Classical psychedelics produce visual hallucinations that are coherent at a low level but dream-like at a high level, yet no concrete mechanistic model explains these effects while remaining consistent with known pharmacology. The authors propose the 'oneirogen hypothesis': psychedelics induce neural activity states similar to dreaming. They simulate this by manipulating neural network models trained with the Wake-Sleep algorithm, partially shifting the model to a 'Sleep' state with greater top-down influence, mimicking effects on apical dendrites. This captures observed phenomena like hallucinations, increased stimulus-conditioned variability, and synaptic plasticity. The work offers testable predictions to validate the hypothesis.
Transcranial direct current stimulation (tDCS) applied to the prefrontal cortex alters the dynamic organization of functional connectivity in the primate brain, with effects depending on the state of consciousness. In awake macaques, cathodal tDCS disrupted the repertoire of connectivity patterns, increased structure-function correlation, decreased Shannon entropy, and favored transitions toward anatomically based patterns. Under deep sedation, anodal tDCS significantly altered brain pattern distribution and reduced structure-function correlation. The stimulation also modified dynamic connectivity arrangements typically associated with consciousness and unconsciousness. These findings suggest that prefrontal tDCS can modulate brain dynamics differently in conscious and unconscious states, offering insights into mechanisms relevant to disorders of consciousness.
Criterion shifts—changes in how people decide whether they have seen something—can distort neural measures of consciousness, causing simultaneous over- or under-estimation of both conscious and unconscious processing. While it was already known that subjective reports are vulnerable to such biases, new simulations and empirical work show that these effects have concrete consequences when analyzing real brain data. The authors argue that their findings are novel and that the experimental manipulations they used are not unrealistic compared to natural variations across experiments.
Conscious perception of a stimulus is linked to a specific sequence of brain processes that unfold after about 270 milliseconds, involving superior parietal and superior frontal regions. Using EEG and MEG recordings during a task where participants reported the location and visibility of a brief visual target, multivariate pattern analysis showed that information about stimulus location is still processed in the cortex even when the stimulus is not consciously seen (blindsight). However, only consciously perceived stimuli trigger additional, time-limited neural activity in higher-order brain areas, whereas unconscious processing decays slowly without this chain of activity.
During binocular rivalry, a constant visual stimulus produces a changing conscious percept. A concern has been that brain activity measured during rivalry might reflect the act of reporting the percept rather than the percept itself. This study recorded single neurons from face patches in the inferotemporal cortex of macaques using a no-report paradigm, inferring the animal's conscious percept from its eye movements. Large proportions of inferotemporal neurons represented the conscious percept even without active report. On single trials, both the conscious percept and the suppressed stimulus could be decoded. These findings indicate that inferotemporal cortex contains a true neural correlate of consciousness, consisting of a population code where single cells multiplex representation of the conscious percept and the physical stimulus.