bioRxiv Preprint Server
April 18, 2023
Martin Breyton, Jan Fousek, Giovanni Rabuffo et al.
preprint
Consciousness depends on the brain's ability to produce complex, variable patterns of activity after a perturbation, but measuring this directly is difficult. Using a whole-brain model, researchers found that such complexity only arises when spontaneous brain activity is highly fluid—meaning functional networks reorganize extensively. This fluid regime can be captured by a small set of dynamical systems metrics, which predict the effects of consciousness-altering drugs like Xenon, Propofol, and Ketamine. These predictions were validated in 15 subjects at different consciousness levels, showing agreement with established perturbational complexity measures but using a simpler, more accessible paradigm. The findings point to complexity properties underlying consciousness.
bioRxiv Preprint Server
January 27, 2023
Michael Pereira, Nathan Faivre, Fosco Bernasconi et al.
preprint
Neurons in the subthalamic nucleus and thalamus, subcortical brain structures, modulate their activity during expectation of a weak vibrotactile stimulus on the hand, and 23% of these neurons show firing rates that differ between detected and undetected stimuli. This provides direct neurophysiological evidence that these subcortical regions are involved in perceptual consciousness, challenging the prevailing cortico-centric view.
bioRxiv Preprint Server
September 28, 2022
Yonatan Sanz Perl, Carla Pallavicini, Juan Piccinini et al.
preprint
Brain states are often described on a single scale from full consciousness to unconsciousness, but this ignores the complex, high-dimensional nature of brain activity. By combining whole-brain modeling, data augmentation, and deep learning, researchers mapped states of consciousness into a low-dimensional space where distances reflect similarities between states. They found an orderly trajectory from wakefulness to brain-injured patients, with coordinates related to functional modularity and structure-function coupling, both increasing as consciousness is lost. Model perturbations provided a geometric interpretation of state stability and reversibility. The work suggests conscious awareness depends on functional patterns encoded as a low-dimensional trajectory within the vast space of brain configurations.
bioRxiv Preprint Server
March 21, 2022
Danilo Menicucci, Valentina Cesari, Enrico Cipriani et al.
preprint
The fragmented sleep, fragmented mind hypothesis links sleep disturbances to dissociative states in people with dissociative traits, supported by neurophysiological theories that altered states of consciousness may arise from disrupted functional interaction among brain modules due to inefficient sleep processes.
bioRxiv Preprint Server
November 8, 2021
Maria Volodina, Nikolai Smetanin, Mikhail Lebedev et al.
preprint
During guided Taoist meditation, experienced meditators split into two subgroups with distinct physiological patterns. One subgroup showed general relaxation, with changes in heart rate variability, respiratory rate, and EEG activity. The other subgroup exhibited mind concentration patterns visible in EEG but no autonomic responses. Neither the duration or type of prior meditation experience nor baseline indicators explained this split. These results suggest two distinct meditation strategies may be used by experienced meditators, partly explaining inconsistent findings in earlier studies.
bioRxiv Preprint Server
September 2, 2021
Laura De la Fuente, Federico Zamberlan, Hernán Bocaccio et al.
preprint
The laws of physics are time-symmetric, but dissipative systems like the brain show a preferred temporal direction. Using a deep learning framework inspired by stochastic thermodynamics, researchers analyzed electrocorticography signals from non-human primates. Brain activity during conscious wakefulness could be distinguished from its time-reversed version with high accuracy, using both frequency and phase information. This ability was reduced during deep sleep and ketamine-induced anesthesia. Transitions between slow (≈20 Hz) and fast frequencies (> 40 Hz) mainly contributed to the temporal asymmetry seen during wakefulness. The findings suggest that a preferred temporal direction in neural activity correlates with conscious awareness, linking brain processes to the subjective experience of time's passage.
bioRxiv Preprint Server
August 17, 2021
Nicolas Fuentes, Alexis García, Ramón Guevara et al.
