Wednesday, March 28, 2007

Correlation of conscious perception with synchronization of neural activity across cortical areas.

Melloni et al. offer interesting measurements that correlate electrical activity with stimuli that are consciously versus unconsciously perceived. Their abstract:
Subliminal stimuli can be deeply processed and activate similar brain areas as consciously perceived stimuli. This raises the question which signatures of neural activity critically differentiate conscious from unconscious processing. Transient synchronization of neural activity has been proposed as a neural correlate of conscious perception. Here we test this proposal by comparing the electrophysiological responses related to the processing of visible and invisible words in a delayed matching to sample task. Both perceived and nonperceived words caused a similar increase of local (gamma) oscillations in the EEG, but only perceived words induced a transient long-distance synchronization of gamma oscillations across widely separated regions of the brain. After this transient period of temporal coordination, the electrographic signatures of conscious and unconscious processes continue to diverge. Only words reported as perceived induced (1) enhanced theta oscillations over frontal regions during the maintenance interval, (2) an increase of the P300 component of the event-related potential, and (3) an increase in power and phase synchrony of gamma oscillations before the anticipated presentation of the test word. We propose that the critical process mediating the access to conscious perception is the early transient global increase of phase synchrony of oscillatory activity in the gamma frequency range.

(click on image to make it larger). Scalp topography of induced gamma power and phase synchrony for the visible and invisible condition. Top row, Visible condition. Bottom row, Invisible condition. The background color indicates induced gamma power averaged in a 50–57 Hz frequency range. Each head represents the average of a 150 ms time window. Time 0 indicates the onset of the sample word. Lines connect pairs of electrodes displaying significant synchronization. The full article, which contains further color illustrations, can be downloaded HERE.


  1. Hi!

    I've just published what I believe is a breakthrough paper on meditation and consciousness (formal abstract and link below). It is the first to interrelate the work on synchronized gamma in consciousness with the well-attested work on gamma in meditation. It adduces experimental and simulated data to show that what both have in common is the ability to put the brain into a state in which it is maximally sensitive and consumes zero power, briefly. It is argued that this may correspond to a “selfless” state and the more typical non-zero state, in which gamma is not so prominent, corresponds to a state of empirical self. Thus, the “zero power” in the title refers not only to the power spectrum of the brain as measured by the Hilbert transform, but also to a psychological state of personal renunciation.Finally, the general perspective is compatible with panpsychism.

    The paper is;

    Zero Power and Selflessness: What Meditation and Conscious Perception Have in Common (Sean O Nuallain) and it's at


    This paper attempts to reconstrue the art and science of meditation in the context of an overall theory of cognition, and with reference to evidence from simulated and real data analysed in a neurodynamical framework. First, we discuss the phenomenology of meditation and its relation to the known evidence. It is argued that meditation is on a continuum with the types of conscious mental activity characterized by synchronized gamma. Specifically, it is suggested that gamma synchrony in meditation allows the normally prominent background noise of the brain momentarily to subside. Secondly, a set of experiments using both simulated and real data and interpreted in a neurodynamical context that bear on the issue of meditation is described. Thirdly, the theoretical and experimental frameworks are brought together into an overall perspective that impacts on cognition as on applied experientialism. Most of the material alludes to books and other refereed published material by the author.

  2. Amazing article just out in "Scientific American mind" citing work by Chawla proposing a spike in gamma (in the frontal lobe, at least) for up to 3 minutes just before death;

    It could be argued that nature gives one a chance to identify with pure awareness while passing.

    Hard to see what happens if one is blown up, however.

  3. Hi all,

    We are currently offering a course on “Neuroscience and experience” as
    taught as an advanced seminar in Stanford. A sample lecture and
    outline of the course can be found at

    The ethos of our institution can be found at the (under construction site;

    Queries can be sent to

    Best wishes


  4. Zero Power and Selflessness: What Meditation and Conscious Perception Have in Common (Sean O Nuallain)

    The idea sounds very interesting. But where can I read the paper, it could not be download here: nor in other major search engines available in the university.

    It is possible to send Thanks in advance!