Neural correlates of consciousness: progress and problems

Journal name:
Nature Reviews Neuroscience
Year published:
Published online
Corrected online


There have been a number of advances in the search for the neural correlates of consciousness — the minimum neural mechanisms sufficient for any one specific conscious percept. In this Review, we describe recent findings showing that the anatomical neural correlates of consciousness are primarily localized to a posterior cortical hot zone that includes sensory areas, rather than to a fronto-parietal network involved in task monitoring and reporting. We also discuss some candidate neurophysiological markers of consciousness that have proved illusory, and measures of differentiation and integration of neural activity that offer more promising quantitative indices of consciousness.

At a glance


  1. Identifying the neural correlates of consciousness.
    Figure 1: Identifying the neural correlates of consciousness.

    This schematic diagram illustrates the absolute levels of brain activity across different conditions designed to identify the neural correlates of consciousness (NCC). a | Haemodynamic activity in a report-based paradigm in which the experience of seeing a face or other stimulus manipulations such as backward masking is contrasted with not seeing it as a result of image noise142. The participant presses a button to report seeing (yes) or not seeing (no) the face. This isolates the brain regions involved in conscious face recognition, a content-specific NCC, but also the regions involved in the maintenance of the face in working memory and access to the concept 'face' for decision making. Note that the background conditions for consciousness, such as an active reticular activating system, are eliminated by this contrast. b | Haemodynamic activity in a no-report, seen/not seen paradigm, similar to part a, in which the participants do not report on their percept during the trial. Instead, either retrospective reports or physiological indicators, such as eye movements or pupil dilation, are used to avoid confounds related to the act of reporting34, 36. This allows the content-specific NCC to be isolated. The union of all such content-specific NCC constitutes the full NCC. c | In a between-states paradigm, the haemodynamic activity associated with the experience of seeing anything (here the experience of seeing pure black) while awake is contrasted with the activity associated with the condition of no experience that would occur during dreamless sleep37. This analysis identifies brain regions involved in having any conscious experience, but also regions that mediate being awake rather than being asleep. d | In a within-state, no-task paradigm, participants are awakened at random during sleep (stage N2) and are asked whether, before they were awakened, they were dreaming and, if so, about what. This paradigm identifies brain activity associated with having dream experiences up to 20 s before awakening44 — a candidate for the full NCC of dreaming consciousness — and avoids confounds associated with task execution and state change. NREM, non-rapid eye movement.

  2. Identifying content-specific and full neural correlates of consciousness.
    Figure 2: Identifying content-specific and full neural correlates of consciousness.

    a | Findings from a functional MRI (fMRI) experiment searching for content-specific neural correlates of consciousness (NCC). This experiment contrasts activity during the presentation of visual words with activity when the same words are masked and therefore invisible. This task involves an explicit report via button-press. Such studies have suggested that activity in the fronto-parietal networks and extrastriate occipital regions142 constitute the NCC. b | Similar fronto-parietal activity patterns are found during a binocular rivalry paradigm in which volunteers actively report their percept (task). However, when the volunteers experience rivalry without explicitly reporting perceptual alternations (no task), neural activity in the frontal areas is absent, whereas activation of the occipital and parietal regions remains36. c | Findings from an electrocorticogram (ECoG) study using a visual one-back paradigm in patients with epilepsy implanted with subdural electrode arrays. Participants press a button when two consecutive pictures are identical (the target trial). The colours indicate how strongly neural activity is modulated by the motor task (red represents low modulation and yellow represents high modulation) across all significantly responsive electrodes (either during non-target or target trials). Occipito-temporal visual cortical regions (shown to the right of the dashed white line) respond rapidly to the seen stimulus irrespective of the type of task (red), whereas the frontal regions are modulated by the type of task (yellow)117. d | Findings from a positron emission tomography (PET) study using a between-states paradigm that contrasts brain activity during deep non-rapid eye movement (NREM) sleep with wakefulness indicate that there are decreased levels of absolute cerebral blood flow in both parietal and frontal cortices during sleep. This suggested that activity in a fronto-parietal network may be essential for consciousness110. e | Voxel-by-voxel maps of the mean percentage change in fMRI signals during absence seizures: fronto-parietal activity increases during the loss of consciousness (warm colours) and decreases during the subsequent recovery of consciousness (cool colours)112. Part a is adapted with permission from Ref. 142, Elsevier. Part b is adapted from Ref. 36, republished with permission of Society for Neuroscience, from Binocular rivalry: frontal activity relates to introspection and action but not to perception, Frässle, S., Sommer, J., Jansen, A., Naber, M. & Einhäuser, W., 34, 5, 2014; permission conveyed through Copyright Clearance Center, Inc. Part c is adapted with permission from Ref. 117, Elsevier. Part d is adapted from Ref. 110, republished with permission of Society for Neuroscience, from Activity of midbrain reticular formation and neocortex during the progression of human non-rapid eye movement sleep, Kajimura, N., Uchiyama, M., Takayama, Y., Uchida, S., Uema, T., Kato, M., Sekimoto, M., Watanabe, T., Nakajima, T., Horikoshi, S., Ogawa, K., Nishikawa, M., Hiroki, M., Kudo, Y., Matsuda, H., Okawa, M. & Takahashi, K., 19, 22, 1999; permission conveyed through Copyright Clearance Center, Inc. Part e is adapted from Ref. 112, republished with permission of Society for Neuroscience, from Dynamic time course of typical childhood absence seizures: EEG, behavior, and functional magnetic resonance imaging, Bai, X., Vestal, M., Berman, R., Negishi, M., Spann, M., Vega, C., Desalvo, M., Novotny, E. J., Constable, R. T. & Blumenfeld, H., 30, 17, 2010; permission conveyed through Copyright Clearance Center, Inc.

  3. Candidate neurophysiological markers of consciousness.
    Figure 3: Candidate neurophysiological markers of consciousness.

    a | Gamma synchrony has been proposed as a correlate of consciousness. Cross-correlograms computed from the firing responses of two units recorded 7 mm apart in the visual cortex of cats reveal a strong gamma band synchronization when a moving bar stimulates the receptive fields of the two neurons162. b | In the high-level visual cortex in humans, however, the intracranial gamma band responses increase when a degraded stimulus is made visible by increasing sensory evidence, but not when visibility is increased to the same extent by previous exposure33. c | Visible grating stimuli elicit robust gamma oscillations (30–80 Hz) in the human visual cortex, whereas equally visible noise patterns or natural images do not, indicating that gamma activity is not necessary for visual conciousness175. d | The late positive component of the event-related potential (known as the P3b) was also proposed as a signature of consciousness. In attentional blink paradigms, the P3b is a robust correlate of stimulus visibility178. e | When visual awareness and task relevance are manipulated independently, however, the P3b is absent for task-irrelevant stimuli regardless of whether the participants are aware of them or not34. f | Stimuli that are not consciously detected can trigger a significant P3b component180. g | A shift in electroencephalography (EEG) activity from low to high frequencies has been proposed as a correlate of consciousness. Electrical stimulation of the midbrain reticular formation (MRF) elicits EEG activation and behavioural awakening in a cat; EEG slow waves are replaced by low-voltage fast activity and by a steady membrane potential in the cortex247, 248. h | High-amplitude bilateral slow waves have been observed in awake, conscious patients in some cases of non-convulsive status epilepticus199. Part a is from Ref. 162, Nature Publishing Group. Part b is adapted from Ref. 33, Society for Neuroscience, from Local category-specific gamma band responses in the visual cortex do not reflect conscious perception, Aru, J., Axmacher, N., Do Lam, A. T., Fell, J., Elger, C. E., Singer, W. & Melloni, L., 32, 43, 2012; permission conveyed through Copyright Clearance Center, Inc. Part c is adapted from Ref. 175, Hermes, D., Miller, K. J., Wandell, B. A. & Winawer, J. Stimulus dependence of gamma oscillations in human visual cortex. Cereb. Cortex, 2015, 25, 9, 29512959, by permission of Oxford University Press. Part d is from Ref. 178, Nature Publishing Group. Part e is adapted from Ref. 34. Part f is adapted with permission from Ref. 180, Elsevier. Part g is adapted with permission from Ref. 248, American Association for the Advancement of Science. Part h is adapted with permission from Ref. 199, John Wiley &Sons.

