Individual fish were administered with a noxious stimulus to the lip under The only effect seen in hooked fish was brief episodes of lateral head Rank correlation) and inter-observer reliability tests performed on three of the. is often decoupled from noxious stimuli and motor responses are no longer relationships between noxious stimuli, pain perception, and. Responses to step-wise noxious stimuli cannot be reduced to a linear . stimulus response relationships but are predicted by the model.
To fulfill these functions, a noxious stimulus might induce a percept which, in turn, induces a behavioral response. Here, we investigated an alternative view in which behavioral responses do not exclusively depend on but themselves shape perception. We tested this hypothesis in an experiment in which healthy human subjects performed a reaction time task and provided perceptual ratings of noxious and tactile stimuli.
A multi-level moderated mediation analysis revealed that behavioral responses are significantly involved in the translation of a stimulus into perception. This involvement was significantly stronger for noxious than for tactile stimuli. These findings show that the influence of behavioral responses on perception is particularly strong for pain which likely reflects the utmost relevance of behavioral responses to protect the body. These observations parallel recent concepts of emotions and entail implications for the understanding and treatment of pain.
Pain is commonly defined as an unpleasant sensory and emotional experience associated with actual or potential tissue damage 1. Pain has, thus, been mostly conceptualized as a perceptual phenomenon. However, the crucial protective function of pain depends on appropriate behavioral responses rather than on perception. The precise relationship between noxious stimuli, pain perception and behavioral responses is, however, not fully clear yet. Common models of stimulus-perception-behavior relationships in the somatosensory domain 2 suggest that such behavioral responses result from a percept which, in turn, results from a stimulus.
In view of the utmost relevance of protective behavioral responses for pain, we considered a view in which behavioral responses are in part directly elicited by the stimulus and then themselves shape pain perception.
Such a partial independence of behavioral responses from perceptual processes could serve the protective functions of pain particularly fast and efficiently. For pressure and ischemic pain assessments, the order of intensity and unpleasantness ratings was varied across subjects. Thermal Pain Procedures Thermal procedures involved assessment of warmth threshold, heat pain threshold, and heat pain tolerance.
- There was a problem providing the content you requested
- A central mechanism enhances pain perception of noxious thermal stimulus changes
The 9-cm2 contact probe was applied to the left volar forearm. Warmth thresholds, heat pain thresholds, and heat pain tolerances were assessed using an ascending method of limits. Four trials of warmth threshold, heat pain threshold, and heat pain tolerance were presented. Within each block of trials, the position of the thermode was altered slightly between individual trials resulting in a total of four stimulation sites on the volar forearmand interstimulus intervals of at least 30 seconds were maintained between successive stimuli.
Pressure Pain Procedures A Somedic algometer Sollentuna, Sweden was used to assess responses to noxious mechanical pressure.
Mechanical pressure was applied using a 0. Pressure was increased steadily at an application rate of 30 kPa per second until the subject responded by pressing a button, at which point stimulation was terminated. Pressure pain thresholds were assessed at two sites: Pressure pain thresholds were assessed four consecutive times at each site, and the order of sites was randomized.
Modified Submaximal Effort Tourniquet Procedure Following completion of thermal and mechanical pain assessment procedures, a second baseline blood pressure assessment was performed. Next, subjects underwent the modified submaximal effort tourniquet procedure, which involves exercising the hand as blood flow to the arm is occluded, evoking ischemic pain Maximum grip strength of the right hand was determined using a Lafayette hand-held dynamometer Lafayette Instrument Co.
Next, the right arm was exsanguinated by elevating it above heart level for 30 seconds, after which the arm was occluded with a standard blood pressure cuff positioned proximal to the elbow and inflated to mm Hg using a Hokanson E20 rapid cuff inflator D.What is NOXIOUS STIMULUS? What does NOXIOUS STIMULUS mean? NOXIOUS STIMULUS meaning & explanation
Cuff inflation was maintained until the perceived pain became intolerable; the procedure was terminated by the experimenter if pain tolerance had not been achieved at 15 minutes following initiation of the handgrip exercises. Every 30 seconds, subjects alternately rated either the intensity or unpleasantness of their pain using the rating scales described previously.
In addition to these ratings, the time to ischemic pain threshold and time to ischemic pain tolerance were assessed. Data Analysis Data are presented as means and standard errors.
Warmth thresholds, thermal pain thresholds, thermal pain tolerances, and pressure pain thresholds were determined by calculating the mean of the second, third, and fourth trials. Initially, for the purposes of the overall analysis, all pain-response variables were standardized to distributions with a mean of 1 and a standard deviation of 1.
