A proposed subcortical arousal network, crucial for wakefulness, has been mapped in the human brain, revealing connections between key areas like the brainstem and hypothalamus. Utilizing data from three neurologically normal individuals' brains and advanced imaging techniques, this study identified pathways linking the default ascending arousal network with the cortical default mode network. Notably, the dopaminergic ventral tegmental area emerged as a central hub connecting these networks. This work enhances our understanding of how arousal and awareness integrate in human consciousness.
Serotonin receptor binding in the human brainstem peaks before birth, then declines sharply by infancy, especially in regions controlling cardiovascular function, respiration, and pain. Using [3H]LSD autoradiography on brainstem tissue from 5 fetuses (19-25.5 weeks postconception), 5 infants (42-55.5 weeks postconception), and 3 mature individuals (4, 20, and 52 years), the highest binding occurred prenatally throughout the brainstem, with the rostral raphe showing the highest relative binding at all ages. This fetal peak suggests serotonin plays a trophic role in developing human brainstem, and the subsequent decrease indicates reduced serotonergic modulation of vegetative functions after birth.
Consciousness depends on both arousal (wakefulness) and awareness. While cortical networks for awareness are well studied, the subcortical networks supporting arousal are less understood. By combining ex vivo diffusion MRI, immunohistochemistry, and in vivo 7 Tesla functional MRI in three human brain specimens, the authors identified a default ascending arousal network (dAAN) in the brainstem, hypothalamus, thalamus, and basal forebrain. They mapped connections within the dAAN and between the dAAN and the cortical default mode network (DMN), suggesting a structural basis for integrating arousal and awareness. The data and methods are released to aid further mapping of human consciousness.