Every time I do a post on ANYTHING concerning space, I have to reference this:
Also, I have to put in a plug for Mary Roach's Packing for Mars, which is the weird science of space. It's awesome. There's POOP in space, you guys.
Anyway. Gravity, or the lack thereof, changes a lot of things about the way we live. How hard our hearts work, our bone and muscle conditioning, changes in hormones, not to mention the motion sickness. But the question here was...what about pain? Conditions which simulate microgravity may affect cognitive function (though results on whether it actually does are mixed), and this may in turn affect how we process things like pain.
And how do you study something like this? Put a bunch of guys in beds, and point their heads at the floor.
Spironelli and Angrilli. "Influence of Body Position on Cortical Pain-Related Somatosensory Processing: An ERP Study" PLoS ONE, 2011.
What they used here was something called head-down bed rest, or sometimes head-tilt bed rest. You make someone lie down and position them with their head 6 degrees below flat. It's not much of an angle, but it actually simulates some of the conditions of microgravity very well. Some studies have people in this position for WEEKS at a time (don't worry, well paid and I hope they bring you lots of books), but this one only had them in it for about two hours.
They had them head down, and then they tested their pain threshold compared to people who were just sitting around. I've been in a pain study before. This one appears to be a bit milder than the one I was in, the pain episodes look a lot shorter. They attached a gold electrode to the inside of the patients' wrists (all the patients for this study were dudes, by the way). They put recording electrode on the outside of their heads, to record the activity in the brain during stimulation. They then started administering mild electric shocks to the wrist, starting so low they couldn't be felt, and heading up to detect the point at which they started to hurt.
When they compared the control group with the head down bed rest, they looked at how the activity in the brain (measured by the recording electrodes) compared when the participants got shocks that were just BELOW pain threshold (nah, doesn't hurt), AT pain threshold (ok, yeah, I guess it hurts), and just ABOVE pain threshold (definitely stings a little).
What they found was that controls showed distinct regional changes in the right and left hemispheres of the brain when their wrists were stimulated. The bed rest guys, on the other hand, showed smaller changes in cortical response. They also showed a delay in response in the first place. So it looks like the sensory processing of pain may be disrupted in this model of microgravity.
Unfortunately, they didn't check how SENSITIVE the guys were to pain. I'd be really interested to see if the guys got more or less sensitive to pain by their own measures when they were sitting up vs lying down.
But it does make me wonder. This was only TWO HOURS of head down tilt and they saw significant effects. Would it go away, or get more severe, with prolonged head tilt? Does this affect how people EXPERIENCE the pain? If it does, this could have effects both on people in space (maybe they feel less pain), as well as people on chronic bed rest, who might under report a pain state. It's definitely an interesting thought, but I think it'd have to wait until we can tell how people's EXPERIENCE of the pain differs.
In the meantime though. PAIN. IN. SPAAAAAAAAACE.
Spironelli, C., & Angrilli, A. (2011). Influence of Body Position on Cortical Pain-Related Somatosensory Processing: An ERP Study PLoS ONE, 6 (9) DOI: 10.1371/journal.pone.0024932