BOGEN'S APPROACH TO CONSCIOUSNESS: OUTLINE

(See also Bogen, ¹93, ¹95a, ¹95b, ¹97 refs shown at the end of Synopsis as well as in the recent biblio)

1. Consciousness exists, not only in ourselves but in others, including other species.

2. Consciousness is important, in the sense that:

2.1 Consciousness can be causal for behavior. (There are also occasions when it is epiphenomenal.)

2.2 It deserves, and is susceptible to, scientific study because it depends on brain. (See Why I Believe . . .) Consciousness can be usefully explored in anatomical and physiological terms, as well as by a variety of other approaches. This neurobiological approach (a la Crick & Koch) is less likely than most approaches to produce interminable argument or non-falsifiable hypotheses.

3. Consciousness has both intensity and content.

3.1 The content is represented by patterns (Pi) of neuronal activity.

3.2 Some Pi are accessible to consciousness; others are not. Those Pi which are accessible are usually accessed only transiently and fragmentarily.

3.3 The contents of consciousness are often represented by Pi in neocortex, but also elsewhere (e.g., the experiences of thirst, sweetness or shortness of breath minimally, if at all, require neocortex).

4. There are many, varied usages of "consciousness", too many for us to look for their physiology at this time. However, practically all of these usages have in common a crucial core (their commonality or intersection) which I call C. Whatever else consciousness may include, without C there is no consciousness.

5. C has four characteristics. That is, when a Pi is endowed with C (symbolized as CPi), it acquires three additional properties:

5.0 It acquires subjectivity (meaning: one experiences that Pi).

5.1 It varies in intensity (e.g., one may be highly conscious of thirst or only minimally so).

5.2 It gains greater access to other Pi. This "broadcasting" or "global workspace" (a la Baars) feature of CPi is not a defining feature; it is an empirically observable aspect of consciousness (see 9.2 below).

5.3 CPi may (or may not) influence behavior by virtue of its access to the Pj of developing motor plans.

5'. C is not characterized by language (e.g., aphasics), ordering events in time (e.g., bifrontal patients), self-image (e.g., anosognosia) or "higher" thoughts (e.g., many animals).

6. C is provided by some cerebral mechanism ,Mc. It is this mechanism which transforms Pi to CPi.

7. We are looking for Mc, not C. Trying to look at C may be like looking at the wind. We see only the effects of the wind. However, we have considerable understanding of the mechanism (often many miles away) which produces the wind. Similarly (in those entities considered conscious, i.e., that exhibit the effects of C), we can look for the mechanism which produces C.

7'. This approach, while explicitly mechanistic is not necessarily materialistic, totally deterministic or completely reductionistic (see Bogen, 1998 in refs to Synopsis). I assume only that Mc necessarily involves neural activity whose locus and nature are discoverable.

8. The how of Mc will be more readily investigated if we know the where of Mc. That is, we should find, so far as possible, the structural basis for Mc. Explaining the "how" of C (what D. Chalmers calls "the hard problem") is more likely to follow rather than precede the identification of the structural what and where of Mc.

9. Locating Mc can be guided by several considerations as follows:

9.1 Since large portions of cerebrum can be removed, as with bifrontal, bitemporal, bioccipital or biparietal infarctions, without reducing the dynamic range of C, then those brain parts are not essential to Mc, however important they may be for particular contents.

By contrast, if quite small lesions abolish consciousness (and C) their locations mark brain parts which are essential for Mc.

9.2A suitable candidate for Mc must have widespread anatomic connections, both afferent and efferent, in order to satisfy proposition 5.2. As Kinsbourne and Goodale among others have noted, the coordination of attention with complex, seemingly purposeful action does not require consciousness. Anatomic connections subserving attention/action coordination are a necessary aspect of Mc, and can help us identify likely candidates; but they also exist for mechanisms not usually associated with C (e.g., midbrain orienting responses; also, in all likelihood, the phenomenon of the alien [aka anarchic] hand.)

9.3A suitable candidate for Mc must have direct, robust efference into motor systems, in order to satisfy proposition 5.3.

10. The best candidates for Mc are the intralaminar nuclei (ILN) of each thalamus because:

10.1 Surprisingly small bimedial thalamic lesions profoundly affect consciousness if they involve the ILN.

10.2 The ILN have remarkably widespread connections, both afferent and efferent.

10.3 The ILN project heavily to striatum.

11. The conviction of volition depends upon anatomic connections actively involving some motor plan (Pj), Mc, and an observable activity change in the ILN-to-striatum projection. (See the Synopsis as well as Synopsis¹ ref. Bogen, 1997.)