Analytical and numerical studies of thalamo-cortical neural population models during general anesthesia

Abstract : Although general anaesthesia is an indispensable tool in today’s medical surgery, its precise underlying mechanisms are still unknown. During the propofol-induced sedation, the anaesthetic actions on the microscopic single neuron scale lead to specific changes in macroscopic-scale observables such as electroencephalogram (EEG) signals. For low concentration of propofol these characteristic changes comprised increased activity in the delta (0.5-4 Hz) and alpha (8-13 Hz) frequency bands over the frontal head region, but increased delta and decreased alpha power activity over the occipital region. In this thesis, we employ thalamo-cortical neural population models, and based on the experimental data, the propofol effects on the synaptic and extrasynaptic GABAergic receptors located in the cortex and thalamus are modelized to understand the mechanisms underlying the observed certain changes in EEG-spectral power. It is shown that the models reproduce well the characteristic spectral features observed experimentally. A key finding of this work is that the origin of delta rhythm is fundamentally different from the alpha rhythm. Our results indicate that dependent on the mean potential values of the system resting states, an increase or decrease in the thalamo-cortical gain functions results in an increase or decrease in the alpha power, respectively. In contrast, the evolution of the delta power is rather independent of the system resting states; the enhancement of spectral power in the delta band results from the increased synaptic or extra-synaptic GABAergic inhibition for both increasing and decreasing nonlinear gain functions. Furthermore, we aim to identify the parameters of a thalamo-cortical model by fitting the model power spectrum to the EEG recordings. To this end, we address the task of parameter estimation in the models that are described by a set of stochastic ordinary or delay differential equations. Two case studies dealing with noisy pseudo-experimental data are first carried out to compare the performance of different optimization methods. The results of this elaboration show that the method used in this study is able to accurately estimate the independent model parameters while it allows us to avoid the computational costs of the numerical integrations. Taken together, the findings of this thesis provide new insights into the mechanisms responsible for the specific changes in EEG patterns that are observed during propofol-induced sedation.
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https://hal.univ-lorraine.fr/tel-01754610
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Meysam Hashemi. Analytical and numerical studies of thalamo-cortical neural population models during general anesthesia. Other [cs.OH]. Université de Lorraine, 2016. English. ⟨NNT : 2016LORR0014⟩. ⟨tel-01754610v1⟩

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