Consciousness studies

This is 1) to make it look like I'm working on blog updates more often than I actually am, and 2) for the one or two people who may possibly be interested in uber-complex high-range theories of consciousness. This is all just copied from an e-mail I sent to a friend, trying to give him a very basic intro to some all-encompassing theories of consciousness prevalent in the science community. :)

I've read a lot of these things, but I certainly haven't read all of them--especially some of the longer, more technical papers.

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In 2001, Daniel Dennett had a paper in Cognition, "Are We Explaining Consciousness Yet?". The whole thing is pretty technical, and if you don't know anything about Global Workspace theory (or, as Dennett calls it, "global neuronal workspace model of consciousness"), you'd need to get caught up on that first. The Wiki article could probably suffice for that. Quoting a little bit from it:

Conversely, conscious perception is believed to require more sustained, reverberatory neural activity, most likely via global feedback from frontal regions of neocortex back to sensory cortical areas (Crick and Koch, 1995) that builds up over time until it exceeds a critical threshold. At this point, the sustained neural activity rapidly propagates to parietal, prefrontal and anterior cingulate cortical regions, thalamus, claustrum and related structures that support short-term memory, multi-modality integration, planning, speech, and other processes intimately related to consciousness. Competition prevents more than one or a very small number of percepts to be simultaneously and actively represented. (see Baars 1988, Dehaene et al. 2003)

Bernard Baars is the main creator of this theory--I think this is a slightly technical summary of some of its main ideas...

Shit, I guess if you want to take a step backwards before getting into some of the more technical things, you could do Chalmers' What Is a Neural Correlate of Consciousness? (2000).

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Gerald Edelman is also pretty big figure in these areas... I think he's the one who came up with the term "neural Darwinism", which Dennett has also worked with. You should read up a bit about him. I've only read one paper of his, but it had some cool stuff: Naturalizing Consciousness (2003). Here's a little section:

Higher-order consciousness emerges later in evolution and is seen in animals with semantic capabilities such as chimpanzees. It is present in its richest form in the human species, which is unique in possessing true language made up of syntax and semantics. Higher-order consciousness allows its possessors to go beyond the limits of the remembered present of primary consciousness. An individual's past history, future plans, and consciousness of being conscious all become accessible. Given the constitutive role of linguistic tokens, the temporal dependence of consciousness on present inputs is no longer limiting. Nevertheless, the neural activity underlying primary consciousness must still be present in animals with higher-order consciousness.

With these distinctions in hand, we may consider how the neural mechanisms underlying primary consciousness arose and were maintained during evolution. The proposal is as follows. At some time around the divergence of reptiles into mammals and then into birds, the embryological development of large numbers of new reciprocal connections allowed rich reentrant activity to take place between the more posterior brain systems carrying out perceptual categorization and the more frontally located systems responsible for value-category memory (Fig. 1). This reentrant activity provided the neural basis for integration of a scene with all of its entailed qualia. The ability of an animal so equipped to discriminatively relate a present complex scene to its own unique previous history of learning conferred an adaptive evolutionary advantage. At much later evolutionary epochs, further reentrant circuits appeared that linked semantic and linguistic performance to categorical and conceptual memory systems. This development enabled the emergence of higher-order consciousness.

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I really don't know how valid these ideas are in the big scheme of things, but it was really interesting reading Sevush's Single-neuron theory of consciousness (2006). If his overall theory isn't very valid, he at least probably introduced some awesome smaller insights from the perspective. I know one of the main hypotheses is that the left lateral preforntal cortex is like... the highest-level seat of consciousness that exists in the brain.

The first question is whether the left lateral PFC is appropriately positioned to be the recipient of afferent connections pertaining to each of the sensory, emotional, and mnemonic components that comprise VR-conscious experience. This possibility is often dismissed summarily, but without accompanying analysis (e.g., see Dahaene et al. (1998)). Yet a review of the neuroanatomical literature suggests that the idea of a convergence zone should not be so casually disregarded. It has been suggested, for example, that the PFC as a whole functions as a convergence zone, receiving input from most other brain regions (Nauta, 1971; Miller and Cohen, 2001; Elston, 2003). Since PFC subregions are strongly interconnected (Barbas and Pandya, 1989), any one PFC subregion could be capable of serving as a convergence target for all the other PFC subregions. In the single-neuron theory, it is the left lateral PFC that is assumed to serve as the final convergence area for the sensory, emotional, and mnemonic components of VR-consciousness. Evidence in support of this contention is available for each of these components.

And it's certainly testable:

To begin with, the single-neuron theory makes the anatomical prediction that pyramidal neurons will be found in the left lateral PFC that are individually the recipients of convergent axonal input derived from brain regions considered to be involved in the processing of the sensory, mnemonic, and emotional stimuli that compose VR-conscious content. In addition, the theory makes the electrophysiologic prediction that left lateral PFC neurons will be found that respond in single-cell recording experiments to combinations of stimuli that typically comprise VR-conscious experience. As noted above, direct single-cell recordings have already identified neurons in lateral PFC that respond selectively to conjoint visual and auditory stimuli (Aou et al. 1983), to conjoint visual, auditory and tactile stimuli (Tanila et al. 1992), and to conjoint object and location features (Rao et al. 1997). The question is whether lateral PFC neurons exist that respond to conjoint input from the full complement of sensory, emotional, and mnemonic stimuli that comprise VR-conscious experience. The demonstration of the existence of neurons that are suitably anatomically and electrophysiologically convergent, while expected with the single-neuron theory, would be difficult to justify within the network NCC framework. Alternatively, the failure to identify such neurons despite a concerted effort to do so would militate against the single-neuron theory and favor the network approach.

He mentions a couple of other people who are involved in similar research: "Bieberich (2002) has proposed a 'recurrent fractal neural network' model in which information at the network level is reflected at the single neuron level". I haven't even read this one yet, but this is another major paper I just got that uses a lot of these ideas: Is Consciousness Only a Property of Individual Cells? (Edwards 2005)