preprint
The complexity of brain activity can serve as a correlate of consciousness. In monkeys, electrocorticogram recordings were analyzed using information quantifiers to compare stages of general anesthesia. For propofol and medetomidine, the anesthetized state showed a reduction in brain activity complexity. Conversely, ketamine produced an increase in complexity measurements, linked to increased activity in certain brain regions. Complexity of brain activity is a good indicator for evaluating different levels of consciousness awareness, in both anesthetized and non-anesthetized states.
bioRxiv Preprint Server
July 27, 2021
Michelle J. Redinbaugh, Mohsen Afrasiabi, Jessica M. Phillips et al.
preprint
Deep brain stimulation (DBS) of the central lateral thalamus in macaques can produce episodes resembling absence epilepsy, termed absence-like activity (ALA), characterized by decreased behavior, vacant staring, and low-frequency oscillations. The likelihood of ALA depended on stimulation frequency. During ALA, neural complexity (entropy) and integration (Φ*), an index of consciousness, decreased, and communication within cortico-striato-thalamic circuits changed substantially. Power spectral density and coherence at low frequencies increased, especially in thalamo-parietal and cortico-striatal pathways. Decreased consciousness and neural integration corresponded to shifts in network configurations that dissociated parietal and subcortical structures. The same DBS method, at different frequencies, can also increase consciousness in anesthetized macaques, offering a flexible tool for studying consciousness and informing clinical research on absence epilepsy and other disorders of consciousness.
bioRxiv Preprint Server
July 12, 2021
Jun Kitazono, Yuma Aoki, Masafumi Oizumi
preprint
A method for hierarchically decomposing a brain network into cores based on the strength of bidirectional connections helps identify regions likely essential for consciousness. Applied to a whole-brain mouse connectome, cores with strong bidirectional connections included the isocortex, thalamus, and claustrum—areas thought to support consciousness—and excluded the cerebellum, which is not considered relevant. Simpler methods that ignore bidirectionality failed to show this correspondence. The findings suggest that analyzing bidirectional connectivity offers a novel way to relate brain network structure to consciousness.
bioRxiv Preprint Server
November 20, 2020
Mor Regev, Andrea R. Halpern, Adrian M. Owen et al.
preprint
When people imagine music they have previously memorized, the brain's auditory cortices show melody-specific activity patterns similar to those during actual listening. Functional MRI data from participants who memorized six one-minute instrumental pieces revealed that during silent imagery, these patterns reappeared in right associative auditory cortices. Adding rhythmic tapping while imagining extended the melody-specific neural patterns to both left and right associative cortices. The findings suggest that the contents of conscious auditory experience are encoded similarly during imagery and perception, and that rhythmic motion can enhance the reinstatement of neural patterns associated with complex sounds, supporting models of motor-to-sensory influences in auditory processing.
bioRxiv Preprint Server
November 10, 2020
A. Fontan, L. Lindgren, T. Pedale et al.
preprint
Sedation with Propofol alters non-conscious brain processes as much as conscious ones, challenging the assumption that anesthetics selectively suppress consciousness. By manipulating both the content (conscious vs. non-conscious perception) and level (arousal via sedation) of consciousness during fMRI, the authors found that these two aspects are dissociable. This suggests that level and content of consciousness are separate phenomena, prompting a re-evaluation of what it means to be conscious.
bioRxiv Preprint Server
July 2, 2020
Yonatan Sanz Perl, Carla Pallavicini, Ignacio Pérez Ipiña et al.
preprint
The level of consciousness—how conscious someone is—is often measured by how similar their brain activity is to normal wakefulness. However, this approach misses important information about how stable that state is. Using computer models of the whole brain, the authors show that the stability of a conscious state—how easily it can be disrupted—provides additional, complementary information. They propose a new framework that sorts brain states by both their similarity to wakefulness and their stability, which helps distinguish between different types of unconsciousness: natural sleep, anesthesia, and brain injury. This framework offers a more complete way to characterize and differentiate states of consciousness.
bioRxiv Preprint Server
June 4, 2020
Camilo Miguel Signorelli, Lynn Uhrig, Morten Kringelbach et al.
