Local and Global Contrast Adaptation in Retinal Ganglion Cells

SummaryRetinal ganglion cells react to changes in visual contrast by adjusting their sensitivity and temporal filtering characteristics. This contrast adaptation has primarily been studied under spatially homogeneous stimulation. Yet, ganglion cell receptive fields are often characterized by spatial subfields, providing a substrate for nonlinear spatial processing. This raises the question whether contrast adaptation follows a similar subfield structure or whether it occurs globally over the receptive field even for local stimulation. We therefore recorded ganglion cell activity in isolated salamander retinas while locally changing visual contrast. Ganglion cells showed primarily global adaptation characteristics, with notable exceptions in certain aspects of temporal filtering. Surprisingly, some changes in filtering were most pronounced for locations where contrast did not change. This seemingly paradoxical effect can be explained by a simple computational model, which emphasizes the importance of local nonlinearities in the retina and suggests a reevaluation of previously reported local contrast adaptation

Neural plasticity in decision making and memory formation

Goal-directed behaviour is characterized by an ability to make inferences without direct experience. This requires a model of the environment and of ourselves, which is flexibly adjusted in light of new incoming information. This thesis uses representational functional magnetic resonance imaging (fMRI) techniques in combination with computational modelling to investigate (1) whether humans can construct models of other people’s preferences and whether this process influences their own value representation, and (2) how statistical relationships between discrete, non-spatial objects are combined into a model of the world. The first part of the thesis investigates how subjective values are computed in an intertemporal choice paradigm, and how these value computations are updated as a consequence of learning about the preferences of another. Critically, subjects’ own preferences shift towards those of the other when learning about their choices, suggesting that subjects incorporate new knowledge about others into a model of their own preferences. The underlying mechanism involves prediction errors, which introduce plasticity into subjects’ mPFC value representations, in turn resulting in a shift in subjects’ own preferences. The second part of this thesis investigates how relationships between arbitrary objects are represented in the brain. Relational knowledge is often considered analogous to spatial reasoning, where relationships are encoded in a hippocampal-entorhinal ‘cognitive map’. Here, I show that maps can also be extracted from the entorhinal cortex for discrete relationships between arbitrary stimuli, and in the absence of conscious knowledge. The representation of abstract knowledge in map-like structures suggests that inferences do not need to rely on direct experiences but can be computed anew from mapped knowledge. Together, these studies reveal how world models are represented and updated at the level of neural representations, providing a bridge between representational codes and cognitive computations

Determinanten der Pachtpreise in Deutschland – Biogasförderung und Direktzahlungen im Fokus

Der Pachtmarkt in Deutschland ist in den letzten Jahren verstärkt in die Diskussion geraten. Die Land-wirte beklagen steigende Pachtpreise, die nur noch von wenigen gezahlt werden können (DBV, 2014). Als Grund für das hohe Pachtpreisniveau wird vielfach die staatliche Biogasförderung angeführt, die angeblich zu einer hohen Zahlungsbereitschaft für Pachtflächen zum Gärsubstratanbau führt. Gleichzeitig wird von vielen Landwirten berichtet, dass die Direktzahlungen im Rahmen der Pachtverhandlungen an die Verpächter weitergereicht werden und somit die eigentlich aktiven Bewirtschafter weniger finanzielle Unterstützung von Seiten der EU erfahren. Mittlerweile will auch die Politik auf diese Situation reagieren und die Pachtpreise analog zu den Mietpreisen in ihrer Entwicklung ausbremsen (NMELV, 2016). Ziel dieser Arbeit ist es, die oben dargestellten Diskussionspunkte zu beleuchten, die Determinanten der Pachtpreisbildung in Deutschland zu erklären und dabei insbesondere auf die Bedeutung der Biogasförderung und der Direktzahlungen einzugehen. Aufbauend auf den Ergebnissen sollen Implikationen für die weitere Politikgestaltung abgeleitet werden.In recent years the German land rental market has increasingly become the subject of discussion. Farmers complain about rising rental prices that only few can afford. They often invoke the biogas state subsidy as a reason for high price levels. Due to higher ground rents for the cultivation of fermenting substrate the willingness to pay for agricultural land outpaces traditional types of production. At the same time many farmers report that they have to forward direct payments to the landlords. As a consequence, less financial support from the EU is provided to those who actually cultivate the land. Politics respond to the situation and aim at thwarting price development similar to the price curb recently established for rental prices of flats and houses. This thesis examines the above mentioned points of discussion by analysing the determinants of land rental prices in Germany. Here the primary focus is on biogas subsidies and direct payments. Building on the results we derive implications for further decision-making of the EU agricultural policy

