Summation

About: Summation is a research topic. Over the lifetime, 954 publications have been published within this topic receiving 45593 citations. The topic is also known as: summation & sum of a sequence.

Mechanisms of pain relief by vibration and movement.

Abstract: Mechanisms of pain relief induced by vibration and movement were investigated. A CO2 laser beam, which is useful for pure nociceptive stimulation, was used for recording pain-related somatosensory evoked potentials (pain SEPs) and for measuring pain threshold and reaction time (RT). Concurrently applied vibratory stimuli to and active movements of the fingers significantly reduced and prolonged pain SEPs, increased pain threshold, and prolonged RT, indicating that an increase in the inhibitory mechanisms of painful feeling was induced by the concurrently adopted sensory inputs mediated by large myelinated fibres. In contrast, continuous cooling enhanced pain SEPs and decreased pain threshold, probably due to the spatial summation of two kinds of nociceptive impulses mediated by the same pathways. The results of this investigation throw light on the mechanisms of the alleviation of pain by vibration and movement.

Effect of racemic mixture and the (S+)-isomer of ketamine on temporal and spatial summation of pain.

Abstract: We have compared the analgesic efficacy of the racemic mixture and the stereoisomer (S+) of the NMDA antagonist ketamine. In a double-blind, three-way crossover, placebo-controlled study, we assessed the following: pain evoked by small/large area pressure stimuli, pain detection threshold and pain ratings to small/large area of heat stimuli, pain detection threshold and pain rating to heat stimuli of brief/long duration, summation pain threshold and pain ratings to repeated heat/electrical stimuli, side effects and reaction time. Plasma concentrations of 350 ng ml-1 for ketamine (racemic) and 180 ng ml-1 for ketamine (S+) were tried. We found that ketamine (racemic) prolonged the reaction time more than ketamine (S+). Both drugs affected pain caused by repeated stimuli or stimuli of long duration equally or more than a single stimulus of short duration. They also affected pain evoked from large areas equally or more than pain evoked from small areas. The (S+)-isomer was approximately twice as potent as the racemic mixture of ketamine in inhibiting central summation.

The effect of Ketamine on stimulation of primary and secondary hyperalgesic areas induced by capsaicin--a double-blind, placebo-controlled, human experimental study.

Abstract: The non-competitive NMDA-antagonist, Ketamine, was infused (i.v.) in healthy volunteers to study the effect on central excitability with the presence of cutaneous hyperalgesia. Hyperalgesia was established experimentally on the dorsum of the foot by topical application of capsaicin (1%). Different thermal and mechanical conditioning stimuli were applied to the primary and secondary hyperalgesic areas to modulate the central nociceptive excitability monitored by the nociceptive reflex. When the elicited reflex was combined with an activation of the secondary hyperalgesic area by continuous, non-painful, electrical stimulation, a facilitation of the reflex was observed. This indicates that summation of activity in non-nociceptive and nociceptive afferents can occur under mild pathological conditions. Conditioning thermal stimuli of the primary hyperalgesic area were employed to intensify the allodynia prior to testing this interaction between tactile and nociceptive activity. The same reflex facilitation was inhibited by Ketamine. Furthermore, Ketamine decreased the pain intensity associated with the stimuli eliciting the reflex. Psychophysical measures to single and repeated electrical and thermal (laser) stimuli applied within the hyperalgesic areas were also obtained. The intensity of pain sensations produced by single, painful, electrical stimuli applied to the primary hyperalgesic region was reduced after Ketamine infusion. Finally, five repeated, electrical stimuli applied to the secondary hyperalgesic area were used to assess the temporal summation threshold. Ketamine caused an increase in the summation threshold compared to the placebo treatment. In conclusion, these results demonstrate that (1) summation of activity in non-nociceptive and nociceptive afferents occurs under hyperalgesic conditions and, (2) this summation can be inhibited by NMDA-antagonists. Therefore, the study shows an apparent involvement of NMDA-receptors in some of the central mechanisms underlying secondary hyperalgesia.