L’éloge de Saint Eudocime par Constantin Acropolite (BHG 606)

L’étude comprend la présentation et l’édition critique de l’éloge que Constantin Acropolite a écrit en l’honneur de saint Eudocime qui a vécu et œuvré en Cappadoce pendant la deuxième phase de la période iconoclaste. La tradition manuscrite de l’oraison et ses similitudes avec la version antérieure de la vie d’Eu­do­cime, attribuée à Syméon Métaphraste (BHG 607), ou les autres éloges de l’auteur en l’honneur de saints divers sont étudiées dans l’introduction. Les diver­ses graphies des manuscrits, mais aussi les fautes ou les corrections de la prémière édition figurent dans l’apparat critique de l’édition, tandis qu’un détaillé apparat de sources est également ajouté.

… ἤτοι κάλλους ἔκφρασις. Ομορφιά και ερωτισμός στην ποίηση του 12ου αιώνα. Η περίπτωση των εκφράσεων του Νικήτα Ευγενειανού

The study examines the ideal of beauty and its visual reception, the concept of eroticism and the impact of erotic emotion in Byzantine poetry in general. Moreover, the case of the erotic literature of the comnenian era is studied and in this context the ekphraseis of Nicetas Eugenianos, which are included both in his novel Drossilla and Charikles, as well as in his Epithalamium entitled Ἐπιθαλάμιοι ἤτοι κάλλους ἔκφρασις τῶν συναφθέντων, are presented in detail. The thorough examination of the particular thematic and stylistic characteristics of the different descriptions (ekphrasis of garden, fountain, Drosilla, beauty of a newlywed couple) makes clear that Nicetas Eugenianos with his ekphraseis managed to transform the beauty into a higher ideal, in order to create an intensely sensual atmosphere in his texts, to demonstrate through words the power of erotic feelings and to give the opportunity to the human desire to become the object of free expression. 

Some Remarks on the Structure of John Eugenikos' Ekphraseis of Cities and Places

This article attempts a global survey of the similarities observed in the ekphraseisof cities and places composed by John Eugenikos, on the one hand identifying the structural similarity they display and on the other tracing the form they appear to follow. The ultimate object is to highlight the differences between them, which are not simply a matter of divergence from the common framework but on the contrary demonstrate the writer’s striving for originality in these texts.

Modelling and analysis of cortico-hippocampal interactions and dynamics during sleep and anaesthesia

The standard memory consolidation model assumes that new memories are temporarily stored in the hippocampus and later transferred to the neocortex, during deep sleep, for long-term storage, signifying the importance of studying functional and structural cortico-hippocampal interactions. Our work offers a thorough analysis on such interactions between neocortex and hippocampus, along with a detailed study of their intrinsic dynamics, from two complementary perspectives: statistical data analysis and computational modelling. The first part of this study reviews mathematical tools for assessing directional interactions in multivariate time series. We focus on the notion of Granger Causality and the related measure of generalised Partial Directed Coherence (gPDC) which we then apply, through a custom built numerical package, to electrophysiological data from the medial prefrontal cortex (mPFC) and hippocampus of anaesthetized rats. Our gPDC analysis reveals a clear lateral-to-medial hippocampus connectivity and suggests a reciprocal information flow between mPFC and hippocampus, altered during cortical activity. The second part deals with modelling sleep-related intrinsic rhythmic dynamics of the two areas, and examining their coupling. We first reproduce a computational model of the cortical slow oscillation, a periodic alteration between activated (UP) states and neuronal silence. We then develop a new spiking network model of hippocampal areas CA3 and CA1, reproducing many of their intrinsic dynamics and exhibiting sharp wave-ripple complexes, suggesting a novel mechanism for their generation based on CA1 interneuronal activity and recurrent inhibition. We finally couple the two models to study interactions between the slow oscillation and hippocampal activity. Our simulations propose a dependence of the correlation between UP states and hippocampal spiking on the excitation-to-inhibition ratio induced by the mossy fibre input to CA3 and by a combination of the Schaffer collateral and temporoammonic input to CA1. These inputs are shown to affect reported correlations between UP states and ripples

Influence of slow oscillation on hippocampal activity and ripples through cortico-hippocampal synaptic interactions, analyzed by a cortical-CA3-CA1 network model