Entorhinal and ventromedial prefrontal cortices abstract and generalize the structure of reinforcement learning problems

Knowledge of the structure of a problem, such as relationships between stimuli, enables rapid learning and flexible inference. Humans and other animals can abstract this structural knowledge and generalize it to solve new problems. For example, in spatial reasoning, shortest-path inferences are immediate in new environments. Spatial structural transfer is mediated by cells in entorhinal and (in humans) medial prefrontal cortices, which maintain their co-activation structure across different environments and behavioral states. Here, using fMRI, we show that entorhinal and ventromedial prefrontal cortex (vmPFC) representations perform a much broader role in generalizing the structure of problems. We introduce a task-remapping paradigm, where subjects solve multiple reinforcement learning (RL) problems differing in structural or sensory properties. We show that, as with space, entorhinal representations are preserved across different RL problems only if task structure is preserved. In vmPFC and ventral striatum, representations of prediction error also depend on task structure

Retracted Article: Agro-Economic Analysis of the use of Glyphosate in Germany

Ein Rücknahme-Hinweis wurde für diesen Artikel am 18. Dezember 2019 publiziert, https://doi.org/10.5073/JfK.2012.05.02.retraction Der intensive Ackerbau ist in der gesellschaftlichen Wahr­nehmung oft sehr negativ belegt. Der durch den Pflanzen­schutz generierte Nutzen für die Sicherstellung qualitativ hochwertiger Lebensmittel für die wachsende Weltbevölkerung wird als selbstverständlich angesehen und nicht dementsprechend gewürdigt. In diesem Artikel wird daher am Beispiel des Wirkstoffes Glyphosat gezeigt, welche ökonomische Bedeutung einzelne Pflanzenschutzwirkstoffe im Ackerbau in Deutschland haben können. Dazu sind im Frühjahr 2011 14 Experteninterviews mit Offi­zial­beratern aus unterschiedlichen Regionen Deutschlands geführt worden. Die Ergebnisse zeigen, dass Glyphosat vor allem für die konservierende Bodenbearbeitung in vielen Regionen eine Standardmaßnahme ist. Insgesamt wird es auf 30% bis 35% der Wintergetreidefläche und 50% der Winterrapsfläche eingesetzt. In Folge der zuneh­menden Resistenzentwicklungen bei einem Glyphosatverbot würden in einzelnen Regionen die Erträge um bis zu 10% zurückgehen, obwohl zusätzliche Bodenbearbeitungsgänge und Pflanzenschutzmaßnahmen eingesetzt würden. Aufbauend auf diese Ergebnisse sind dann die Deckungsbeiträge der einzelnen Kulturen bei einem Verbot von Glyphosat berechnet worden. Die Deckungsbeiträge würden in Ostdeutschland um bis zu 27%, in Norddeutschland um bis zu 3% und in den norddeutschen Küstengebieten um bis zu 36% zurückgehen. Dabei sind die Anstiege der Erzeugerpreise berücksichtigt worden, die sich durch einen Rückgang der Produktion in der EU-27 um 5% und höhere Produktionskosten ergeben würden. Die Erzeugerpreise sind mit dem partiellen Gleichgewichts­modell AGRISIM ermittelt worden. Mit dem Modell kann ebenfalls gezeigt werden, dass die Kostenanstiege und Ertragsrückgänge in der EU-27 zu Produktionsrückgängen bei Weizen, Futtergetreide, Mais und Ölsaaten in Höhe von 4,3% bis 7,1% führen würden. Die Europäische Union würde von einem Nettoexporteur zu einem Netto­importeur von Weizen und Futtergetreide und die Import­defizite für Ölsaaten und Mais würden weiter ansteigen. Dies würde zu einem jährlichen Wohlfahrtsverlust in der Europäischen Union in Höhe von 1,4 Milliarden US- führen.    A Retraction Note to this article was published on December 18, 2019, https://doi.org/10.5073/JfK.2012.05.02.retraction Intensive agricultural cultivation is often perceived very negatively in society. The benefit generated through plant protection for ensuring the availability of high quality food for the growing world population is taken for granted and thus is not appreciated accordingly. In this article, by the example of the active substance Glyphosate, it is shown which economic importance certain plant protection substances can have in German agriculture. For this, in spring 2011 14 expert interviews with consultants from different regions of Germany were conducted. The results reveal that in many regions Glyphosate foremost is a standard measure for the conservation tillage. Overall it is applied on 30% to 35% of the winter grain area and 50% of the winter rape area. In the hypothetical case of a glyphosate ban in some areas despite additional tillage and plant protection measures yield depressions of up to 10% would be possible. Based on these findings the profit margins for individual crops in case of a Glyphosate ban have been calculated. The profit margins would decrease by up to 27% in Eastern Germany, 3% in Northern Germany and 36% in the Northern Coastal Areas. For this, the increase in the producer prices due to a decrease in production in the EU-27 by 5% and higher production costs has been accounted for. The producer prices have been estimated using the partial equilibrium model AGRISIM. With the model it can also be shown that cost increases and yield depressions in the EU-27 would lead to decreases in production in the case of wheat, fodder, maize and oilseeds to the tune of 4,3% to 7,1%. The European Union from being a net exporter of wheat and fodder would become a net importer and import deficits for oilseeds and maize would increase further. This would lead to an annual welfare loss of 1,4 billion US- in the European Union.   &nbsp

