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> Being No One, the Self-Model Theory of Subjectivity, by Thomas Metzinger, June 2005
lucid_dream
post Mar 12, 2006, 12:30 AM
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This is an excellent, albeit somewhat lengthy (31 pages excluding bibliography), read. Lots of speculation on neural correlates for various aspects of consciousness. Here are a few excerpts:

2.6.3. Neural correlates of the centeredness of representational space. There
are many empirical results pointing to mechanisms constituting a persisting functional
link between certain localized brain processes and the center of representational space.
These mechanisms, for instance, include the activity of the vestibular organ, the spatial
"matrix" of the body schema, visceral forms of self-representation and, in particular, the
input of a number of specific nuclei in the upper brain stem, engaged in the homeostatic
regulation of the "internal milieu" (see Parvizi and Damasio 2001, Damasio 1999,
Chapter 8; Damasio 2000). The function of these mechanisms consists in generating a
high degree of invariance and stability, by providing the system with a continuous
internal source of input. This source of input is what anchors the human self-model: The
conscious self-model characteristically differs from all other phenomenal representations
by being causally locked to this persistent functional link.


The link for the pdf is:
http://psyche.cs.monash.edu.au/symposia/metzinger/precis.pdf

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lucid_dream
post Mar 12, 2006, 12:34 AM
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2.2.4. Neural correlates of the window of presence. Very little is known in
terms of implementational details. Ernst Pöppel, in a whole series of publications, has
emphasized how certain empirically well-documented oscillatory phenomena in the brain
could serve as providing a rigid internal rhythm for internal information-processing
namely by generating "elementary integration units" (EIUs; this is Pöppel’s terminology
see Pöppel 1994, 1995, see also 1988). The generation of such EIU can be interpreted as
a process of internal data-reduction: the system deletes information about its own
physical processuality, by not defining temporal relations between elements given within
such a basal window of simultaneity. Using philosophical terminology, we might say tha
the physical temporality of the actual vehicles participating in this elementary
representational process, thereby, is not reflected on the level of their content anymore
The fine structure of physical time is now internally invisible for the system, by
becoming transparent (see BNO, section 3.2.7 and Section 2.3 below).
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lucid_dream
post Mar 12, 2006, 12:36 AM
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2.1.4. Neural correlates of global integrational functions. Currently no detailed
theories concerning the possible neural correlates, in particular of the minimally sufficient
correlate (Chalmers 2000), for the appearance of a coherent, conscious model of the
world do exist. However, there are a number of interesting speculative hypotheses.
A first core intuition has been to study the mechanism of action common to
different anaesthetics, that is, to study the conditions under which phenomenal experience
as a whole disappears and re-emerges (for further references and a recent discussion of
the potential role of the NMDA-receptor-complex in achieving large-scale integrations of
ongoing activity, see Flohr 2000, Franks and Lieb 2000, Hardcastle 2000, and Andrade
2000).
A second important insight is that the globality-constraint applies to two
fundamentally different classes of phenomenal states: to dreams (see BNO, Section 4.2.5)
and to waking states. In dreams, as well as during ordinary waking phases, the system
operates under one single, more or less coherent world-model while its global functional
properties differ greatly. Rodolfo Llinás and his co-workers have long emphasized that
one of the most fruitful strategies in searching for the NCC will be in "subtracting"
certain global properties of the waking world-model from the dreaming world-model,
thereby arriving at a common neurophysiological denominator or at global functional
states which are basically equivalent between phenomenal experience during REM-sleep
and waking (Llinás and Paré 1991, p. 522 pp.). The intuition behind this neuroscientific
research program carries a distinct philosophical flavor: What we call waking life is a
form of "online dreaming". If there is a common functional core to both global state-
classes, then conscious waking would then be just a dreamlike state that is currently
modulated by the constraints produced by specific sensory input (Llinás and Ribary 1993,
1994; Llinás and Paré 1991). A specific candidate for a global integrational function
offered by Llinás and colleagues is a rostrocaudal 12-ms phase shift of 40-Hz-activity
related to synchronous activity in the thalamocortical system, modulated by the brain
stem (the most detailed presentation of Llinás’ thalamocortical model can be found in
Llinás and Paré 1991, p. 531; see also Llinás and Ribary 1992; Llinás, Ribary, Joliot and
Wang 1994; Llinás and Ribary 1998; Llinás, Ribary, Contreras and Pedroarena 1998).
The strategy of approaching the globality-constraint by researching globally
coherent states (as initially proposed in Metzinger 1995b) leads to a new way of defining
research targets in computational neuroscience (e.g., von der Malsburg 1997). However,
it must be noted that what is actually needed is a theoretical model that allows us to find
global neural properties exhibiting a high degree of integration and differentiation at the
same time. The neural correlate of the global, conscious model of the world must be a
distributed process which can be described as the realization of a functional cluster,
combining a high internal correlation strength between its elements with the existence of
distinct functional borders. This cluster directly corresponds to the distinct causal role
