Brain damage

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Friends,

I'm cross-posting this to the cryonet and extropians list.

I've been thinking lately about brain damage. When exactly is identity destroyed? I mean really obliterated?

Specifically, I'm wondering about the difference between loss of information, and loss of ACCESS TO information. This last attributed to the loss of higher-order function.

When a brain is damaged--I'm thinking here of strokes, traumatic injury, brain tumors, and alzheimer's--certain structural changes take place. Think of the spatial distribution of the damage.

Some of those changes presumably involve actual cell death. But how many cells die, what fraction of the whole is that, how is the damage distributed regionally/topologically, and what happens to the dead cell bodies? (I assume fully necrotic cells undergo apoptosis and "digest" themselves, the by-products being dispersed for either local or distant consumption or disposal.) What of "scar tissue" and other structural remnants?

Then too, what degree of brain damage is characterized by cell damage without cell death--membrane or cytoskeletal damage/alteration; organelle damage/reduced function--such that the cell still lives, but is not capable of supporting the coordinated global activity characteristic of normal brain function?(Does this happen, or am I describing a non-fact? I recall that mitochondria sometimes suffer gradual degradation from, at least, inherited defect.)

When a person is brain dead, is there actually a great lump of dead tissue inside the skull (I don't think so), or does the absence of brain waves--the flatline on the electroencephalograph that provokes the term "persistant vegetative state"--only suffice to imply loss of global function, but not large-scale cell death, maybe not even small-scale cell death, or (here's the crux)maybe not nearly as much information loss as we're inclined to think?

To what extent is the topology of damage responsible for disruptions of neuronal firing patterns? Could the loss of memory or personality be due not to the loss of the information, but to the inability of the organ to fire that pattern, due to a disrupted firing path. Would the accumulation of many small areas of damage, such as in the case of alzheimer's, so "damp out" the spatially dynamic, electrochemical resonance of thought--of memory and personality EXPRESSION--that the person seems to fade away? In a man-made electronic system, a simple broken wire can result in a complete system failure even though the actual structural deficit may be only an infinitesimally small fraction of all the atoms of the system, and the information deficit zero.

Are dementia et al victims really as far gone as we fear they are when we view with dismay their varying degrees of vegetative-ness? Or is the information there, but just not expressible?

Identity survival is central to cryonics. Some aspects of the (gradual) process of identity deterioration provoke an interpretation of irreversible loss. We look at them and say "They're gone." How valid is this? How subject to reevaluation?

One final detail. I'm a strong believer in the "elegant design" of natural systems. "Nature" squeezes as many uses out of any system component as she can. (Please excuse the teleological and anthropomorphic modes of expression.) Thus a local brain region with a specialized function is likely to have multiple roles. In larger scale global function--like memory or personality pattern storage and expression--it may have a supporting but not a critical role. Thus limited local damage which may cause striking loss of specific function may, as regards memory or personality, have only a mild impact. In fact, let me repeat what has been suggested before: that memory and personality may be broadly distributed across the cortex and cerebellum (and elswhere?), that such distributed expression is arguably inherently robust, and that these features strongly suggest the importance of memory and personality to the individual and the species (not to mention to cryonicists and extropians).

	   "Everything's hard till you know how to do it."
					Ray Charles				

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