Brain Sciences
August 30, 2024
Hyunwoo Jang, Rui Dai, George A. Mashour et al.
A machine learning model that combines functional connectivity, graph-theoretic metrics, and cortical gradient features can classify brain states—including unconsciousness (NREM2 sleep, propofol sedation and anesthesia), psychedelic states (ketamine, LSD, nitrous oxide), and neuropsychiatric disorders (ADHD, bipolar disorder, schizophrenia)—with an average balanced accuracy of 79% (range 62–98%). The ensemble model outperformed individual feature-based models (70–76%). Transferability across datasets varied, and feature importance analysis indicated that different brain states rely on distinct neural mechanisms, suggesting that tailored approaches are needed for accurate classification. The findings highlight the value of integrating multiple feature types for robust brain-state classification, though further work is needed for broader generalizability.
Anesthesia and analgesia
June 1, 2022
Michael A. Brito, Duan Li, Christopher W Fields et al.
Cortical acetylcholine levels correlate with neurophysiologic complexity and frontoparietal connectivity during altered states of consciousness. In rats under isoflurane anesthesia, subanesthetic ketamine (10 mg/kg/h) produced sustained increases in brain complexity and high gamma connectivity, accompanied by progressive rises in prefrontal (104%) and parietal (159%) acetylcholine. Nitrous oxide caused a transient increase in complexity and connectivity with smaller acetylcholine increases (prefrontal 56%, parietal 43%), followed by a later phase of decreased acetylcholine, reduced complexity, and weaker connectivity. These findings link cortical acetylcholine to changes in consciousness level.
Frontiers in Systems Neuroscience
December 1, 2021
Minkyung Kim, Hyoungkyu Kim, Zirui Huang et al.
The brain's ability to switch between internal and external modes is crucial for generating models of self and world, and this switching may rely on a state near criticality—a balanced condition between order and disorder. Large synchronization fluctuations of brain networks near criticality create temporal windows that favor either integrating internal information or processing external stimuli. Using computational modeling, EEG, and fMRI analyses across altered states of consciousness, synchronized networks bias toward internal information while incoherent networks bias toward external information. These preferences are most prominent at criticality and in conscious states associated with 4–12 Hz bandwidth.
eNeuro
January 1, 2021
Matthew S Willsey, Chrono S Nu, Samuel R Nason et al.
Inhaling 70% nitrous oxide (N2O) increases spiking rates and beta- and gamma-band power in the primary motor cortex of macaques while degrading the representation of somatosensory information. The proportion of correctly classified finger touches dropped from 0.50 to 0.34 during N2O inhalation, indicating impaired information transfer. The increased firing rate was not correlated with changes in neuronal tuning, suggesting a dissociation between overall activity and sensory processing.
Proceedings of the National Academy of Sciences of the United States of America
August 27, 2013
Jimo Borjigin, UnCheol Lee, Tiecheng Liu et al.
During cardiac arrest, the mammalian brain can generate a transient surge of highly coherent gamma oscillations that exceed levels seen during conscious waking. In rats undergoing experimental cardiac arrest, continuous electroencephalography revealed a global increase in gamma power, coherence, and directed connectivity within the first 30 seconds after arrest, before the electroencephalogram became isoelectric. These gamma waves were tightly phase-coupled to theta and alpha waves. The findings suggest that near-death, the brain can paradoxically produce neural correlates of heightened conscious processing.
Frontiers in Psychology
January 1, 2013
Neil Mehta, George A. Mashour
A complete theory of consciousness must explain both general consciousness (what makes any state conscious) and specific consciousness (what gives a conscious state its particular quality). First-order representationalism holds that consciousness consists of sensory representations directly available to a subject for action, belief, and planning. The authors provide a neuroscientific framework: neural correlates of general consciousness include prefrontal cortex, posterior parietal cortex, and non-specific thalamic nuclei, while specific consciousness involves sensory cortex and specific thalamic nuclei. They argue that recent data favor first-order representationalism over competing theories such as biological theory, higher-order representationalism, recurrent processing theory, information integration theory, and global workspace theory.
Advances in Consciousness Research
October 28, 2010
Lucas Campos, Adrian Pichurko, George A. Mashour
General anaesthetics rapidly and reversibly stop consciousness, making them a powerful tool for studying the transition between conscious and unconscious states. With 40 million patients in North America alone receiving general anaesthesia each year, the operating room offers a controlled environment to investigate the molecular and cognitive mechanisms underlying consciousness.
The American Journal of Psychology
January 1, 2010
Katherine MacDuffie, George A. Mashour
Dreaming is a unique state of consciousness that integrates three temporal dimensions: experiencing the present, processing the past, and preparing for the future. This temporal complexity is enabled by the neurobiological environment of sleep, where stimuli are internally generated and many constraints of waking thought are absent. Because dream consciousness is not determined by sensory input, it allows flexible integration of past experiences and formation of novel connections. Different dream theories may not be mutually exclusive but instead relate to different temporal domains of the dream state.
Consciousness and Cognition
December 1, 2008
George A. Mashour, Eric LaRock
Philosophical p-zombies are imagined beings that behave like humans but lack consciousness, used to challenge physicalist theories of mind. Inverting this concept yields i-zombies: beings that appear unconscious but are actually conscious. A real-world approximation of i-zombies exists in anesthesia awareness, where 1-2 per 1000 patients under general anesthesia become conscious during surgery despite appearing unconscious due to paralysis and intubation. Additionally, 22% of patients in a recent study reported dreaming during anesthesia. P-zombies raise the hard problem of explaining qualia; i-zombies pose the practical problem of detecting qualia. The work compares these concepts and examines the hard problem of unconsciousness through anesthesia awareness.
Rui Dai, Hyunwoo Jang, Anthony G. Hudetz et al.
Across altered states of consciousness, psychedelics and sedatives produce opposite patterns of brain network organization. Psychedelics increase large-scale integration and reduce segregation of brain network interactions, while sleep and propofol sedation show the opposite pattern. These opposing integration-segregation patterns were consistently observed across multiple measures of functional connectivity, network topology, and interaction complexity, and reliably differentiated conscious states in an unbiased, data-driven manner. The findings demonstrate that psychedelic and sedated states are characterized by systematic and opposing shifts in large-scale brain organization.