Coverage, Continuity and Visual Cortical Architecture

The primary visual cortex of many mammals contains a continuous representation of visual space, with a roughly repetitive aperiodic map of orientation preferences superimposed. It was recently found that orientation preference maps (OPMs) obey statistical laws which are apparently invariant among species widely separated in eutherian evolution. Here, we examine whether one of the most prominent models for the optimization of cortical maps, the elastic net (EN) model, can reproduce this common design. The EN model generates representations which optimally trade of stimulus space coverage and map continuity. While this model has been used in numerous studies, no analytical results about the precise layout of the predicted OPMs have been obtained so far. We present a mathematical approach to analytically calculate the cortical representations predicted by the EN model for the joint mapping of stimulus position and orientation. We find that in all previously studied regimes, predicted OPM layouts are perfectly periodic. An unbiased search through the EN parameter space identifies a novel regime of aperiodic OPMs with pinwheel densities lower than found in experiments. In an extreme limit, aperiodic OPMs quantitatively resembling experimental observations emerge. Stabilization of these layouts results from strong nonlocal interactions rather than from a coverage-continuity-compromise. Our results demonstrate that optimization models for stimulus representations dominated by nonlocal suppressive interactions are in principle capable of correctly predicting the common OPM design. They question that visual cortical feature representations can be explained by a coverage-continuity-compromise.Comment: 100 pages, including an Appendix, 21 + 7 figure

Overcoming catastrophic forgetting in neural networks

The ability to learn tasks in a sequential fashion is crucial to the development of artificial intelligence. Until now neural networks have not been capable of this and it has been widely thought that catastrophic forgetting is an inevitable feature of connectionist models. We show that it is possible to overcome this limitation and train networks that can maintain expertise on tasks that they have not experienced for a long time. Our approach remembers old tasks by selectively slowing down learning on the weights important for those tasks. We demonstrate our approach is scalable and effective by solving a set of classification tasks based on a hand-written digit dataset and by learning several Atari 2600 games sequentially

Coordinated optimization of visual cortical maps (II) Numerical studies

It is an attractive hypothesis that the spatial structure of visual cortical architecture can be explained by the coordinated optimization of multiple visual cortical maps representing orientation preference (OP), ocular dominance (OD), spatial frequency, or direction preference. In part (I) of this study we defined a class of analytically tractable coordinated optimization models and solved representative examples in which a spatially complex organization of the orientation preference map is induced by inter-map interactions. We found that attractor solutions near symmetry breaking threshold predict a highly ordered map layout and require a substantial OD bias for OP pinwheel stabilization. Here we examine in numerical simulations whether such models exhibit biologically more realistic spatially irregular solutions at a finite distance from threshold and when transients towards attractor states are considered. We also examine whether model behavior qualitatively changes when the spatial periodicities of the two maps are detuned and when considering more than 2 feature dimensions. Our numerical results support the view that neither minimal energy states nor intermediate transient states of our coordinated optimization models successfully explain the spatially irregular architecture of the visual cortex. We discuss several alternative scenarios and additional factors that may improve the agreement between model solutions and biological observations.Comment: 55 pages, 11 figures. arXiv admin note: substantial text overlap with arXiv:1102.335

Nasal Chemosensory-Stimulation Evoked Activity Patterns in the Rat Trigeminal Ganglion Visualized by In Vivo Voltage-Sensitive Dye Imaging

Mammalian nasal chemosensation is predominantly mediated by two independent neuronal pathways, the olfactory and the trigeminal system. Within the early olfactory system, spatiotemporal responses of the olfactory bulb to various odorants have been mapped in great detail. In contrast, far less is known about the representation of volatile chemical stimuli at an early stage in the trigeminal system, the trigeminal ganglion (TG), which contains neurons directly projecting to the nasal cavity. We have established an in vivo preparation that allows high-resolution imaging of neuronal population activity from a large region of the rat TG using voltage-sensitive dyes (VSDs). Application of different chemical stimuli to the nasal cavity elicited distinct, stimulus-category specific, spatiotemporal activation patterns that comprised activated as well as suppressed areas. Thus, our results provide the first direct insights into the spatial representation of nasal chemosensory information within the trigeminal ganglion imaged at high temporal resolution

