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Biomedical subjects

J Duncan

Publications and source records attributed to J Duncan.

At least 55 records · Page 3Linked to original sources
PubMed1999

Passive smoking as well as active smoking increases the risk of acute stroke.

OBJECTIVE: To estimate the relative risk of stroke associated with exposure to environmental tobacco smoke (ETS, passive smoking) and to estimate the risk of stroke associated with current smoking (active smoking) using the traditional baseline group (never-smokers) and a baseline group that includes lifelong non-smokers and long-term (> 10 years) ex-smokers who have not been exposed to ETS. DESIGN AND SETTING: Population-based case-control study in residents of Auckland, New Zealand. SUBJECTS: Cases were obtained from the Auckland stroke study, a population-based register of acute stroke. Controls were obtained from a cross-sectional survery of major cardiovascular risk factors measured in the same population. A standard questionnaire was administered to patients and controls by trained nurse interviewers. RESULTS: Information was available for 521 patients with first-ever acute stroke and 1851 community controls aged 35-74 years. After adjusting for potential confounders (age, sex, history of hypertension, heart disease, and diabetes) using logistic regression, exposure to ETS among non-smokers and long-term ex-smokers was associated with a significantly increased risk of stroke (odds ratio (OR) = 1.82; 95% confidence interval (95% CI) = 1.34 to 2.49). The risk was significant in men (OR = 2.10; 95% CI = 1.33 to 3.32) and women (OR = 1.66; 95% CI = 1.07 to 2.57). Active smokers had a fourfold risk of stroke compared with people who reported they had never smoked cigarettes (OR = 4.14; 95% CI = 3.04 to 5.63); the risk increased when active smokers were compared with people who had never smoked or had quit smoking more than 10 years earlier and who were not exposed to ETS (OR = 6.33; 95% CI = 4.50 to 8.91). CONCLUSIONS: This study is one of the few to investigate the association between passive smoking and the risk of acute stroke. We found a significantly increased risk of stroke in men and in women. This study also confirms the higher risk of stroke in men and women who smoke cigarettes compared with non-smokers. The stroke risk increases further when those who have been exposed to ETS are excluded from the non-smoking reference group. These findings also suggest that studies investigating the adverse effects of smoking will underestimate the risk if exposure to ETS is not taken into account.

Acute Disease↗
PubMed1998

Converging levels of analysis in the cognitive neuroscience of visual attention.

Experiments using behavioural, lesion, functional imaging and single neuron methods are considered in the context of a neuropsychological model of visual attention. According to this model, inputs compete for representation in multiple visually responsive brain systems, sensory and motor, cortical and subcortical. Competition is biased by advance priming of neurons responsive to current behavioural targets. Across systems competition is integrated such that the same, selected object tends to become dominant throughout. The behavioural studies reviewed concern divided attention within and between modalities. They implicate within-modality competition as one main restriction on concurrent stimulus identification. In contrast to the conventional association of lateral attentional focus with parietal lobe function, the lesion studies show attentional bias to be a widespread consequence of unilateral cortical damage. Although the clinical syndrome of unilateral neglect may indeed be associated with parietal lesions, this probably reflects an assortment of further deficits accompanying a simple attentional imbalance. The functional imaging studies show joint involvement of lateral prefrontal and occipital cortex in lateral attentional focus and competition. The single unit studies suggest how competition in several regions of extrastriate cortex is biased by advance priming of neurons responsive to current behavioural targets. Together, the concepts of competition, priming and integration allow a unified theoretical approach to findings from behavioural to single neuron levels.

Attention↗
PubMed1998

Physical and geometrical modeling for image-based recovery of left ventricular deformation.

Information about left ventricular (LV) mechanical performance is of critical importance in understanding the etiology of ischemic heart disease. Regional measurements derived from non-invasive imaging to assist in assessing this performance have been in use for decades, and certain parameters derived from these measurements often are useful clinically, as they correlate to some extent with gross physiological hypotheses. However, relatively little work has been done to date to carefully understand the relationship of regional myocardial injury to the local mechanical performance of the heart as derived from image data acquired non-invasively for a particular patient in 3 spatial dimensions over time. This paper describes efforts to take advantage of recent developments in 3D non-invasive imaging and biomechanical modeling to design an integrated computational platform capable of assembling a variety of displacement and velocity data derived from each image frame to deform a volumetric model representation of a portion of the myocardium. A brief description of the reasoning behind this strategy an overview of the approach and some initial results are described.

