Know your limits : the role of boundaries in the development of spatial representation

In this issue of Neuron, Bjerknes et al. (2014) show that cells responding to environmental boundaries (border/boundary cells) are present as soon as rat pups can independently explore their environment. These boundary-based representations may thus provide a scaffold for other, later emerging, spatial representations

Vector trace cells in the subiculum of the hippocampal formation

Successfully navigating in physical or semantic space requires a neural representation of allocentric (map-based) vectors to boundaries, objects and goals. Cognitive processes such as path-planning and imagination entail the recall of vector representations, but evidence of neuron-level memory for allocentric vectors has been lacking. Here, we describe a novel neuron type, vector trace cell (VTC), whose firing generates a new vector field when a cue is encountered and a ‘trace’ version of that field for hours after cue removal. VTCs are concentrated in subiculum, distal to CA1. Compared to non-trace cells, VTCs fire at further distances from cues and exhibit earlier-going shifts in preferred theta phase in response to newly introduced cues, which demonstrates a theta-linked neural substrate for memory encoding. VTCs suggest a vector-based model of computing spatial relationships between an agent and multiple spatial objects, or between different objects, freed from the constraints of direct perception of those objects

Methane transport in agricultural soil after injection of isotopically-enriched methane in the sub-surface

Small quantities of radioactive methane (14CH4) may be released over prolonged periods from geological disposal facilities for radioactive waste. The impact of this release depends on the capacity of soil to oxidise 14CH4 to 14CO2 during transport from the sub-surface to the atmosphere. We investigated this capacity by pulse-injecting isotopically-enriched methane 50 cm below the surface of an agricultural soil in central England. Three sequential injections were made during growth of a spring wheat crop. Samples of gas were taken from the pore space throughout the soil profile at predetermined time points after injection, accompanied by samples of the atmosphere above the soil collected in sampling chambers, deployed at scheduled intervals. Methane and CO2 were measured in soil and above-ground gas using gas chromatography; the isotopic composition of CH4 and CO2 was determined using gas chromatography with isotopic ratio mass spectrometry. Supporting measurements of environmental variables were made during the experiment. The data can be used to test mathematical models describing CH4 and CO2 transport and fate in temperate agricultural soils

The effects of using the PReDicT Test to guide the antidepressant treatment of depressed patients: study protocol for a randomised controlled trial

Background Antidepressant medication is commonly used to treat depression. However, many patients do not respond to the first medication prescribed and improvements in symptoms are generally only detectable by clinicians 4–6 weeks after the medication has been initiated. As a result, there is often a long delay between the decision to initiate an antidepressant medication and the identification of an effective treatment regimen. Previous work has demonstrated that antidepressant medications alter subtle measures of affective cognition in depressed patients, such as the appraisal of facial expression. Furthermore, these cognitive effects of antidepressants are apparent early in the course of treatment and can also predict later clinical response. This trial will assess whether an electronic test of affective cognition and symptoms (the Predicting Response to Depression Treatment Test; PReDicT Test) can be used to guide antidepressant treatment in depressed patients and, therefore, hasten treatment response compared to a control group of patients treated as usual. Methods/design The study is a randomised, two-arm, multi-centre, open-label, clinical investigation of a medical device, the PReDicT Test. It will be conducted in five European countries (UK, France, Spain, Germany and the Netherlands) in depressed patients who are commencing antidepressant medication. Patients will be randomised to treatment guided by the PReDicT Test (PReDicT arm) or to Treatment as Usual (TaU arm). Patients in the TaU arm will be treated as per current standard guidelines in their particular country. Patients in the PReDicT arm will complete the PReDicT Test after 1 (and if necessary, 2) weeks of treatment. If the test indicates non-response to the treatment, physicians will be advised to immediately alter the patient’s antidepressant therapy by dose escalation or switching to another compound. The primary outcome of the study is the proportion of patients showing a clinical response (defined as 50% or greater decrease in baseline scores of depression measured using the Quick Inventory of Depressive Symptoms – Self-Rated questionnaire) at week 8. Health economic and acceptability data will also be collected and analysed. Discussion This trial will test the clinical efficacy, cost-effectiveness and acceptability of using the novel PReDicT Test to guide antidepressant treatment selection in depressed patients

Reducing the environmental impact of surgery on a global scale: systematic review and co-prioritization with healthcare workers in 132 countries