preprint
Anesthesia disrupts the brain's hierarchical organization, which may be a key mechanism behind loss of consciousness. By analyzing resting-state fMRI data from awake and anesthetized macaques, the authors found that anesthesia reduces the flexibility and richness of brain dynamics, making them more rigid and driven by brain structure. The depth of anesthesia and the specific anesthetic agent used both modulate these effects. Spatial and temporal aspects of cortical hierarchy are affected differently, involving distinct brain networks. The findings suggest that a breakdown in brain hierarchy is a new signature of unconsciousness.
bioRxiv Preprint Server
April 7, 2020
Mohsen Afrasiabi, Michelle J. Redinbaugh, Jessica M. Phillips et al.
preprint
Simultaneous recordings from frontal, parietal, striatal, and thalamic regions in macaques during wakefulness, sleep, and anesthesia, along with deep-brain thalamic stimulation, show that parietal cortex, striatum, and thalamus contribute more to the level of consciousness than frontal cortex. This supports Integrated Information Theory over Global Neuronal Workspace Theory and Higher-order Theories, but Integrated Information Theory does not account for subcortical structures like the striatum. The authors propose that thalamo-striatal circuits have a cause-effect structure that generates integrated information.
bioRxiv Preprint Server
February 11, 2020
Christopher J. Whyte, Ryan Smith
preprint
A new computational model called the 'predictive global workspace' combines ideas from the global neuronal workspace (GNW) theory of consciousness with Active Inference, a framework that treats brain activity as Bayesian inference. The model reproduces electrophysiological and behavioral results from studies of inattentional blindness and a four-way taxonomy linking consciousness, attention, and sensory signal strength. It also reconciles conflicting findings, extends the taxonomy to include prior expectations, and suggests new experimental paradigms. The model addresses limitations of current GNW research by enabling precise, testable predictions at both behavioral and neural levels.
bioRxiv Preprint Server
January 28, 2020
Vishal Kapoor, Abhilash Dwarakanath, Shervin Safavi et al.
preprint
The prefrontal cortex can represent the contents of conscious perception even when no overt report is required. Recordings from macaque monkeys during binocular rivalry—where perception alternates between two conflicting images—showed that neural ensemble activity in the prefrontal cortex decoded which image the animal was seeing as accurately as when images were presented without competition. This decoding remained significant even when eye movements were suppressed, indicating that the signals were not solely due to oculomotor confounds. The findings suggest that prefrontal population dynamics reflect internally driven changes in conscious perception during multistable vision.
bioRxiv Preprint Server
October 1, 2019
Michelle J. Redinbaugh, Jessica M. Phillips, Niranjan A. Kambi et al.
preprint
Consciousness requires the capacity to experience the environment and internal states. Recordings from macaques show that during unconsciousness, spiking activity is selectively reduced in deep cortical layers and thalamus, along with diminished interactions at alpha and gamma frequencies. Gamma-frequency stimulation of the central lateral thalamus in anesthetized macaques counteracted these changes and restored consciousness. The findings suggest that the neural correlates of consciousness involve coordinated activity across corticocortical feedforward and feedback pathways, intracolumnar loops, and thalamocortical circuits.
bioRxiv Preprint Server
October 1, 2019
Tf. Varley, M. Craig, R. Adapa et al.
preprint
Brain activity's fractal dimension—a measure of complexity—decreases with loss of consciousness. Healthy volunteers showed higher fractal dimension than patients in a minimally conscious state, who in turn showed higher dimension than those in a vegetative state, regardless of injury cause. Fractal dimension of functional connectivity networks, adjacency matrices, and BOLD time-series all correlated with level of consciousness. These findings support the idea that consciousness requires complex, critically organized brain activity, consistent with prior EEG, MEG, and fMRI work.
bioRxiv Preprint Server
August 7, 2019
Matthew J Davidson, Irene Graafsma, Naotsugu Tsuchiya et al.