Parallel cognitive maps for short-term statistical and long-term semantic relationships in the hippocampal formation

The hippocampal-entorhinal system uses cognitive maps to represent spatial knowledge and other types of relational information, such as the transition probabilities between objects. However, objects can often be characterized in terms of different types of relations simultaneously, e.g. semantic similarities learned over the course of a lifetime as well as transitions experienced over a brief timeframe in an experimental setting. Here we ask how the hippocampal formation handles the embedding of stimuli in multiple relational structures that differ vastly in terms of their mode and timescale of acquisition: Does it integrate the different stimulus dimensions into one conjunctive map, or is each dimension represented in a parallel map? To this end, we reanalyzed functional magnetic resonance imaging (fMRI) data from Garvert et al. (2017) that had previously revealed an entorhinal map which coded for newly learnt statistical regularities. We used a triplet odd-one-out task to construct a semantic distance matrix for presented items and applied fMRI adaptation analysis to show that the degree of similarity of representations in bilateral hippocampus decreases as a function of semantic distance between presented objects. Importantly, while both maps localize to the hippocampal formation, this semantic map is anatomically distinct from the originally described entorhinal map. This finding supports the idea that the hippocampal-entorhinal system forms parallel cognitive maps reflecting the embedding of objects in diverse relational structures

Evidence for proposed ICD-11 PTSD and complex PTSD: a latent profile analysis

Background: The WHO International Classification of Diseases, 11th version (ICD-11), has proposed two related diagnoses, posttraumatic stress disorder (PTSD) and complex PTSD within the spectrum of trauma and stress-related disorders. Objective: To use latent profile analysis (LPA) to determine whether there are classes of individuals that are distinguishable according to the PTSD and complex PTSD symptom profiles and to identify potential differences in the type of stressor and severity of impairment associated with each profile. Method: An LPA and related analyses were conducted on 302 individuals who had sought treatment for interpersonal traumas ranging from chronic trauma (e.g., childhood abuse) to single-incident events (e.g., exposure to 9/11 attacks). Results: The LPA revealed three classes of individuals: (1) a complex PTSD class defined by elevated PTSD symptoms as well as disturbances in three domains of self-organization: affective dysregulation, negative self-concept, and interpersonal problems; (2) a PTSD class defined by elevated PTSD symptoms but low scores on the three self-organization symptom domains; and (3) a low symptom class defined by low scores on all symptoms and problems. Chronic trauma was more strongly predictive of complex PTSD than PTSD and, conversely, single-event trauma was more strongly predictive of PTSD. In addition, complex PTSD was associated with greater impairment than PTSD. The LPA analysis was completed both with and without individuals with borderline personality disorder (BPD) yielding identical results, suggesting the stability of these classes regardless of BPD comorbidity. Conclusion: Preliminary data support the proposed ICD-11 distinction between PTSD and complex PTSD and support the value of testing the clinical utility of this distinction in field trials. Replication of results is necessary.For the abstract or full text in other languages, please see Supplementary files under Article Tools onlin