  4. Neural differentiation and integration as neural correlates of consciousness.
    Figure 4: Neural differentiation and integration as neural correlates of consciousness.

    a | Schematic diagram showing two idealized time series of spontaneous brain activity (electroencephalography (EEG)) and the corresponding maps of cortical connectivity. Integration, as measured by indices of functional connectivity, tends to be high when time series are highly correlated (top panel) and low when time series are not highly correlated (bottom panel). b | The same two time series are shown together with the corresponding maps of spatiotemporal variability in brain activity. Differentiation, here reflected in the difference between subsequent maps of cortical activity, tends to be high (top panel) when the time series are not highly correlated (maximum for random time series) and low when they are highly correlated (bottom panel). c | The perturbational complexity index (PCI) simultaneously quantifies integration and differentiation. Calculating the PCI involves perturbing the brain with transcranial magnetic stimulation (TMS), recording the results of EEG to detect the pattern of causal cortical interactions engaged by the TMS perturbation (integration) and compressing this pattern to calculate its spatiotemporal variability with algorithmic complexity measures (differentiation). Responses that are both integrated and differentiated are less compressible, resulting in high PCI values. By contrast, local (low integration) or stereotypical (low differentiation) EEG responses to TMS can be effectively compressed, yielding low PCI values. As shown in the right-hand panel (real data), jointly measuring integration and differentiation with PCI establishes a common measurement scale that is valid across many different conditions along the unconsciousness–consciousness spectrum and is reliable at the level of single paticipants219, 220, including: those who are awake and able to report immediately that they are conscious (red circles); participants in rapid eye movement (REM) sleep and under ketamine anaesthesia who are unresponsive, but able to report retrospectively that they were conscious (green circles); participants in non-REM (NREM) sleep or general anaesthesia (midazolam, propofol and xenon) who provide no conscious report on awakening (dark blue circles); vegetative state/unresponsive wakefulness syndrome (VS/UWS) patients (light blue circles); and responsive brain-injured patients who are in a minimally conscious state (MCS), emerged from the MCS (EMCS) or in a locked-in syndrome (LIS) (light red circles). Part c is adapted with permission from Ref. 219, American Association for the Advancement of Science.

Change history

Corrected online 06 May 2016
The traces in panel e of Figure 3 were incorrectly colour coded. The colour coding has been corrected in the online version of the article.


