Negative Affectivity, Depression, and Resting HRV as Possible Moderators of Endogenous Pain Modulation in.., 2018, Van den Bergh et al

My paradigm for countering irritation is to walk away from this thread and go and have breakfast.

 

My levels of negative affectivity (NA) are at the highest when I read such BS.

 

Nope, my paradigm is inadequate, I'm still irritated.

 

Have some more breakfast.

 

Whenever I read FSS I just see FFS instead

 

That would be evidence for PEM, and hence perhaps not so surprising.

 

Yes, I wasn't sure I understood that, as I've only read the abstract, but that thought occurred to me too - if ME patients had delayed pain following the painful stimulus, unlike healthy controls, that seems to imply some sort of biological delayed recovery process, maybe like PEM.

Although I dismissed this trial because of the psychosomatic assumptions they thought they were testing, it may actually have value in that it helps to disprove those psychosomatic assumptions, and comes up with an unexpected (to them) difference not explained by their BPS assumptions. Maybe it's another small nail in the BPS coffin.

 

So for the baseline pain tolerance (electric shocks to the ankle and selection of an intensity for use later in the experiment) - there was no difference between patients and controls. Which suggests pain thresholds aren't different.

For the difference in the rating of the ankle electric shocks 1. before the application of a cold pack to the arm (Phase 1) and 2. after the application of the cold pack (Phase 2), there was no difference between patients and controls. This comparison was supposed to show that patients are less able to be distracted by another stimulus. But it didn't. In actual fact, neither patients nor controls showed the distraction effect. It's possible that this was because of a flaw in the design of the trial that had the subjects focusing on the pain after each shock to rate it, rather than rating at the end of each phase as has been done in other studies.

The one difference they did find was in Phase 3, after the removal of the cold pack. Patients found the ankle electric shocks a little bit more painful in this phase than they had in the other two phases while the controls didn't. But, it wasn't a big difference, so it's probably not worth getting very creative with an explanation unless it was replicated. Maybe the patients were just starting to get a bit fed up with the long series of experiments and questionnaires.

I'm surprised the researchers didn't make more of the fact that around half of the patients were taking some sort of analgesic. They did some comparisons of patients with and without analgesics- but it's not completely clear what they were comparing. They refer to comparisons of the ratings of the pain. So, it doesn't sound as if they compared the choice of the shock intensity at the beginning of the study between patients taking analgesics and those who did not, which would have been helpful in drawing conclusions about the patients' pain thresholds.

I find it an expression of the researchers' arrogance that people with fibromyalgia and people with CFS were all lumped together as the patient cohort. As in 'oh yes, all you people - it really doesn't matter that you have quite different symptoms because they are all equally imaginary'. At the very least, I would have thought the researchers would have been interested to do analyses of the group of people who rate pain as their most troublesome symptom and the group of people who rate PEM as their most troublesome symptom.

But it doesn't matter in the end, because this study really didn't tell us very much. Unfortunately, I doubt this is going to stop researchers continuing to give sick people electric shocks while suggesting that their pain control mechanisms are inferior.

 

In the third phase, after the cold pack was taken away, patients rated the electric shocks to the ankle as, on average, a bit more painful, even though the electric shocks were the same intensity throughout. So, they weren't actually rating the pain of the cold pack. The researchers were expecting that during the Phase 2, healthy people would be distracted by the cold pack and rate the ankle pain lower than in Phase 1 and Phase 3 (which didn't happen).

You are so right, that is my experience. So conceivably the reason the ratings of the ankle pain went up in Phase 3 for patients was that, on average, after nearly 2 hours of the study including dealing with pain, they were exhausted.