Experimental studies of the short-term memory of pain

Researchers:

J.-C. DOUCET, Université de Montreal, Canada, and P. RAINVILLE, University of Montreal, Canada

Objectives:

It is well accepted that the memory of pain is often inaccurate, but little is known about the ability to encode, retain, and recall pain.

Subject Respondents:

The 50 College of Psychology students served as the respondents of the study. And this study was conducted in University on Montreal, Canada, in March 2005.

Methods:

We used a delayed-discrimination task to investigate the effects of stimulus intensity (Exp. 1), delay (Exp. 2), and stimulus duration (Exp. 3) on the short-term memory of thermal intensity in the painful (heat pain) and non-painful ranges (cool in Exp. 1 and warm in Exp. 1-3). Subject discriminated the intensity of pairs of phasic stimulations and indicated the degree of certainty of their response.

Results:

In all ranges of temperature tested, the performance improved and the degree of certainty increased with larger delta-T° (0.5-5°C; Exp. 1), shorter delays (12-4s.; Exp. 2), and longer durations of stimulation (2-6s.; Exp. 3) (ANOVA’s, all p’s < .05). With longer stimulus durations, subjective evaluations of both warmth and pain also increased (temporal summation), as well as the difference in mean ratings between the two levels of stimulation used (increased “discriminability”). The increased performance with larger differences in temperature (Exp. 1) and perceived pain (Exp. 3) attests of the subject’s ability to encode, retain, and compare intensities of thermal stimulations. The decrease in performance with longer delays (Exp. 2) is consistent with a progressive, time-dependent, degradation of the memory trace of sensory information. The longer stimulus duration used in experiment 3 (6s) produced a perceptual difference of more than 20 points between the two levels of pain stimulation used (47.5 and 48.5°C), on the 0-100 pain rating scale. However, in spite of those perceptual differences, the delayed-discrimination performance was only 83% correct with an 8s delay.

Conclusions:

These results suggest that the proprieties of the short-term memory of pain are consistent with the properties of short-term episodic memory, and that the fast and important degradation of the memory trace of pain sensory information contributes to the inaccuracy of retrospective pain ratings.

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