Spatial navigation and multiscale representation by hippocampal place cells

Hippocampal lesions are known to impair success in navigation tasks. While such tasks could be solved by memorizing complete paths from a starting location to the goal, animals still perform successfully when placed in a novel starting position. We propose a navigation algorithm to solve the latter problem by exploiting two facts about hippocampal organization: (1) The size of the place fields of hippocampal place cells varies systematically along the dorsoventral axis, with dorsal place cells having smaller place fields than ventral (Kjelstrup et. al. 2008); and (2) the theta oscillation propagates as a traveling wave from dorsal to ventral hippocampus (Lubenov and Siapas, 2009). Taken together, these observations imply that the hippocampal representation of space progresses from fine- to coarse-grained within every theta cycle. 

The algorithm assumes that place cells can be activated by the animal's imagining a goal location, in addition to physically standing in the appropriate location. In the proposed algorithm, place cell activation propagates from small scale to large scale until place cells are found which respond strongly to both the physical location and the goal location. These place fields have their centers aligned roughly in the direction of the goal, providing a crude estimate of which direction the animal should step to approach the goal. Fine-grained directional information is contained in the smaller scale place fields within these large ones. Our algorithm therefore identifies a sequence of place cells, one from each scale, whose centers lie roughly along the line to the goal. 

Simulations reveal successful navigation to the goal, even around obstacles. By minimizing the number of steps the animal takes to reach the goal, we predict the organization of the optimal place field "map"; specifically the fraction of place cells which should be allocated to each spatial scale. This prediction is, in principle, experimentally testable.

The set of place fields with centers lying along a line to the goal is used to compute a step direction by maximizing the probability that those cells will be active in the next time step, given that a particular step direction is chosen.

The proposed algorithm handles navigation around obstacles by including "border cells" (Solstad et. al. 2008) which inhibit place cells in proportion to the degree of overlap between the place field and the obstacle. Furthermore, including firing rate adaptation of place cells prevents the animal from getting stuck in one spot

Association between antimicrobial usage, biosecurity measures as well as farm performance in German farrow-to-finish farms

Background: Antimicrobial usage in food producing animals is of major concern. A clear link between the extent of use and the development of antimicrobial resistance has already been demonstrated. To evaluate strategies that may reduce the antimicrobial usage while assuring pig health and welfare, it requires profound knowledge of factors that are associated with antimicrobial usage. Data on biosecurity and herd management practices are important parameters to identify risk factors which are related to a higher antimicrobial usage. To investigate between-farm variations of high and low usage the treatment incidence (TI) per age group in 60 German farrow-to-finish herds was qualitatively and quantitatively analysed and linked to biosecurity measures, and herd management characteristics. Results: Weaned pigs received most of the treatments (median TI=487.6), followed by suckling pigs (median TI=138.9). Suckling pigs were treated with critically important antimicrobials (3rd and 4th generation cephalosporines) to a remarkable extent. The number of sows present at site (p<0.01) and a low score for external biosecurity (p=0.06) were associated with a higher antimicrobial usage in pigs from birth till slaughter. Herds with a higher treatment incidence in growing pigs (TI 200days): i) were located in a region with a high pig density (p<0.01), ii) had a less strict access check for visitors and personnel (p<0.01) and iii) scored lower in the subcategory cleaning and disinfection' (internal biosecurity) (p<0.01). Herds with a higher treatment incidence in breeding pigs weaned more piglets per sow and year and scored better in the internal biosecurity level (p=0.02). Conclusions: With the main focus on the treatment incidence in pigs from birth till slaughter and in breeding pigs risk factors for a high usage in these age groups were identified. The level of biosecurity of a herd was associated with the amount of antimicrobials used. Therefore, the findings in this study indicate possible points of action in the reduction and prudent use of antimicrobials in Germany. The active improvement of biosecurity measures could be a promising alternative to reduce antimicrobial usage on herd level

First language attrition and reversion among older migrants

Emigration usually requires speakers to become bilingual, and eventually they may even become dominant in their second language. This can lead to a gradual loss of proficiency in the first language, a phenomenon referred to as first language attrition. As migrants become elderly, however, they sometimes report a "reversion" in language dominance, whereby the second language, which they have used in their daily lives for years or decades, recedes and the first language becomes stronger again. There are largely anecdotal cases of communication between such speakers and their children who were not brought up to speak their parents' first language becoming impossible. It is, however, very difficult to separate fact from fiction in such reports. This article will give an overview of changes in lexical access and fluency in the first language of adult migrants. It will assess simplistic predictions for a linear development of first and second languages against a more complex perspective which takes into account psycholinguistic aspects of activation, inhibition, and cognitive ageing. The predictions made on this basis will be tested on a large-scale quantitative investigation of language proficiency among migrants of German and Dutch descent in the Netherlands and Canada. © 2009 by Walter de Gruyter GmbH & Co. KG

