Search PubMed⌕ Search

Biomedical subjects

R Walker

Publications and source records attributed to R Walker.

At least 91 records · Page 5Linked to original sources
PubMed1999

A model of saccade generation based on parallel processing and competitive inhibition.

During active vision, the eyes continually scan the visual environment using saccadic scanning movements. This target article presents an information processing model for the control of these movements, with some close parallels to established physiological processes in the oculomotor system. Two separate pathways are concerned with the spatial and the temporal programming of the movement. In the temporal pathway there is spatially distributed coding and the saccade target is selected from a "salience map." Both pathways descend through a hierarchy of levels, the lower ones operating automatically. Visual onsets have automatic access to the eye control system via the lower levels. Various centres in each pathway are interconnected via reciprocal inhibition. The model accounts for a number of well-established phenomena in target-elicited saccades: the gap effect, express saccades, the remote distractor effect, and the global effect. High-level control of the pathways in tasks such as visual search and reading is discussed; it operates through spatial selection and search selection, which generally combine in an automated way. The model is examined in relation to data from patients with unilateral neglect.

Attention↗
PubMed1999

Seizure-alert dogs--fact or fiction?

Anecdotal evidence suggests that some dogs may be able to sense the onset of seizures and other medical conditions in humans, although this has never been explored scientifically. There is, however, evidence that dogs can be specially trained to recognize specific changes preceding a seizure and give an overt signal enabling the dog to warn his/her owner. The introduction of the use of dogs to detect and accurately predict the onset of a seizure, giving sufficient time for a person to take control of the situation will have a dramatic impact on quality of life. Support Dogs, a registered charity which trains dogs to assist disabled people, has successfully trained several 'Seizure-alert dogs'. As training progressed, the dogs were able to provide overt signals to their owners within time periods varying from 15 to 45 minutes prior to a seizure occurring. Each dog had an accurate prediction time and, in each case, the owner's seizure frequency was reduced.

Adolescent↗
PubMed1999

Ignorance about Chlamydia among sexually active women--a two centre study.

Chlamydia trachomatis is the micro-organism causing the most common sexually transmitted disease in the UK and Europe. The majority of female infections are asymptomatic and recognized sequelae include pelvic inflammatory disease, infertility, and ectopic pregnancy. Over 1200 sexually active women from two urban centres in the UK were questioned about awareness and knowledge of Chlamydia genito-urinary infection. Awareness was poor, as half of the study population had never heard of Chlamydia. Overall, less than one-quarter demonstrated adequate knowledge regarding transmission, immunity, symptoms, and sequelae. Better knowledge was found in women over the age of 25 years, in those cohabiting, in those with a professional/management occupation, and in those attending family planning clinics. The Chief Medical Officer's Expert Advisory Group on Chlamydia (1998) has recommended opportunistic screening of asymptomatic sexually active women in the UK. This study gives insight into the considerable task facing the Department of Health, as only an informed public will take up the offer of screening. Research is urgently needed to assess the impact of different approaches to education regarding sexually transmitted infection.

Chlamydia Infections↗
PubMed1999

Adherence of Candida albicans to oral epithelial cells differentiated by Papanicolaou staining.

OBJECTIVE: To examine the relative adherence of Candida albicans to oral epithelial cells differentiated by Papanicolaou staining. METHODS: Oral epithelial cells were collected from 10 healthy adults (five male, five female) and counted. Equal volumes of oral epithelial cells and candida were mixed and incubated. The epithelial cells from this mix were collected by filtration through 10 microns polycarbonate membrane filters. Cells retained on the membrane filters were stained with crystal violet followed by Papanicolaou stain. The number of yeast attached to each of 100 red, orange, and green staining oral epithelial cells was determined by direct microscopic examination. RESULTS: C albicans had a higher level of adherence (p < 0.001) to red staining oral epithelial cells (mean (SD) number of candida attached to 100 oral epithelial cells 562 (159)) than to cells staining either orange (105 (47)) or green (161 (66)). CONCLUSIONS: Oral epithelial cell variability for candidal adherence is confirmed. The technique provides an opportunity to examine the relation between oral epithelial cell type and oral candidosis in specific groups, such as tobacco smokers, where increased epithelial cell keratinisation and candidal colonisation has been reported.

Adult↗
PubMed1999

'Niche Selection' and the evolution of a complex behavior in a changing environment--a simulation.

One of the key problems in theoretical biology is the identification of the mechanisms underlying the evolution of complexity. This paper suggests that some difficulties in current models could be avoided by taking account of"niche selection"as proposed by Waddington [21] and subsequent authors [2]. Computer simulations, in which an evolving population of artificial organisms"selects"the niche(s) that maximize their fitness, are compared with a Control Model in which"Niche Selection"is absent. In the simulations the Niche Selection Model consistently produced a greater number of"fit"organisms than the Control Model; although the Niche Selection Model tended, in general, to produce organisms occupying simple niches, it was nonetheless more effective than the Control Model in producing well-adapted organisms inhabiting complex niches. It is shown that the production of these organisms is critically dependent on the rate of environmental change: Slow change leads to fit but undifferentiated populations, dominated by organisms occupying simple niches; differentiated populations, including well-adapted organisms living in complex niches, require rates of environmental change lying just beyond a mathematically well-defined critical value. In simulation"Niche Selection,"unlike conventional"Natural Selection,"provides a permanent selective bias in favor of simplicity. This tendency is counterbalanced by statistical forces favoring shifts from rare"simple niches"to commoner niches of greater complexity. Fit organisms inhabiting complex niches only emerge in conditions where the rate of environmental change is high enough to avoid the concentration of the population in very simple niches, but slow enough to permit step-by-step adaptation to niches of gradually increasing complexity. This result appears to be robust to changes in simulation parameters and assumptions, and leads to interesting conjectures about the real world behavior of biological organisms (and other complex adaptive systems). It is suggested that some of these conjectures might be relatively easy to test.