mentioned above. Edelman and Tononi have called this the "dynamic core hypothesis"
(see Tononi and Edelman 1998a,b; Edelman and Tononi 2000a, Tononi 2003; for a
comprehensive popular account see Edelman and Tononi 2000b). The hypothesis states
that any group of neurons can contribute directly to conscious experience only if it is part
of a distributed functional cluster that, through reentrant interactions in the
thalamocortical system, achieves high integration in hundreds of milliseconds. At the
same time it is essential that this functional cluster possesses high values of complexity.
Converging evidence seems to point towards a picture in which large-scale integration is
mediated by the transient formation of dynamical links through neural synchrony over
multiple frequency bands (Varela, Lachaux, Rodriguez, and Martinerie 2001, Singer
2004).
This way of looking at the globality-constraint on the neural level is
philosophically interesting for a number of reasons. First, it makes the prediction that any
system operating under a conscious model of reality will be characterized by the
existence of one single area of maximal causal density within its information-processing
mechanisms. To have an integrated, globally coherent model of the world means to create
a global functional cluster, i.e., an island of maximal causal density within one’s own
representational system. Philosophical functionalists will like this approach, because it
offers a specific and global functional property (a "vehicle property") that might
correspond to the global phenomenal property of the unity of consciousness. In short,
what you subjectively experience upon experiencing your world as coherent is the high
internal correlation strength between a subset of physical events in your own brain.
Second, it is interesting to note how the large group of neurons constituting the dynamical
core in the brain of an organism currently enjoying an integrated conscious model of
reality will very likely be different at every single instant. The physical composition of
the core state will change from millisecond to millisecond. At any given point in time
there will be one global, minimally sufficient neural correlate of consciousness, but at the
next instant this correlate will already have changed, because the consciousness cluster
only constitutes a functional border which can easily transgress anatomical boundaries
from moment to moment. Third, it has to be noted that the informational content of the
dynamical core is determined to a much higher degree by internal information already
active in the system than by external stimuli. Just as in the Llinás-model, an overall
picture emerges of the conscious model of reality essentially being an internal construct,
which is only perturbed by external events forcing it to settle into ever-new stable states.
In short, there may be many functional bundles - individual and episodically
indivisible, integrated neural processes - within a system, and typically there will be one
single, largest island of maximal causal density underlying the current conscious model
of the world. "Indivisible" here means that although one could, from a third-person
perspective, still find causal divisions and a fine-structure characterizing the events
causally integrated by such a process. For a certain period of time, they would be
indivisible for the system, in which they occur, because the sheer dynamical coherence of
these bundles would be something which the system, using its own resources of causal
interaction, could not dissolve. Still, the philosophical question remains of what it is that
makes this cluster into the subjective world the organism lives in. It is plausible to assume
that at any given time this typically is the largest functional cluster (for a dissenting view,
see Zeki and Bartels 1998). Nevertheless, the question remains how such a cluster
becomes tied to an individual first-person perspective, to a representation of the system
itself, and thereby becomes a truly subjective global model of reality (see the
perspectivalness-constraint in BNO, Section 3.2.6 and Chapter 6; plus Section 4 below).
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lucid_dream
post Mar 12, 2006, 12:41 AM
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2.4.3. Neural correlates of convolved holism. Once again, we have to admit that
not enough empirical data are currently available, in order to be able to make any precise
statements (but see Singer 2000, 2004, 2005; Varela, Lachaux, Rodriguez and Martinerie
2001).
In an earlier publication (Metzinger 1995b), I proposed the necessity for a
subsymbolic and global integrational function that fulfils two conditions. First, that
function would have to achieve global integration of representational contents active in
the brain without causing a "superposition catastrophe", i.e., without causing
interferences, misassociations and the mutual deletion of different representational
patterns. Let us assume for a moment that the correct neurobiological theory describing
the mechanism of integration, would explain it in terms of the temporal coherence of
neural responses established through synchronous firing. Then the situation to be avoided
would correspond to states of global synchrony as in epilepsy or deep sleep. In these
states all conscious experience is typically absent. Therefore, what is needed is a function
achieving a dynamical and global form of metarepresentation by functional integration,
not simply deleting or "glossing over" all the lower-order contents, but preserving its
differentiated structure. Second, the holism-producing mechanism should be conceivable
as selectively operating at different levels of granularity. Therefore, what is needed to
establish a differentiated type of large-scale coherence on the level of the brain itself will
not be uniform synchrony, but dynamic, specific cross-system relations binding subsets
of signals in different modalities and using different frequency bands at the same time
(see Engel and Singer 2000; Singer 2004, 2005).
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