  1. Tononi, G. The integrated information theory of consciousness: an updated account. Arch. Ital. Biol. 150, 5690 (2012).
  2. Posner, J. B., Saper, C. B., Schiff, N. D. & Plum, F. Plum and Posner's Diagnosis of Stupor and Coma (Oxford University Press, 2007).
    Describes the canonical clinical tests for disorders of consciousness.
  3. Rees, G., Kreiman, G. & Koch, C. Neural correlates of consciousness in humans. Nat. Rev. Neurosci. 3, 261270 (2002).
  4. Faivre, N., Salomon, R. & Blanke, O. Visual consciousness and bodily self-consciousness. Curr. Opin. Neurol. 28, 2328 (2015).
  5. Merrick, C., Godwin, C., Geisler, M. & Morsella, E. The olfactory system as the gateway to the neural correlates of consciousness. Front. Psychol. 4, 1011 (2014).
  6. Gallace, A. & Spence, C. The cognitive and neural correlates of 'tactile consciousness': a multisensory perspective. Conscious. Cogn. 17, 370407 (2008).
  7. Fleming, S. M. & Dolan, R. J. The neural basis of metacognitive ability. Phil. Trans. R. Soc. B 367, 13381349 (2012).
  8. Laureys, S. The neural correlate of (un)awareness: lessons from the vegetative state. Trends Cogn. Sci. 9, 556559 (2005).
  9. Giacino, J. T., Kalmar, K. & Whyte, J. The JFK Coma Recovery Scale — Revised: measurement characteristics and diagnostic utility. Arch. Phys. Med. Rehabil. 85, 20202029 (2004).
  10. Schnakers, C. et al. Diagnostic accuracy of the vegetative and minimally conscious state: clinical consensus versus standardized neurobehavioral assessment. BMC Neurol. 9, 35 (2009).
  11. Owen, A. M. et al. Detecting awareness in the vegetative state. Science 313, 1402 (2006).
    The first study to use fMRI to infer consciousness in a behaviourally non-responsive patient in a vegetative state.
  12. Kunimoto, C., Miller, J. & Pashler, H. Confidence and accuracy of near-threshold discrimination responses. Conscious. Cogn. 10, 294340 (2001).
  13. Reingold, E. M. & Merikle, P. M. Using direct and indirect measures to study perception without awareness. Percept. Psychophys. 44, 563575 (1988).
  14. Weiskrantz, L. Is blindsight just degraded normal vision? Exp. Brain Res. 192, 413416 (2009).
  15. Snodgrass, M., Bernat, E. & Shevrin, H. Unconscious perception: a model-based approach to method and evidence. Percept. Psychophys. 66, 846867 (2004).
  16. Sandberg, K., Timmermans, B., Overgaard, M. & Cleeremans, A. Measuring consciousness: is one measure better than the other? Conscious. Cogn. 19, 10691078 (2010).
    A study comparing different behavioural measures of consciousness.
  17. Del Cul, A., Baillet, S. & Dehaene, S. Brain dynamics underlying the nonlinear threshold for access to consciousness. PLoS Biol. 5, e260 (2007).
  18. Cowey, A. & Stoerig, P. Blindsight in monkeys. Nature 373, 247249 (1995).
  19. Kepecs, A., Uchida, N., Zariwala, H. A. & Mainen, Z. F. Neural correlates, computation and behavioural impact of decision confidence. Nature 455, 227231 (2008).
  20. Leopold, D. A. Primary visual cortex: awareness and blindsight. Annu. Rev. Neurosci. 35, 91109 (2012).
  21. Crick, F. & Koch, C. Towards a neurobiological theory of consciousness. Semin. Neurosci. 2, 263275 (1990).
    One of the principal publications that triggered the contemporary search for the NCC.
  22. Koch, C. The Quest for Consciousness: a Neurobiological Approach (Roberts, 2004).
  23. Baars, B. A. Cognitive Theory of Consciousness (Cambridge Univ. Press, 1988).
    Introduces the global workspace theory of consciousness.
  24. Blake, R. & Logothetis, N. K. Visual competition. Nat. Rev. Neurosci. 3, 1321 (2002).
  25. Tsuchiya, N. & Koch, C. Continuous flash suppression reduces negative afterimages. Nat. Neurosci. 8, 10961101 (2005).
    Reports the discovery of a widely used long-lasting visual masking technique.
  26. Imamoglu, F., Kahnt, T., Koch, C. & Haynes, J. D. Changes in functional connectivity support conscious object recognition. Neuroimage 63, 19091917 (2012).
  27. Breitmeyer, B. G. & Ögmen, H. Recent models and findings in visual backward masking: a comparison, review, and update. Percept. Psychophys. 62, 15721595 (2000).
  28. Francis, G. Quantitative theories of metacontrast masking. Psychol. Rev. 107, 768785 (2000).
  29. Koivisto, M. & Revonsuo, A. Event-related brain potential correlates of visual awareness. Neurosci. Biobehav. Rev. 34, 922934 (2010).
  30. Miller, S. M. Closing in on the constitution of consciousness. Front. Psychol. 5, 1293 (2014).
  31. Aru, J., Bachmann, T., Singer, W. & Melloni, L. Distilling the neural correlates of consciousness. Neurosci. Biobehav. Rev. 36, 737746 (2012).
  32. de Graaf, T. A., Hsieh, P.-J. & Sack, A. T. The 'correlates' in neural correlates of consciousness. Neurosci. Biobehav. Rev. 36, 191197 (2012).
  33. Aru, J. et al. Local category-specific gamma band responses in the visual cortex do not reflect conscious perception. J. Neurosci. 32, 1490914914 (2012).
  34. Pitts, M. A., Metzler, S. & Hillyard, S. A. Isolating neural correlates of conscious perception from neural correlates of reporting one's perception. Front. Psychol. 5, 1078 (2014).
  35. Tsuchiya, N., Wilke, M., Frässle, S. & Lamme, V. A. No-report paradigms: extracting the true neural correlates of consciousness. Trends Cogn. Sci. 19, 757770 (2015).
  36. Frässle, S., Sommer, J., Jansen, A., Naber, M. & Einhäuser, W. Binocular rivalry: frontal activity relates to introspection and action but not to perception. J. Neurosci. 34, 17381747 (2014).
    Pioneering application of a no-report paradigm to study binocular rivalry.
  37. Maquet, P. et al. Functional neuroanatomy of human slow wave sleep. J. Neurosci. 17, 28072812 (1997).
  38. Massimini, M. et al. Breakdown of cortical effective connectivity during sleep. Science 309, 22282232 (2005).
    The first study to use TMS and EEG to measure the breakdown of causal integration and differentiation during slow wave sleep.
  39. Alkire, M. T., Hudetz, A. G. & Tononi, G. Consciousness and anesthesia. Science 322, 876880 (2008).
  40. Brown, E. N., Lydic, R. & Schiff, N. D. General anesthesia, sleep, and coma. N. Engl. J. Med. 363, 26382650 (2010).
  41. Laureys, S., Owen, A. M. & Schiff, N. D. Brain function in coma, vegetative state, and related disorders. Lancet Neurol. 3, 537546 (2004).
  42. Gosseries, O., Di, H., Laureys, S. & Boly, M. Measuring consciousness in severely damaged brains. Annu. Rev. Neurosci. 37, 457478 (2014).
    A comprehensive review of clinical and neuroimaging aspects of disorders of consciousness.
  43. Hohwy, J. The neural correlates of consciousness: new experimental approaches needed? Conscious. Cogn. 18, 428438 (2009).
  44. Siclari, F., LaRocque, J. J., Bernardi, G., Postle, B. R. & Tononi, G. The neural correlates of consciousness in sleep: a no-task, within-state paradigm. Preprint at (2014).
  45. Herculano-Houzel, S. The remarkable, yet not extraordinary, human brain as a scaled-up primate brain and its associated cost. Proc. Natl Acad. Sci. USA 109 (Suppl. 1), 1066110668 (2012).
  46. Baumann, O. et al. Consensus paper: the role of the cerebellum in perceptual processes. Cerebellum 14, 197220 (2015).
  47. Lemon, R. N. & Edgley, S. A. Life without a cerebellum. Brain 133, 652654 (2010).
  48. Yu, F., Jiang, Q. J., Sun, X. Y. & Zhang, R. W. A new case of complete primary cerebellar agenesis: clinical and imaging findings in a living patient. Brain 138, e353 (2015).
    A case study of a patient born without a cerebellum who lives a normal life.
  49. Moruzzi, G. & Magoun, H. W. Brain stem reticular formation and activation of the EEG. Electroencephalogr. Clin. Neurophysiol. 1, 455473 (1949).
  50. Parvizi, J. & Damasio, A. R. Neuroanatomical correlates of brainstem coma. Brain 126, 15241536 (2003).
  51. Parvizi, J. & Damasio, A. Consciousness and the brainstem. Cognition 79, 135160 (2001).
    An up-to-date account of the current understanding of the role of the brainstem in enabling consciousness.
  52. Nir, Y. et al. Regional slow waves and spindles in human sleep. Neuron 70, 153169 (2011).
  53. Brown, R. E., Basheer, R., McKenna, J. T., Strecker, R. E. & McCarley, R. W. Control of sleep and wakefulness. Physiol. Rev. 92, 10871187 (2012).
