Gerald Edelman, Consciousness Researcher - Abstracts

Posted by:

Alfredo Pereira Jr (group admin)

Date:

25 August 2007

Comments:

2 comments

1: Proc Natl Acad Sci U S A. 2006 Jul 11;103(28):10799-804. Epub 2006 Jul 3.

Theories and measures of consciousness: an extended framework.

Seth AK, Izhikevich E, Reeke GN, Edelman GM.

Neurosciences Institute, 10640 John Jay Hopkins Drive, San Diego, CA 92121, USA.

A recent theoretical emphasis on complex interactions within neural systems
underlying consciousness has been accompanied by proposals for the quantitative
characterization of these interactions. In this article, we distinguish key
aspects of consciousness that are amenable to quantitative measurement from those
that are not. We carry out a formal analysis of the strengths and limitations of
three quantitative measures of dynamical complexity in the neural systems
underlying consciousness: neural complexity, information integration, and causal
density. We find that no single measure fully captures the multidimensional
complexity of these systems, and all of these measures have practical
limitations. Our analysis suggests guidelines for the specification of
alternative measures which, in combination, may improve the quantitative
characterization of conscious neural systems. Given that some aspects of
consciousness are likely to resist quantification altogether, we conclude that a
satisfactory theory is likely to be one that combines both qualitative and
quantitative elements.

Publication Types: Research Support, Non-U.S. Gov’t Review

PMID: 16818879 [PubMed – indexed for MEDLINE]

2: Proc Natl Acad Sci U S A. 2003 Apr 29;100(9):5520-4. Epub 2003 Apr 17.

Naturalizing consciousness: a theoretical framework.

Edelman GM.

Neurosciences Institute, San Diego, CA 92121, USA. edelman@nsi.edu

Consciousness has a number of apparently disparate properties, some of which seem
to be highly complex and even inaccessible to outside observation. To place these
properties within a biological framework requires a theory based on a set of
evolutionary and developmental principles. This paper describes such a theory,
which aims to provide a unifying account of conscious phenomena.

Publication Types: Research Support, Non-U.S. Gov’t

PMID: 12702758 [PubMed – indexed for MEDLINE]

3: Ann N Y Acad Sci. 2001 Apr;929:111-22.

Consciousness: the remembered present.

Edelman G.

Neurosciences Institute, San Diego, California 92121, USA.

This chapter summarizes a theory of consciousness based on brain structure and
dynamics. The theory centers around the notion of reentry—on-going recursive
signaling across multiple reciprocally connected brain regions present mainly in
the thalamocortical system. It recognized the fundamental beginnings provided by
the complementary efforts of Ramon y Cajal and William James.

Publication Types: Review

PMID: 11349421 [PubMed – indexed for MEDLINE]

4: Brain Res Brain Res Rev. 2000 Mar;31(2-3):391-400.

Schizophrenia and the mechanisms of conscious integration.

Tononi G, Edelman GM.

The Neurosciences Institute, 10640 John J. Hopkins Drive, San Diego, CA, USA.
tononi@nsi.edu

This article considers the possibility that defective interactions among
distributed brain areas may underlie certain dysfunctions of conscious
integration such as those seen in schizophrenia. Recent experimental evidence
obtained using whole-head magnetoencephalography during binocular rivalry is
first reviewed. The results outline a cortical network that underlies conscious
integration in the normal brain. This network is not localized to a small part of
the brain but it is distributed over frontal, parietal, temporal, and occipital
areas. Large-scale simulations of the dynamics of thalamocortical integration are
then examined. These studies indicate that several factors can affect the rapid
integration of the activity of distributed thalamocortical regions and the
resulting behavioral performance. These simulations show that an altered dynamics
of corticothalamic and corticocortical re-entrant circuits can result from
increased conduction delays, blockade of voltage-dependent connections, reduced
synaptic density, and disruptions of the local connectivity within a single
cortical area. It can also result from alterations in the activity of diffuse
ascending systems that lead to defective reinforcement of integrated activity
patterns. Finally, the article briefly reviews theoretical measures of the
integration of multiple brain areas, such as measures of functional clustering.
These measures have been applied to PET data obtained from schizophrenic subjects
and controls while performing cognitive tasks. The results show a change in the
functional interactions among distributed brain areas in schizophrenics despite
the absence of a change in activation patterns. The possibility is raised that
disruption of re-entrant interactions among cortical areas may contribute to the
pathophysiology of schizophrenia.

Publication Types: Research Support, Non-U.S. Gov’t Review

PMID: 10719167 [PubMed – indexed for MEDLINE]

5: J Neurosci. 1999 Jul 1;19(13):5435-48.

Increased synchronization of neuromagnetic responses during conscious perception.

Srinivasan R, Russell DP, Edelman GM, Tononi G.

The Neurosciences Institute, San Diego, California 92121, USA.

In binocular rivalry, the observer views two incongruent images, one through each
eye, but is conscious of only one image at a time. The image that is perceptually
dominant alternates every few seconds. We used this phenomenon to investigate
neural correlates of conscious perception. We presented a red vertical grating to
one eye and a blue horizontal grating to the other eye, with each grating
continuously flickering at a distinct frequency (the frequency tag for that
stimulus). Steady-state magnetic fields were recorded with a 148 sensor
whole-head magnetometer while the subjects reported which grating was perceived.
The power of the steady-state magnetic field at the frequency associated with a
grating typically increased at multiple sensors when the grating was perceived.
Changes in power related to perceptual dominance, presumably reflecting local
neural synchronization, reached statistical significance at several sensors,
including some positioned over occipital, temporal, and frontal cortices. To
identify changes in synchronization between distinct brain areas that were
related to perceptual dominance, we analyzed coherence between pairs of widely
separated sensors. The results showed that when the stimulus was perceived there
was a marked increase in both interhemispheric and intrahemispheric coherence at
the stimulus frequency. This study demonstrates a direct correlation between the
conscious perception of a visual stimulus and the synchronous activity of large
populations of neocortical neurons as reflected by stimulus-evoked steady-state
neuromagnetic fields.

Publication Types: Clinical Trial Research Support, Non-U.S. Gov’t

PMID: 10377353 [PubMed – indexed for MEDLINE]

6: Science. 1998 Dec 4;282(5395):1846-51.

Consciousness and complexity.

Tononi G, Edelman GM.

Neurosciences Institute, 10640 John J. Hopkins Drive, San Diego, CA 92121, USA.
tononi@nsi.edu

Conventional approaches to understanding consciousness are generally concerned
with the contribution of specific brain areas or groups of neurons. By contrast,
it is considered here what kinds of neural processes can account for key
properties of conscious experience. Applying measures of neural integration and
complexity, together with an analysis of extensive neurological data, leads to a
testable proposal-the dynamic core hypothesis-about the properties of the neural
substrate of consciousness.

Publication Types: Research Support, Non-U.S. Gov’t Review

PMID: 9836628 [PubMed – indexed for MEDLINE]

Please note only group admins can post notices. Group members can post comments.