All the chloride solutions, irrespective of the cations to which they were associated, elicited significantly greater dipsogenic response as compared to the control, or the bicarbonate solutions. Response of the bicarbonate solutions was more than the control only in the observation taken 30 min after the infusions. In the later observations, there was no significant difference. Drinking was not affected significantly by the cationic composition of the infusion fluids. Anionic concentration of the solutions has predominantly influenced the dipsogenic response. Enhancement of drinking following infusions of chloride solutions suggests the possibility of the CSF anions exerting active physiological influences over the juxtacerebroventricular sensors.

Animals↗