Establish Which Brain Regions Constitute the Physical Substrate of Consciousness in the Brain: Within-State Paradigms During Sleep and Parasomnias
INSTITUTE: University of Wisconsin-Madison / Department of Psychiatry / Center for Sleep and Consciousness
PROJECT LEADER: Giulio Tononi
PROJECT DURATION: 3 years
LAB WEBSITE: Center for Sleep and Consciousness
Characterizing the neural substrate of experience is a crucial goal for the science of consciousness. Experience is all we have and all we are. For each of us, all that exists—ourselves, the world around us, and all we care about—only exists through our own individual consciousness. Ultimately, each of us lives in their own private universe, which is both vast and beautiful, but also limited by what we can perceive and understand. From a scientific perspective, identifying the neural correlates of consciousness in the brain is a key step for understanding who we are, what our limits are, and how they can be modified and expanded.
As a step in this direction, we have recently pioneered a within-state, no-task paradigm that can pinpoint the substrate of consciousness while avoiding many confounding factors (Siclari et al., 2107). To do so, we have employed high-density electroencephalography (hd-EEG) to contrasted brain activity within the same behavioral state, namely sleep. Within both NREM and REM sleep, sometimes we are conscious (dreaming) and sometimes unconscious (dreamless). Furthermore, when we sleep we are not engaged in any task that involves dealing with external stimuli or performing executive functions. Therefore, this paradigm is well-suited to reveal the neural correlates of consciousness (NCC) unconfounded by state changes and behavioral tasks. The results so far indicate that the NCC are found primarily in posterior cortex (a temporo- parieto-occipital ‘hot zone’ (Siclari et al., 2017; Perogamvros et al., 2017). We have also found that the NCC of specific conscious contents experienced during dreams, such as faces, places, movement, and speech, can be found in specific regions of posterior cortex.
Figure 1. Identifying the NCC. The figure illustrates a ‘hot zone’ in posterior cortex that shows low delta power when subjects report having been conscious (dreaming) or unconscious (dreamless) upon awakening from either NREM or REM sleep.
In this project, we will extend these findings by exploring neural correlates of other contents of consciousness, such as self, thought, and will. We will also employ EEG-fMRI to record brain activity during dreaming and dreamless sleep with greater spatial resolution. To do so, we will take advantage of our recent finding that the power of BOLD oscillation in a sub-slow frequency range (0.1-0.2 Hz) is highly correlated with EEG slow wave activity, which is low in posterior cortex when subjects are dreaming and high when they are unconscious.
Furthermore, we will take advantage of intracranial recordings in epileptic subjects admitted to the epilepsy monitoring unit in clinical settings. We will again probe the NCC during sleep by collecting subjective reports when subjects are awakened by nurses. Intracranial recordings will allow us to directly assess neural activity within posterior and anterior cortex during dreaming and dreamless sleep.
Finally, we will record hd-EEG in sleep-walking, sleep-talking, and other parasomnias. Parasomnias offer another opportunity to assess the NCC within the same behavioral state, because consciousness can be either present or absent during episodes that are otherwise similar. The coexistence of sleep and wake-like states within the cerebral cortex represents a unique opportunity to assess which areas are most consistently part of the NCC.
Broader Impact:
There is still much uncertainty about the neural substrate of consciousness in the brain. Yet it is essential to establish, on solid scientific grounds, what underlies our own private universe of experience, with its unique characteristics and inevitable limitations. Only in this way can we hope to better understand the nature of experience and to devise new ways to change and expand our perception of ourselves and the world.
Publications:
Valomon, Amandine, et al. "A high-density electroencephalography study reveals abnormal sleep homeostasis in patients with rapid eye movement sleep behavior disorder." Scientific reports 11.1 (2021): 1-13.
Sterpenich, Virginie, et al. "Fear in dreams and in wakefulness: Evidence for day/night affective homeostasis." Human brain mapping 41.3 (2020): 840-850.
Siclari, Francesca, et al. "Dreaming in NREM sleep: a high-density EEG study of slow waves and spindles." Journal of Neuroscience 38.43 (2018): 9175-9185.
Siclari, Francesca, et al. "The neural correlates of dreaming." Nature neuroscience 20.6 (2017): 872-878.