John D. Gehrig

Human pain responsivity in a tonic pain model: psychological determinants.

&NA; Human pain responsivity was defined as the subjects behavioral pain endurance time (PET) to the 1 ± 0.3°C cold‐pressor test, a naturalistic and clinical analogue tonic pain model. Over the past 2 years, we have consistently observed a behavioral dichotomy of pain responsivity in each of our 6 studies (all at P < 0.000001 effect level), totaling 205 subjects. Overall, the pain‐tolerant (PT) subjects could endure the whole 5 min (note that 3 min was the ceiling criterion in the last study) of cold‐pressor test, while the pain‐sensitive (PS) subjects could merely tolerate the test for an overall mean of 60 sec, 20% of PET in the PT group. No overlapping of distribution was observed between these 2 populations. Further, we observed that the percentage of subjects in each of these 2 groups varied substantially across studies. The mean pain perception (Visual Analogue Scale) of tonic pain ranged from 60–70 for both aversiveness and intensity scales. The characteristics of this tonic pain, assessed by the McGill Pain Questionnaire (MPQ), showed similar patterns across each study with a high degree of consistency. Although ratings of pain aversiveness did not differ in the PT vs. PS subjects, ratings of pain intensity did differ, with the PT subject reporting less pain. It was found that state anxiety correlated with MPQ scores for PS, but not PT, subjects. Additionally, psychological tests (Tellegen Absorbance Scale, Kleinknecht Fear, Spielberger Trait‐Anxiety) were positively correlated with certain MPQ measures for PS, but not PT subjects. Multivariate regression analyses indicated, in the PS but not the PT group, that 36% of variance in pain score (MPQ‐T) could be predicted by the psychological trait factors. The general level of fear contributed singularly as the major predictor variable in the pain‐sensitive individuals. We consider this tonic pain model indeed offers a succinct empirical paradigm to study human pain responsivity in general. The psychological/physiological etiology of such drastic human pain responsivity requires intense systematic investigations. This report discusses the results in: (a) individual differences in pain responsivity, (b) characterization of the cold‐pressor test as a model for tonic pain, (c) contrast between PS and PT groups of pain perception and state anxiety, and (d) psychological determinants of measures for cognitive, perceptual and affective domains. Discussion was also focused on the experimental tonic pain model and its generality for clinical pain, as well as the basic model of the cold‐pressor test for human tonic pain responsivity.

Topographic brain measures of human pain and pain responsivity

&NA; Individual differences in human pain responsivity were characterized by the 1°C cold‐pressor test. Behaviorally, a pain‐tolerant group (PT = 29 Ss) tolerated the entire 3‐min test (X = 180 ± 0 sec), while a pain‐sensitive group (PS = 13 Ss) averaged only 50.31 ± 20.81 sec of the cold‐pressor test (t = 16.75, P < 0.0001), replicating our earlier studies. Physiologically, the PT group exhibited no mean differences from the PS group in cortical power densities at the baseline stage. Under the noxious stress of the cold‐pressor test, both groups exhibited markedly heightened delta and beta cortical power densities. However, the PS subjects showed significantly higher delta power, but not beta power, than the PT subjects. We conclude that heightened delta activity may reflect the stress component of human pain responsivity, and that beta activity reflects the vigilance scanning of pain processes.

Evoked potential assessment of acupunctural analgesia: Attempted reversal with naloxone

&NA; The effects of electrical acupunctural stimulation (2 Hz) on pain judgments and evoked potentials are reported for two experiments using dental dolorimetry. In the first experiment subjects received acupuncture at points located in the same neurologic segment as the test tooth. In the second experiment subjects received acupuncture at points on the hands located on acupuncture meridians. In both instances acupuncture resulted in a reduction in pain intensity and smaller evoked potential amplitudes, but naloxone neither reversed the analgesia nor did it affect the evoked potentials. A pilot study was carried out to determine whether manual rather than electrical stimulation would produce an analgesia reversible by naloxone, but it failed to do so. These findings contribute to the growing evidence that acupunctural stimulation significantly reduces pain sensibility in volunteers undergoing dolorimetric testing, but they do not support the hypothesis that endorphin release is a mechanism by which acupuncture exerts analgesia.

Comparative effects of acupuncture and transcutaneous stimulation on the perception of painful dental stimuli

&NA; The effects of acupunctural stimulation on the perception of induced dental pain were compared with those of placebo acupuncture and transcutaneous electrical stimulation (TES) at an acupuncture site. Each of 4 groups of 15 subjects received one of the following treatments: acupuncture, placebo acupuncture, TES, or control conditions. Every subject was tested twice, once in a baseline session and on another day in a test session. Four levels of painful dental stimuli were delivered repeatedly and in random order to each subject in each session, who rated the perceived intensity of each stimulus on a pain category scale. All three treatment groups showed a significant reduction in magnitude of stimulus ratings after treatment. A Sensory Decision Theory analysis of the data was employed to assess the sensory sensitivity of each subject to each of 4 levels of dental stimulation and the willingness of the subject to label the strongest stimulus as painful. Acupuncture and TES groups showed a small but significant sensory analgesic response to treatment and a significant reduction in willingness to identify the strongest stimulus as painful when contrasted to controls, but placebo acupuncture subjects failed to show significant change on either of the response measures. The effects of acupuncture were most pronounced at the lowest level of stimulation, while TES affected the perception of all levels of dental stimuli. The observed effects appeared to be small, reliable, and dependent on the stimulation of a particular anatomical locus.

