Validation of Measures of Consciousness using Propofol Anesthesia

One of the biggest challenges in the field of consciousness research today is to find a reliable objective measure. The currently most promising measures are perturbational complexity index (PCI), Lempel-Ziv complexity (LZC), amplitude coalition entropy (ACE) and synchrony coalition entropy (SCE). However, all these measures were tested on states where unconsciousness was merely assumed. The current thesis sought to investigate these measures by applying them to data from awake and anesthetized states, while controlling for experiences in unresponsive states. For this we collected electroencephalographic (EEG) data with applied transcranial magnetic stimulation (TMS) from participants while they were awake and under anesthesia. Importantly, participants were woken up intermittently, in order to additional experience reports. In nearly 70% of the awakenings participants reported having dreams. Additionally, results showed a significant difference between measures for awake and anesthetized states, albeit for LZC, ACE and SCE only under eyes open condition during awake state. Further, LZC, ACE and SCE correlated with the vividness of reports given by subjects, while PCIST did not. While our results indicate that current measures of consciousness can distinguish between awake and non-responsive states, it is not clear whether this truly reflects unconsciousness or what part of consciousness these measures reflect