I think that whether an invertebrate "feels pain" depends not on what we mean
by "feeling", but rather on what we mean by "pain".
In human physiology, pain is described as "an _unpleasant_ sensation that is
elicited by strong tactile, thermal or other stimuli". Pain has two components:
a neurogenic (thalamic) and a psychic (cortical) one. Only the cortical compo-
nent is conscious, discriminant, and can be reasoned upon. Of course, inverte-
brates lacking a cortex cannot have this second component, so the unpleasant
requisite of our definition cannot be satisfied. No one (except perhaps a
masochist...) would argue that pain is pleasant...
Moreover, even in humans there are interventions (some lobotomies) that can
surgically eliminate the unpleasant component (suffering) of a painful
sensation, and have been used for intractable pain due to cancer or other
diseases; the patients still feels "something" where he felt pain previously,
but his sensation is vague and has no unpleasant characteristics. Since the
operation disconnects the cortex from the lower (thalamic) centers, we might
finally assume that "pain" as we mean it (i.e. an unpleasant sensation) cannot
exist without a fully functional cortex. The fact that a withdraw reflex or
even memory can be present without a cortex does not prove that the animal
feels pain: we instinctively avoid touching cold, soft and wet objects
(because they are unpleasant) yet no pain is caused by the action.
On the other hand, as someone has argued in a previous posting, we will never
know what the lobster thinks of all this... :-)
Paolo Tomasi
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Paolo Tomasi MD PhD voice: +39-79-228283
Ist. di Endocrinologia voice: +39-79-271692
Viale S. Pietro 12 fax : +39-79-228282
07100 Sassari - Italy fax : +39-79-219220
E-Mail: TOMASI at MVCHSS.CINECA.IT | Sardinia - the sun island
E-Mail: UY8SSQ21 at CINE88.CINECA.IT
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