preprint
Perceptual filling-in (PFI) makes a visible target disappear from awareness while the background fills its location. In this experiment, participants viewed four peripheral targets on a background updating at 20 Hz. Brain activity tracked via steady-state visually evoked potentials (SSVEPs) showed that background signals closely matched participants' reports of target disappearances. More filled-in targets led to longer disappearances, suggesting interactions between targets in different visual quadrants. Distinct neural responses appeared at different harmonics: the second harmonic (40 Hz) increased before the first (20 Hz) prior to genuine PFI, possibly reflecting attention. No such difference occurred for physically removed stimuli. The results demonstrate PFI as a tool for studying multi-object perceptual suppression and the neural correlates of consciousness.
bioRxiv Preprint Server
July 29, 2019
Nikita Agarwal, Aditi Kathpalia, Nithin Nagaraj
preprint
A novel measure called Network Causal Activity, based on Compression-Complexity Causality, was used to analyze electrocorticographic signals from the lateral cortex of four monkeys. Network Causal Activity was consistently higher in the awake state compared with the anaesthetized state, suggesting it may serve as a quantitative indicator of consciousness.
bioRxiv Preprint Server
July 10, 2019
Joel Frohlich, Lynne M. Bird, John Dell’italia et al.
preprint
Children with Angelman syndrome, who are fully conscious, have brainwave patterns that look like those seen during unconsciousness, challenging theories that link consciousness to complex neural activity. However, when comparing wakefulness to sleep, the brainwaves of 35 children with Angelman syndrome show greater complexity during wakefulness, even when accounting for slow-wave activity. This supports the idea that consciousness is tied to neural complexity and warns against assuming a lack of consciousness based solely on EEG readings.
bioRxiv Preprint Server
May 27, 2019
William Wong, Valdas Noreika, Levente Móró et al.
preprint
A test called the Dream Catcher test was conducted for the first time in a simplified form to see if brain activity alone can reveal whether someone is dreaming. Data Team collected brain measurements (polysomnograms) during NREM sleep from 9 participants, producing 54 one-minute recordings—27 from dreamful sleep and 27 from dreamless sleep. A blinded Analysis Team tried to classify each recording as dreamful or dreamless using an unsupervised machine learning classifier based on EEG spectral power and electrode location. Over five iterations with gradually reduced blindness, the team never performed significantly better than chance. The results suggest that EEG spectral power does not carry signatures of phenomenal consciousness, and the study also failed to replicate key findings from earlier reports on dreaming consciousness.
bioRxiv Preprint Server
April 12, 2019
Valdas Noreika, Jennifer M. Windt, Markus Kern et al.
preprint
Applying transcranial direct current stimulation (tDCS) over the sensorimotor cortex during REM sleep reduces reported dream movement, particularly repetitive actions, without affecting other bodily sensations like touch or balance. This effect coincides with reduced interhemispheric coherence in parietal areas and altered muscle activity correlation between arms. The findings indicate that tDCS causally interferes with the neural mechanisms underlying dream movement, confirming the spatial specificity of the stimulation site and suggesting a reorganization of the motor network during dreaming.
bioRxiv Preprint Server
March 22, 2019
André S. Nilsen, Bjørn E. Juel, Johan F. Storm
preprint
Measures that distinguish conscious from unconscious brain states may also be influenced by attentional load and cognitive resource use within conscious states. Testing several proposed measures, the study examines whether they are modulated by changes in attention and cognitive demands, which has rarely been tested before. The findings suggest that these measures are not solely markers of consciousness but can vary with attentional load within conscious states.
bioRxiv Preprint Server
March 12, 2019
Siouar Bensaid, Julien Modolo, Isabelle Merlet et al.
preprint
A computational model called COALIA simulates human cortical micro-circuits, including specific neuron types and thalamo-cortical regulation of cortico-cortical connectivity. The model generates EEG that matches brain rhythms recorded in humans during wakefulness and sleep. It reproduces disynaptic disinhibition of basket cells and pyramidal neurons via long-range activation of VIP interneurons. The model predicts that thalamic output strength and dynamics control local and long-range cortical information processing. It also reproduces and explains clinical TMS-evoked EEG complexity in disorders of consciousness patients and healthy volunteers through modulation of thalamo-cortical connectivity governing cortico-cortical communication.