Articles: pain-threshold.
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The gate-control theory of pain, as originally proposed by Melzack and Wall [8], is nothing but a hypothesis concerning the spinal processing of non-noxious and noxious afferent information. Its basic tenant is that the P cells (projecting neurons) convey noxious information to supraspinal pain systems only after a critical threshold of excitation has been passed, and that access to the P cells is controlled by the SG cells (cells of the substantia gelatinosa Rolandi) or, in other words, the SG cells act as the gate. Since the primary afferent fibres have monosynaptic connections with the P cells the gate can only operate-and this is the critical point of the whole hypothesis-via presynaptic inhibition exerted by axoaxonic contacts on these afferents (Fig. 1). ⋯ As a consequence, Melzack and Wall [9] have now modified their hypothesis considerably. Its present formulation is not much more than a very general statement to the effect that all kinds of afferent input, including noxious input, is under the modulating influence of various mechanisms operating both at the spinal level and from supraspinal (descending) structures. No implications for therapy can be derived directly from such an undefined, in many ways trivial, assumption.
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This paper reviews several recently developed animal models that allow a quantitative assessment of the magnitude of nocifensive behavioral responses across a range of noxious stimulus intensities. Models discussed in detail include: (a) the rodent tail flick reflex, and a modification that allows measurement of tail flick magnitude, (b) rat hindlimb flexion withdrawal reflex elicited by noxious thermal stimulation of the paw, and (c) a learned operant response (nose bar press) evoked by noxious thermal stimulation of the rat's tail. These models are discussed in terms of their advantages over previous methods measuring response threshold, their fulfillment of criteria for ideal pain assessment models, and the neuronal circuitry underlying the behavioral response.
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1. Most quantitative examinations of nociception are performed with thermal or mechanical stimuli. Because nociceptive processing mechanisms may depend on the modality of the stimuli, comparable studies on chemonociception are necessary. 2. ⋯ The discriminatory capacity of WDR and NS neurons was reduced in the highest concentration range (75-100% CO2). The proportion of NS neurons significantly discriminating between these intensities tended to be higher compared with WDR neurons when stimuli were applied with long ISIs (120 s). 5. To examine the effects of the duration of the ISI, identical test sequences were performed with ISIs of 30 and 120 s. (ABSTRACT TRUNCATED AT 400 WORDS)
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Somatosensory perception threshold (SPT) and pain perception threshold (PPT) were studied in 16 patients with major depression, compared to the findings in an age-matched and gender-matched control group and related to the psychopathological state evaluated by means of the Hamilton Depression Scale. Perception thresholds were assessed by means of a noninvasive high-frequency electric skin stimulation. ⋯ RPPT was positively correlated with retardation. It was negatively correlated with anxiety, suggesting that a reduction of pain perception thresholds in depressive patients may be attributed to anxiety and impaired stress-coping.
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Acta Neurol. Scand. · Nov 1993
Effects of movement-related cortical activities on pain-related somatosensory evoked potentials following CO2 laser stimulation in normal subjects.
We investigated the change in pain perception produced by the application of movement and vibration to areas adjacent to, and remote from, the painful stimulus. Pain-related somatosensory evoked potentials (pain SEPs) and the pain threshold were evaluated following CO2 laser stimulation in 17 normal subjects. ⋯ This finding was not produced by vibration or movement imagery of the limbs without active movement. Therefore, interactions between pain perception and movement-related cortical activities must take place in some areas of the brain without relieving pain.