An analysis of coherence and connectivity in the anesthetized and awake brain using EEG recordings

Abstract

This project is part of a larger work towards building a bionic eye to aid the blind. This bionic eye is a retinal prosthesis that can replace the damaged eye and restore vision in cases of either partial or total blindness. This prosthesis will require constant electrical stimulation to the retina and to certain specific parts of the brain, which is expected to heavily influence the neural oscillations underlying the cognitive functions in the brain. These responses evoked in the brain as a result of stimulation to the retina have not been well studied and are a crucial pivoting point in this project. The main aim of this project is to analyse electroencephalogram (EEG) signals to understand what the differences in characteristics in the awake and anesthetized states are. An understanding of brain functioning in both these states is essential to this work. A mouse is implanted with electrodes in various sections of the brain. Brain oscillation frequencies are recorded, and these signals are analysed by studying the various frequency bands under different parameters. This project can be divided into two main parts: the collection and acquisition of neural signals from specimens conducted by research assistants; and signal processing and analysis of biological signals. Four methods were used to analyse the signals – (1) analysis of relative power, (2) magnitude squared coherence, (3) entropy and (4) mutual information. These calculations were performed for both anesthetized and awake states for 3 C57 specimens over 3 days. Multiple recordings are performed in individual specimen to reduce the number of animals used. Various statistical significance tests were carried out, including the one-way ANOVA and Mann-Whitney U test. The results were used to derive inferences based on the known research in the field. Most of the results carried out were in line with the research papers and journals used to aid in the analysis of the data. In cases of discrepancy or abnormality, discussions were carried out in order to explain possible reasoning. The results obtained from these tests will be the baseline information or control group for the future analyses on the effect of prolonged retinal stimulation on the neural oscillations.