A search for factors controlling the formation and maintenance of connections between the thelamus and cortex in vitro

Although the development of the nervous system is continuous, the neurones that constitute the nervous system proceed through specific developmental stages. Such stages included: birth, differentiation, migration, the formation of efferent and afferent connections, and the organisation of these connections based on exogenous and endogenous cues. Alternatively, a neuron may undergo "natural occurring" cell death at various points during development.When considering the complexity of the nervous system, it is not surprising that our knowledge, as to the factors that control these development stages, is limited One significant obstacle for experimentally addressing these questions, for practical and/or ethical reasons, has been the animal itself. Thus, the advent of tissue culture techniques has greatly facilitated research in this area.In addition to in vivo Dil tract-tracing experiments, I have used three different in vitro techniques: (i) co-cultures of organotypic explants on a two-dimensional collagen substrate, (ii) organotypic explants co-cultured within a three-dimensional collagen gel, and (iii) co-cultures of dissociated cells. Because serum is known to contain many trophic factors, only serum-free medium was used for all of these experiments. Using the above in vitro techniques, I investigated questions concerning the development of connections between the thalamus and cortex.These experiments yielded the following results, (i) When thalamocortical and corticothalamic efferent fibres began to grow in vivo at embryonic day 15 (El5), conserved diffusible target-derived factors enhanced their neurite elongation in vitro, (ii) The survival of El 5 thalamic and cortical neurones was independent from target-derived iii trophic support, since both the thalamus and cortex promoted their own survival in vitro. possibly through the production of endogenous trophic factors. However (iii), between E17 and postnatal day 2, a time coincident with the arrival of their fibres to their target, the survival of thalamocortical and corticothalamic neurones was dependent on factors released from their target, (iv) The production of growth promoting factors within the cortex increased with postnatal age and was at least partially regulated by afferent activity. And finally (v), it seems that the recognition/stop-signalling molecules expressed within these targets are also highly conserved since they were recognised in inter-species co-culture experiments. Thus, in general, the development of both thalamocortical and corticothalamic efferents are highly influenced by factors produced by their target cells in vitro. In vivo, these factors may play various roles during the different developmental stages from promoting neurite outgrowth and cell survival, to regulating the reorganisation of connection

Deviate: the Science of Seeing Differently

World-renowned neuroscientist Beau Lotto reveals the truths of human perception and devises a cognitive toolkit for how to succeed in a world of uncertainty. Perception is the foundation of human experience, but few of us understand how our own perception works. By revealing the startling truths about the brain and perception, Beau Lotto shows that the next big innovation is not a new technology: it is a new way of seeing. In his first major book, Beau Lotto draws on over a decade of pioneering research to show how our brains play tricks on us. With an innovative combination of case studies and optical- and perception-illusion exercises, DEVIATE will revolutionise the way you see the world. With this new understanding of how the brain works and its perceptive trickery, we can apply these insights to every aspect of life and work. DEVIATE is not just an engaging look into the neuroscience of thought, behaviour and creativity: it is a call to action, enlisting readers in their own journey of self-discovery

Soma: Live musical performance where congruent visual, auditory, and proprioceptive stimuli fuse to form a combined aesthetic narrative

Artists and scientists have long had an interest in the relationship between music and visual art, leading up to the present-day artform of correlated animation and music, “visual music.” Current live performance tools and paradigms for visual music however are subject to several limitations. The work detailed addresses these through a transdisciplinary integration of findings from several research areas, detailing the resulting ideas and their implementation in three interconnected software applications. This culminates in the art form of Soma, where correlated auditory, visual and proprioceptive stimuli form a combined narrative

What Are Lightness Illusions and Why Do We See Them?

Lightness illusions are fundamental to human perception, and yet why we see them is still the focus of much research. Here we address the question by modelling not human physiology or perception directly as is typically the case but our natural visual world and the need for robust behaviour. Artificial neural networks were trained to predict the reflectance of surfaces in a synthetic ecology consisting of 3-D “dead-leaves” scenes under non-uniform illumination. The networks learned to solve this task accurately and robustly given only ambiguous sense data. In addition—and as a direct consequence of their experience—the networks also made systematic “errors” in their behaviour commensurate with human illusions, which includes brightness contrast and assimilation—although assimilation (specifically White's illusion) only emerged when the virtual ecology included 3-D, as opposed to 2-D scenes. Subtle variations in these illusions, also found in human perception, were observed, such as the asymmetry of brightness contrast. These data suggest that “illusions” arise in humans because (i) natural stimuli are ambiguous, and (ii) this ambiguity is resolved empirically by encoding the statistical relationship between images and scenes in past visual experience. Since resolving stimulus ambiguity is a challenge faced by all visual systems, a corollary of these findings is that human illusions must be experienced by all visual animals regardless of their particular neural machinery. The data also provide a more formal definition of illusion: the condition in which the true source of a stimulus differs from what is its most likely (and thus perceived) source. As such, illusions are not fundamentally different from non-illusory percepts, all being direct manifestations of the statistical relationship between images and scenes

Como experimentamos los entornos virtuales inmersivos: el concepto de presencia y su medición

