Two-photon imaging and analysis of neural network dynamics

The glow of a starry night sky, the smell of a freshly brewed cup of coffee or the sound of ocean waves breaking on the beach are representations of the physical world that have been created by the dynamic interactions of thousands of neurons in our brains. How the brain mediates perceptions, creates thoughts, stores memories and initiates actions remains one of the most profound puzzles in biology, if not all of science. A key to a mechanistic understanding of how the nervous system works is the ability to analyze the dynamics of neuronal networks in the living organism in the context of sensory stimulation and behaviour. Dynamic brain properties have been fairly well characterized on the microscopic level of individual neurons and on the macroscopic level of whole brain areas largely with the help of various electrophysiological techniques. However, our understanding of the mesoscopic level comprising local populations of hundreds to thousands of neurons (so called 'microcircuits') remains comparably poor. In large parts, this has been due to the technical difficulties involved in recording from large networks of neurons with single-cell spatial resolution and near- millisecond temporal resolution in the brain of living animals. In recent years, two-photon microscopy has emerged as a technique which meets many of these requirements and thus has become the method of choice for the interrogation of local neural circuits. Here, we review the state-of-research in the field of two-photon imaging of neuronal populations, covering the topics of microscope technology, suitable fluorescent indicator dyes, staining techniques, and in particular analysis techniques for extracting relevant information from the fluorescence data. We expect that functional analysis of neural networks using two-photon imaging will help to decipher fundamental operational principles of neural microcircuits.Comment: 36 pages, 4 figures, accepted for publication in Reports on Progress in Physic

Justifying the Origin of Real Options and their Difficult Evaluation in Strategic Management.

This work explores and reviews the introduction of real option in the strategic management literature. The aim is to contribute to a better understanding of the origin of the real option. By distinguishing between shadow and real option, and implementing entrepreneurship in the traditional option valuation framework we obtain a more exhaustive representation of the strategic decision processes in the firm. We explain the creation of a real option as an entrepreneurial process, which transforms inventive ideas into profitable innovation. This constitutes a step toward an option based-theory of the firm by describing the emergence of a firm’s options and the strategic building of new competences for exercising these options. In addition, this approach offers a parallel understanding of why the real option theory is less used in practice than in theory.Real Option, Theory of the Firm, Entrepreneurship, Dynamic Capabilities.

How do real options come into existence? A step toward an option- based theory of the firm

To be relevant to a firm a real option needs to fit into a theory of the firm explaining its existence, exercise conditions and value. We make a step toward an option based-theory of the firm by describing the emergence of a firm’s options and the strategic building of new competences for exercising these options. We explain the creation of a real option as an entrepreneurial process which transform inventive ideas into profitable innovation. The subsequent development of competence necessary to exercise the option gives boundaries, based on theories of the firm, for the often overoptimistic real option evaluation.Real Option, Theory of the Firm, Capabilities

Plural-entrepreneurial activity for a single start-up: a case study.

Based on a longitudinal case study of a high tech start-up, this paper explores how different forms of entrepreneurship coexist and interplay to create a firm’s innovative dynamics. A particular focus is given to knowledge-based entrepreneurship linked to technological innovation and exploitation, service entrepreneurship, and organizational-marketing entrepreneurship. Findings suggest that firms can realize performance benefits when their members divide those entrepreneurial activities between themselves during the launching phase of the firm, and then adapt the configuration of the activities, and their behaviours into a managerial form during the expansion phase of the firm. Our work offers a dynamic view of the conditions a firm has to fulfil to survive in a knowledge-based environment and we analyse the process that produces a good integration of plural-entrepreneurship behaviours.

ARE USERS THE NEXT ENTREPRENEURS? A CASE STUDY ON THE VIDEO GAME INDUSTRY.

Knowledge based-entrepreneurial firms struggle to survive because they must be simultaneously entrepreneurial on several dimensions. Can those firms rely on users to achieve sufficient efficiency in some entrepreneurial dimensions? To answer this question we drew on the entrepreneurial theories of the firm and on the users/innovator literature. In this work we present the plural entrepreneurship framework and then with a longitudinal case study of a mobile phone video-game firm which relies on users to improve their games we show that the user can significantly enhance the efficiency of the innovation of the firm. We also show that the other important dimensions of the firm behavior (organization, business model) can be significantly improved by the implication of users.Plural entrepreneurship; management of innovation; Video-game case study.