Hippocampal sharp wave-ripple complexes (SWRs) involve the synchronous discharge of thousands of cells throughout the CA3-CA1-subiculum-entorhinal cortex axis. Their strong transient output affects cortical targets, rendering SWRs a possible means for memory transfer from the hippocampus to the neocortex for long-term storage. Neurophysiological observations of hippocampal activity modulation by the cortical slow oscillation (SO) during deep sleep and anesthesia, and correlations between ripples and UP states, support the role of SWRs in memory consolidation through a cortico-hippocampal feedback loop. We couple a cortical network exhibiting SO with a hippocampal CA3-CA1 computational network model exhibiting SWRs, in order to model such cortico-hippocampal correlations and uncover important parameters and coupling mechanisms controlling them. The cortical oscillatory output entrains the CA3 network via connections representing the mossy fiber input, and the CA1 network via the temporoammonic pathway (TA). The spiking activity in CA3 and CA1 is shown to depend on the excitation-to-inhibition ratio, induced by combining the two hippocampal inputs, with mossy fiber input controlling the UP-state correlation of CA3 population bursts and corresponding SWRs, whereas the temporoammonic input affects the overall CA1 spiking activity. Ripple characteristics and pyramidal spiking participation to SWRs are shaped by the strength of the Schaffer collateral drive. A set of in vivo recordings from the rat hippocampus confirms a model-predicted segregation of pyramidal cells into subgroups according to the SO state where they preferentially fire and their response to SWRs. These groups can potentially play distinct functional roles in the replay of spike sequences

Local Field Potentials Encode Place Cell Ensemble Activation during Hippocampal Sharp Wave Ripples

Whether the activation of spiking cell ensembles can be encoded in the local field potential (LFP) remains unclear. We address this question by combining in vivo electrophysiological recordings in the rat hippocampus with realistic biophysical modeling, and explore the LFP of place cell sequence spiking (“replays”) during sharp wave ripples. We show that multi-site perisomatic LFP amplitudes, in the ∼150–200 Hz frequency band, reliably reflect spatial constellations of spiking cells, embedded within non-spiking populations, and encode activation of local place cell ensembles during in vivo replays. We find spatiotemporal patterns in the LFP, which remain consistent between sequence replays, in conjunction with the ordered activation of place cell ensembles. Clustering such patterns provides an efficient segregation of replay events from non-replay-associated ripples. This work demonstrates how spatiotemporal ensemble spiking is encoded extracellularly, providing a window for efficient, LFP-based detection and monitoring of structured population activity in vivo

Modelling and analysis of cortico-hippocampal interactions and dynamics during sleep and anaesthesia

The standard memory consolidation model assumes that new memories are temporarily stored in the hippocampus and later transferred to the neocortex, during deep sleep, for long-term storage, signifying the importance of studying functional and structural cortico-hippocampal interactions. Our work offers a thorough analysis on such interactions between neocortex and hippocampus, along with a detailed study of their intrinsic dynamics, from two complementary perspectives: statistical data analysis and computational modelling. The first part of this study reviews mathematical tools for assessing directional interactions in multivariate time series. We focus on the notion of Granger Causality and the related measure of generalised Partial Directed Coherence (gPDC) which we then apply, through a custom built numerical package, to electrophysiological data from the medial prefrontal cortex (mPFC) and hippocampus of anaesthetized rats. Our gPDC analysis reveals a clear lateral-to-medial hippocampus connectivity and suggests a reciprocal information flow between mPFC and hippocampus, altered during cortical activity. The second part deals with modelling sleep-related intrinsic rhythmic dynamics of the two areas, and examining their coupling. We first reproduce a computational model of the cortical slow oscillation, a periodic alteration between activated (UP) states and neuronal silence. We then develop a new spiking network model of hippocampal areas CA3 and CA1, reproducing many of their intrinsic dynamics and exhibiting sharp wave-ripple complexes, suggesting a novel mechanism for their generation based on CA1 interneuronal activity and recurrent inhibition. We finally couple the two models to study interactions between the slow oscillation and hippocampal activity. Our simulations propose a dependence of the correlation between UP states and hippocampal spiking on the excitation-to-inhibition ratio induced by the mossy fibre input to CA3 and by a combination of the Schaffer collateral and temporoammonic input to CA1. These inputs are shown to affect reported correlations between UP states and ripples