Temple cooling increases parasympathetic activity and decreases pressure pain on the hand

Abstract

Background: Applying an ice cube to the temple (the conditioning stimulus) inhibits electrically evoked pain in the forearm. The present study aimed to determine whether temple cooling also inhibits pressure-and heat-pain test stimuli in the upper limb and, if so, to investigate the intra-session test-retest reliability of this response. Additional aims were to establish whether pain inhibition evoked by temple cooling was associated with parasympathetic activity; and to explore sex differences in response. Methods:The sample consisted of 40 healthy adults (24 females). Heart rate was recorded continuously throughout the session. An ice cube (3 × 4 cm contact area) was applied for 1 min to the temple on the dominant side. Before and immediately afterwards, the pressure pain threshold was measured from the dorsal hand and sensitivity to heat (individually adjusted at baseline to elicit moderate pain) was measured from the ventral forearm. The procedures were repeated 15 min later. Results:Temple cooling inhibited pressure pain on the hand but not heat pain on the forearm. However, test-retest reliability of pressure pain inhibition was poor.Heart rate decreased during temple cooling, consistent with a "diving" reflex. Males had stronger pressure pain inhibition, lower heart rate and higher overall autonomic activity than females. However, cardiac parasympathetic activation during temple cooling was comparable in both sexes and was unrelated to pain inhibition. Conclusions: These findings indicate that temple cooling evokes pain inhibition that is stronger in males than in females. Cardiac parasympathetic activity does not appear to mediate this response. Significance:The conditioning stimulus in the conditioned pain modulation paradigm is often applied to the upper or lower limbs. This may confound paininhibitory effects in people with peripheral neuropathy who typically have enhanced or diminished sensation in the extremities. Applying an ice cube at the temple area induces pain-inhibitory effects on the upper limb after the ice is removed. Future research examining pain modulation in people with peripheral neuropathy may consider adopting temple cooling as the conditioning stimulus.