Effect of Acute Experimental Hand Pain on Left-Right Discrimination Response Latency for Hand Recognition

N. Phillips*, S. McLaren**, J. Mannion*, R. Moran*
*Healthcare Network, Unitec, Institute of Technology, Auckland, NZ
**Affiliation GP, Greenwood Medical Centre, Epsom, Auckland, NZ

Introduction: Acute experimental pain appears to affect left-right discrimination latency. This phenomenon is interesting as it suggests an effect of pain on the cortex that may have potential as a clinical assessment of pain state.  However, this effect has received relatively little attention to date.  A more thorough understanding of the magnitude and characteristics of this phenomenon is needed.

Aims: This study aims to investigate response latency for left-right discrimination judgements during acute experimental hand pain. 

Methods: A sample of 22 right-handed participants took part in this study.  All participants were free from pain/related conditions, pain catastrophising, analgesia use, upper limb trauma/conditions, visual impairment and dyslexia. During the 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. Experimental pain was achieved using an intramuscular injection of hypertonic saline into the thenar eminence.  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.

Conclusions:  Our results were not consistent with previous hand left-right discrimination response latency results.  There was neither an immediate main effect of the pain stimulus nor an effect of pain location on response times. There was, however, an image laterality effect which interacted with right-hand but not left-hand pain location which was consistent across all pain conditions.  These 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. Alternatively, our findings may suggest that asymmetrical hemispheric function can affect left-right discrimination latency notwithstanding of pain condition.