When one looks at the science of pain, especially at what has happened since the publications of Melzack and Wall's (1965) and Melzack and Casey's (1968), which revolutionized the scientific research on pain, we see that the science of pain has increasingly conceived of pain as less like perception of an objective reality and more like emotions by first drawing the sensory/affective distinction and then emphasizing more and more its affective aspect.
The trend in philosophy, on the other hand, has been in the other direction: as naturalism has started to become an orthodoxy in the second part of the 20th century, philosophers have increasingly sought for ways in which they could assimilate pain to ordinary perception like vision, audition, etc.
One of the main motivations behind the perceptual/representational views of pain in philosophy is the belief (or hope) that perception as a species of information gathering can be accounted for entirely in physicality terms.
Of course, this is a controversial claim.
There are many who think that perception involving as it does conscious phenomenal experience cannot be a purely physical phenomenon. However, even these theorists may agree that it is a plausible theoretical strategy to pursue an understanding of pain and other intransitive bodily sensations in perceptual/representational terms.
This strategy, if it works, minimizes the diversity of mental phenomena, and thus potentially offers the prospects of a more unified theory of mind.
If this theory turns out to be in harmony with the rest of our sciences and their fundamental metaphysical and methodological assumptions, so much the better.
Indeed, it was the plausibility of this strategy and the belief that we will eventually succeed in understanding perception in purely naturalistic terms that have prompted many philosophers to advance perceptual/representational theories of pain.
But does the scientific trend towards understanding pain as a subjective experience less like a perception and more like an emotion with quite a variable link to injurious stimuli undermine the philosophical project?
Nothing in the scientific understanding of pain itself seems to show that pain involves no perception at all.
On the contrary, as the science of pain has unearthed in the last forty years or so, there are physiologically specialized systems that process nociceptive stimuli from the moment they effect peripheral receptors to the central processing of these signals in the spinal cord and the brain. This is what happens in all classical five sense modalities, including touch. Indeed, pain may be classified as a submodality of touch.
If we take the weaker claim to the effect that feeling pain involves sensory perception but doesn't exhaust its nature due to its affective dimension, we may still preserve a naturalistic view of pain by giving a functionalist (or, psychofunctionalist) account of its affective aspect.
According to this proposal, even though the sensory-discriminative aspect of pain can perhaps be handled representationally, the affective aspect reduces to the way in which the sensory-discriminative information is processed, not for analysis to extract information about the proximal or distal properties of the stimuli, but rather for its significance for the effector or motor systems, to set motivational parameters for action on the basis of stimuli's informational content.
There is in fact strong supporting evidence for such a thesis in the evolutionary stories of different organisms at different developmental hierarchies. The neuroscientific evidence about the affective brain seems also to support this idea in general.
This is a view that treats pain as both a representational and a functional state.
Such a view still needs to provide a good answer to the problem of focus that we have seen afflicts all perceptual/representationalist views.
Why is there an asymmetry in concept application, or in the focus of conceptual categorization? There are other philosophical as well as scientific questions about pain.
Do animals feel pain?
If they do, is it comparable to the way we feel pain?
What are the social, economical, ethical and religious implications of affirmative answers to these questions?
How can animal pain be scientifically studied?
What should be the methodology of scientific research on animals in general and of animal pain in particular?
How can we project the results obtained by pain research on animals onto humans?
Parallel or similar questions arise in the case of fetuses and young infants that are even more pressing and urgent for obvious reasons.
What is the relationship between pain and pleasure, or pain and emotions in general?
What are the ethical and religious status and implications of pain? These and many other questions remain to be the focus of many researchers in the field.