Metabolic activation pattern of distinct hippocampal subregions during spatial learning and memory retrieval.

Activation dynamics of hippocampal subregions during spatial learning and their interplay with neocortical regions is an important dimension in the understanding of hippocampal function. Using the (14C)-2-deoxyglucose autoradiographic method, we have characterized the metabolic changes occurring in hippocampal subregions in mice while learning an eight-arm radial maze task. Autoradiogram densitometry revealed a heterogeneous and evolving pattern of enhanced metabolic activity throughout the hippocampus during the training period and on recall. In the early stages of training, activity was enhanced in the CA1 area from the intermediate portion to the posterior end as well as in the CA3 area within the intermediate portion of the hippocampus. At later stages, CA1 and CA3 activations spread over the entire longitudinal axis, while dentate gyrus (DG) activation occurred from the anterior to the intermediate zone. Activation of the retrosplenial cortex but not the amygdala was also observed during the learning process. On recall, only DG activation was observed in the same anterior part of the hippocampus. These results suggest the existence of a functional segmentation of the hippocampus, each subregion being dynamically but also differentially recruited along the acquisition, consolidation, and retrieval process in parallel with some neocortical sites.

The role of auditory cortices in the retrieval of single-trial auditory-visual object memories.

Single-trial encounters with multisensory stimuli affect both memory performance and early-latency brain responses to visual stimuli. Whether and how auditory cortices support memory processes based on single-trial multisensory learning is unknown and may differ qualitatively and quantitatively from comparable processes within visual cortices due to purported differences in memory capacities across the senses. We recorded event-related potentials (ERPs) as healthy adults (n = 18) performed a continuous recognition task in the auditory modality, discriminating initial (new) from repeated (old) sounds of environmental objects. Initial presentations were either unisensory or multisensory; the latter entailed synchronous presentation of a semantically congruent or a meaningless image. Repeated presentations were exclusively auditory, thus differing only according to the context in which the sound was initially encountered. Discrimination abilities (indexed by d') were increased for repeated sounds that were initially encountered with a semantically congruent image versus sounds initially encountered with either a meaningless or no image. Analyses of ERPs within an electrical neuroimaging framework revealed that early stages of auditory processing of repeated sounds were affected by prior single-trial multisensory contexts. These effects followed from significantly reduced activity within a distributed network, including the right superior temporal cortex, suggesting an inverse relationship between brain activity and behavioural outcome on this task. The present findings demonstrate how auditory cortices contribute to long-term effects of multisensory experiences on auditory object discrimination. We propose a new framework for the efficacy of multisensory processes to impact both current multisensory stimulus processing and unisensory discrimination abilities later in time.

Temporalités des commémorations du Centenaire sur Twitter

Du 1er avril 2014 au 1er avril 2015, plus d'un million de tweets ont été émis sur les commémorations du centenaire de la Première Guerre mondiale. Ces tweets, qui ont été collectés par l'auteur de cette proposition sur la base de hashtags liés au centenaire, contiennent de nombreuses traces de temporalités : le flux (twitter), le tweet (date de publication), mais aussi les nombreuses références aux temporalités propres aux utilisateurs de twitter, au Centenaire et à la Première Guerre mondiale. L'historien ne peut alors que se poser la question suivante : de quelle manière ces temporalités sont-elles reliées entre elles ? Comment s'imbriquent ces différentes strates de temps ?

Échos du centenaire sur le web et sur Twitter : partage de liens et Grande Guerre

Depuis avril 2014, plus de deux millions de tweets ont été publiés, touchant aux commémorations du Centenaire de la Grande Guerre, principalement en Anglais et en Français. Cette communication s'intéresse à une pratique précise lié aux modalités d'usage de Twitter: le partage de liens. En s'intéressant notamment aux liens pointant vers des pages web francophones partagés le 11 novembre 2015, l'auteur a constitué un corpus d'environ 1000 pages web et en analyse le contenu. Il s'interroge notamment sur l'émergence en tant que lieu de mémoire du site « Mémoire des Hommes » et plus particulièrement de la base de données des morts pour la France.

A Social Network Analysis of Twitter: Mapping the Digital Humanities Community

Defining digital humanities might be an endless debate if we stick to the discussion about the boundaries of this concept as an academic "discipline". In an attempt to concretely identify this field and its actors, this paper shows that it is possible to analyse them through Twitter, a social media widely used by this "community of practice". Based on a network analysis of 2,500 users identified as members of this movement, the visualisation of the "who's following who?" graph allows us to highlight the structure of the network's relationships, and identify users whose position is particular. Specifically, we show that linguistic groups are key factors to explain clustering within a network whose characteristics look similar to a small world.