  54. Siclari, F., Larocque, J. J., Postle, B. R. & Tononi, G. Assessing sleep consciousness within subjects using a serial awakening paradigm. Front. Psychol. 4, 542 (2013).
  55. Bhatia, K. P. & Marsden, C. D. The behavioural and motor consequences of focal lesions of the basal ganglia in man. Brain 117, 859876 (1994).
  56. Wijdicks, E. F. & Cranford, R. E. Clinical diagnosis of prolonged states of impaired consciousness in adults. Mayo Clin. Proc. 80, 10371046 (2005).
  57. Lutkenhoff, E. S. et al. Thalamic and extrathalamic mechanisms of consciousness after severe brain injury. Ann. Neurol. 78, 6876 (2015).
  58. Jain, S. K. et al. Bilateral large traumatic basal ganglia haemorrhage in a conscious adult: a rare case report. Brain Inj. 27, 500503 (2013).
  59. Straussberg, R. et al. Familial infantile bilateral striatal necrosis: clinical features and response to biotin treatment. Neurology 59, 983989 (2002).
  60. Caparros-Lefebvre, D., Destee, A. & Petit, H. Late onset familial dystonia: could mitochondrial deficits induce a diffuse lesioning process of the whole basal ganglia system? J. Neurol. Neurosurg. Psychiatry 63, 196203 (1997).
  61. Alexander, G. E., DeLong, M. R. & Strick, P. L. Parallel organization of functionally segregated circuits linking basal ganglia and cortex. Annu. Rev. Neurosci. 9, 357381 (1986).
  62. McHaffie, J. G., Stanford, T. R., Stein, B. E., Coizet, V. & Redgrave, P. Subcortical loops through the basal ganglia. Trends Neurosci. 28, 401407 (2005).
  63. Torgerson, C. M., Irimia, A., Goh, S. Y. & Van Horn, J. D. The DTI connectivity of the human claustrum. Hum. Brain Mapp. 36, 827838 (2015).
  64. Crick, F. C. & Koch, C. What is the function of the claustrum? Phil. Trans. R. Soc. B 360, 12711279 (2005).
  65. Koubeissi, M. Z., Bartolomei, F., Beltagy, A. & Picard, F. Electrical stimulation of a small brain area reversibly disrupts consciousness. Epilepsy Behav. 37, 3235 (2014).
  66. Damasio, A., Damasio, H. & Tranel, D. Persistence of feelings and sentience after bilateral damage of the insula. Cereb. Cortex 23, 833846 (2013).
  67. Bogen, J. E. On the neurophysiology of consciousness: I. An overview. Conscious. Cogn. 4, 5262 (1995).
  68. Van der Werf, Y. D., Witter, M. P. & Groenewegen, H. J. The intralaminar and midline nuclei of the thalamus. Anatomical and functional evidence for participation in processes of arousal and awareness. Brain Res. Brain Res. Rev. 39, 107140 (2002).
  69. Schiff, N. D. et al. Behavioural improvements with thalamic stimulation after severe traumatic brain injury. Nature 448, 600603 (2007).
  70. Jones, E. G. A new view of specific and nonspecific thalamocortical connections. Adv. Neurol. 77, 4971; discussion 7273 (1998).
  71. Theyel, B. B., Llano, D. A. & Sherman, S. M. The corticothalamocortical circuit drives higher-order cortex in the mouse. Nat. Neurosci. 13, 8488 (2010).
  72. Fuller, P. M., Sherman, D., Pedersen, N. P., Saper, C. B. & Lu, J. Reassessment of the structural basis of the ascending arousal system. J. Comp. Neurol. 519, 933956 (2011).
  73. Laureys, S. et al. Cortical processing of noxious somatosensory stimuli in the persistent vegetative state. Neuroimage 17, 732741 (2002).
  74. Lehky, S. R. & Maunsell, J. H. No binocular rivalry in the LGN of alert macaque monkeys. Vision Res. 36, 12251234 (1996).
  75. Wilke, M., Mueller, K. M. & Leopold, D. A. Neural activity in the visual thalamus reflects perceptual suppression. Proc. Natl Acad. Sci. USA 106, 94659470 (2009).
  76. Panagiotaropoulos, T. I., Kapoor, V. & Logothetis, N. K. Subjective visual perception: from local processing to emergent phenomena of brain activity. Phil. Trans. R. Soc. B 369, 20130534 (2014).
  77. Boly, M. et al. Connectivity changes underlying spectral EEG changes during propofol-induced loss of consciousness. J. Neurosci. 32, 70827090 (2012).
  78. Velly, L. J. et al. Differential dynamic of action on cortical and subcortical structures of anesthetic agents during induction of anesthesia. Anesthesiology 107, 202212 (2007).
  79. Magnin, M. et al. Thalamic deactivation at sleep onset precedes that of the cerebral cortex in humans. Proc. Natl Acad. Sci. USA 107, 38293833 (2010).
  80. Crick, F. & Koch, C. Are we aware of neural activity in primary visual cortex? Nature 375, 121123 (1995).
    Proposes that neurons in V1 are not the neural correlates of visual consciousness.
  81. Silvanto, J. Is primary visual cortex necessary for visual awareness? Trends Neurosci. 37, 618619 (2014).
  82. Jiang, Y., Zhou, K. & He, S. Human visual cortex responds to invisible chromatic flicker. Nat. Neurosci. 10, 657662 (2007).
  83. He, S. & MacLeod, D. I. Orientation-selective adaptation and tilt after-effect from invisible patterns. Nature 411, 473476 (2001).
  84. Haynes, J. D. & Rees, G. Predicting the orientation of invisible stimuli from activity in human primary visual cortex. Nat. Neurosci. 8, 686691 (2005).
    A study showing that the haemodynamic response in human V1 contains information not accessible to subjects during a visual masking task.
  85. Logothetis, N. K. Single units and conscious vision. Phil. Trans. R. Soc. Lond. B 353, 18011818 (1998).
    A review of Logothetis' classic single-neuron studies in the visual cortex of monkeys undergoing binocular competition.
  86. Leopold, D. A. & Logothetis, N. K. Multistable phenomena: changing views in perception. Trends Cogn. Sci. 3, 254264 (1999).
  87. Polonsky, A., Blake, R., Braun, J. & Heeger, D. J. Neuronal activity in human primary visual cortex correlates with perception during binocular rivalry. Nat. Neurosci. 3, 11531159 (2000).
  88. Lee, S. H., Blake, R. & Heeger, D. J. Traveling waves of activity in primary visual cortex during binocular rivalry. Nat. Neurosci. 8, 2223 (2005).
  89. Harrison, S. A. & Tong, F. Decoding reveals the contents of visual working memory in early visual areas. Nature 458, 632635 (2009).
  90. Donner, T. H., Sagi, D., Bonneh, Y. S. & Heeger, D. J. Opposite neural signatures of motion-induced blindness in human dorsal and ventral visual cortex. J. Neurosci. 28, 1029810310 (2008).
  91. Weiskrantz, L. Blindsight revisited. Curr. Opin. Neurobiol. 6, 215220 (1996).
  92. Horton, J. C. & Hoyt, W. F. Quadrantic visual field defects. A hallmark of lesions in extrastriate (V2/V3) cortex. Brain 114, 17031718 (1991).
  93. Mazzi, C., Mancini, F. & Savazzi, S. Can IPS reach visual awareness without V1? Evidence from TMS in healthy subjects and hemianopic patients. Neuropsychologia 64C, 134144 (2014).
  94. Zeki, S. A Vision of the Brain (Blackwell Scientific, 1993).
  95. Pollen, D. A. Fundamental requirements for primary visual perception. Cereb. Cortex 18, 19911998 (2008).
  96. Oizumi, M., Albantakis, L. & Tononi, G. From the phenomenology to the mechanisms of consciousness: integrated information theory 3.0. PLoS Comput. Biol. 10, e1003588 (2014).
  97. Meyer, K. Primary sensory cortices, top-down projections and conscious experience. Prog. Neurobiol. 94, 408417 (2011).
  98. Wiegand, K. & Gutschalk, A. Correlates of perceptual awareness in human primary auditory cortex revealed by an informational masking experiment. Neuroimage 61, 6269 (2012).
  99. Cauller, L. J. & Kulics, A. T. The neural basis of the behaviorally relevant N1 component of the somatosensory-evoked potential in SI cortex of awake monkeys: evidence that backward cortical projections signal conscious touch sensation. Exp. Brain Res. 84, 607619 (1991).
  100. Goodale, M. A. & Milner, D. A. Sight Unseen: an Exploration of Conscious and Unconscious Vision (Oxford Univ. Press, 2004).
  101. Grill-Spector, K. & Weiner, K. S. The functional architecture of the ventral temporal cortex and its role in categorization. Nat. Rev. Neurosci. 15, 536548 (2014).
  102. Karnath, H. O., Ruter, J., Mandler, A. & Himmelbach, M. The anatomy of object recognition — visual form agnosia caused by medial occipitotemporal stroke. J. Neurosci. 29, 58545862 (2009).
  103. Milner, A. D. Is visual processing in the dorsal stream accessible to consciousness? Proc. Biol. Sci. 279, 22892298 (2012).
  104. Konen, C. S. & Kastner, S. Two hierarchically organized neural systems for object information in human visual cortex. Nat. Neurosci. 11, 224231 (2008).