Variation of organic carbon and nitrate with river flow within an oceanic regime in a rural area and potential impacts for drinking water production

International audienceOver the last two decades, climate change has become a major environmental and public health concern due to the increase of the mean temperature on the Earth and its consequences on extreme meteorological events such as floods and droughts. These events induce very low or very high river flows that may impair surface water quality, and therefore result in potential health impacts when used for drinking water production. The present study aims at assessing the impact of hydrologic regime on surface water quality with a particular emphasis on total organic carbon (TOC) and nitrate. Water quality data from three French rivers acquired over a 27 years period, from January 1983 to December 2009, show the influence of extreme flows. Variation in TOC and nitrate concentrations showed opposite patterns for the whole range of flow rate (from less than 10% up to more than 100% of the mean flow). Regarding fluxes, TOC increased continuously with flow rate while nitrate was stable for very high discharges. The C/N ratio expressed from TOC and nitrate concentrations showed high values for extreme flows and particularly for very low flow rates, generally in summer, where nitrate is assimilated by biomass. Considering TOC and nitrate fluxes, it is confirmed that the worst situations were encountered for very high flow rates, namely for TOC exportation during surface runoff which was related to heavy rains or floods. These findings are of great importance with regard to the adaptation for drinking water treatment in facing extreme hydrological conditions, of which the frequency is increasing with climate change

Exploring the associations of culture with careers and the mediating role of HR practices:A conceptual model

Purpose: The conceptual framework developed in the present study aims to highlight the importance of human resource (HR) practices as a mediator between national culture and employees' careers. Design/methodology/approach: The approach taken is a literature review and the development of a conceptual model. Findings: The paper contributes to the literature by focusing on how culture via HR practices might influence career success. Drawing on Hofstede's cultural dimensions, five propositions are developed regarding the impact of culture on career‐relevant HR practices, and how these practices are likely to influence employee career success. Research limitations/implications: Culture's effect should not be overstated. Looking at the propositions, it is possible that the influence of HR practices on career success is more pronounced than the direct effects of culture on career success. Future work is needed to measure and compare the relative strength of different associations as well as the possibility that other HR dimensions relevant to the study of career success may exist. Originality/value: At a general level, there is ample evidence of the impact of culture on the effectiveness of a variety of individual outcomes. The paper focused on the mediating role of HR practices as opposed to advancing hypotheses about direct relationships between culture and career success

Nonsurgical Treatment of Neuralgia and Cervicogenic Headache:A Systematic Review and Meta-Analysis

BACKGROUND: Extracranial compression of peripheral sensory nerves is one of many origins of chronic headaches. Identifying these patients can be difficult, and they are often diagnosed with neuralgia or cervicogenic headache. The recent literature provides the outcomes of surgical decompression in patients with these headaches. This study aimed to give an overview of the current literature on the nonsurgical treatment options and to evaluate the effectiveness of these treatments in patients with neuralgia and cervicogenic headache. METHODS: Databases were searched to identify all published clinical studies investigating nonsurgical treatment outcomes in patients with neuralgia or cervicogenic headaches. Studies that reported numerical pain scores, nonnumerical pain scores, headache-free days, or the number of adverse events after nonsurgical treatment were included. RESULTS: A total of 22 articles were included in qualitative analysis. The majority of studies included patients who received injection therapy. Treatment with oral analgesics achieved good results in only 2.5% of the patients. Better outcomes were reported in patients who received local anesthetics injection (79%) and corticosteroid injection (87%). Treatment with botulinum toxin injection yielded the highest percentage of good results (97%; 95% CI, 0.81–1.00). The duration of headache relief after injection therapy varied from 30 minutes to 5 months. CONCLUSIONS: The nonsurgical treatment of patients with neuralgia or cervicogenic headache is challenging. Injection therapy in patients with these types of headaches achieved good pain relief but only for a limited time. Surgical decompression may result in long-lasting pain relief and might be a more sustainable treatment option