This paper reviews the concept of presence in immersive virtual environments, the sense of being there signalled by people acting and responding realistically to virtual situations and events. We argue that presence is a unique phenomenon that must be distinguished from the degree of engagement, involvement in the portrayed environment. We argue that there are three necessary conditions for presence: the (a) consistent low latency sensorimotor loop between sensory data and proprioception; (b) statistical plausibility: images must be statistically plausible in relation to the probability distribution of images over natural scenes. A constraint on this plausibility is the level of immersion; (c) behaviour-response correlations: Presence may be enhanced and maintained over time by appropriate correlations between the state and behaviour of participants and responses within the environment, correlations that show appropriate responses to the activity of the participants. We conclude with a discussion of methods for assessing whether presence occurs, and in particular recommend the approach of comparison with ground truth and give some examples of this.En este artículo se revisa el concepto de presencia en entornos virtuales inmersivos; es decir, la sensación de estar dentro del entorno virtual indicada por el modo de responder al mismo como si fuera real. La presencia debe distinguirse de otros fenómenos como el compromiso o la implicación. Hay tres condiciones necesarias para la presencia. La primera es un bucle sensomotor consistente y de baja latencia entre los datos sensoriales y propioceptivos. La segunda es la plausibilidad estadística, referente a que las imágenes deben ser estadísticamente plausibles en relación con la distribución de probabilidad de las imágenes en escenas naturales. Un límite para esta condición viene dado por el nivel de inmersión. La tercera es la correlación entre el comportamiento del sujeto y la respuesta del entorno. La presencia se mantiene e incrementa a lo largo del tiempo como consecuencia de la correlación entre, por un lado, el estado y el comportamiento del sujeto y, por otro, las respuestas del entorno, indicando que el entorno responde de forma adecuada a la actividad del sujeto. Se concluye con una discusión de los métodos que se pueden emplear para evaluar la presencia y se recomienda para ello, en particular, la comparación con datos obtenidos sobre el terreno; es decir, la comparación entre las respuestas del sujeto ante estímulos virtuales y las respuestas ante los correspondientes estímulos reales

Code Bending: A New Creative Coding Practice

Creative coding, or artistic creation through the medium of program instructions, is constantly gaining traction, and there is a steady stream of new resources emerging to support it. However, the question of how creative coding is carried out still deserves more attention. In what ways may the act of program development be rendered conducive to artistic creativity? As one possible answer to this question, the authors present and discuss a new creative coding practice, that of code bending, alongside examples and considerations regarding its applications

Floral Morphogenesis: Stochastic Explorations of a Gene Network Epigenetic Landscape

In contrast to the classical view of development as a preprogrammed and deterministic process, recent studies have demonstrated that stochastic perturbations of highly non-linear systems may underlie the emergence and stability of biological patterns. Herein, we address the question of whether noise contributes to the generation of the stereotypical temporal pattern in gene expression during flower development. We modeled the regulatory network of organ identity genes in the Arabidopsis thaliana flower as a stochastic system. This network has previously been shown to converge to ten fixed-point attractors, each with gene expression arrays that characterize inflorescence cells and primordial cells of sepals, petals, stamens, and carpels. The network used is binary, and the logical rules that govern its dynamics are grounded in experimental evidence. We introduced different levels of uncertainty in the updating rules of the network. Interestingly, for a level of noise of around 0.5–10%, the system exhibited a sequence of transitions among attractors that mimics the sequence of gene activation configurations observed in real flowers. We also implemented the gene regulatory network as a continuous system using the Glass model of differential equations, that can be considered as a first approximation of kinetic-reaction equations, but which are not necessarily equivalent to the Boolean model. Interestingly, the Glass dynamics recover a temporal sequence of attractors, that is qualitatively similar, although not identical, to that obtained using the Boolean model. Thus, time ordering in the emergence of cell-fate patterns is not an artifact of synchronous updating in the Boolean model. Therefore, our model provides a novel explanation for the emergence and robustness of the ubiquitous temporal pattern of floral organ specification. It also constitutes a new approach to understanding morphogenesis, providing predictions on the population dynamics of cells with different genetic configurations during development

Rendering a Digital Object

Rendering a digital element is disclosed. An indication that a device is within a region associated with the digital element is received. It is determined that the digital element is to be rendered. A representation of the digital element is generated in a rendered view of the region. The digital element is provided upon receiving an indication that the digital element has been selected

The Brightness of Colour

Background: The perception of brightness depends on spatial context: the same stimulus can appear light or dark depending on what surrounds it. A less well-known but equally important contextual phenomenon is that the colour of a stimulus can also alter its brightness. Specifically, stimuli that are more saturated (i.e. purer in colour) appear brighter than stimuli that are less saturated at the same luminance. Similarly, stimuli that are red or blue appear brighter than equiluminant yellow and green stimuli. This non-linear relationship between stimulus intensity and brightness, called the Helmholtz-Kohlrausch (HK) effect, was first described in the nineteenth century but has never been explained. Here, we take advantage of the relative simplicity of this 'illusion' to explain it and contextual effects more generally, by using a simple Bayesian ideal observer model of the human visual ecology. We also use fMRI brain scans to identify the neural correlates of brightness without changing the spatial context of the stimulus, which has complicated the interpretation of related fMRI studies.Results: Rather than modelling human vision directly, we use a Bayesian ideal observer to model human visual ecology. We show that the HK effect is a result of encoding the non-linear statistical relationship between retinal images and natural scenes that would have been experienced by the human visual system in the past. We further show that the complexity of this relationship is due to the response functions of the cone photoreceptors, which themselves are thought to represent an efficient solution to encoding the statistics of images. Finally, we show that the locus of the response to the relationship between images and scenes lies in the primary visual cortex (V1), if not earlier in the visual system, since the brightness of colours (as opposed to their luminance) accords with activity in V1 as measured with fMRI.Conclusions: The data suggest that perceptions of brightness represent a robust visual response to the likely sources of stimuli, as determined, in this instance, by the known statistical relationship between scenes and their retinal responses. While the responses of the early visual system (receptors in this case) may represent specifically the statistics of images, post receptor responses are more likely represent the statistical relationship between images and scenes. A corollary of this suggestion is that the visual cortex is adapted to relate the retinal image to behaviour given the statistics of its past interactions with the sources of retinal images: the visual cortex is adapted to the signals it receives from the eyes, and not directly to the world beyond