Source coding by efficient selection of ground states clusters

In this letter, we show how the Survey Propagation algorithm can be generalized to include external forcing messages, and used to address selectively an exponential number of glassy ground states. These capabilities can be used to explore efficiently the space of solutions of random NP-complete constraint satisfaction problems, providing a direct experimental evidence of replica symmetry breaking in large-size instances. Finally, a new lossy data compression protocol is introduced, exploiting as a computational resource the clustered nature of the space of addressable states.Comment: 4 pages, 4 figure

Die physiologische Funktion der GABAA Autorezeptoren im Kleinhirn

Diplomarbeit from Joel Chavas at the university of Goettingen. Supervisor: Dr Alain MartyThe physiological effect of GABAA autoreceptors in the cerebellum. In this Diplomarbeit, I measured the reversal potential of GABAA receptors (-56 mV) in the interneurons of the rat cerebellum, using gramicidin perforated patch, . I then determined that the GABAA autoreceptors can be excitatory. Last, I proved that a tonic activation of the GABAA receptors increases the intracellular calcium concentration. To obtain this last result, I performed cell-attached experiments. I used the opening probablity of the BK channels as a probe of the intracellular calcium concentration,

Die physiologische Funktion der GABAA Autorezeptoren im Kleinhirn

Diplomarbeit from Joel Chavas at the university of Goettingen. Supervisor: Dr Alain MartyThe physiological effect of GABAA autoreceptors in the cerebellum. In this Diplomarbeit, I measured the reversal potential of GABAA receptors (-56 mV) in the interneurons of the rat cerebellum, using gramicidin perforated patch, . I then determined that the GABAA autoreceptors can be excitatory. Last, I proved that a tonic activation of the GABAA receptors increases the intracellular calcium concentration. To obtain this last result, I performed cell-attached experiments. I used the opening probablity of the BK channels as a probe of the intracellular calcium concentration,

Optimizing contrastive learning for cortical folding pattern detection

The human cerebral cortex has many bumps and grooves called gyri and sulci. Even though there is a high inter-individual consistency for the main cortical folds, this is not the case when we examine the exact shapes and details of the folding patterns. Because of this complexity, characterizing the cortical folding variability and relating them to subjects' behavioral characteristics or pathologies is still an open scientific problem. Classical approaches include labeling a few specific patterns, either manually or semi-automatically, based on geometric distances, but the recent availability of MRI image datasets of tens of thousands of subjects makes modern deep-learning techniques particularly attractive. Here, we build a self-supervised deep-learning model to detect folding patterns in the cingulate region. We train a contrastive self-supervised model (SimCLR) on both Human Connectome Project (1101 subjects) and UKBioBank (21070 subjects) datasets with topological-based augmentations on the cortical skeletons, which are topological objects that capture the shape of the folds. We explore several backbone architectures (convolutional network, DenseNet, and PointNet) for the SimCLR. For evaluation and testing, we perform a linear classification task on a database manually labeled for the presence of the "double-parallel" folding pattern in the cingulate region, which is related to schizophrenia characteristics. The best model, giving a test AUC of 0.76, is a convolutional network with 6 layers, a 10-dimensional latent space, a linear projection head, and using the branch-clipping augmentation. This is the first time that a self-supervised deep learning model has been applied to cortical skeletons on such a large dataset and quantitatively evaluated. We can now envisage the next step: applying it to other brain regions to detect other biomarkers.Comment: 9 pages, 6 figures, 1 table, SPIE Imaging 202

High brightness, highly directional organic light-emitting diodes as light sources for future light-amplifying prosthetics in the optogenetic management of vision loss

Funding: Engineering and Physical Sciences Research Council (Grant Number(s): EP/R010595/1). National Science Foundation (Grant Number(s): 1706207). Defense Sciences Office, DARPA (Grant Number(s): N66001-17-C-4012). Leverhulme Trust (Grant Number(s): RPG-2017-231). Alexander von Humboldt-Stiftung (Grant Number(s): Humboldt Professur). National Research Foundation of Korea (GrantNumber(s): 2017R1A6A3A03012331). China Sponsorship Council.Optogenetic control of retinal cells transduced with light-sensitive channelrhodopsins can enable restoration of visual perception in patients with vision loss. However, a light intensity orders of magnitude higher than ambient light conditions is required to achieve robust cell activation. Relatively bulky wearable light amplifiers are currently used to deliver sufficient photon flux (>1016 photons/cm2/s in a ±10° emission cone) at a suitable wavelength (e.g., 600 nm for channelrhodopsin ChrimsonR). Here, ultrahigh brightness organic light-emitting diodes (OLEDs) with highly directional emission are developed, with the ultimate aim of providing high-resolution optogenetic control of thousands of retinal cells in parallel from a compact device. The orange-emitting phosphorescent OLEDs use doped charge transport layers, generate narrowband emission peaking at 600 nm, and achieve a luminance of 684 000 cd m–2 at 15 V forward bias. In addition, tandem-stack OLEDs with a luminance of 1 152 000 cd m–2 and doubled quantum efficiency are demonstrated, which greatly reduces electrical and thermal stress in these devices. At the photon flux required to trigger robust neuron firing in genetically modified retinal cells and when using heat sinking and realistic duty cycles (20% at 12.5 Hz), the tandem-stack OLEDs therefore show a greatly improved half-brightness lifetime of 800 h.Publisher PDFPeer reviewe

Survey-propagation decimation through distributed local computations

We discuss the implementation of two distributed solvers of the random K-SAT problem, based on some development of the recently introduced survey-propagation (SP) algorithm. The first solver, called the "SP diffusion algorithm", diffuses as dynamical information the maximum bias over the system, so that variable nodes can decide to freeze in a self-organized way, each variable making its decision on the basis of purely local information. The second solver, called the "SP reinforcement algorithm", makes use of time-dependent external forcing messages on each variable, which let the variables get completely polarized in the direction of a solution at the end of a single convergence. Both methods allow us to find a solution of the random 3-SAT problem in a range of parameters comparable with the best previously described serialized solvers. The simulated time of convergence towards a solution (if these solvers were implemented on a distributed device) grows as log(N).Comment: 18 pages, 10 figure

Coexistence of excitatory and inhibitory GABA synapses in the cerebellar interneuron network.

International audienceFunctional GABA synapses are usually assumed to be inhibitory. However, we show here that inhibitory and excitatory GABA connections coexist in the cerebellar interneuron network. The reversal potential of GABAergic currents (E(GABA)) measured in interneurons is relatively depolarized and contrasts with the hyperpolarized value found in Purkinje cells (-58 and -85 mV respectively). This finding is not correlated to a specific developmental stage and is maintained in the adult animal. E(GABA) in interneurons is close to the mean membrane potential (-56.5 mV, as measured with a novel "equal firing potential" method), and both parameters vary enough among cells so that the driving force for GABA currents can be either inward or outward. Indeed, using noninvasive cell-attached recordings, we demonstrate inhibitory, excitatory, and sequential inhibitory and excitatory responses to interneuron stimulation [results obtained both in juvenile (postnatal days 12-14) and subadult (postnatal days 20-25) animals]. In hyperpolarized cells, single synaptic GABA currents can trigger spikes or trains of spikes, and subthreshold stimulations enhance the responsiveness to subsequent excitatory stimulation over at least 30 msec. We suggest that the coexistence of excitatory and inhibitory GABA synapses could either buffer the mean firing rate of the interneuron network or introduce different types of correlation between neighboring interneurons, or both

Effets de l'activation des récepteurs GABAA sur l'activité électrique des interneurones de la couche moléculaire du cervelet de rat

PARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF