Probing the (Un)Conscious Brain : EEG and PET Studies on Healthy Human Subjects Using Propofol, Dexmedetomidine and Natural Sleep
Year: 2022
Type: dissertation
Abstract: Consciousness cannot be objectively measured. By employing anesthesia and neurophysiologic measurements to study human consciousness, unconsciousness has been found to associate with suppression of regional brain activity and with breakdown of communication between different brain areas. However, due to conceptual and methodological heterogeneity, a unified theory on the “mechanisms” of (un)consciousness is lacking. Many anesthesia studies have employed arbitrary dosing schemes and disregarded the pharmacologic effects of the used drugs. Thus, many inferences on human consciousness have been premature. The aim of this study was to use rigorous experimental protocols to study human consciousness in healthy subjects. Two anesthetics (propofol and dexmedetomidine) and natural sleep were used. First, we explored EEG changes in association to different states of consciousness during increasing doses and a steady-state infusion of two anesthetics. Second, by measuring N400 event related potentials, we explored whether or not sematic processing persists during an unresponsive state induced by the two drugs. Finally, positron emission tomography (PET) imaging was conducted to reveal brain activity alterations between connected and disconnected states (confirmed by subjective reports of mental content) induced by anesthesia and sleep. Based on EEG and PET findings, we discovered that the state-related changes were distinct and separable from the overall effects of the different interventions. At awakening from steady-state anesthesia, spectral EEG patterns only partially reverted towards baseline values despite a restored conscious state, illustrating the multifaceted nature of anesthesia-EEG. PET imaging revealed that activity of a core brain network correlated best to the connected state per se. Furthermore, unresponsiveness and sleep rarely depicted unconsciousness (i.e., complete absence of subjective experiences) and semantic processing was partly preserved during dexmedetomidine-induced unresponsiveness. This study highlights the multidimensional nature of human consciousness and the related experimental challenges.
Source: UTUPub (University of Turku)
Author: Scheinin, Annalotta
Language: English
Subfield: Anesthesiology and Pain Medicine
Field: Medicine
Domain: Health Sciences
Open Access status: green
OpenAlex ID: W7042762108