Section: New Results

From the microscopic to the mesoscopic scale

Participants: Laure Buhry, Axel Hutt, Francesco Giovannini, LieJune Shiau

The Highlight of the Year bridges the microscopic scale and the mesoscopic scale. One partial result has already been used in one of our publications [3] to study the link between population dynamics on the mesoscopic scale and the EEG on the macroscopic scale.

In addition, the work of Francesco Giovannini aims at gaining a better understanding of the effects of anaesthesia on the neural correlates of memory, focusing on how anaesthetics disrupt the interaction between the hippocampus and the cerebral cortex. Studies have shown that these two brain structures exhibit a strong synchronisation of their respective neural activity, when performing memory tasks. Neurophysiology experiments have identified various possible candidate generators for rhythmic activity in the area CA1, CA3 and Dentate Gyrus areas of the hippocampus. However the mechanisms by which cortico- hippocampal synchronisation is elicited, and maintained, are yet to be fully understood. As a first step towards this objective, Francesco obtained a working mathematical model of a biologically plausible hippocampal CA1-3 neural cell, based on the Hodgkin-Huxley neuron, capable of exhibiting long-lasting persistent firing activity when subject to a strong transient stimulus. This behaviour is underlay by an intrinsic membrane current activated by the increase of intracellular Calcium ions, following the discharge of an action potential by the neuron. Our hypothesis is that large ensembles of such persistent-firing neurons could sustain the memory-related rhythmic activity displayed by the hippocampus. In this context, Laure Buhry and Axel Hutt work with LieJune Shiau (University of Houston) on a better understanding of the models used by the community of computational neuroscientists. The goal is to show in which extent models are comparable or interchangeable. We focus on the comparison of oscillatory mechanisms of neuronal populations in different spiking models, especially in the Hodgkin-Huxley and the adaptive exponential integrate-and-fire model.

These latter studies link the two description scales by a bottom-up approach.

Conversely, Axel Hutt and collaboration partners from the University of Noth Carolina - Chapel Hill have analysed Local Field Potentials measured in ferrets prefrontal cortex and visual cortex under anesthesia in a top-down analysis [21] . This data allows to extract network interactions in prefrontal cortex and visual cortex and hence revealing underlying mechanisms in general anaesthesia.