Combining Feature Selection and Integration—A Neural Model for MT Motion Selectivity

Background: The computation of pattern motion in visual area MT based on motion input from area V1 has been investigated in many experiments and models attempting to replicate the main mechanisms. Two different core conceptual approaches were developed to explain the findings. In integrationist models the key mechanism to achieve pattern selectivity is the nonlinear integration of V1 motion activity. In contrast, selectionist models focus on the motion computation at positions with 2D features. Methodology/Principal Findings: Recent experiments revealed that neither of the two concepts alone is sufficient to explain all experimental data and that most of the existing models cannot account for the complex behaviour found. MT pattern selectivity changes over time for stimuli like type II plaids from vector average to the direction computed with an intersection of constraint rule or by feature tracking. Also, the spatial arrangement of the stimulus within the receptive field of a MT cell plays a crucial role. We propose a recurrent neural model showing how feature integration and selection can be combined into one common architecture to explain these findings. The key features of the model are the computation of 1D and 2D motion in model area V1 subpopulations that are integrated in model MT cells using feedforward and feedback processing. Our results are also in line with findings concerning the solution of the aperture problem. Conclusions/Significance: We propose a new neural model for MT pattern computation and motion disambiguation that i

The Structural Complexity of the Human BORIS Gene in Gametogenesis and Cancer

BORIS/CTCFL is a paralogue of CTCF, the major epigenetic regulator of vertebrate genomes. BORIS is normally expressed only in germ cells but is aberrantly activated in numerous cancers. While recent studies demonstrated that BORIS is a transcriptional activator of testis-specific genes, little is generally known about its biological and molecular functions.Here we show that BORIS is expressed as 23 isoforms in germline and cancer cells. The isoforms are comprised of alternative N- and C-termini combined with varying numbers of zinc fingers (ZF) in the DNA binding domain. The patterns of BORIS isoform expression are distinct in germ and cancer cells. Isoform expression is activated by downregulation of CTCF, upregulated by reduction in CpG methylation caused by inactivation of DNMT1 or DNMT3b, and repressed by activation of p53. Studies of ectopically expressed isoforms showed that all are translated and localized to the nucleus. Using the testis-specific cerebroside sulfotransferase (CST) promoter and the IGF2/H19 imprinting control region (ICR), it was shown that binding of BORIS isoforms to DNA targets in vitro is methylation-sensitive and depends on the number and specific composition of ZF. The ability to bind target DNA and the presence of a specific long amino terminus (N258) in different isoforms are necessary and sufficient to activate CST transcription. Comparative sequence analyses revealed an evolutionary burst in mammals with strong conservation of BORIS isoproteins among primates.The extensive repertoire of spliced BORIS variants in humans that confer distinct DNA binding and transcriptional activation properties, and their differential patterns of expression among germ cells and neoplastic cells suggest that the gene is involved in a range of functionally important aspects of both normal gametogenesis and cancer development. In addition, a burst in isoform diversification may be evolutionarily tied to unique aspects of primate speciation

Gaze following in an asocial reptile (Eublepharis macularius)

Gaze following is the ability to utilise information from another's gaze. It is most often seen in a social context or as a reflexive response to interesting external stimuli. Social species can potentially reveal utilisable knowledge about another's future intentions by attending to the target of their gaze. However, in even more fundamental situations, being sensitive to another's gaze can also be useful such as when it can facilitate greater foraging efficiency or lead to earlier predator detection. While gaze sensitivity has been shown to be prevalent in a number of social species, little is currently known about the potential for gaze following in asocial species. The current study investigated whether an asocial reptile, the leopard gecko (Eublepharis macularius), could reliably use the visual indicators of attention to follow the gaze of a conspecific around a barrier. We operated three trial conditions and found subjects (N = 6) responded significantly more to the conspecific demonstrator looking up at a laser stimulus projected onto an occluder during the experimental condition compared to either of two control conditions. The study's findings point toward growing evidence for gaze-following ability in reptiles, who are typically categorised as asocial. Furthermore, our findings support developing comparative social cognition research showing the origins of gaze following and other cognitive behaviours that may be more widely distributed across taxonomic groups than hitherto thought

Recurrent network dynamics reconciles visual motion segmentation and integration

In sensory systems, a range of computational rules are presumed to be implemented by neuronal subpopulations with different tuning functions. For instance, in primate cortical area MT, different classes of direction-selective cells have been identified and related either to motion integration, segmentation or transparency. Still, how such different tuning properties are constructed is unclear. The dominant theoretical viewpoint based on a linear-nonlinear feed-forward cascade does not account for their complex temporal dynamics and their versatility when facing different input statistics. Here, we demonstrate that a recurrent network model of visual motion processing can reconcile these different properties. Using a ring network, we show how excitatory and inhibitory interactions can implement different computational rules such as vector averaging, winner-take-all or superposition. The model also captures ordered temporal transitions between these behaviors. In particular, depending on the inhibition regime the network can switch from motion integration to segmentation, thus being able to compute either a single pattern motion or to superpose multiple inputs as in motion transparency. We thus demonstrate that recurrent architectures can adaptively give rise to different cortical computational regimes depending upon the input statistics, from sensory flow integration to segmentation

Deletion of a Csf1r enhancer selectively impacts CSF1R expression and development of tissue macrophage populations.

The proliferation, differentiation and survival of mononuclear phagocytes depend on signals from the receptor for macrophage colony-stimulating factor, CSF1R. The mammalian Csf1r locus contains a highly conserved super-enhancer, the fms-intronic regulatory element (FIRE). Here we show that genomic deletion of FIRE in mice selectively impacts CSF1R expression and tissue macrophage development in specific tissues. Deletion of FIRE ablates macrophage development from murine embryonic stem cells. Csf1r mice lack macrophages in the embryo, brain microglia and resident macrophages in the skin, kidney, heart and peritoneum. The homeostasis of other macrophage populations and monocytes is unaffected, but monocytes and their progenitors in bone marrow lack surface CSF1R. Finally, Csf1r mice are healthy and fertile without the growth, neurological or developmental abnormalities reported in Csf1r rodents. Csf1r mice thus provide a model to explore the homeostatic, physiological and immunological functions of tissue-specific macrophage populations in adult animals