Dental sensory receptor structure in human teeth

Abstract Electron microscopy was used to study normal human extracted teeth in order to define the junctions between sensory nerve endings and other cells in external pulp and inner dentin at the crown tip. Two sets of associated cells were found: (1) Connective tissue cells. The pulpal fibroblast network made occasional desmosome junctions with the odontoblast network, and the cells of each network formed many gap junctions and desmosomes with one another. (2) Nerve endings. The terminal axons formed a succession of appositions with each other or with Schwann cells in the plexus of Raschkow and the cell‐free zone, possibly with fibroblasts inthe cell‐free zone and odontoblast layer, and with odontoblasts in the odontoblast layer, predentin and dentin. The appositions between nerve endings and their companion cells at all levels usually maintained a regular intercellular spacing of at least 15–20 nm. In predentin and dentin, axons could be easily identified by their distinctive vesicles and mitochondria, and they often occurred within clusters of adjacent dentinal tubules; in the odontoblast layer axon identification was much more difficult. Axo‐axonic appositions were found in the plexus of Raschkow, the cell‐free zone, predentin and dentin; in many cases, bare axons were separated from each other only by a 5–10 nm extracellular space. Dental sensory mechanisms are discussed in relation to these observations.

Acupuncture compared with 33 per cent nitrous oxide for dental analgesia: A sensory decision theory evaluation.

Responses to electrical stimulation of the tooth pulp were obtained in both baseline and test sessions for subjects receiving acupuncture, 33 per cent nitrous oxide, or control conditions. A signal-detection analysis across sessions showed that both treatment groups demonstrated reduced sensitivity to stimulation, and increases in bias against reporting strong stimuli as painful. (Key words: Acupuncture; Anesthetics, gases, nitrous oxide; Measurement techniques, sensory decision theory; Pain, sensory decision theory).

Restoring facial contour with implanted silicone rubber: Report of two cases

Abstract Silicone rubber is a relatively new implant substance. It has shown itself to be compatible with the tissues, and it is adaptable to several techniques for the restoration of defects of facial contour. Because of the simplicity of its insertion and the lack of reported complications, silicone rubber may be the material of choice when an implant is indicated. A review of the literature and illnstrative cases have been presented.

Reply to Peters and Schmidt

We are very pleased that our recent papers [1,2] have now aroused strong interest. Peters and Schmidt have conducted a laudable study extending the observations of dichotomy of pain responsiveness to a clinical pain condition. The generalizability of these individual differences in human pain responsiveness we conclusively reported over 6 studies is demonstrated by their findings. Peters and Schmidt raise several related questions regarding the description of our results. They argue ‘ . . it seems rather awkward to run a t test on the mean scores of 2 groups on the same variable which was used in the first place to create the groups’ and, later, ‘. . . one cannot speak of a distribution of scores in the PT group where everyone had a score of 300 sec.’ These and related comments lead Peters and Schmidt to wonder how trait and state measures could be correlated with tolerance time for PT subjects when there seemed no variability in tolerance time for PT (i.e.. 300 set). In principle, we are in agreement with the view they expressed and acknowledge that the confusion they discern arises from an incomplete description of one of our findings and rationale for certain statistical decisions. Regarding the dichotomizing of the groups into PS and PT, it was of course the subjects who dichotomized them-

Letter to the editorReply to Peters and Schmidt

We are very pleased that our recent papers [1,2] have now aroused strong interest. Peters and Schmidt have conducted a laudable study extending the observations of dichotomy of pain responsiveness to a clinical pain condition. The generalizability of these individual differences in human pain responsiveness we conclusively reported over 6 studies is demonstrated by their findings. Peters and Schmidt raise several related questions regarding the description of our results. They argue ‘ . . it seems rather awkward to run a t test on the mean scores of 2 groups on the same variable which was used in the first place to create the groups’ and, later, ‘. . . one cannot speak of a distribution of scores in the PT group where everyone had a score of 300 sec.’ These and related comments lead Peters and Schmidt to wonder how trait and state measures could be correlated with tolerance time for PT subjects when there seemed no variability in tolerance time for PT (i.e.. 300 set). In principle, we are in agreement with the view they expressed and acknowledge that the confusion they discern arises from an incomplete description of one of our findings and rationale for certain statistical decisions. Regarding the dichotomizing of the groups into PS and PT, it was of course the subjects who dichotomized them-

The MPQ in the assessment of phasic and tonic pain: Behavioral evaluation of “taloxone” action on human pain responsiveness

Aim of Investigation: Studies investigating the efficacy of hypnotic analgesia in experimental settings have provided varying results as a function of the nature of the pain stimulus and the adequacy of the psychophysical procedures used to assess pain. While for humans ischemic pain is demonstrably closer to clinical pain states than almost any other experimental pain stimulus. little is known about the psychophysics of this stimulus. This study examined the effects of hypnotic analgesia, comparing it to a baseline and a placebo control condition. Subjects reported their pain using Stevenss magnitude estimation procedure. Methods: Sixty undergraduate subjects, who had been pretested on hypnotic susceptibility, were administered three trials of ischemic pain. The first trial consisted of a baseline control trial; the second and third trials consisted of either a hypnotic analgesia trial or a placebo analgesia trial in counterbalanced order. Subjects gave magnitude estimates of their pain every 30 set until they reached tolerance. Results: Analyses of variance of the magnitude estimates indicated a reduction in pain for hypnotic analgesia comnared to baseline or placebo analgesia, but only in the condition where it followed a trial of placebo analgesia. Various psychophysical functions were fitted to the data and tested for goodness of fit. The parameters of these functions however did not differentiate between treatment conditions. Conclusions: As with other experimental pain stimuli, ischemic pain is (a) sensitive to manipulations known to affect pain intensity, (b) sensitive to the experimental context, and (c) reliably measured using magnitude estimation procedures.