Temporal summation is a phenomenon in which repeated and equal-intensity noxious stimuli at a specific frequency cause an increase in the pain experienced. Results are usually obtained by comparing pain ratings of the first to the last equal intensity stimulus.
When using a psychophysical temporal summation of pain protocol, the researcher evokes the human behavioral derivate of wind-up.
Wind-up and central sensitization
Wind-up as described in animal models, is a phenomenon that occurs in the dorsal horn of the spinal cord, in which repeated first-order neuron presynaptic inputs at specific frequencies, cause increased response of the postsynaptic neuron.
Increased temporal summation is considered a manifestation of central sensitization. This important marker is therefore often implemented in pain research.
Pain research has shown that there are differences in experimentally elicited temporal summation responses between healthy controls and patients suffering from pain syndromes, but also between sexes, and age groups. Interestingly, the presence of increased temporal summation has also been shown to be linked to chronic pain after surgery.
The temporal summation phenomenon can be elicited by different psychophysical test modalities, among them
thermal and mechanical stimuli. Thermal temporal summation may be assessed in two different ways; by introducing fast, short and repeated stimuli: phasic temporal summation, or by introducing a sustained noxious thermal stimulus: tonic temporal summation.
Temporal Summation of Pain paradigms
Medoc’s thermal devices have been widely used to assess tonic and phasic temporal summation of pain in healthy participants and patients alike. Medoc’s TSA-II, now followed by the TSA2 is a great tool for eliciting tonic temporal summation. PATHWAY CHEPS, now followed by the CHEPS for TSA2, allowed performing phasic temporal summation, offering ultra-fast rates.
In human studies the outcome of temporal summation is commonly assessed by following pain consecutive ratings along the stimulation paradigm.
Rating Temporal Summation
A great tool to rate pain along the temporal summation protocol is the CoVAS. The CoVAS is a continuous computerized visual analogue scale which has a slider operated by the research participant and samples the pain rating indicated by the user at 20/milisecond. This will allow to introduce high temporal resolution to the analysis of the pain ratings. It has the additional advantage of reducing the cognitive burden of the study participants, reducing delays in pain ratings, and enhancing standardization in pain VAS collection.
You may find some leading research links in which temporal summation has been assessed using Medoc’s devices at the bottom of this page.
Download Windup Application datasheet