A recurrent model of orientation maps with simple and complex cells

We describe a neuromorphic chip that utilizes transistor heterogeneity, introduced by the fabrication process, to generate orientation maps similar to those imaged in vivo. Our model consists of a recurrent network of excitatory and inhibitory cells in parallel with a push-pull stage. Similar to a previous model the recurrent network displays hotspots of activity that give rise to visual feature maps. Unlike previous work, however, the map for orientation does not depend on the sign of contrast. Instead, sign-independent cells driven by both ON and OFF channels anchor the map, while push-pull interactions give rise to sign-preserving cells. These two groups of orientation-selective cells are similar to complex and simple cells observed in V1

Frequency Bin Entangled Photons

A monochromatic laser pumping a parametric down conversion crystal generates frequency entangled photon pairs. We study this experimentally by addressing such frequency entangled photons at telecommunication wavelengths (around 1550 nm) with fiber optics components such as electro-optic phase modulators and narrow band frequency filters. The theory underlying our approach is developed by introducing the notion of frequency bin entanglement. Our results show that the phase modulators address coherently up to eleven frequency bins, leading to an interference pattern which can violate a Bell inequality adapted to our setup by more than five standard deviations.Comment: 10 pages, 4 figures (extended version

Functional outcomes and clinical strength assessment after infraspinatus-sparing surgical approach to scapular fracture: Does it really make a difference?

Background: Surgical treatment of scapular fractures with posterior approach is frequently associated with postoperative infraspinatus hypotrophy and weakness. The aim of this retrospective study is to compare infraspinatus strength and functional outcomes in patients treated with the classic Judet versus modified Judet approach for scapular fracture. Patients and methods: 20 cases with scapular neck and body fracture treated with posterior approach for lateral border plate fixation were reviewed. In 11 of 20 cases, we used the modified Judet approach (MJ group), and in 9 cases we used the classic Judet approach (CJ group). All fractures were classified according to the AO classification system. At follow-up examinations, patients had X-ray assessment with acromiohumeral distance (AHD) measurement, clinical evaluation, active range of motion (ROM) examination, Constant Shoulder Score, and Disability of the Arm, Shoulder and Hand (DASH) Score. Infraspinatus strength assessment was measured using a dynamometer during infraspinatus strength test (IST) and infraspinatus scapular retraction test (ISRT). Results: Demographic data did not significantly differ between the CJ group and MJ group, except for mean follow-up, which was 4.15\ua0years in the CJ group and 2.33 in the MJ group (p\ua0<\ua00.001). All X-ray examinations showed fracture healing. AHD was significantly decreased in the CJ group (p\ua0=\ua00.006). We did not find significant differences in active ROM between the MJ and CJ groups in the injured arm (p\ua0<\ua00.05). The Constant Score was 75.83 (\ub114.03) in the CJ group and 82.75 (\ub110.72) in the MJ group (p\ua0=\ua00.31); DASH Score was 10.16 in the CJ group and 6.25 in the MJ group (p\ua0=\ua00.49). IST showed mean strength of 8.38\ua0kg (\ub11.75) in the MJ group and 4.61\ua0kg (\ub11.98) in the CJ group (p\ua0=\ua00.002), ISRT test was 8.7 (\ub11.64) in the MJ group and 4.95 (\ub12.1) in the CJ group (p\ua0=\ua00.002). Infraspinatus hypotrophy was detected during inspection in six patients (five in the CJ group and one in the MJ group); it was related to infraspinatus strength weakness in IST and ISRT (p\ua0<\ua00.001). Conclusions: Infraspinatus-sparing surgical approach for scapular fracture avoids infraspinatus hypotrophy and external-rotation strength weakness. We suggest use of the modified Judet approach for scapular fracture and to restrict the classic Judet approach to only when the surgeon believes that the fracture is not easily reducible with a narrower exposure. Level of evidence: Level\ua0IV

Implementing two-photon interference in the frequency domain with electro-optic phase modulators

