Spatially Structured Sparse Morphological Component Separation for Voltage-Sensitive Dye Optical Imaging

International audienceBackground. Voltage-sensitive dye optical imaging is a promising technique for studying in vivo neural assemblies dynamics where functional clustering can be visualized in the imaging plane. Its practical potential is however limited by many artifacts. New Method. We present a novel method, that we call "SMCS" (Spatially Structured Sparse Morphological Component Separation), to separate the relevant biological signal from noise and artifacts. It extends Generalized Linear Models (GLM) by using a set of convex non-smooth regularization priors adapted to the morphology of the sources and artifacts to capture. Results. We make use of first order proximal splitting algorithms to solve the corresponding large scale optimization problem. We also propose an automatic parameters selection procedure based on statistical risk estimation methods. Comparison with Existing Methods. We compare this method with blank subtraction and GLM methods on both synthetic and real data. It shows encouraging perspectives for the observation of complex cortical dynamics. Conclusions. This work shows how recent advances in source separation can be integrated into a biophysical model of VSDOI. Going beyond GLM methods is important to capture transient cortical events such as propagating waves

Serotonin 3A Receptor Subtype as an Early and Protracted Marker of Cortical Interneuron Subpopulations

To identify neocortical neurons expressing the type 3 serotonergic receptor, here we used transgenic mice expressing the enhanced green fluorescent protein (GFP) under the control of the 5-HT3A promoter (5-HT3A:GFP mice). By means of whole-cell patch-clamp recordings, biocytin labeling, and single-cell reversed-transcriptase polymerase chain reaction on acute brain slices of 5-HT3A:GFP mice, we identified 2 populations of 5-HT3A-expressing interneurons within the somatosensory cortex. The first population was characterized by the frequent expression of the vasoactive intestinal peptide and a typical bipolar/bitufted morphology, whereas the second population expressed predominantly the neuropeptide Y and exhibited more complex dendritic arborizations. Most interneurons of this second group appeared very similar to neurogliaform cells according to their electrophysiological, molecular, and morphological properties. The combination of 5-bromo-2-deoxyuridine injections with 5-HT3A mRNA detection showed that cortical 5-HT3A interneurons are generated around embryonic day 14.5. Although at this stage the 5-HT3A receptor subunit is expressed in both the caudal ganglionic eminence and the entopeduncular area, homochronic in utero grafts experiments revealed that cortical 5-HT3A interneurons are mainly generated in the caudal ganglionic eminence. This protracted expression of the 5-HT3A subunit allowed us to study specific cortical interneuron populations from their birth to their final functional phenotype

Mapping whisker sensory cortex using voltage-sensitive dye imaging

International audienceSince the first description of its remarkable cellular organization by Woolsey and Van der Loos (1970), the whiskers representation in the rodent primary somatosensory cortex (S1) has become a major model for studying the cortical processing of tactile sensory information. In its layer 4, neurons form clusters, called barrels, that share the same topology as the whiskers on the snout of the animal, each neuronal column associated with a barrel receiving primarily inputs coming from its corresponding whisker.A huge amount of information has been collected over the past 50 years on the whiskers sensory system, however it is still largely unknown how it really integrates distributed information to build a global percept of the tactile scene. Working at a mesoscopic scale that allows visualizing how the information flows throughout cortical columns and further propagates to other cortical areas is a real asset to address this question.Voltage sensitive dye imaging, which benefits from a sub-columnar spatial resolution and a millisecond time resolution reveals how, upon tactile stimulation of a given whisker, information is rapidly transmitted to its corresponding column in S1, but also, within the next couple of milliseconds, to the secondary somatosensory cortex and then to the primary motor cortex. Using this method, we described with an unprecedented precision the topography of whiskers representation, as well as the lateral propagation of sensory inputs within these cortical areas, thus providing insights in the neuronal dynamics at play for integration of complex multi-whisker inputs in the cortical network

Étude des propriétés fonctionnelles d’une population d’interneurones GABAergiques inhibiteurs du néocortex

The aim of this work was to carry out a functional study of a population of neocortical GABAergic interneurons. The combination of electrophysiological, molecular biology and histochemical techniques enabled us to demonstrate that interneurons sensitive to nicotinic agonists expressing vasoactive intestinal peptide and cholecystokinin can be synaptically activated by afferent serotonergic fibers originating from the raphé nucleus via the type 3 serotonergic receptor. Evidence of the selective expression of the μ-opioid receptor together with preproenkephalin in this neuronal population led us to demonstrate the existence of an enkephalinergic autoregulatory loop specific to these interneurons. The identification of such mechanisms controlling the activity of a neuronal population enables us to propose a specific role for these interneurons in the physiology of the neocortical network.Ce travail avait pour objectif l’étude fonctionnelle d’une population d’interneurones GABAergiques du néocortex. La combinaison des techniques d’électrophysiologie, de biologie moléculaire et d’histochimie nous a permis de montrer que les interneurones sensibles aux agonistes nicotiniques, qui expriment le peptide vasoactif intestinal et la cholecystokinine, peuvent être activés de manière synaptique par les fibres sérotoninergiques afférentes originaires des noyaux du raphé, via le récepteur à la sérotonine de type 3. La mise en évidence de l’expression sélective du récepteur opioïde de type μ et de la préproenképhaline dans cette population neuronale nous a conduit à démontrer l’existence d’une boucle d’autorégulation enképhalinergique, spécifique de ces interneurones. L’identification de mécanismes contrôlant la mise en jeu d’une population neuronale restreinte dans l’activité du réseau néocortical nous a permis de mieux cerner la place qu’elle occupe dans la physiologie du néocortex

Review: How do spontaneous and sensory-evoked activities interact?

International audienceTwenty years ago, the seminal work of Grinvald et al. revolutionized the view cast on spontaneous cortical activity by showing how, instead of being a mere measure of noise, it profoundly impacts cortical responses to a sensory input and therefore could play a role in sensory processing. This paved the way for a number of studies on the interactions between spontaneous and sensory-evoked activities. Spontaneous activity has subsequently been found to be highly structured and to participate in high cognitive functions, such as influencing conscious perception in humans. However, its functional role remains poorly understood, and only a few speculations exist, from the maintenance of the cortical network to the internal representation of an a priori knowledge of the environment. Furthermore, elucidation of this functional role could stem from studying the opposite relationship between spontaneous and sensory-evoked activities, namely, how a sensory input influences subsequent internal activities. Indeed, this question has remained largely unexplored, but a recent study by the Grinvald laboratory shows that a brief sensory input largely dampens spontaneous rhythms, suggesting a more sophisticated view where some spontaneous rhythms might relate to sensory processing and some others not

Etude des propriétés fonctionnelles d'une population d'interneurones gabaergiques inhibiteurs du Néocortex

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