  105. Kravitz, D. J., Saleem, K. S., Baker, C. I. & Mishkin, M. A new neural framework for visuospatial processing. Nat. Rev. Neurosci. 12, 217230 (2011).
  106. Bagattini, C., Mazzi, C. & Savazzi, S. Waves of awareness for occipital and parietal phosphenes perception. Neuropsychologia 70C, 114125 (2015).
  107. Laureys, S., Lemaire, C., Maquet, P., Phillips, C. & Franck, G. Cerebral metabolism during vegetative state and after recovery to consciousness. J. Neurol. Neurosurg. Psychiatry 67, 121 (1999).
  108. Kaisti, K. K. et al. Effects of surgical levels of propofol and sevoflurane anesthesia on cerebral blood flow in healthy subjects studied with positron emission tomography. Anesthesiology 96, 13581370 (2002).
  109. Maquet, P. Functional neuroimaging of normal human sleep by positron emission tomography. J. Sleep Res. 9, 207231 (2000).
  110. Kajimura, N. et al. Activity of midbrain reticular formation and neocortex during the progression of human non-rapid eye movement sleep. J. Neurosci. 19, 1006510073 (1999).
  111. Vogt, B. A. & Laureys, S. Posterior cingulate, precuneal and retrosplenial cortices: cytology and components of the neural network correlates of consciousness. Prog. Brain Res. 150, 205217 (2005).
  112. Bai, X. et al. Dynamic time course of typical childhood absence seizures: EEG, behavior, and functional magnetic resonance imaging. J. Neurosci. 30, 58845893 (2010).
  113. Safavi, S., Kapoor, V., Logothetis, N. K. & Panagiotaropoulos, T. I. Is the frontal lobe involved in conscious perception? Front. Psychol. 5, 1063 (2014).
  114. Melloni, L., Schwiedrzik, C. M., Muller, N., Rodriguez, E. & Singer, W. Expectations change the signatures and timing of electrophysiological correlates of perceptual awareness. J. Neurosci. 31, 13861396 (2011).
  115. Sandberg, K. et al. Distinct MEG correlates of conscious experience, perceptual reversals and stabilization during binocular rivalry. Neuroimage 100, 161175 (2014).
  116. Andersen, L. M., Pedersen, M. N., Sandberg, K. & Overgaard, M. Occipital MEG activity in the early time range (<300 ms) predicts graded changes in perceptual consciousness. Cereb. Cortex (2015).
  117. Noy, N. et al. Ignition's glow: ultra-fast spread of global cortical activity accompanying local “ignitions” in visual cortex during conscious visual perception. Conscious. Cogn. 35, 206224 (2015).
  118. Nir, Y. & Tononi, G. Dreaming and the brain: from phenomenology to neurophysiology. Trends Cogn. Sci. 14, 88100 (2010).
  119. Postle, B. R. The cognitive neuroscience of visual short-term memory. Curr. Opin. Behav. Sci. 1, 4046 (2015).
  120. Selimbeyoglu, A. & Parvizi, J. Electrical stimulation of the human brain: perceptual and behavioral phenomena reported in the old and new literature. Front. Hum. Neurosci. 4, 46 (2010).
  121. Rangarajan, V. et al. Electrical stimulation of the left and right human fusiform gyrus causes different effects in conscious face perception. J. Neurosci. 34, 1282812836 (2014).
    Demonstrates that electrical stimulation of the right but not the left fusiform face regions in humans with implanted electrodes causes changes in visual face perception.
  122. Desmurget, M. et al. Movement intention after parietal cortex stimulation in humans. Science 324, 811813 (2009).
    A neurosurgical account reporting that direct electrical stimulation of the posterior parietal cortex causes a conscious intention to move without an actual motor response.
  123. Brickner, R. M. Brain of patient A. after bilateral frontal lobectomy; status of frontal-lobe problem. AMA Arch. Neurol. Psychiatry 68, 293313 (1952).
    A classic account of a patient with an almost complete bilateral frontal lobectomy who was clearly conscious.
  124. Hebb, D. O. & Penfield, W. Human behavior after extensive bilateral removal from the frontal lobes. Arch. Neurol. Psychiatry 42, 421438 (1940).
  125. Fulton, J. F. Functional Localization in Relation to Frontal Lobotomy (Oxford Univ. Press, 1949).
  126. Mettler, F. A. Selective Partial Ablation of the Frontal Cortex, a Correlative Study of its Effects on Human Psychotic Subjects (Hoebar, 1949).
  127. Markowitsch, H. J. & Kessler, J. Massive impairment in executive functions with partial preservation of other cognitive functions: the case of a young patient with severe degeneration of the prefrontal cortex. Exp. Brain Res. 133, 94102 (2000).
  128. Mataró, M. et al. Long-term effects of bilateral frontal brain lesion: 60 years after injury with an iron bar. Arch. Neurol. 58, 11391142 (2001).
  129. VanRullen, R. & Koch, C. Visual selective behavior can be triggered by a feed-forward process. J. Cogn. Neurosci. 15, 209217 (2003).
  130. Schmidt, T. & Schmidt, F. Processing of natural images is feedforward: a simple behavioral test. Atten. Percept. Psychophys. 71, 594606 (2009).
  131. Koivisto, M., Kastrati, G. & Revonsuo, A. Recurrent processing enhances visual awareness but is not necessary for fast categorization of natural scenes. J. Cogn. Neurosci. 26, 223231 (2014).
  132. Lamme, V. A. & Roelfsema, P. R. The distinct modes of vision offered by feedforward and recurrent processing. Trends Neurosci. 23, 571579 (2000).
    Argues that a rapid, sensory-driven feedforward wave of neural activity mediates unconscious behaviour, whereas top-down feedback gives rise to conscious experience.
  133. Tang, H. et al. Spatiotemporal dynamics underlying object completion in human ventral visual cortex. Neuron 83, 736748 (2014).
  134. Super, H., Spekreijse, H. & Lamme, V. A. Two distinct modes of sensory processing observed in monkey primary visual cortex (V1). Nat. Neurosci. 4, 304310 (2001).
  135. Auksztulewicz, R., Spitzer, B. & Blankenburg, F. Recurrent neural processing and somatosensory awareness. J. Neurosci. 32, 799805 (2012).
  136. Sachidhanandam, S., Sreenivasan, V., Kyriakatos, A., Kremer, Y. & Petersen, C. C. Membrane potential correlates of sensory perception in mouse barrel cortex. Nat. Neurosci. 16, 16711677 (2013).
    A study showing how transgenic mice and molecular tools can be applied to study the neuronal circuitry underlying tactile perception.
  137. Boly, M. et al. Preserved feedforward but impaired top-down processes in the vegetative state. Science 332, 858862 (2011).
  138. Ku, S. W., Lee, U., Noh, G. J., Jun, I. G. & Mashour, G. A. Preferential inhibition of frontal-to-parietal feedback connectivity is a neurophysiologic correlate of general anesthesia in surgical patients. PLoS ONE 6, e25155 (2011).
  139. Tononi, G. & Edelman, G. M. Consciousness and complexity. Science 282, 18461851 (1998).
  140. Lamme, V. A. F. Towards a true neural stance on consciousness. Trends Cogn. Sci. 10, 494501 (2006).
  141. Dehaene, S. & Naccache, L. Towards a cognitive neuroscience of consciousness: basic evidence and a workspace framework. Cognition 79, 137 (2001).
  142. Dehaene, S. & Changeux, J.-P. Experimental and theoretical approaches to conscious processing. Neuron 70, 200227 (2011).
    A recent account of the neuronal global workspace theory of consciousness.
  143. Butti, C., Santos, M., Uppal, N. & Hof, P. R. Von Economo neurons: clinical and evolutionary perspectives. Cortex 49, 312326 (2013).
  144. Livingstone, M. S. & Hubel, D. H. Effects of sleep and arousal on the processing of visual information in the cat. Nature 291, 554561 (1981).
  145. Larkum, M. A cellular mechanism for cortical associations: an organizing principle for the cerebral cortex. Trends Neurosci. 36, 141151 (2013).
  146. Harris, K. D. & Shepherd, G. M. The neocortical circuit: themes and variations. Nat. Neurosci. 18, 170181 (2015).
  147. Douglas, R. J. & Martin, K. A. Neuronal circuits of the neocortex. Annu. Rev. Neurosci. 27, 419451 (2004).
  148. Binzegger, T., Douglas, R. J. & Martin, K. A. Topology and dynamics of the canonical circuit of cat V1. Neural Netw. 22, 10711078 (2009).
  149. Markov, N. T. et al. Anatomy of hierarchy: feedforward and feedback pathways in macaque visual cortex. J. Comp. Neurol. 522, 225259 (2014).
  150. Zhang, S. et al. Long-range and local circuits for top-down modulation of visual cortex processing. Science 345, 660665 (2014).
    A study analysing the circuits mediating top-down visual attention in transgenic mice using optogenetics.
