From: Elizaphanian (elizaphanian@tiscali.co.uk)
Date: Fri May 30 2003 - 11:21:25 BST
Hi Johnny, Phyllis, all interested in the hot stove example,
I've mentioned Antonio Damasio on this list before, especially with regard to emotions (his analysis
is a large part of what lies behind my 'eudaimonic' thesis). I thought this extract from his "The
feeling of what happens" would be of interest, as it is the description of a reaction to a hot stove
situation by one of the academic world's foremost neurologists. The passage is from pp 72-73 of my
copy, published by Heinemann, 2000.
"Pain does not qualify for emotion, either. Pain is the consequence of a state of local dysfunction
in a living tissue, the consequence of a stimulus -- impending or actual tissue damage -- which
causes the sensation of pain but also causes regulatory responses such as reflexes and may also
induce emotions on its own. In other words, emotions can be caused by the same stimulus that causes
pain, but they are a different result from that same cause. Subsequently, we can come to know that
we have pain and that we are having an emotion associated with it, provided there is consciousness.
When you picked up that hot plate the other day and burned the skin of your fingers, you had pain
and might even have suffered from having it. Here is what happened to you, in the simplest
neurobiological terms:
First, the heat activated a large number of thin and unmyelinated nerve fibres, known as C-fibres,
available near the burn. (These fibres, which are distributed literally everywhere in the body, are
evolutionarily old and are largely dedicated to carrying signals about internal body states,
including those that will end up causing pain. They are called unmyelinated because they lack the
insulating sheath known as myelin. Lightly myelinated fibres known as A-δ fibres travel along with
C-fibres and perform a similar role. Together they are called nociceptive because they respond to
stimuli that are potentially or actually damaging to living tissues.)
Second, the heat destroyed several thousand skin cells, and the destruction released a number of
chemical substances in the area.
Third, several classes of white blood cell concerned with repairing tissue damage were called to the
area, the call having come from some of the released chemicals (e.g. a peptide known as substance P
and ions such as potassium).
Fourth, several of those chemicals activated nerve fibres on their own, joining their signaling
voices to that of the heat itself.
Once the activation wave was started in the nerve fibres, it traveled to the spinal cord and a chain
of signals was produced across several neurons (a neuron is a nerve cell) and several synapses (a
synapse is the point where two neurons connect and transmit signals) along the appropriate pathways.
The signals went all the way into the top levels of the nervous system: the brain stem, the
thalamus, and even the cerebral cortex.
What happened as a result of the succession of signals? Ensembles of neurons located at several
levels of the nervous system were temporarily activated and the activation produced a neural
pattern, a sort of map of the signals related to the injury in your fingers. The central nervous
system was now in possession of multiple and varied neural patterns of tissue damage selected
according to the biological specifications of your nervous system and of the body proper with which
it connects. The conditions needed to generate a sensation of pain had been met.
The question that I am leading to arrives at this point: would one or all of those neural patterns
of injured tissue be the same thing as knowing that you had pain? And the answer is, not really.
Knowing that you have pain requires something else that occurs after the neural patterns that
correspond to the substratum of pain -- the nociceptive signals -- are displayed in the appropriate
areas of the brain stem, thalamus, and cerebral cortex and generate an image of pain, a feeling of
pain. But note that the "after" process to which I am referring is not beyond the brain, it is very
much in the brain and, as far as I can fathom, is just as biophysical as the process that came
before. Specifically, in the example above, it is a process that interrelates neural patterns of
tissue damage with the neural patterns that stand for you, such that yet another neural pattern can
arise -- the neural pattern of you knowing, which is just another name for consciousness. If the
latter interrelating process does not take place, you will never know that there was tissue damage
in your organism -- if there is no you and there is no knowing, there is no way for you to know,
right?
Curiously, if there had been no you, ie, if you were not conscious and if there had been no self and
no knowing relative to hot plates and burning fingers, the wealthy machinery of your self-less brain
would still have used the nociceptive neural patterns generated by tissue damage to produce a number
of useful responses. For instance, the organism would have been able to withdraw the arm and hand
from the source of heat within hundreds of milliseconds of the beginning of tissue damage, a reflex
process mediated by the central nervous system. But notice that in the previous sentence I said
"organism" rather than "you". Without knowing and self, it would not have been quite "you"
withdrawing the arm. Under those circumstances the reflex would belong to the organism but not
necessarily to "you". Moreover, a number of emotional responses would be engaged automatically,
producing changes in facial expression and posture, along with changes in heart rate and control of
blood circulation -- we do not learn to wince with pain, we just wince. Although all of these
responses, simple and not so simple, occur reliably in comparable situations in all conscious human
beings, consciousness is not needed at all for the responses to take place."
Lots of comments could be made, but I'll save them for another post (I'm working on several!!)
Sam
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