Differential feedback modulation of center and surround mechanisms in parvocellular cells in the visual thalamus.

Many cells in both the central visual system and other sensory systems exhibit a center surround organization in their receptive field, where the response to a centrally placed stimulus is modified when a surrounding area is also stimulated. This can follow from laterally directed connections in the local circuit at the level of the cell in question but could also involve more complex interactions. In the lateral geniculate nucleus (LGN), the cells relaying the retinal input display a concentric, center surround organization that in part follows from the similar organization characterizing the retinal cells providing their input. However, local thalamic inhibitory interneurons also play a role, and as we examine here, feedback from the visual cortex too. Here, we show in the primate (macaque) that spatially organized cortical feedback provides a clear and differential influence serving to enhance both responses to stimulation within the center of the receptive field and the ability of the nonclassical surround mechanism to attenuate this. In short, both center and surround mechanisms are influenced by the feedback. This dynamically sharpens the spatial focus of the receptive field and introduces nonlinearities from the cortical mechanism into the LGN.

Using geographical information systems and cartograms as a health service quality improvement tool.

INTRODUCTION: Disease prevalence can be spatially analysed to provide support for service implementation and health care planning, these analyses often display geographic variation. A key challenge is to communicate these results to decision makers, with variable levels of Geographic Information Systems (GIS) knowledge, in a way that represents the data and allows for comprehension. The present research describes the combination of established GIS methods and software tools to produce a novel technique of visualising disease admissions and to help prevent misinterpretation of data and less optimal decision making. The aim of this paper is to provide a tool that supports the ability of decision makers and service teams within health care settings to develop services more efficiently and better cater to the population; this tool has the advantage of information on the position of populations, the size of populations and the severity of disease. METHODS: A standard choropleth of the study region, London, is used to visualise total emergency admission values for Chronic Obstructive Pulmonary Disease and bronchiectasis using ESRI's ArcGIS software. Population estimates of the Lower Super Output Areas (LSOAs) are then used with the ScapeToad cartogram software tool, with the aim of visualising geography at uniform population density. An interpolation surface, in this case ArcGIS' spline tool, allows the creation of a smooth surface over the LSOA centroids for admission values on both standard and cartogram geographies. The final product of this research is the novel Cartogram Interpolation Surface (CartIS). RESULTS: The method provides a series of outputs culminating in the CartIS, applying an interpolation surface to a uniform population density. The cartogram effectively equalises the population density to remove visual bias from areas with a smaller population, while maintaining contiguous borders. CartIS decreases the number of extreme positive values not present in the underlying data as can be found in interpolation surfaces. DISCUSSION: This methodology provides a technique for combining simple GIS tools to create a novel output, CartIS, in a health service context with the key aim of improving visualisation communication techniques which highlight variation in small scale geographies across large regions. CartIS more faithfully represents the data than interpolation, and visually highlights areas of extreme value more than cartograms, when either is used in isolation.

Assessment of 180° rotation of the choroid as a novel surgical treatment for age-related macular degeneration.

PURPOSE: Our objective was to examine the feasibility of rotating choriocapillaris, Bruch's membrane (BM), and retinal pigment epithelium (RPE) through 180° on a vascular pedicle and to assess revascularization and tissue preservation postoperatively. Such an approach could be used in the treatment of age-related macular degeneration where there is focal disease at the macula with healthy tissues located peripherally. METHODS: Successful surgery was performed in six rhesus macaque monkeys, which have a very similar choroidal blood supply to humans. After inducing a retinal detachment, the recurrent branch of the long posterior ciliary artery was used as a pedicle around which a graft stretching to the temporal equator was rotated. Retina was reattached over the rotated graft and eyes were followed up for up to 6 months with repeated angiography and optical coherence tomography (OCT). The morphology of retinal cells and BM were assessed by immunohistochemistry and electron microscopy. RESULTS: Revascularization of the choroid was limited, with reestablishment of drainage to the vortex veins seen in only one case. There was a secondary loss of the RPE and outer retina evident on histological analysis three months after surgery. The underlying BM however remained intact. CONCLUSIONS: Pedicled choroidal rotation surgery is technically feasible in vivo with intraoperative control of bleeding. However, lack of graft revascularization with the technique in its current form leads to neuroretinal and RPE tissue loss, and graft shrinkage. We found no evidence that rotational grafts are likely to improve the outcomes presently achieved with free graft techniques.