  151. Maier, A., Adams, G. K., Aura, C. & Leopold, D. A. Distinct superficial and deep laminar domains of activity in the visual cortex during rest and stimulation. Front. Syst. Neurosci. 4, 31 (2010).
  152. Buffalo, E. A., Fries, P., Landman, R., Buschman, T. J. & Desimone, R. Laminar differences in gamma and alpha coherence in the ventral stream. Proc. Natl Acad. Sci. USA 108, 1126211267 (2011).
  153. Funk, C.M., Honjoh, S., Rodriguez, A.V., Cirelli, C. & Tononi, G. Local slow waves in superficial layers of primary cortical areas during REM sleep. Curr. Biol. 26, 396403 (2016).
  154. Sakata, S. & Harris, K. D. Laminar structure of spontaneous and sensory-evoked population activity in auditory cortex. Neuron 64, 404418 (2009).
  155. Shew, W. L. & Plenz, D. The functional benefits of criticality in the cortex. Neuroscientist 19, 88100 (2013).
  156. He, B. J. & Raichle, M. E. The fMRI signal, slow cortical potential and consciousness. Trends Cogn. Sci. 13, 302309 (2009).
  157. Libet, B., Alberts, W. W., Wright, E. W. Jr & Feinstein, B. Responses of human somatosensory cortex to stimuli below threshold for conscious sensation. Science 158, 15971600 (1967).
  158. Pins, D. & Ffytche, D. The neural correlates of conscious vision. Cereb. Cortex 13, 461474 (2003).
  159. Fitzgerald, R. D. et al. Direct current auditory evoked potentials during wakefulness, anesthesia, and emergence from anesthesia. Anesth. Analg. 92, 154160 (2001).
  160. Arezzo, J. C., Vaughan, H. G. Jr & Legatt, A. D. Topography and intracranial sources of somatosensory evoked potentials in the monkey. II. Cortical components. Electroencephalogr. Clin. Neurophysiol. 51, 118 (1981).
  161. Cauller, L. J. & Kulics, A. T. A comparison of awake and sleeping cortical states by analysis of the somatosensory-evoked response of postcentral area 1 in rhesus monkey. Exp. Brain Res. 72, 584592 (1988).
  162. Gray, C. M., Konig, P., Engel, A. K. & Singer, W. Oscillatory responses in cat visual cortex exhibit inter-columnar synchronization which reflects global stimulus properties. Nature 338, 334337 (1989).
    A study that triggered new research into the functional relevance of synchronized spiking in the gamma range for perceptual processes.
  163. Singer, W. Time as coding space? Curr. Opin. Neurobiol. 9, 189194 (1999).
  164. Roelfsema, P. R., Engel, A. K., Konig, P. & Singer, W. Visuomotor integration is associated with zero time-lag synchronization among cortical areas. Nature 385, 157161 (1997).
  165. Munk, M. H., Roelfsema, P. R., Konig, P., Engel, A. K. & Singer, W. Role of reticular activation in the modulation of intracortical synchronization. Science 272, 271274 (1996).
  166. Herculano-Houzel, S., Munk, M. H., Neuenschwander, S. & Singer, W. Precisely synchronized oscillatory firing patterns require electroencephalographic activation. J. Neurosci. 19, 39924010 (1999).
  167. Fries, P., Roelfsema, P. R., Engel, A. K., Konig, P. & Singer, W. Synchronization of oscillatory responses in visual cortex correlates with perception in interocular rivalry. Proc. Natl Acad. Sci. USA 94, 1269912704 (1997).
  168. Rodriguez, E. et al. Perception's shadow: long-distance synchronization of human brain activity. Nature 397, 430433 (1999).
  169. Melloni, L. et al. Synchronization of neural activity across cortical areas correlates with conscious perception. J. Neurosci. 27, 28582865 (2007).
  170. Wyart, V. & Tallon-Baudry, C. Neural dissociation between visual awareness and spatial attention. J. Neurosci. 28, 26672679 (2008).
    One of several recent papers arguing that visual attention can operate independently of visual consciousness.
  171. Imas, O. A., Ropella, K. M., Ward, B. D., Wood, J. D. & Hudetz, A. G. Volatile anesthetics disrupt frontal-posterior recurrent information transfer at gamma frequencies in rat. Neurosci. Lett. 387, 145150 (2005).
  172. Murphy, M. J. et al. Propofol anesthesia and sleep: a high-density EEG study. Sleep 34, 283-91A (2011).
  173. Pockett, S. & Holmes, M. D. Intracranial EEG power spectra and phase synchrony during consciousness and unconsciousness. Conscious. Cogn. 18, 10491055 (2009).
  174. Luo, Q. et al. Visual awareness, emotion, and gamma band synchronization. Cereb. Cortex 19, 18961904 (2009).
  175. Hermes, D., Miller, K. J., Wandell, B. A. & Winawer, J. Stimulus dependence of gamma oscillations in human visual cortex. Cereb. Cortex 25, 29512959 (2015).
    A study showing that many perceived images do not evoke gamma band activity as assessed by subdural electrodes placed above the visual cortex in patients with epilepsy.
  176. Ray, S. & Maunsell, J. H. Network rhythms influence the relationship between spike-triggered local field potential and functional connectivity. J. Neurosci. 31, 1267412682 (2011).
  177. Sutton, S., Braren, M., Zubin, J. & John, E. R. Evoked-potential correlates of stimulus uncertainty. Science 150, 11871188 (1965).
  178. Sergent, C., Baillet, S. & Dehaene, S. Timing of the brain events underlying access to consciousness during the attentional blink. Nat. Neurosci. 8, 13911400 (2005).
  179. Pitts, M. A., Martínez, A. & Hillyard, S. A. Visual processing of contour patterns under conditions of inattentional blindness. J. Cogn. Neurosci. 24, 287303 (2012).
  180. Silverstein, B. H., Snodgrass, M., Shevrin, H. & Kushwaha, R. P3b, consciousness, and complex unconscious processing. Cortex 73, 216227 (2015).
    Demonstrates that unconscious stimuli can trigger a P3b.
  181. Sitt, J. D. et al. Large scale screening of neural signatures of consciousness in patients in a vegetative or minimally conscious state. Brain 137, 22582270 (2014).
  182. Kotchoubey, B. Event-related potential measures of consciousness: two equations with three unknowns. Prog. Brain Res. 150, 427444 (2005).
  183. Fischer, C., Luaute, J. & Morlet, D. Event-related potentials (MMN and novelty P3) in permanent vegetative or minimally conscious states. Clin. Neurophysiol. 121, 10321042 (2010).
  184. Holler, Y. et al. Preserved oscillatory response but lack of mismatch negativity in patients with disorders of consciousness. Clin. Neurophysiol. 122, 17441754 (2011).
  185. Faugeras, F. et al. Probing consciousness with event-related potentials in the vegetative state. Neurology 77, 264268 (2011).
  186. King, J. R. et al. Single-trial decoding of auditory novelty responses facilitates the detection of residual consciousness. Neuroimage 83, 726738 (2013).
  187. Tzovara, A., Simonin, A., Oddo, M., Rossetti, A. O. & De Lucia, M. Neural detection of complex sound sequences in the absence of consciousness. Brain 138, 11601166 (2015).
  188. Railo, H., Koivisto, M. & Revonsuo, A. Tracking the processes behind conscious perception: a review of event-related potential correlates of visual consciousness. Conscious. Cogn. 20, 972983 (2011).
    A pioneering description of the visual awareness negativity, one of the most specific evoked-potential correlates of visual experience.
  189. Steriade, M. Corticothalamic resonance, states of vigilance and mentation. Neuroscience 101, 243276 (2000).
  190. Steriade, M., Timofeev, I. & Grenier, F. Natural waking and sleep states: a view from inside neocortical neurons. J. Neurophysiol. 85, 19691985 (2001).
  191. McCormick, D. A., Wang, Z. & Huguenard, J. Neurotransmitter control of neocortical neuronal activity and excitability. Cereb. Cortex 3, 387398 (1993).
  192. Schiff, N. D. Central thalamic deep-brain stimulation in the severely injured brain: rationale and proposed mechanisms of action. Ann. NY Acad. Sci. 1157, 101116 (2009).
  193. Timofeev, I., Grenier, F., Bazhenov, M., Sejnowski, T. J. & Steriade, M. Origin of slow cortical oscillations in deafferented cortical slabs. Cereb. Cortex 10, 11851199 (2000).
  194. Fernandez-Espejo, D. et al. Diffusion weighted imaging distinguishes the vegetative state from the minimally conscious state. Neuroimage 54, 103112 (2011).
  195. Kertai, M. D., Whitlock, E. L. & Avidan, M. S. Brain monitoring with electroencephalography and the electroencephalogram-derived bispectral index during cardiac surgery. Anesth. Analg. 114, 533546 (2012).
  196. Purdon, P. L. et al. Electroencephalogram signatures of loss and recovery of consciousness from propofol. Proc. Natl Acad. Sci. USA 110, E1142E1151 (2013).
