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Ségolen Geffray

Publications and source records attributed to Ségolen Geffray.

3 recordsLinked to original sources

Simulation Based Inference of a Simple Neural Network Structure

Neurophysiologists are nowadays able to record from a large number of extracellular electrodes and to extract, from the raw data, the sequences of action potentials or spikes generated by many neurons. Unfortunately these ''many neurons'' still represent only a tiny fraction of the neuronal population that constitutes the network. Using association statistics such as the estimation of the cross-correlation functions, they are trying to infer the structure of the network formed by the recorded neurons. But this inference is compromised by the tremendous under-sampling of the neuronal population. We propose to focus instead on simple spike train statistics, like the empirical spikes frequency, or the interspike interval distribution. Their sampling distributions can be estimated by simulations, and, given a few observed spike train statistics, they provide enough information to infer the structure of the underlying network. We show that, on a ''toy model'', our method gives significantly better results than the sub-network reconstruction method with regards to the inference of the connection probability of the original network.

stat.AP↗

ToMATo: an efficient and robust clustering algorithm for high dimensional datasets. An illustration with spike sorting

Clustering algorithms became an essential part of the neurophysiological data analysis toolbox in the last twenty five years. Many problems, from the definition of cell types/groups based on morphological, molecular and physiological data to the identification of sub-networks in fMRI data, are now routinely tackled with clustering analysis. Since the datasets to which this type of analysis is applied tend to be defined in larger and larger dimensional spaces, there is a need for efficient and robust clustering methods in high dimension. There is also a need for methods that assume as little as possible about the clusters shape and size. We report here our experience with the ToMATo (Topological Mode Analysis Tool) algorithm. It is based on a definitely deep mathematical theory (algebraic topology), but its Python based open-source implementation is easily accessible to practitioners. We applied ToMATo to a problem we know well, spike sorting. Its capability to work in the ''native'' space of the data (no dimension reduction is required) is remarkable, as well as its robustness with respect to outliers (superposed spikes).

stat.AP↗

Semiparametric inference for the recurrent event process by means of a single-index model

In this paper, we introduce new parametric and semiparametric regression techniques for a recurrent event process subject to random right censoring. We develop models for the cumula- tive mean function and provide asymptotically normal estimators. Our semiparametric model which relies on a single-index assumption can be seen as a dimension reduction technique that, contrary to a fully nonparametric approach, is not stroke by the curse of dimensional- ity when the number of covariates is high. We discuss data-driven techniques to choose the parameters involved in the estimation procedures and provide a simulation study to support our theoretical results.

math.ST↗