Trial Outcomes & Findings for Mechanisms of Affective Touch in Chronic Pain (NCT NCT04206397)

Mechanisms of Affective Touch in Chronic Pain

The investigators will measure chronic pain levels using the Characteristic Pain Intensity score, a subscale of the Chronic Pain Grade Questionnaire (CPGQ). The questions that contribute to the subscale each use a scale from 0-10 where 0 is 'no pain' and 10 is 'pain as bad could be', and their mean is multiplied by 10. The intensity subscale score thus ranges from 0 to 100, where 0 would be least pain reported and 100 would be the most pain reported. This measure will be included in a linear regression model to determine whether this measure significantly predicts differences in ratings of touch pleasantness.

The investigators will measure trauma history using the Childhood Trauma Questionnaire. The total score ranges from 25-125, where 25 is the least childhood trauma (better) and 125 is the greatest childhood trauma (worse). This measure will be included in a linear regression model to determine whether this measure significantly predicts differences in ratings of touch pleasantness.

The investigators will measure current depression using the Hospital Anxiety and Depression Scale (HADS). The HADS consists of two sub scales for depression and anxiety. The depression sub scale ranges from 0 - 21 where 0 indicates no depression (better) and 21 indicates highest depression levels (worse). This measure will be included in a linear regression model to determine whether this measure significantly predicts differences in ratings of touch pleasantness.

Touch pleasantness/unpleasantness ratings will be assessed in response to each sensory stimulus (brushing, tapping, and pressure) using a Visual Analog Scale. Anchors were defined as far left = 'extremely unpleasant' (coded as -100), midpoint = 'neutral' (coded as 0), and far right = 'extremely pleasant' (coded as 100). Affective touch perception is defined as the difference in ratings between the affective and neutral touch conditions (rating of brushing minus rating of tapping) during the Day 1 baseline and will be compared between individuals with and without chronic pain. This value ranged from 200 (brushing extremely pleasant and tapping extremely unpleasant) to -200 (tapping extremely pleasant and brushing extremely unpleasant). These values are not inherently 'better' or 'worse' but represent individual differences in preference for affective touch.

Pain intensity will be measured before and after the left hand is submerged in cold water (conditioned pain modulation task). Pain intensity will be assessed with a Visual Analog Scale. Anchors are defined as far left = 'no sensation' (coded as -100), midpoint = 'pain threshold' (coded as 0), and far right = 'intolerable pain' (coded as 100). Change in heat pain ratings after cold water bath ranges from -200 to 200 where higher scores indicate pain increases after cold water bath (worse) and lower scores indicate pain reduction (better).

Pain intensity will be measured before and after gentle brushing (affective-touch-pain task) on a Visual Analog Scale. Anchors are defined as far left = 'no sensation' (coded as -100), midpoint = 'pain threshold' (coded as 0), and far right = 'intolerable pain' (coded as 100). Change in heat pain ratings after brushing ranges from -200 to 200 where higher scores indicate pain increases (worse) and lower scores indicate pain reduction (better).

Respiration rate will be measured during baseline affective touch (brushing).