Temporal Summation (Additive Properties) of Pain

Temporal Summation of Pain” is just a fancy and scientifically specific way of saying that repeated pain is additive: after we’ve been whacked once, another hit in the same spot hurts more; If we get hit there over and over, we start cringing because it hurts more and more.

Evoked Temporal Summation in Cats to Highlight Central Sensitization Related to Osteoarthritis-Associated Chronic Pain: A Preliminary Study – Free full-text PMC4032234 – PLoS One. 2014 May

In cats, osteoarthritis causes significant chronic pain.

Chronicity of pain is associated with changes in the central nervous system related to central sensitization, which have to be quantified. 

Our objectives were:

1) to develop a quantitative sensory testing device in cats for applying repetitive mechanical stimuli that would evoke temporal summation;

2) to determine the sensitivity of this test to osteoarthritis-associated pain, and

3) to examine the possible correlation between the quantitative sensory testing and assessment using other pain evaluation methods

We hypothesized that mechanical sub-threshold repetitive stimuli would evoke temporal summation, and that cats with osteoarthritis would show a faster response.

A blinded longitudinal study was performed in 4 non-osteoarthritis cats and 10 cats with naturally occurring osteoarthritis. Quantification of chronic osteoarthritis pain-related disability was performed over a two week period using peak vertical force kinetic measurement, motor activity intensity assessment and von Frey anesthesiometer-induced paw withdrawal threshold testing

The cats afflicted with osteoarthritis demonstrated characteristic findings consistent with osteoarthritis-associated chronic pain. After a 14-day acclimation period, repetitive mechanical sub-threshold stimuli were applied using a purpose-developed device

Four stimulation profiles of predetermined intensity, duration and time interval were applied randomly four times during a four-day period. The stimulation profiles were different (P<0.001): the higher the intensity of the stimulus, the sooner it produced a consistent painful response.

The cats afflicted with osteoarthritis responded more rapidly than cats osteoarthritis free (P = 0.019).

There was a positive correlation between the von Frey anesthesiometer-induced paw withdrawal threshold and the response to stimulation profiles #2 (2N/0.4 Hz) and #4 (2N/0.4 Hz): Rhos = 0.64 (P = 0.01) and 0.63 (P = 0.02) respectively.

This study is the first report of mechanical temporal summation in awake cats.

Our results suggest that central sensitization develops in cats with naturally occurring osteoarthritis, providing an opportunity to improve translational research in osteoarthritis-associated chronic pain.

In humans, our increasingly strong reactions to repeated (or continuing) pain are often considered a sign of “catastrophizing” – making our pain worse by our attitude toward it.

The good news: the purely physical chronic pain of osteoarthritis alone, stripped of any social or psychological factors humans might involve, leads to central sensitization (and hyperalgesia).

This proves that “catastrophizing”, which cats cannot do, is in no way responsible for the transition from chronic physical pain to the hyperalgesia of central sensitization.


Below is another article on the temporal summation of pain, pointing out that this, too, is not a standard value even for pain-free people.

Temporal Summation of Second Pain: Variability in Responses to a Fixed Protocol Free full-text PMC3502719 – 2012 Aug

Background

Temporal summation of second pain (TSSP) is relevant for the study of central sensitization, and refers to increased pain evoked by repetitive stimuli at a constant intensity.

While the literature reports on participants whose pain ratings increase with successive stimuli, response to a TSSP protocol can be variable.

The aim of this study was to characterize the full range of responses to a TSSP protocol in pain-free adults.

Method

312 adults received a train of brief, repetitive heat stimuli at a fixed temperature and rated the intensity of second pain after each pulse.

TSSP response (Δ in pain ratings) was quantified using the most common methods in the literature, and response groups were formed:

  • TSSP (Δ>0),
  • no change (Δ=0), and
  • temporal decrease in second pain (TDSP) (Δ<0).

A cluster analysis was performed on the Δ values to empirically derive response groups.

Results

Depending on how TSSP response was quantified,

  • 61 – 72% of the sample demonstrated TSSP,
  • 11 – 28% had no change in pain ratings, and
  • 0 – 20% demonstrated TDSP.

The cluster analysis found that the

  • majority (59%) of participants fell in the no change cluster,
  • 29% clustered into the TSSP group, and1
  • 2% in the TDSP cluster.

Conclusions

Using a fixed thermal paradigm, pain-free adults exhibit substantial variability in response to a TSSP protocol not well characterized by group-mean slopes.

Studies are needed to determine TSSP response patterns in clinical samples, identify predictors of response, and determine the clinical implications of response variability.

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