Animals↗
PubMed1998

A double-blind, placebo-controlled trial of tiagabine given three-times daily as add-on therapy for refractory partial seizures. Northern European Tiagabine Study Group.

In a multicentre, double-blind, parallel-group, placebo-controlled trial, a three-times daily regimen of tiagabine was evaluated as add-on therapy in 154 adult patients with refractory partial seizures. A total of 77 patients were randomised to treatment in each arm. Tiagabine HCl was titrated from an initial dose of 12-30 mg/day over 4 weeks. During the 12-week fixed-dose period, there was a significant reduction in the median 4-weekly seizure rate for all partial seizures and simple partial seizures (P < 0.05 in each case). Furthermore, the proportion of patients with a reduction of 50% or more in all partial seizures was higher in the tiagabine group than in the placebo group (14 versus 6%), though the difference did not achieve statistical significance. The difference with respect to simple partial seizures was significant (21 versus 6%, P < 0.01). The percentage of patients achieving an increase of at least 50% in the proportion of days free of all partial seizures was significantly greater in the tiagabine group compared to placebo (14 versus 4%, P<0.01). Tiagabine did not appear to influence the plasma concentrations of other concomitant antiepileptic drugs and was generally well tolerated, with most drug-related adverse events being mild or moderate in severity. The most common adverse events were dizziness, asthenia, headache and somnolence. Adverse event incidence was similar between tiagabine and placebo groups, except for dizziness which was more common with tiagabine (29 versus 10%, P < 0.01). Tiagabine had no significant effects on laboratory tests or vital signs. The present study shows that tiagabine, at a dose of 10 mg administered three-times daily, which is at the lower end of the usual recommended dose range (30-50 mg/day, tiagabine base), is generally well tolerated and demonstrates efficacy for the treatment of refractory partial seizures.

Adolescent↗
PubMed1998

Random generation and the executive control of working memory.

A series of experiments explores the capacity for generating sequences of random responses, relating it to the central executive component of working memory. Experiment 1 shows a broadly similar pattern of redundancy increasing with speed of generation for both the verbal generation of digits and the manual pressing of keys. In both cases deviations from randomness are shown to reflect the increasing use of a limited number of stereotyped response sets. The remaining experiments use keyboard generation. Experiment 2 demonstrates that concurrent immediate serial recall decreases randomness, and that longer recall sequences produce less random output. Experiments 3 and 4 show that whereas simple counting has no effect on randomness, serial recall, semantic category generation, and concurrent digit generation have substantial effects, and a concurrent fluid intelligence test has the greatest influence on the randomness of key pressing. It is suggested that the task of random generation resembles that of category fluency because it requires the subject to switch retrieval plans and inhibit repetition. On this basis it is predicted that a task involving repeated switching of categories will interfere with generation, despite being predictable and having a low memory load. Experiments 5 and 6 confirm this prediction. Strengths and limitations of the switching hypothesis are discussed, as are the implications of our results for the analysis of executive processes.

Adult↗
PubMed1998

Responses of neurons in inferior temporal cortex during memory-guided visual search.

Responses of neurons in inferior temporal cortex during memory-guided visual search. J. Neurophysiol. 80: 2918-2940, 1998. A typical scene will contain many different objects, few of which are relevant to behavior at any given moment. Thus attentional mechanisms are needed to select relevant objects for visual processing and control over behavior. We examined this role of attention in the inferior temporal cortex of macaque monkeys, using a visual search paradigm. While the monkey maintained fixation, a cue stimulus was presented at the center of gaze, followed by a blank delay period. After the delay, an array of two to five choice stimuli was presented extrafoveally, and the monkey was rewarded for detecting a target stimulus matching the cue. The behavioral response was a saccadic eye movement to the target in one version of the task and a lever release in another. The array was composed of one "good" stimulus (effective in driving the cell when presented alone) and one or more "poor" stimuli (ineffective in driving the cell when presented alone). Most cells showed higher delay activity after a good stimulus used as the cue than after a poor stimulus. The baseline activity of cells was also higher preceding a good cue, if the animal expected it to occur. This activity may depend on a top-down bias in favor of cells coding the relevant stimulus. When the choice array was presented, most cells showed suppressive interactions between the stimuli as well as strong attention effects. When the choice array was presented in the contralateral visual field, most cells initially responded the same, regardless of which stimulus was the target. However, within 150-200 ms of array onset, responses were determined by the target stimulus. If the target was the good stimulus, the response to the array became equal to the response to the good stimulus presented alone. If the target was a poor stimulus, the response approached the response to that stimulus presented alone. Thus the influence of the nontarget stimulus was eliminated. These effects occurred well in advance of the behavioral response. When the array was positioned with stimuli on opposite sides of the vertical meridian, the contralateral stimulus appeared to dominate the response, and this dominant effect could not be overcome by attention. Overall, the results support a "biased competition" model of attention, according to which 1) objects in the visual field compete for representation in the cortex, and 2) this competition is biased in favor of the behaviorally relevant object by virtue of "top-down" feedback from structures involved in working memory.

