Crick and Koch: A framework with many unknowns

A commentary of “A framework for consciousness” by Francis Crick and Christof Koch

The paper by Crick and Koch presents their updated perspective on the brain in relation to consciousness. It may let us gauge what we do not yet know, as much as calling attention to some specific proposals.

Let me illustrate. The paper raised two questions in my mind.

1. What kind of threshold?

According to the authors, neural activity in a “coalition” of neurons must cross a threshold to reach consciousness. In effect, the neural problem of consciousness proper — as opposed to various supporting and ancillary conditions shared with other neural activity — has been reduced to the circumstances surrounding A salutary reminder of the current limits to our knowledge regarding neural mechanisms of consciousness. this hypothetical threshold. The fact that the authors are unable to specify either the type of neural activity that must cross the threshold nor the difference made in neural terms by having crossed, is a salutary reminder of the current limits to our knowledge regarding neural mechanisms of consciousness.

The crucial circumstance appears to be neither coalition membership as such — since coalitions are apparently similar whether they end up capturing consciousness or not — nor is it necessarily attended by the capture of behavior — since what the authors call “zombie modes” provide non-conscious routes to behavior. The threshold a winning coalition must cross is unspecified, so far.

To extend the political analogy used by the authors, one result of electoral victory is to give the leader of the winning coalition occupancy of the White House. Are there any neural analogs of “the White House” for consciousness? We are told only that it definitely is not a “house” (i.e. a place “where it all comes together”), nor is it a “flag” of oscillatory activity — at least not of the 40 Hz variety previously proposed in this role. Hence the question: “what is the threshold of consciousness a threshold of, in neural terms?”

2. Anatomy

One use of a well-framed hypothesis regarding neural mechanisms of consciousness would be to constrain the range of anatomical systems involved. In their “cortical system” the authors include closely associated structures such as the thalamus, the claustrum, “and probably the basal ganglia, the cerebellum and the many widespread brainstem projection systems.” This is a wide range of diverse structures, indeed, yet the arguments that follow are framed almost exclusively in terms of the cerebral cortex itself, with passing references to the thalamus.

One would like to know, therefore, whether any part of the brain besides the thalamocortical complex plays an obligatory role in implementing consciousness (beyond that of supplying tonic “enabling functions”). To turn this question into one with testable implications, let the “thalamocortical complex” Does any part of the brain besides the thalamocortical complex play an obligatory role in implementing consciousness? include the cerebral cortex, the claustrum, the dorsal thalamus and the thalamic reticular nucleus, and let that complex be supplied with normal input including the tonic global inputs that normally support waking consciousness. Under these circumstances is a change in the contents of consciousness from one object to another causally dependent on change in any part of the brain outside of the thalamocortical complex?

© 2003 B. Merker

Author Information

Dr. Bjorn Merker
Department of Psychology
Uppsala University
SE-75142 Uppsala, Sweden
E-mail: gyr694c@tninet.se

References

1. A framework for consciousness Francis Crick & Christof Koch, Nature Neuroscience, February 2003 Volume 6 Number 2 pp 119 – 126. Abstract: Here we summarize our present approach to the problem of consciousness. After an introduction outlining our general strategy, we describe what is meant by the term ‘framework’ and set it out under ten headings. This framework offers a coherent scheme for explaining the neural correlates of (visual) consciousness in terms of competing cellular assemblies. Most of the ideas we favor have been suggested before, but their combination is original. We also outline some general experimental approaches to the problem and, finally, acknowledge some relevant aspects of the brain that have been left out of the proposed framework.