Abstract Background Healthcare cannot achieve net-zero carbon without addressing operating theatres. The aim of this study was to prioritize feasible interventions to reduce the environmental impact of operating theatres. Methods This study adopted a four-phase Delphi consensus co-prioritization methodology. In phase 1, a systematic review of published interventions and global consultation of perioperative healthcare professionals were used to longlist interventions. In phase 2, iterative thematic analysis consolidated comparable interventions into a shortlist. In phase 3, the shortlist was co-prioritized based on patient and clinician views on acceptability, feasibility, and safety. In phase 4, ranked lists of interventions were presented by their relevance to high-income countries and low–middle-income countries. Results In phase 1, 43 interventions were identified, which had low uptake in practice according to 3042 professionals globally. In phase 2, a shortlist of 15 intervention domains was generated. In phase 3, interventions were deemed acceptable for more than 90 per cent of patients except for reducing general anaesthesia (84 per cent) and re-sterilization of ‘single-use’ consumables (86 per cent). In phase 4, the top three shortlisted interventions for high-income countries were: introducing recycling; reducing use of anaesthetic gases; and appropriate clinical waste processing. In phase 4, the top three shortlisted interventions for low–middle-income countries were: introducing reusable surgical devices; reducing use of consumables; and reducing the use of general anaesthesia. Conclusion This is a step toward environmentally sustainable operating environments with actionable interventions applicable to both high– and low–middle–income countries

Hippocampal neuron firing in geometrically different environments: Evidence for long-term, incidental, and incremental learning

When rats move around environments, hippocampal neurons fire in restricted portions of these environments. These neurons are thus called place cells, and are thought to provide the rat with a map-like representation of space, which can be used to guide behaviours such as navigation, and environmental discrimination. Previous work has indicated that place cells can show different firing patterns in different environments (O'Keefe and Conway, 1978; Kubie and Ranck, 1983). This phenomenon is often referred to as "remapping" (Muller, 1996). Previous studies had shown different patterns of firing in differently-shaped walled environments (Muller and Kubie, 1987). In particular, place cell remapping was reported between square-walled, and circular-walled boxes (Quirk et al, 1992; Sharp, 1997). The present study re-examined the remapping phenomenon in square-walled and circular-walled boxes under controlled conditions which did not alter the rats' directional sense. All the experiments conducted for this study showed that remapping did not take place on initial trials in the boxes; the firing patterns in the two boxes were similar. This basic result stands in contrast to that of Quirk et al, 1992 and Sharp, 1997. Further experiments showed that although place cell patterns were initially very similar across the two boxes, the patterns diverged with experience. In the time-series experiment designed to examine this issue carefully, the results showed a correlation between the amount of experience and the amount of remapping. The transition from similar to remapped firing patterns was gradual. This is interpreted as evidence for incidental and incremental hippocampal discriminatory learning; the hippocampus learns to represent two boxes as different that it initially considers similar. Further study showed that this acquired pattern-alteration was stable after a delay period of a month, during which the animals were not exposed to the testing environment. When re-tested the patterns showed similar levels of remapping to that obtained at the end of the time-series experiment. This is interpreted as important evidence for long-term storage of learned patterns. Other tests are described which were intended to probe the nature of the initial similarity, and subsequent divergence, of the place cell firing patterns. Also described is an attempt to show transfer of knowledge from one environment to another. It is argued that the present thesis makes a contribution to our understanding of learning and memory processes in the hippocampus

Hippocampal neuron firing in geometrically different environments Evidence for long term, incidental and incremental learning

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The neurobiology of mammalian navigation

Mammals have evolved specialized brain systems to support efficient navigation within diverse habitats and over varied distances, but while navigational strategies and sensory mechanisms vary across species, core spatial components appear to be widely shared. This review presents common elements found in mammalian spatial mapping systems, focusing on the cells in the hippocampal formation representing orientational and locational spatial information, and ‘core’ mammalian hippocampal circuitry. Mammalian spatial mapping systems make use of both allothetic cues (space-defining cues in the external environment) and idiothetic cues (cues derived from self-motion). As examples of each cue type, we discuss: environmental boundaries, which control both orientational and locational neuronal activity and behaviour; and ‘path integration’, a process that allows the estimation of linear translation from velocity signals, thought to depend upon grid cells in the entorhinal cortex. Building cognitive maps entails sampling environments: we consider how the mapping system controls exploration to acquire spatial information, and how exploratory strategies may integrate idiothetic with allothetic information. We discuss how ‘replay’ may act to consolidate spatial maps, and simulate trajectories to aid navigational planning. Finally, we discuss grid cell models of vector navigation