Author: Jaxon Mitchell
Mitchell, Jaxon, 2023 Clarifying the Unconscious Mind, Flinders University, College of Science and Engineering
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Unconsciousness is defined as the state of being where a person is unable to respond to any stimulus, be it tactile, auditory or otherwise. This plays a big part in surgeries, where doctors use anaesthesia to induce unconsciousness in patients to prevent them from feeling pain during the surgery. However, a known phenomenon is for patients to be able to rouse from unconsciousness mid-surgery, causing complications for both the patient and surgeon.
Various tools have been attempted to be made to measure depth of anaesthesia (DOA) over the last 3 decades, but they still aren’t used widely in clinical settings due to high variability in results and a lack of interpretability for surgeons to use their judgement when algorithms fail.
This project aimed to expand knowledge surrounding how the unconscious brain works, using a data set that demonstrates participants transitioning from consciousness to unconsciousness. As compared to similar studies, this one is unique as one of the largest sources of noise in brain recordings, skeletal muscle noise, was removed by pharmaceutically paralysing the participant prior to sedation. This data was to be processed to produce spectrograms that could be viewed multiple ways, and a connectivity analysis.
The methods used to generate spectra of the EEG recordings were new to the brain signals laboratory (BSL), designed after the ‘multitaper method’ of spectrum estimation employed by other papers. It was found that this algorithm had great performance in creating ‘smooth’ spectra, although using additional methods such as ‘smoothing priors’ could help advance spectra estimation tools within the BSL further. The spectra and spectrograms generated using this method revealed a lot of hidden gamma activity within the brain during unconsciousness, in addition to recurring landmarks found to approximate LOC.
From the connectivity analysis, it was found that regardless of baseline used, there was a significant number of connections demonstrating information flow towards the temporal regions of the brain. Whilst there is no further evidence to support this theory, it is hypothesised that this could be an intentional inhibitory signal towards the auditory processing centre of the brain.
The project ended by setting up future works to find evidence for a hypothesised ‘inhibitory signal’ in the gamma band of frequencies that inhibits sensory function during unconsciousness.
Keywords: EEG, Brain Signals, Signal Processing, Unconsciousness, Paralysis, Noise, Spectrogram, Connectivity Analysis
Subject: Engineering thesis
Thesis type: Masters
Completed: 2023
School: College of Science and Engineering
Supervisor: Kenneth Pope