Animals↗
PubMed1999

Heading off boundary problems: clinical supervision as risk management.

The effective management of risk in clinical practice includes steps to limit harm to clients resulting from ethical violations or professional misconduct. Boundary problems constitute some of the most damaging ethical violations. The authors propose an active use of clinical supervision to anticipate and head off possible ethical violations by intervening when signs of boundary problems appear. The authors encourage a facilitative, Socratic method, rather than directive approaches, to help supervisees maximize their learning about ethical complexities. Building on the idea of a slippery slope, in which seemingly insignificant acts can lead to unethical patterns of behavior, the authors discuss ten cues to potential boundary problems, including strong feelings about a client; extended sessions with clients; gift giving between clinician and client; loans, barter, and sale of goods; clinician self-disclosures; and touching and sex. The authors outline supervisory interventions to be made when the cues are detected.

Ethics, Professional↗
PubMed1999

The Americanization of British welfare: a case study of policy transfer.

The Labour Government came to power in Britain in 1997 on a platform to reform welfare that owed a great deal to the social policy views of the Clinton administration. In the subsequent months major reforms were implemented and more announced. Yet by July 1998 the key politicians entrusted with reform either had been sacked or had resigned. This article compares and contrasts welfare policy in Britain and the United States and discusses Labour's welfare reforms, then considers whether the current impasse is due to the failure of U.S. policies to travel well.

Diffusion of Innovation↗
PubMed1999

The -308.1 polymorphism in the promoter region of the tumor necrosis factor gene is associated with ankylosing spondylitis independent of HLA-B27.

OBJECTIVE: To investigate the allele frequencies of 6 polymorphic sites spanning the region of the genome close to the tumor necrosis factor (TNF) gene in a group of HLA-B27 positive patients with ankylosing spondylitis (AS) in the West of Scotland. METHODS: One hundred sixty-seven patients with AS, 93 healthy controls, and 88 HLA-B27 positive healthy controls, all from the West of Scotland, were typed by polymerase chain reaction (PCR) for 3 restriction fragment length polymorphisms (RFLP) and 3 microsatellite polymorphic sites spanning the TNF gene cluster. The distribution of these alleles was correlated with the presence of extraspinal manifestations such as peripheral joint disease and uveitis. RESULTS: The frequency of the Nco-1.2 allele was significantly reduced in patients compared to the genetically unselected control population (p < 0.05), but was no different from the HLA-B27 positive controls. However, the -308.1 allele was significantly increased in the patients compared to the HLA-B27 positive controls (p < 0.03). CONCLUSION: This study confirms the importance of correct matching in genetic analysis in disease association studies, and provides further evidence supporting the involvement of genes other than the MHC class I locus in the pathogenesis and features of AS.

Adolescent↗
PubMed1999

Whole-body MR imaging. Practical issues, clinical applications, and future directions.

Whole-body MR imaging is in evolution, and although accepting and recognizing limitations, it is likely that both technique and incurred acquisition times will shorten over the next decade. Although the development of dedicated whole-body MR scanners appears to offer the greatest promise for the future, the development of moving table tops, optimized pulse sequences, and advances in gradient technology now facilitate practical whole-body MR imaging using existing clinical systems.

Adult↗
PubMed1998

Enterotoxigenic Clostridium perfringens type A necrotic enteritis in a foal.

A Thoroughbred-Quarter Horse crossbred foal developed hemorrhagic enteritis and died < 48 hours after birth. Gross and histologic findings were suggestive of Clostridium perfringens type C infection, and large numbers of C perfringens were isolated from intestinal contents. However, genotyping of isolates indicated that they were enterotoxigenic C perfringens type A, and isolates were found to produce C perfringens enterotoxin in vitro. This case suggests that enterotoxigenic C perfringens type A may cause enteric disease in horses.

Animals↗
PubMed1998

Hydrophobic forces dominate the thermodynamic characteristics of UvrA-DNA damage interactions.

The Escherichia coli DNA repair proteins UvrA, UvrB and UvrC work together to recognize and incise DNA damage during the process of nucleotide excision repair (NER). To gain an understanding of the damage recognition properties of UvrA, we have used fluorescence spectroscopy to study the thermodynamics of its interaction with a defined DNA substrate containing a benzo[a]pyrene diol epoxide (BPDE) adduct. Oligonucleotides containing a single site-specifically modified N2-guanine (+)-trans-, (-)-trans-, (+)-cis-, or (-)-cis-BPDE adducts were ligated into 50-base-pair DNA fragments. All four stereoisomers of DNA-BPDE adducts show an excitation maximum at 350 nm and an emission maximum around 380 to 385 nm. Binding of UvrA to the BPDE-DNA adducts results in a five to sevenfold fluorescence enhancement. Titration of the BPDE-adducted DNA with UvrA was used to generate binding isotherms. The equilibrium dissociation constants for UvrA binding to (+)-trans-, (-)-trans-, (+)-cis-, and (-)-cis- BPDE adduct were: 7.4+/-1.9, 15. 8+/-5.4, 11.3+/-2.7 and 22.4+/-2.0 nM, respectively. There was a large negative change in heat capacity DeltaCpo,obs, (-3.3 kcal mol-1 K-1) accompanied by a relatively unchanged DeltaGoobs with temperature. Furthermore, varying the concentration of KCl showed that the number of ions released upon formation of UvrA-DNA complex is about 3.4, a relatively small value compared to the contact size of UvrA with the substrate. These data suggest that hydrophobic interactions are an important driving force for UvrA binding to BPDE-damaged DNA.

7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide↗