Bank lending networks, experience, reputation, and borrowing costs.

We investigate the network structure of syndicated lending markets and evaluate the impact of lenders’ network centrality, considered as measures of their experience and reputation, on borrowing costs. We show that the market for syndicated loans is a “small world” characterized by large local density and short social distances between lenders. Such a network structure allows for better information and resources flows between banks thus enhancing their social capital. We then show that lenders’ experience and reputation play a significant role in reducing loan spreads and thus increasing borrower’s wealth.agency costs, bank syndicate, experience, loan syndication, reputation, small world, social network analysis.

Calcium indicator loading of neurons using single-cell electroporation

Studies of subcellular Ca2+ signaling rely on methods for labeling cells with fluorescent Ca2+ indicator dyes. In this study, we demonstrate the use of single-cell electroporation for Ca2+ indicator loading of individual neurons and small neuronal networks in rat neocortex in vitro and in vivo. Brief voltage pulses were delivered through glass pipettes positioned close to target cells. This approach resulted in reliable and rapid (within seconds) loading of somata and subsequent complete labeling of dendritic and axonal arborizations. By using simultaneous whole-cell recordings in brain slices, we directly addressed the effect of electroporation on neurons. Cell viability was high (about 85%) with recovery from the membrane permeabilization occurring within a minute. Electrical properties of recovered cells were indistinguishable before and after electroporation. In addition, Ca2+ transients with normal appearance could be evoked in dendrites, spines, and axonal boutons of electroporated cells. Using negative-stains of somata, targeted single-cell electroporation was equally applicable in vivo. We conclude that electroporation is a simple approach that permits Ca2+ indicator loading of multiple cells with low background staining within a short amount of time, which makes it especially well suited for functional imaging of subcellular Ca2+ dynamics in small neuronal network

Post hoc immunostaining of GABAergic neuronal subtypes following in vivo two-photon calcium imaging in mouse neocortex

GABAergic neurons in the neocortex are diverse with regard to morphology, physiology, and axonal targeting pattern, indicating functional specializations within the cortical microcircuitry. Little information is available, however, about functional properties of distinct subtypes of GABAergic neurons in the intact brain. Here, we combined in vivo two-photon calcium imaging in supragranular layers of the mouse neocortex with post hoc immunohistochemistry against the three calcium-binding proteins parvalbumin, calretinin, and calbindin in order to assign subtype marker profiles to neuronal activity. Following coronal sectioning of fixed brains, we matched cells in corresponding volumes of image stacks acquired in vivo and in fixed brain slices. In GAD67-GFP mice, more than 95% of the GABAergic cells could be unambiguously matched, even in large volumes comprising more than a thousand interneurons. Triple immunostaining revealed a depth-dependent distribution of interneuron subtypes with increasing abundance of PV-positive neurons with depth. Most importantly, the triple-labeling approach was compatible with previous in vivo calcium imaging following bulk loading of Oregon Green 488 BAPTA-1, which allowed us to classify spontaneous calcium transients recorded in vivo according to the neurochemically defined GABAergic subtypes. Moreover, we demonstrate that post hoc immunostaining can also be applied to wild-type mice expressing the genetically encoded calcium indicator Yellow Cameleon 3.60 in cortical neurons. Our approach is a general and flexible method to distinguish GABAergic subtypes in cell populations previously imaged in the living animal. It should thus facilitate dissecting the functional roles of these subtypes in neural circuitr

Création de la firme et genèse de l’organisation, une approche évolutionniste du processus entrepreneurial.

Ce travail définit la notion de processus entrepreneurial dans un cadre évolutionniste. Il apporte un éclairage sur la formation de la firme et de l’organisation. En ouvrant la « boîte noire » du processus entrepreneurial, nous montrons que ce mécanisme peut être découpé en étapes conformes aux caractéristiques des modèles évolutionnistes (variation, sélection, rétention). Le modèle conceptuel proposé s’appuie sur les notions de vision (fruit de la variation), de communautés (lieu de sélection), et de routines (rétention).Théorie évolutionniste, Entrepreneuriat, Communautés, Création, Approche conceptuelle.