Effect of acute experimental hand pain on left-right discrimination response latency for hand recognition

Abstract

BACKGROUND: Acute experimental pain appears to affect left-right discrimination latency. This phenomenon is an interesting observation as it highlights an effect of pain on the cortex that may have potential significant clinical importance as an assessment of pain state. However, this effect has received relatively little attention detail to date (only two studies, n = 35). A more thorough understanding of the magnitude and characteristics of this phenomenon is needed before further steps can be taken in this area.

OBJECTIVE: This study aims to closely replicate previous studies that have investigated response latency for left-right discrimination judgements during acute experimental pain.

PARTICIPANTS: A sample of 22 (n = 11 female, n = 11 male) right-handed participants took part in this study. All participants were free from pain, analgesia use, pain-related conditions, upper limb trauma/conditions, visual impairment and dyslexia.

METHODS: During our repeated measures cross-over study, participants completed a hand left-right discrimination judgement task before, during and after an experimental pain stimulus was delivered to each hand separately. The experimental pain was achieved using an intramuscular injection of hypertonic (5%) saline into the thenar eminence of the left and right hands. Mean response times for the left-right discrimination task were determined and compared for pain location, pain condition and image laterality. Participants were also asked to report the pain intensity at 20 second intervals during each left-right discrimination task.

RESULTS: There was neither an immediate main effect of the pain stimulus on response times (p = 1), nor an effect of pain location on response times (p = 0.202). There was, however, an image laterality effect (p = 0.004) which interacted with a right-hand pain location (p = 0.005) but not a left-hand pain location (p = 0.515). The image laterality and pain location interaction was consistent across all pain conditions.

CONCLUSION: Our results were not consistent with previous hand left-right discrimination response latency results. Our results do not support the attentional or information processing bias hypothesis that is currently thought to underpin hand left-right discrimination response latency changes during acute experimental pain in the hand. Our findings may, however, suggest that asymmetrical hemispheric function can affect left-right discrimination latency regardless of pain.