University of Sussex
SethEtal_PNAS2006.pdf (71.54 kB)

Theories and measures of consciousness: an extended framework

Download (71.54 kB)
journal contribution
posted on 2023-06-07, 14:17 authored by Anil SethAnil Seth, Eugene Izhikevich, George N. Reeke, Gerald M. Edelman
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 status

  • Published


Proceedings of the National Academy of Sciences




National Academy of Sciences





Page range


Department affiliated with

  • Informatics Publications


Publisher's version available at official url. Originality: Provides a critical and constructive analysis of quantitative neurophysiological theories of consciousness. Introduces a novel measure, based on causal time series analysis, of the quantitative component of neural activity relevant to consciousness. Rigour: Provides a critical assessment of the role of quantitative measurements in theories of consciousness and develops the notion of 'complexity' in spatial, temporal, and hierarchical (recursive) senses. Includes an analytical demonstration of the insufficiency of a 'information integration', a quantitative measure proposed by a different author. Significance: Enriches the landscape of neuroscientific theories of consciousness and forcefully challenges one currently popular idea while providing an attractive, testable alternative. Impact: Listed in the PNAS 'top 50' for two months following publication (commendation received from the Editor). The paper has consistently featured among the most popular downloads from the Association for the Scientific Study of Consciousness eprints archive ( with a total of 6900 downloads to date. More generally, the paper has helped catalyze the maturation of the field of consciousness science from looking for correlations to looking for explanations. Comments: Co-authored with a Nobel laureate (Edelman); submitted to PNAS as part of his 'quota' as a member of the National Academy of Sciences.

Full text available

  • Yes

Peer reviewed?

  • Yes

Legacy Posted Date


Usage metrics

    University of Sussex (Publications)


    No categories selected


    Ref. manager