  197. Schiff, N. D., Nauvel, T. & Victor, J. D. Large-scale brain dynamics in disorders of consciousness. Curr. Opin. Neurobiol. 25, 714 (2014).
  198. Westmoreland, B. F., Klass, D. W., Sharbrough, F. W. & Reagan, T. J. Alpha-coma. Electroencephalographic, clinical, pathologic, and etiologic correlations. Arch. Neurol. 32, 713718 (1975).
  199. Gökyiğit, A. & Calişkan, A. Diffuse spike-wave status of 9-year duration without behavioral change or intellectual decline. Epilepsia 36, 210213 (1995).
  200. Vuilleumier, P., Assal, F., Blanke, O. & Jallon, P. Distinct behavioral and EEG topographic correlates of loss of consciousness in absences. Epilepsia 41, 687693 (2000).
  201. Nobili, L. et al. Local aspects of sleep: observations from intracerebral recordings in humans. Prog. Brain Res. 199, 219232 (2012).
  202. Forgacs, P. B. et al. Preservation of electroencephalographic organization in patients with impaired consciousness and imaging-based evidence of command-following. Ann. Neurol. 76, 869879 (2014).
  203. Synek, V. M. Prognostically important EEG coma patterns in diffuse anoxic and traumatic encephalopathies in adults. J. Clin. Neurophysiol. 5, 161174 (1988).
  204. Hudetz, A. G., Liu, X. & Pillay, S. Dynamic repertoire of intrinsic brain states is reduced in propofol-induced unconsciousness. Brain Connect. 5, 1022 (2015).
  205. Barttfeld, P. et al. Signature of consciousness in the dynamics of resting-state brain activity. Proc. Natl Acad. Sci. USA 112, 887892 (2015).
  206. Solovey, G. et al. Loss of consciousness is associated with stabilization of cortical activity. J. Neurosci. 35, 1086610877 (2015).
  207. Sigl, J. C. & Chamoun, N. G. An introduction to bispectral analysis for the electroencephalogram. J. Clin. Monit. 10, 392404 (1994).
  208. Sara, M. et al. Functional isolation within the cerebral cortex in the vegetative state: a nonlinear method to predict clinical outcomes. Neurorehabil. Neural Repair 25, 3542 (2011).
  209. Gosseries, O. et al. Automated EEG entropy measurements in coma, vegetative state/unresponsive wakefulness syndrome and minimally conscious state. Funct. Neurol. 26, 2530 (2011).
  210. Tagliazucchi, E. & Laufs, H. Decoding wakefulness levels from typical fMRI resting-state data reveals reliable drifts between wakefulness and sleep. Neuron 82, 695708 (2014).
  211. Achard, S. et al. Hubs of brain functional networks are radically reorganized in comatose patients. Proc. Natl Acad. Sci. USA 109, 2060820613 (2012).
  212. Monti, M. M. et al. Dynamic change of global and local information processing in propofol-induced loss and recovery of consciousness. PLoS Comput. Biol. 9, e1003271 (2013).
  213. King, J. R. et al. Information sharing in the brain indexes consciousness in noncommunicative patients. Curr. Biol. 23, 19141919 (2013).
  214. Marinazzo, D. et al. Directed information transfer in scalp electroencephalographic recordings: insights on disorders of consciousness. Clin. EEG Neurosci. 45, 3339 (2014).
  215. Chennu, S. et al. Spectral signatures of reorganised brain networks in disorders of consciousness. PLoS Comput. Biol. 10, e1003887 (2014).
  216. Supp, G. G., Siegel, M., Hipp, J. F. & Engel, A. K. Cortical hypersynchrony predicts breakdown of sensory processing during loss of consciousness. Curr. Biol. 21, 19881993 (2011).
  217. Arthuis, M. et al. Impaired consciousness during temporal lobe seizures is related to increased long-distance cortical-subcortical synchronization. Brain 132, 20912101 (2009).
  218. Kaskinoro, K. et al. Wide inter-individual variability of bispectral index and spectral entropy at loss of consciousness during increasing concentrations of dexmedetomidine, propofol, and sevoflurane. Br. J. Anaesth. 107, 573580 (2011).
  219. Casali, A. G. et al. A theoretically based index of consciousness independent of sensory processing and behavior. Sci. Transl. Med. 5, 198ra105 (2013).
    The first study to use a combined TMS and EEG paradigm to quantify the level of consciousness under a variety of conditions and at the level of individual patients.
  220. Sarasso, S. et al. Consciousness and complexity during unresponsiveness induced by propofol, xenon, and ketamine. Curr. Biol. 25, 30993105 (2015).
  221. Miller, S. (ed.) The Constitution of Phenomenal Consciousness: Toward a Science and Theory (John Benjamins Publishing, 2015).
    A recent book discussing conceptual and empirical issues related to the NCC.
  222. Revonsuo, A. in Neural Correlates of Consciousness. (ed. Metzinger, T.) 5776 (MIT Press, 2000).
  223. Coltheart, V. Fleeting Memories: Cognition of Brief Visual Stimuli. (MIT Press, 1999).
  224. Tononi, G., Boly, M., Massimini, M. & Koch, C. Integrated information theory: from consciousness to its physical substrate. Nat. Rev Neurosci. (in the press)
  225. Monti, M. M. et al. Willful modulation of brain activity in disorders of consciousness. N. Engl. J. Med. 362, 579589 (2010).
  226. Schiff, N. et al. Residual cerebral activity and behavioural fragments can remain in the persistently vegetative brain. Brain 125, 12101234 (2002).
  227. Zadra, A., Desautels, A., Petit, D. & Montplaisir, J. Somnambulism: clinical aspects and pathophysiological hypotheses. Lancet Neurol. 12, 285294 (2013).
  228. Bassetti, C., Vella, S., Donati, F., Wielepp, P. & Weder, B. SPECT during sleepwalking. Lancet 356, 484485 (2000).
  229. Terzaghi, M. et al. Dissociated local arousal states underlying essential clinical features of non-rapid eye movement arousal parasomnia: an intracerebral stereo-electroencephalographic study. J. Sleep Res. 21, 502506 (2012).
  230. Blumenfeld, H. Impaired consciousness in epilepsy. Lancet Neurol. 11, 814826 (2012).
  231. Langston, J. W. & Palfreman, J. The Case of the Frozen Addicts (Pantheon, 1995).
  232. Northoff, G. et al. Right lower prefronto-parietal cortical dysfunction in akinetic catatonia: a combined study of neuropsychology and regional cerebral blood flow. Psychol. Med. 30, 583596 (2000).
  233. Lagercrantz, H. & Changeux, J. P. The emergence of human consciousness: from fetal to neonatal life. Pediatr. Res. 65, 255260 (2009).
    Addresses the question of when a newborn infant first experiences anything, and the neuronal events that occur in the developing brain around that time.
  234. Kouider, S. et al. A neural marker of perceptual consciousness in infants. Science 340, 376380 (2013).
  235. Dawkins, M. S. Through Our Eyes Only? (Oxford Univ. Press on Demand, 1998).
  236. Griffin, D. R. Animal Minds (University of Chicago Press, 2001).
  237. Edelman, D. & Seth, A. K. Animal consciousness: a synthetic approach. Trends Neurosci. 32, 476484 (2009).
  238. Koch, C. & Laurent, G. Complexity and the nervous system. Science 284, 9698 (1999).
  239. Berlin, H. A. The neural basis of the dynamic unconscious. Neuropsychoanalysis 13, 168 (2011).
  240. Hassin, R. R. Yes it can: on the functional abilities of the human unconscious. Persp. Psychol. Sci. 8, 195207 (2013).
    An edited volume describing a series of experiments that demonstrate non-conscious processing under a variety of laboratory and real-life conditions.
  241. Hassin, R. R., Uleman, J. S. & Bargh, J. A. The New Unconscious (Oxford Univ. Press, 2005).
  242. Sklar, A. Y. et al. Reading and doing arithmetic nonconsciously. Proc. Natl Acad. Sci. USA 109, 1961419619 (2012).
  243. Kouider, S. & Dehaene, S. Levels of processing during non-conscious perception: a critical review of visual masking. Phil. Trans. R. Soc. B 362, 857875 (2007).
  244. Mudrik, L., Breska, A., Lamy, D. & Deouell, L. Y. Integration without awareness: expanding the limits of unconscious processing. Psychol. Sci. 22, 764770 (2011).
  245. Giurfa, M., Zhang, S., Jenett, A., Menzel, R. & Srinivasan, M. V. The concepts of 'sameness' and 'difference' in an insect. Nature 410, 930933 (2001).
  246. Tononi, G. & Koch, C. Consciousness: here, there, and everywhere? Phil. Trans. R. Soc. B (2015).
  247. Steriade, M., Amzica, F. & Contreras, D. Synchronization of fast (30–40 Hz) spontaneous cortical rhythms during brain activation. J. Neurosci. 16, 392417 (1996).
  248. Steriade, M. Arousal: revisiting the reticular activating system. Science 272, 225226 (1996).