Animals↗
PubMed1998

Changes in subarachnoid hemorrhage mortality, incidence, and case fatality in New Zealand between 1981-1983 and 1991-1993.

BACKGROUND AND PURPOSE: As with total stroke, mortality rates from subarachnoid hemorrhage (SAH) have declined in New Zealand since the mid-1970s. Data from the Auckland Region Stroke studies allow an understanding of reasons for the change, as SAH incidence and 28-day case fatality rates were measured as part of population-based stroke registers. METHODS: National death registrations were used to describe the trends in mortality rates from SAH (International Classification of Diseases [ICD] code 430) among men and women in New Zealand. Changes in incidence and case fatality rates were determined from 2 large-scale population-based stroke registries carried out in 1981-1983 and 10 years later in Auckland. Similar methodology and case ascertainment techniques were used in both studies. RESULTS: The mortality rates from SAH declined in both men and women after the mid-1970s. The mortality rate remained higher among women than men. The incidence of SAH was lower in 1991-1993 (11.3 per 100,000) compared with 1981-1983 (14.6 per 100,000). In the younger age groups, the decrease was mostly due to a lower incidence among men, whereas in the older age groups women older than 65 years had a lower incidence. There was no consistent change in case fatality rates between the 2 periods in either men or women. CONCLUSIONS: Mortality rates from SAH have decreased in both men and women. This decrease may be explained by a decrease in the incidence of SAH, because case fatality rates showed no change.

Adolescent↗
PubMed1997

Restricted attentional capacity within but not between sensory modalities.

Restrictions to attentional capacity are revealed by the interference that commonly results when two sensory inputs must be identified at the same time. To investigate this phenomenon within and between modalities, we presented streams of visual and/or auditory inputs, containing occasional targets to be identified and recalled. For two visual or two auditory streams, identification of one target produced a sustained reduction in the ability to identify a second, the period of interference lasting for several hundred milliseconds. Subjectively, when attention was assigned to one target it was temporarily unavailable for another. In contrast, there was no such time-locked interference between targets in different modalities. The results suggest a modality-specific restriction to concurrent attention and awareness; visual attention to one simple target does not restrict concurrent auditory attention to another.

Acoustic Stimulation↗
PubMed1997

Attention to one or two features in left or right visual field: a positron emission tomography study.

In human vision, two features of the same object can be identified concurrently without loss of accuracy. Performance declines, however, when the features belong to different objects in opposite visual fields. We hypothesized that different positron emission tomography activation patterns would reflect these behavioral results. We first delineated an attention network for single discriminations in left or right visual field and then compared this with the activation pattern when subjects divided attention over two features of a single object or over two objects in opposite hemifields. When subjects attended to a single feature, parietal, premotor, and anterior cingulate cortex were activated. These effects were strongest in the right hemisphere and were, remarkably, unaffected by the direction of attention. In contrast, direction of attention affected occipital and frontal activity: right occipital and left lateral frontal activity were higher with attention to the left, whereas right lateral frontal activity was higher with attention to the right. When subjects identified two features of the same object, parietal, premotor, and anterior cingulate activity was enhanced further, predominantly this time in the left hemisphere. Again, there was no direction sensitivity. Direction-sensitive activation of lateral frontal cortex also was increased. Finally, when subjects divided their attention over opposite hemifields, activity in the direction-sensitive occipital and frontal regions fell to a level midway between those seen during exclusively leftward or rightward attention. Thus, the behavioral efficiency with which we attend to multiple features of a single peripheral object is paralleled by enhanced activity in structures generally active during peripheral selective attention as well as in structures that depend on the specific direction of attention, most notably lateral frontal cortex. In addition, in the direction-sensitive regions, dividing attention over hemifields causes a compromise pattern between the extreme levels obtained during unilateral attention.