Resilience of refugees displaced in the developing world: a qualitative analysis of strengths and struggles of urban refugees in Nepal

BACKGROUND: Mental health and psychosocial wellbeing are key concerns in displaced populations. Despite urban refugees constituting more than half of the world's refugees, minimal attention has been paid to their psychosocial wellbeing. The purpose of this study was to assess coping behaviour and aspects of resilience amongst refugees in Kathmandu, Nepal. METHODS: This study examined the experiences of 16 Pakistani and 8 Somali urban refugees in Kathmandu, Nepal through in-depth individual interviews, focus groups, and Photovoice methodology. Such qualitative approaches enabled us to broadly discuss themes such as personal experiences of being a refugee in Kathmandu, perceived causes of psychosocial distress, and strategies and resources for coping. Thematic network analysis was used in this study to systematically interpret and code the data. RESULTS: Our findings highlight that urban refugees' active coping efforts, notwithstanding significant adversity and resulting distress, are most frequently through primary relationships. Informed by Axel Honneth's theory on the struggle for recognition, findings suggest that coping is a function beyond the individual and involves the ability to negotiate recognition. This negotiation involves not only primary relationships, but also the legal order and other social networks such as family and friends. Honneth's work was used because of its emphasis on the importance of legal recognition and larger structural factors in facilitating daily coping. CONCLUSIONS: Understanding how urban refugees cope by negotiating access to various forms of recognition in the absence of legal-recognition will enable organisations working with them to leverage such strengths and develop relevant programmes. In particular, building on these existing resources will lead to culturally compelling and sustainable care for these populations

“Scald-Cold”: comprehensive dissection of the superficial scald in apple

Apples, after harvest, are stored to enable a continuous year-round availability of fresh fruit on the market. The cold temperature applied to slow down the ripening process can also trigger the development of a series of chilling injury disorders, such as superficial scald. The symptoms of this phenomenon are characterized by the development of brown-discoloured area on the fruit skin, compromising, in the end, the fruit marketability. To comprehensively dissect the underlying physiological mechanisms and genetic control of superficial scald, a multi-disciplinary approach has been designed and presented within the framework of “Scald-Cold”, an interregional project network (IPN) granted by the European Region Tyrol, South Tyrol and Trentino (EGTC). During the ongoing of the “Scald-Cold” project, several technologies will be applied. A QTLome and Systems genetics approaches will be initially used to target the genomic regions involved in the control of several phenotypic entities related to scald. To shed light on the protecting mechanisms against this disorder, the fruit transcriptomes will be also investigated in the attempt to illustrate the physiological effects of different postharvest technologies in preventing the occurrence of the superficial scald. In the end, the development of this disorder will be also monitored with innovative non-destructive methods based on NIR spectroscopy implemented for the definition of predicting tools. The different disciplines representing the core of this project aim to disclose novel regulatory processes of this disorder, providing new series of tools important for both the scientific and technical communities interested in apple breeding and postharvest. To this end, novel molecular markers suitable for the selection of new apple cultivars genetically insensitive to superficial scald will be released as outcome of this project, together with the development of tools for an early detection of this phenomenon and a better understanding about the different postharvest technologies to date employed in apple postharves

SCALD-COLD: joint Austrian-Italian consortium in Euregio project for comprehensive dissection of the superficial scald in apple

After harvest, apples are stored at low temperature to slow down the ripening physiological processes. This strategy can, however, also promote the development of superficial scald, a chilling injury-related disorder showing brown-discoloured areas on the fruit skin, totally compromising its marketability. To examine thoroughly the underlying physiological mechanisms and genetic control of superficial scald, the “Scald-Cold” project, a three-year Interegional Project Network, was granted by the European Region Tyrol, South Tyrol and Trentino (EGTC). The project is centred on a comprehensive approach, integrating into a joint effort different scientific disciplines, ranging from genetics and transcriptomics to NIR spectroscopy and hyperspectral imaging, together with the employment of distinct postharvest storage technologies distinguished by a specific regime of low oxygen. The core of this project aims to disclose novel regulatory processes of this disorder, providing new series of tools important for both the scientific and technical communities interested in apple breeding and postharvest. The “Scald-Cold” project will identify new molecular markers suitable for the selection of new apple varieties genetically resistant to superficial scald, while developing tools for an early detection of this phenomeno