Download references

Author information


  1. Allen Institute for Brain Science, Seattle, Washington 98109 USA.

    • Christof Koch
  2. Department of Biomedical and Clinical Sciences 'Luigi Sacco', University of Milan, Milan, Italy.

    • Marcello Massimini
  3. Instituto Di Ricovero e Cura a Carattere Scientifico, Fondazione Don Carlo Gnocchi, Milan, Italy.

    • Marcello Massimini
  4. Department of Neurology, University of Wisconsin, Madison, Wisconsin 53719, USA.

    • Melanie Boly
  5. Department of Psychiatry, University of Wisconsin, Madison, Wisconsin 53719, USA.

    • Melanie Boly &
    • Giulio Tononi

Competing interests statement

The authors declare no competing interests.

Corresponding authors

Correspondence to:

Author details

  • Christof Koch

    Christof Koch is the President and Chief Scientific Officer of the Allen Institute for Brain Science in Seattle, Washington, USA. He was trained as a physicist. On a quest to understand the physical roots of consciousness before his brain stops functioning, he published his first paper on the neural correlates of consciousness with Francis Crick a quarter of a century ago.

  • Marcello Massimini

    Marcello Massimini is Associate Professor of Neurophysiology at the University of Milan, Italy. He was trained as a medical doctor and devotes his research to understanding the neuronal mechanisms of loss and recovery of consciousness in sleep and anaesthesia, and in brain-injured patients.

  • Melanie Boly

    Melanie Boly is a neurologist and neuroscientist at the University of Wisconsin, Madison, USA. She uses neuroimaging and theoretical approaches to understand the neural substrate of experience and its alterations in sleep, anaesthesia and disorders of consciousness.

  • Giulio Tononi

    Giulio Tononi is a neuroscientist and psychiatrist at the Department of Psychiatry at the University of Wisconsin, Madison, USA, where he works on the nature of consciousness and the functions of sleep.

Supplementary information

PDF files

  1. Supplementary information S1 (box) (96.3 KB)

    Consciousness and other cognitive functions

Additional data