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Modeling Electrical Activities of the Brain and Analysis of the EEG in General Anesthesia

Molaee Ardakani, Behnam | 2008

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  1. Type of Document: M.Sc. Thesis
  2. Language: English
  3. Document No: 41512 (05)
  4. University: Sharif University of Technology; University of Rennes 1
  5. Department: Electrical Engineering
  6. Advisor(s): Shamsollahi, Mohammad Bagher
  7. Abstract:
  8. In this thesis, an enhanced local mean-field (MF) model that is suitable for simulating the electroencephalogram (EEG) in different depths of anesthesia is presented. The main building elements of the model (e.g. excitatory and inhibitory populations) are taken from two pioneer MF models designed by Steyn-Ross et al and Bojak & Liley, and then a new slow ionic mechanism is included in the main model. Generally, in mean-field models, some sigmoid-shape functions determine firing rates of neural populations according to their mean membrane potentials. In the enhanced model, the sigmoid function corresponding to excitatory population is redefined to be also a function of the slow ionic mechanism. This modification adapts the firing rate of neural populations to slow ionic activities of the brain. When an anesthetic drug is administered, the slow mechanism may induce neural cells to alternate between two levels of activity referred to as up and down states. Basically, the frequency of up-down switching is in the delta band (0-4 Hz) and this is the main reason behind high amplitude, low frequency fluctuations of EEG signals in anesthesia. The enhanced model may have different working states driven by anesthetic drug concentration. It is settled in the up state in waking period, it may switch to up and down states in moderate anesthesia while in deep anesthesia it remains in the down state. As a supplementary work, in this thesis the strength and phase of modulation (SOM, POM) between EEG oscillations in alpha band and slower activities in delta band is also investigated on children in various depths of desflurane anesthesia. According to SOM values calculated for different delta sub-bands, delta band may comprise three main sub-bands roughly in 0.1 – 0.5 Hz (very slow delta), 0.5 – 1.5 Hz (slow delta) and 2 – 4 Hz (fast delta) frequency intervals. POM increases with a decrease in desflurane concentration and it can be used for determining depth of anesthesia as a neurophysiologic-based parameter that extracts a kind of time-coding information from the brain. POM values may distinguish deep and moderate anesthesia even better than BIS index.
  9. Keywords:
  10. Brain Signal ; Amplitude Modulation ; Anesthesia Depth ; General Anesthesia ; Mean Field Modeling ; Neural Populations ; Slow Ionic Mechanism ; Delta and Alpha Waves

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