This procedure permits the grouping of all tasks into a single profile analysis The significance of between-group differences in the magnitude of correlation coefficients was assessed using the method of Edwards In addition, no significant order effects were observed for: Data for heat pain threshold and tolerance, ischemic pain threshold and tolerance, and pressure pain threshold and tolerance at both sites were individually standardized to distributions with a mean and standard deviation of 1.
These results are depicted graphically in Fig. Follow-up analyses for each noxious stimulus modality are presented below. Ischemic pain data appear in Fig. Cardiovascular data appear in Table 2.
A central mechanism enhances pain perception of noxious thermal stimulus changes
To examine the relationships between cardiovascular activity and responses to noxious stimuli in both older and younger subjects, correlation coefficients were computed separately for each age group. For both age groups, resting SBP and MAP were generally positively correlated with thermal pain thresholds and tolerances.
However, although higher SBP and MAP were associated with increased ischemic pain thresholds and tolerances among the younger participants, these relationships did not emerge among older subjects, although this difference achieved statistical significance only for the relationship between SBP and ischemic pain tolerance see Table 3. Effect Sizes To determine the relative magnitude of effects for each of the pain response variables, Cohen's d was computed for each measure of pain responses.
Briefly, d is calculated by dividing the difference in group means by the pooled standard deviation. Effect sizes were as follows: Discussion The results of the present study suggest stimulus-specific age effects on responses to noxious stimuli. Several recently published comprehensive reviews of the literature regarding laboratory studies of pain in older adults have noted the difficulty of interpreting a diverse set of empirical findings 2 3 4. Specifically, these reviewers note that although approximately half of the extant studies examining cutaneous pain thresholds using radiant or contact heat suggest increases in pain thresholds in elderly subjects, the remaining studies report no significant age effects.
In the present study, the mean thermal pain threshold for the older subject group was 1.
However, this difference did not achieve statistical significance. Thus, we concur with Harkins 3 4who suggests that age-associated effects on cutaneous pain thresholds are likely minimal. In addition, the present results are somewhat consistent with those of Woodrow and colleagues 8who found decreased pressure pain tolerance in elderly subjects. Even though the present findings relating to pressure pain tolerance did not achieve statistical significance, a trend toward lower pressure pain tolerance in the older group was noted.
Finally, older individuals in the present study demonstrated significantly lower ischemic pain thresholds and tolerances than younger subjects. To our knowledge, this is the first report of age-associated differences in responses to ischemic arm pain.
Overall, although small to moderate age-related effect sizes were observed for thermal and mechanical pain, large effects were evident on ischemic pain measures.
Behavioral responses to noxious stimuli shape the perception of pain
In addition, the directions of the thermal and ischemic effects differed, with older participants demonstrating a nonsignificant 1. One potential explanation for this differential effect may depend on age-associated changes in central nervous system pain-modulatory systems. Bodnar 25 reviewed evidence from a variety of sources suggesting that aging produces decrements in nearly all identified neural and hormonal endogenous pain-modulatory systems, particularly in opioid-mediated antinociception However, putative decrements in these systems in elderly individuals may not be universally evident during noxious stimulation.
Mense 26 and Yu and Mense 27 have reported that descending inhibitory pain-control systems function primarily to modulate deep pain, such as the ischemic pain produced by the tourniquet procedure. Moreover, the selective opioid antagonist naloxone has been found to increase ischemic 11 12 13 14but not thermal pain sensitivity 28 29suggesting greater endogenous opioid influence over ischemic than thermal pain. Thus, age-related decrements in pain inhibition may be most evident for the ischemic task.
Preliminary findings have recently suggested that elderly individuals may be less able to activate endogenous pain-modulatory systems than are younger individuals The present results also hint at the possibility that at least one pain-modulatory system may begin to show decreasing efficacy with advancing age.
Increased arterial blood pressure is associated with reduced responses to noxious stimuli 17and endogenous opioids may mediate this inverse relationship between blood pressure and pain sensitivity 18 31 Our results indicate that although increased arterial blood pressure was generally associated with increased pain thresholds and tolerances, these relationships appeared somewhat stronger among younger subjects, especially with respect to the ischemic pain data. Although higher resting SBP and MAP were associated with decreased sensitivity to ischemic pain among younger subjects, this effect was not present within the older group.
However, given that only 1 of 32 correlations differed significantly in magnitude between older and younger subjects, interpretations of these data must remain cautious. An alternative explanation for the present findings may be related to stimulus-specific age-associated differences in response bias.
Several previous studies by Harkins and Chapman 33 34employing Sensory Decision Theory SDT methodology in the context of electrical stimulation of tooth pulp, suggested that aging had differential effects on willingness to report sensations as painful at varying levels of stimulation.