| dc.description.abstract | One of the great frontiers of consciousness science is understanding how early consciousness arises in the development of the human infant. Although each of us was once a baby, infant consciousness remains mysterious, not least because of uncertainty regarding how best to measure consciousness. Accounts of the ontogeny of consciousness can be divided into two broad camps: `early-onset' views, which locate the emergence of consciousness at, or shortly after, birth, and `late-onset¿ views, which locate the emergence of consciousness significantly after birth. The lack of language and the very limited motor function preclude self-report or behavioural responses and, thus, prevent the empirical assessment of consciousness in neonates at birth. We sidestepped these limitations by asking a foundational question for understanding the capacity for conscious experience in neonates: Are the brain mechanisms of consciousness instantiated in infants from birth? To answer this question, I investigated brain markers that have been developed to test the presence of conscious awareness in behaviourally non-responsive adult populations in full-term neonates (gestational age at birth > 37 weeks) at birth. Additionally, I investigated the effects of premature birth and early neonate age on the development of these brain markers. I used resting-state functional MRI data of full-term neonates (N = 278) from the developing Human Connectome Project and of adults (N = 176) from the Human Connectome Project. The effect of neonate age at the time of assessment was disentangled from the effect of premature birth by the inclusion of two groups: the first (N = 70) born before, but scanned at term-equivalent age (TEA), and the second (N = 70) born and scanned before TEA. In Chapter 2, I investigated whether the reciprocal relationship between the default mode (DMN) and fronto-parietal networks (the dorsal attention and executive control networks)¿a neural circuitry that enables information integration across diverse sensory and high-order functional modules in healthy adults has emerged in neonates at birth. Additionally, I tested how premature birth and early neonate age affected its development. Results showed that the reciprocal relationship between the DMN and dorsal attention network (DAN) was present in neonates at full-term birth or TEA. Although different from the adult networks, the DMN, DAN, and executive control network (ECN) were present as distinct networks at full-term birth or TEA. However, premature birth was associated with lower network coherence in DMN and DAN in neonates at TEA. Before TEA, neonates showed dramatic underdevelopment of these high-order networks and their relationships. In Chapter 3, I investigated the development of the brain¿s functional small-world architecture, which has been shown to enable efficient information differentiation and integration at local and global brain scales in healthy adults. The global scale network efficiency was measured using small-world propensity, and nodal scale communication efficiency was measured using nodal efficiency. Although less pronounced than that in adults, small-world architecture was already present in neonates at full-term birth or TEA. By contrast, premature neonates before TEA showed underdevelopment of small-world architecture and regional communication in 9/11 networks (including DMN, DAN, and ECN), with disruption in 32% of brain nodes. By TEA, premature neonates showed large-scale recuperation of regional communication, with only 1.4% of nodes remaining significantly underdeveloped. In Chapter 4, I investigated the development of neural entropy, which the uncertainty and informational richness of conscious states. Neural entropy decreases when consciousness fades, i.e., during sleep or general anaesthesia, as well as in the minimally conscious state or the unresponsive wakefulness syndrome. By contrast, neural entropy was found to increase in altered states of consciousness, such as during hallucinatory or the psychological state elicited by classic psychedelic drugs (i.e., LSD and psilocybin). Neural entropy was measured by the sample entropy of network configuration, by using graph theoretical analysis combined with a sliding-window approach. I found that neonates exhibited higher neural entropy relative to adults. In addition, premature birth was associated with higher neural entropy in neonates at TEA. Lastly, I found neural entropy decreases with increasing age in preterm neonates from birth to TEA. Taken together, these findings shed light on the ontogeny of brain markers that support conscious awareness and provide evidence for `early-onset' views of conscious awareness. Furthermore, they highlight the importance of the third trimester of pregnancy, the typical period of premature birth, for the development of the brain markers that support conscious awareness. | en |
