Frontiers in Systems Neuroscience
January 1, 2019
Tom Sikkens, Conrado A Bosman, Umberto Olcese
48 citations
Feedback connections, which make up a large portion of neural links in the thalamocortical system, are thought to be essential for conscious perception, according to major theories of consciousness. These theories predict that feedback modulation should be reduced in nonconscious brain states such as non-REM sleep and anesthesia, and when sensory stimuli are not perceived. However, recent experiments on mismatch negativity, a phenomenon linked to top-down modulation, show that feedback modulation persists during nonconscious states, though it is generally dampened. These deviations challenge current theories and may require reevaluating how consciousness is assessed in supposedly nonconscious states.
bioRxiv (Cold Spring Harbor Laboratory)
April 22, 2026
Sabine Gnodde, Vlada Aslanov, Jolien C. Francken et al.
Perceptual awareness is linked to early, posterior brain activity rather than later frontal processes. Using electroencephalography with a cross-decoding method that minimized report-related confounds, participants viewed gratings in backward-masking and no-report tasks. Classifiers trained on stimulus location in the no-report task were tested on masked trials sorted by subjective visibility. Decoding revealed a reliable difference between subjectively visible and invisible stimuli from 130 to 170 milliseconds, driven by posterior sensors over occipital, temporal, and parietal regions. No corresponding effects were observed over frontal sensors, suggesting frontal activity in report-based paradigms reflects post-perceptual processing rather than awareness itself.
PLoS One
January 1, 2026
Clement Abbatecola, Bernard Marius ’t Hart, Belén M. Montabes De la Cruz et al.
The subjective experience of space around the visual blind spot is investigated to test three theories of consciousness: Integrated Information Theory (IIT), Predictive Processing Active Inference (AI), and Predictive Processing Neurorepresentationalism (NREP). IIT predicts that the blind spot region, lacking feedforward input from one eye, should contribute differently to perceived spatial quality. The Predictive Processing accounts argue that internal models accommodate structural deviations based on sensory evidence. Participants evaluate distances, areas, and illusory motion with or without the blind spot involved. Psychometric models quantify bias and precision in perceived versus objective space. Simulated results correspond to each theory's predictions, and challenges for dissemination are discussed.
Neuroscience of Consciousness
January 1, 2025
João Patriota, Giulia Moreni, Jorge Mejías et al.
During the sleep-wake cycle, consciousness changes, and this is thought to relate to how brain areas integrate. Recent work found that people can have conscious experiences during NREM sleep, which is usually considered unconscious. This study tested whether functional connectivity between neurons varies within brain states in a way that matches fluctuating consciousness. Researchers examined directed functional connectivity between neurons across the wake-sleep cycle in rats, over seconds. They observed that NREM sleep contains epochs where inter-areal connectivity patterns resemble those during wakefulness and REM sleep, and vice versa. Thus, circuit-level connectivity patterns are not fixed by brain state but may reflect other factors, such as changes in consciousness level within as well as between brain states.
iScience
December 19, 2025
Antonio Pazienti, Mariel Müller, Conrado A Bosman et al.
Slow-wave activity (SWA) in non-REM sleep and anesthesia is a hallmark of unconsciousness, but how it changes during the return to consciousness is unclear. Recording multi-area and laminar activity in mouse posterior parietal (PPC) and primary visual (V1) cortices during spontaneous awakening from isoflurane anesthesia, the authors show that spectral power is stronger in PPC (especially superficial layers) during deep unconsciousness but stronger in V1 upon awakening. Rostro-caudal (feedback-like) propagation of SWA is state-dependent, particularly in layer 5. Excitability of layer 2/3 neurons, suppressed at high isoflurane, recovers during awakening, when V1 and feedforward pathways reassert a strong role. SWA is a multiscale phenomenon with hierarchical and laminar properties.
bioRxiv Preprint Server
November 14, 2025
João Patriota, Giulia Moreni, Jorge Mejías et al.
preprint
Consciousness is thought to fluctuate with the integration of brain areas across the wake-sleep cycle, but recent evidence suggests consciousness may not be uniformly present or absent within a given brain state, as conscious reports can occur during Non-REM sleep. This study tested whether functional connectivity between neurons varies within brain states in a way that reflects changing levels of consciousness. In rats, directed functional connectivity between neurons was examined across the wake-sleep cycle at a scale of a few seconds. The analysis aimed to determine whether Non-REM sleep contains epochs with inter-areal integration comparable to wakefulness and REM sleep, and vice versa. The findings could reveal circuit-level connectivity patterns consistent with alternating levels of consciousness both between and within brain states.
PLoS One
January 1, 2025
Kengo Takahashi, Samuel Pontes Quero, Julien Fiorilli et al.
A planned experiment will test two competing theories of consciousness: one holding that neuronal activity itself generates conscious experience, the other that the causal structure of neural circuits is responsible. The experiment will optogenetically inactivate a portion of mouse visual cortex that does not respond to behaviorally relevant stimuli, targeting neurons with very low spiking activity that does not significantly affect other cortical areas. The effect on perception of the spatial distribution of stimuli will be measured. Results will be compared against theoretical predictions to help determine the neuronal substrate of consciousness.
eNeuro
September 1, 2024
Simone Ciceri, Matthijs N Oude Lohuis, Vivi Rottschäfer et al.
Conscious report of visual input correlates with two distinct neural responses in the primary visual cortex (V1): an early response tied to stimulus features and a late response linked to report or detection. This late wave, central to theories of consciousness, was thought to be driven by the prefrontal cortex (PFC). Analyzing two electrophysiological studies in mice performing detection tasks, researchers characterized activity in V1, posterior parietal cortex (PPC), and PFC. A minimal network model constrained by known connectivity showed that while PFC is necessary to generate report-related activity in V1, it only does so through PPC mediation. PPC, not PFC, ultimately enables the late wave of V1 activity.
The Journal of neuroscience : the official journal of the Society for Neuroscience
November 8, 2017
Johan F. Storm, Melanie Boly, Adenauer G. Casali et al.
The mind-body problem—how consciousness arises from brain processes—has long been considered a philosophical puzzle but is now being tackled empirically. This review describes progress since Crick and Koch (1998) proposed searching for the neural correlates of consciousness (NCC). It covers content-specific NCCs, which link particular brain activity to specific experiences, and the full NCC, which supports entire conscious states. The authors discuss methodological advances for isolating conscious experience from enabling functions, suggest that reconsidering the frontal cortex's role may refine NCCs, advocate for objective brain-based measures of consciousness independent of sensory or executive processes, and show how animal studies reveal network phenomena relevant to consciousness mechanisms.