Frequency-entangled photons can be readily produced using parametric down-conversion. We have recently shown how such entanglement could be manipulated and measured using electro-optic phase modulators and narrow-band frequency filters, thereby leading to two-photon interference patterns in the frequency domain. Here we introduce new theoretical and experimental developments showing that this method is potentially a competitive platform for the realization of quantum communication protocols in standard telecommunication fibres. We derive a simple theoretical expression for the coincidence probabilities and use it to optimize a Bell inequality. Furthermore, we establish an equivalence between the entangled- photon scheme and a classical interference scheme. Our measurements of two-photon interference in the frequency domain yield raw visibilities in excess of 99%. We use our high quality setup to experimentally validate the theoretical predictions, and in particular we report a violation of the CH74 inequality by more than 18 standard deviations.Comment: 19 pages, 3 figure

Engineering REST-Specific Synthetic PUF Proteins to Control Neuronal Gene Expression: A Combined Experimental and Computational Study

Regulation of gene transcription is an essential mechanism for differentiation and adaptation of organisms. A key actor in this regulation process is the repressor element 1 (RE1)-silencing transcription factor (REST), a transcriptional repressor that controls more than 2000 putative target genes, most of which are neuron-specific. With the purpose of modulating REST expression, we exploited synthetic, ad hoc designed, RNA binding proteins (RBPs) able to specifically target and dock to REST mRNA. Among the various families of RBPs, we focused on the Pumilio and FBF (PUF) proteins, present in all eukaryotic organisms and controlling a variety of cellular functions. Here, a combined experimental and computational approach was used to design and test 8- and 16-repeat PUF proteins specific for REST mRNA. We explored the conformational properties and atomic features of the PUF-RNA recognition code by Molecular Dynamics simulations. Biochemical assays revealed that the 8- and 16-repeat PUF-based variants specifically bind the endogenous REST mRNA without affecting its translational regulation. The data also indicate a key role of stacking residues in determining the binding specificity. The newly characterized REST-specific PUF-based constructs act as excellent RNA-binding modules and represent a versatile and functional platform to specifically target REST mRNA and modulate its endogenous expression

Neuromorphic Implementation of Orientation Hypercolumns

Neurons in the mammalian primary visual cortex are selective along multiple stimulus dimensions, including retinal position, spatial frequency, and orientation. Neurons tuned to different stimulus features but the same retinal position are grouped into retinotopic arrays of hypercolumns. This paper describes a neuromorphic implementation of orientation hypercolumns, which consists of a single silicon retina feeding multiple chips, each of which contains an array of neurons tuned to the same orientation and spatial frequency, but different retinal locations. All chips operate in continuous time, and communicate with each other using spikes transmitted by the address-event representation protocol. This system is modular in the sense that orientation coverage can be increased simply by adding more chips, and expandable in the sense that its output can be used to construct neurons tuned to other stimulus dimensions. We present measured results from the system, demonstrating neuronal selectivity along position, spatial frequency and orientation. We also demonstrate that the system supports recurrent feedback between neurons within one hypercolumn, even though they reside on different chips. The measured results from the system are in excellent concordance with theoretical predictions

Implementation of Olfactory Bulb Glomerular-Layer Computations in a Digital Neurosynaptic Core

We present a biomimetic system that captures essential functional properties of the glomerular layer of the mammalian olfactory bulb, specifically including its capacity to decorrelate similar odor representations without foreknowledge of the statistical distributions of analyte features. Our system is based on a digital neuromorphic chip consisting of 256 leaky-integrate-and-fire neurons, 1024 × 256 crossbar synapses, and address-event representation communication circuits. The neural circuits configured in the chip reflect established connections among mitral cells, periglomerular cells, external tufted cells, and superficial short-axon cells within the olfactory bulb, and accept input from convergent sets of sensors configured as olfactory sensory neurons. This configuration generates functional transformations comparable to those observed in the glomerular layer of the mammalian olfactory bulb. Our circuits, consuming only 45 pJ of active power per spike with a power supply of 0.85 V, can be used as the first stage of processing in low-power artificial chemical sensing devices inspired by natural olfactory systems