Adolescent↗
PubMed1997

Positron emission tomography measurement of cerebral metabolic correlates of yohimbine administration in combat-related posttraumatic stress disorder.

BACKGROUND: We have previously reported an increase in symptoms of anxiety in patients with posttraumatic stress disorder (PTSD) following administration of the beta 2-antagonist yohimbine, which stimulates brain norepinephrine release. Preclinical studies show decreased metabolism in the neocortex and the caudate nucleus with high-dose yohimbine-induced norepinephrine release, but low levels of norepinephrine release result in an increase in metabolism in these areas. METHODS: We used positron emission tomography and fludeoxyglucose F 18 to measure brain metabolism in Vietnam combat veterans with PTSD (n = 10) and healthy age-matched control subjects (n = 10), following administration of yohimbine (0.4 mg/kg) or placebo in a randomized, double-blind fashion. RESULTS: Yohimbine resulted in a significant increase in anxiety in the patients with PTSD, but not in healthy subjects. There was a significant difference in brain metabolic response to yohimbine in patients with PTSD compared with healthy subjects in prefrontal, temporal, parietal, and orbitofrontal cortexes. Metabolism tended to decrease in patients with PTSD and increase in healthy subjects following administration of yohimbine. CONCLUSION: These findings are consistent with our previous hypothesis of enhanced norepinephrine release in the brain with yohimbine in patients with PTSD.

Anxiety Disorders↗
PubMed1997

Positron emission tomography measurement of cerebral metabolic correlates of tryptophan depletion-induced depressive relapse.

BACKGROUND: Short-term depletion of plasma tryptophan has been shown to result in depressive relapse in patients with remission of major depression. Positron emission tomography and single photon emission computed tomography studies implicated the dorsolateral prefrontal cortex, orbitofrontal cortex, thalamus, and caudate nucleus in the pathogenesis of depression. The purpose of this study was to measure cerebral metabolic correlates of tryptophan depletion-induced depressive relapse. METHODS: Patients diagnosed as having major depression (N = 21) who clinically improved with serotonin reuptake inhibitors underwent 2 test days involving tryptophan depletion or placebo, followed 6 hours later by positron emission tomography scanning with fludeoxy-glucose F18. Brain metabolism was compared in patients with (n = 7) and without (n = 14) a tryptophan depletion-induced depressive relapse. RESULTS: Tryptophan depletion resulted in a decrease in brain metabolism in the middle frontal gyrus (dorsolateral prefrontal cortex), thalamus, and orbitofrontal cortex in patients with a depletion-induced depressive relapse (but not in patients without depletion-induced relapse). Decreased brain metabolism in these regions correlated with increased depressive symptoms. Baseline metabolism was increased in prefrontal and limbic regions in relapse-prone patients. CONCLUSION: Specific brain regions, including the middle frontal gyrus, thalamus, and orbitofrontal cortex, may mediate the symptoms of patients with major depression.

Antidepressive Agents↗
PubMed1997

Accumulation of 99mTc-HMPAO and 99mTc-ECD in rodent and human breast tumor cell lines in vitro.

The accumulation of 99mTc-HMPAO and 99mTc-ECD was studied in rat (MatB) and human (MCF-7) breast tumor cell lines in vitro as a function of incubation time. The general pattern was the same for both tracers and both cell lines: the tracer rapidly and extensively accumulated in the cells but a plateau was reached in 15-30 minutes. Accumulation of HMPAO was higher than that of ECD, did not show a difference between rat and human cells, and correction of HMPAO data for intracellular sequestration and extracellular metabolism resulted in a linear increase in accumulation with time. In contrast, accumulation of ECD was approximately 2-fold higher in human cells than in rat cells but after correction for sequestration and metabolism a plateau remained. These experiments show differences between HMPAO and ECD in their accumulation and retention in breast cancer cells in vitro and support that the need for further work on the potential clinical role for HMPAO in tumor characterization.

Animals↗
PubMed1997

Tricyclic antidepressants suppress spawning and fertilization in the zebra mussel, Dreissena polymorpha.