Retracted Article: Conservation tillage in Germany: A solution of soil erosion

Ein Rücknahme-Hinweis für diesen Artikel wurde am 18. Dezember 2019 publiziert, https://doi.org/10.5073/JfK.2015.09.02.retraction Der Verlust von fruchtbarem Ackerboden durch Wind- und Wassererosion ist weltweit ein Problem. Auch in Deutschland sind allein 2 Mio. Hektar als sehr hoch erosionsgefährdet eingestuft mit der Gefahr eines jährlichen Bodenabtrags pro Hektar von bis zu 10 t bei Getreide und bis zu 50 t in Reihenkulturen. Der Verzicht auf eine wendende Bodenbearbeitung und der Anbau von Zwischenfrüchten ermöglicht eine ganzjährige Bedeckung der Bodenoberfläche mit organischem Material und vermindert die Angriffsflächen für Wind und Wasser. Zudem führt eine erhöhte Wasseraufnahme und Wasserhalte­kapazität zur Minderung der Erosionsgefährdung. Plankostenrechnungen verschiedener Fruchtfolgen unter Berücksichtigung der Direktkosten und der Arbeitserle­digungskosten auf Grundlage von Expertengesprächen in Nord-Ostdeutschland und in einer Mittelgebirgsregion zeigen neben den positiven ökologischen Effekten einer konservierenden Bodenbearbeitung auch ökonomische Vorteile für den Landwirt. Mit einer angepassten Glyphosatstra­tegie in der Fruchtfolge können ohne Ertragsreduzierung die Maschinen- und Arbeitskosten sowie der CO2-Ausstoß gesenkt werden. Eingebunden in die Gute Fachliche Praxis des Pflanzenbaus ist die konservierende Bodenbearbeitung mit dem zugehörigen Pflanzenschutzmanagement ein wesentlicher Beitrag für einen nachhaltigen Ackerbau.   DOI: 10.5073/JfK.2015.09.02, https://doi.org/10.5073/JfK.2015.09.02A Retraction Note to this article was published on December 18, 2019, https://doi.org/10.5073/JfK.2015.09.02.retraction The loss of fertile soil by wind and water erosion is a worldwide problem. In Germany alone its 2 million hectares area which is categorised under highly endangered by soil erosion with the risk of annual soil loss of about 10 tones (cereal) and up to 50 tones per hectare (row crop). Minimizing the tillage operations and long term crop rotations with use of catch crop covering the soil surface with organic material reduces the negative effects on soil from wind and water. Additionally, it increases water absorption and water holding capacity of the soil which lowers the risk of soil erosion. Calculating the planned costs from various crop rotations taking into account the direct costs and the labor and machinery costs based on expert interviews from North-East Germany and Low Mountains range regions show the positive ecological effects of conservation tillage along with the economic advantages for the farmers. With an adapted Glyphosate strategy in the crop rotations, machine and labor costs as well as CO2-emissions can be reduced under conservation tillage without affecting the yield of the crops. Conservation tillage associated with crop protection management is a good practice of crop production which makes it an essential contributor to a sustainable agriculture.   DOI: 10.5073/JfK.2015.09.02, https://doi.org/10.5073/JfK.2015.09.0