Pain perception decrement produced through repeated stimulation.

Pain responses (pain detection and pain discomfort) to electrical dental stimulation were studied in 16 normal subjects. The repetition of the dental stimuli induced a significant and long-lasting (60 min) decrease in pain sensitivity at both sensory levels (after 60 min of repetitive stimulation, 79% increase in pain detection, P less than 0.0001, 45% increase in pain discomfort, P less than 0.0004). The sensory response decrement through repeated elicitation was not influenced by naloxone administration (1.2 mg i.m.). This study clearly demonstrates the induction of pain sensory decrease through repetitive stimulation which differs from peripheral sensory receptor adaptation, from the inhibitory gating mechanism or from diffuse inhibitory controls activation; its unresponsiveness to naloxone suggests that this phenomenon is not opioid-dependent. A technique has been standardized which will enable the systematic study of pain decrease under sustained nociceptive stimulation in chronic pain patients.