Phantoms of Pain

One of the more interesting lessons from modern neuroscience and psychology is, I think, the idea that we don’t perceive reality as much as we create it. By this I don’t mean that there is no real reality and that “it’s all in our heads, man” but rather that we get incoming sensory data through our eyes, ears, nose, etc. and our brain then assembles that data into something we can subjectively experience. Of course, sometimes the assembly isn’t perfect—that’s what hallucinations, tricks of light, etc. are.

I was thinking about how certain kinds of pain are perceived differently than most perceptions. With most perceptions we can kind of check one sensory organ’s take on things by comparing it with another. For example, I hear an owl and look up and, yep, there’s an owl. My sight backs up my hearing. Or I see a coffee cup and reach out and grab it. My touch backs up my sight.

With certain kinds of pain, however, this isn’t possible. I feel some internal pain and… well I can’t “double-check” whether it’s real in any way (aside from going to the doctor and having him do an x-ray or something but even that is no guarantee. And the pain is likely gone by that point.) Internal aches and pains are sort of floaty sensations that come and go on a whim. It’s hard to validate them.

Thus I wonder if many of these pains are hallucinatory in some sense. I recall an article in the New York Review of Books where the author reported getting a call from his doctor that he might have cancer in his ribs. As he waited a few days for confirmation, he started to feel pain in his ribs. As it turned out, he didn’t have cancer. That pain seemingly was created by his brain based on the possibility that he had cancer.

At the site Slate Star Codex, a related observation is made.

I’ve been focusing a lot lately on the idea of the Bayesian brain and its input channels. Some input channels, like vision, are high-bandwidth; we get so much data about the real world that (optical illusions and PARIS IN THE THE SPRINGTIME signs aside) we usually see pretty much what is really there.
Other channels, like pain, are low bandwidth. This is why the placebo effect works – we get so little data about how much pain is coming from different parts of our bodies that even our strongest percepts are wild guesses, where we fill in the gaps with predictions and smooth away conflicting evidence. If our predictions change – ie we know we just got morphine and morphine lowers pain – then the brain will happily change its guesses. This would never happen with vision – I can’t use the placebo effect to make you think an orange crayon is blue – but pain is low-bandwidth enough that it works.

This would also seem to tie in with V.S. Ramachandran’s treatment for phantom limb pain.

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