Tricyclic antidepressants (TCAs), which are psychotropic drugs that work in vertebrates by interfering with serotonergic mechanisms, were tested for their effects on the serotonin-elicited spawning behavior of the zebra mussel, Dreissena polymorpha. Exposure of mussels to 10(-4) M imipramine or desipramine for 2 hr prior to serotonin treatment inhibited spawning in male, but not female, zebra mussels (p < 0.05). Clomipramine (10(-4) M) inhibited spawning of both sexes (p < 0.01). Inhibition of spawning was more effective with 2 hr preexposure time than with shorter times (p < 0.0001). Oocytes released in the presence of TCAs had a normal appearance, with no germinal vesicle present; however, fertilization and embryonic development were adversely affected in oocytes released into TCA concentrations as low as 10(-6) M. Oocytes fertilized after TCA treatment rarely developed normally. This is the first report of an inhibitory effect of TCAs on spawning, fertilization, and early embryonic development in any animal. The concentrations that affect embryonic development in zebra mussels are in the same range as therapeutic plasma concentrations in humans.

Analysis of Variance↗
PubMed1997

Competitive brain activity in visual attention.

Visual attention can be considered from the perspective of distributed brain activity engendered by visual input. We propose that visual objects compete for representation in multiple brain systems, sensory and motor, cortical and subcortical. Competition is integrated, however, such that multiple systems converge, working on the different properties and action implications of a selected object. Top-down priming biases competition towards objects relevant to current behaviour. Recent single-unit studies have shown widespread suppression of ignored-object representations in extrastriate cortex, and patterns of spatial and nonspatial priming by task relevance. Human and monkey lesion studies have demonstrated the strong integration tendency of different spatial and nonspatial systems, also revealed in recent studies of normal behaviour. In many cases, no unitary brain system may be responsible for unitary cognitive events such as attention. Such events may emerge as distinct systems converge to work on common cognitive problems.

Attention↗
PubMed1997

A robust point-matching algorithm for autoradiograph alignment.

We present a novel method for the geometric alignment of autoradiographs of the brain. The method is based on finding the spatial mapping and the one-to-one correspondences (or homologies) between point features extracted from the images and rejecting non-homologies as outliers. In this way, we attempt to account for the local, natural and artifactual differences between the autoradiograph slices. We have used the resulting automated algorithm on a set of left prefrontal cortex autoradiograph slices, specifically demonstrated its ability to perform point outlier rejection, validated its robustness property using synthetically generated spatial mappings and provided an anecdotal visual comparison with the well-known iterated closest-point (ICP) algorithm. Visualization of a stack of aligned left prefrontal cortex autoradiograph slices is also provided.

Algorithms↗
PubMed1997

Truncation of the C-terminal acidic transcriptional activation domain of herpes simplex virus VP16 produces a phenotype similar to that of the in1814 linker insertion mutation.

We examined the phenotype of a herpes simplex virus (HSV) type 1 mutant (V422) in which the C-terminal acidic activation domain of the virion transactivator VP16 is truncated at residue 422. The efficiency of plaque formation by V422 on Vero cells was boosted by approximately 100-fold by including hexamethylene bis-acetimide (HMBA) in the growth medium, as previously observed with the in1814 VP16 linker insertion mutant isolated by Preston and colleagues. V422 displayed severely reduced levels of the immediate-early transcripts encoding ICP0 and ICP4 during infection in the presence of cycloheximide, and this defect was partially overcome by the addition of HMBA. The defect in plaque formation exhibited by V422 and in 1814 was efficiently complemented in U2OS osteosarcoma cells, which had previously been shown to complement ICP0 null mutations. Taken in combination, these data confirm the key role of VP16 in triggering the onset of the HSV lytic cycle.

Animals↗
PubMed1997

Relationship between cognitive style and defensive style.

This study examines psychoanalytic psychology, theories of cognitive style, and cognitive developmental psychology to examine the relationship between cognitive style and defensive style. A new set of cognitive styles of visual attention is formulated at the following developmental levels: (1) global, (2) local, (3) global-plus-local at the concrete operational level, and (4) global-plus-local at the formal operational level, 50 subjects were administered global-local sorting tasks, the Sentence Preference Test, the Embedded Figures Test, and the Defense Style Questionnaire. Analysis provided mixed support for the hypothesized cognition-defense relationship. Results suggested that the "pure" character types are not typical and that their styles of cognition and defense are positively correlated, not independent as expected. However, possible measurement problems preclude any firm conclusions at this time.

Adult↗