Andrew C.N. Chen

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.

Brain evoked potentials are functional correlates of induced pain in man

&NA; Electrical potentials evoked by 5 intensities of painful dental stimulation were recorded at the scalp. During testing, volunteers indicated subjective painfulness by verbal pain ratings and visual analogue scales. Evoked potentials (EPs) to each intensity, observed between 50 and 400 msec, were characterized by 4 waveform components. The peak‐to‐peak amplitudes, but not the peak latencies, of all 4 EP components systematically increased with increased stimulation. The amplitudes of the two earlier components correlated with stimulus intensity when the effect of subjective painfulness was controlled, but this was not the case for the later components. In contrast, the amplitudes of the two later components were associated with subjective painfulness but not with stimulus intensity. A strong linear relationship was observed between subjective painfulness and peak‐to‐peak amplitude for the EP component observed between 175 and 260 msec. The data suggest that the earlier EP components may reflect sensory transmission processes while the later components indicate brain activity when pain is perceived.

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.

Human brain measures of clinical pain : a review. I: Topographic mappings

&NA; A comprehensive paper (Parts I and II) has been developed to review the cerebral measures employed in studying the brain neurophysiological activities of clinical pain. Part I focuses on the electro‐, magnetic‐physiological assessment of clinical pain, and Part II concerns the anatomico‐, chemical‐physiological assessment of clinical pain. In Part I, these measures include the qualitative inspection of the conventional electroencephalogram, quantitative assessment of brain electrical spectral activity through cortical power spectrum density and coherence analyses, and quantitative averaging of cortical electrical or magnetic activities using brain evoked potentials. The mapping and measurement of these electrical activities and magnetic fields are results of recent advent in computer technology and advanced algorithms. Promises and limitations of these topographic measures in understanding pain in the brain are stated. The next article (Part II) of this paper will review tomographic imaging of pain‐related brain activities in regional cerebral flow, the scanning of gross and fine brain structures by computerized axial tomography or magnetic resonance imaging, and the imaging and measurement of brain metabolic changes, energy uptake, and receptor bindings through positron emission tomography or single‐photon emission computerized tomography. Molecular chemical transformation by the nuclear magnetic resonance analysis of tissue changes and analgesic‐receptor interactions will also be noted.

The McGill pain questionnaire in the assessment of phasic and tonic experimental pain: behavioral evaluation of the ‘pain inhibiting pain’ effect

&NA; The McGill Pain Questionnaire (MPQ), supplemented with a German version, was administered to 10 healthy subjects to evaluate two laboratory pain models. Ischemia pain was induced as a tonic pain model and electrical intracutaneous stimuli were applied as a model of phasic pain. In addition, both pain models were employed simultaneously in order to evaluate their mutual influence. Tonic pain was rated higher than phasic pain on the affective, evaluative and miscellaneous MPQ subscales. Furthermore, the sensory descriptor choices for the two pain models were dissimilar, although the number of words chosen as well as the intensity represented by these words were of equal magnitude. These findings indicate that the sensory quality of the pain models is different and that the aversive component is much greater for the tonic pain than for the phasic pain. When applied simultaneously, tonic pain was able to inhibit phasic pain perception. This modulation could be demonstrated on visual analog scales of intensity (−44%) and aversiveness (−49%), on a 10‐point category scale (−27%), and on the MPQ scores present pain intensity (PPI) (−29%), number of words chosen (NWC) (−25%) and pain rating intensity (PRI) (−28%). Differences were significant on the 5% level for the visual analog scales, the category scale and PPI. Evaluation of the MPQ subscales revealed that mainly the affective dimension of phasic pain was reduced under concurrent tonic pain. It is concluded that the MPQ is as well‐suited to characterize differential analgesic effects as it is to differentiate properties of pain models.

Effect of Nitrous Oxide Concentration on Event-related: Potentials during Painful Tooth Stimulation

Effects of inhaling three levels of nitrous oxide in oxygen on event-related brain potentials (ERPs) and pain report were examined in 10 volunteers undergoing painful electrical stimulation of tooth pulp. Previous work by the authors demonstrated that inhalation of nitrous oxide 33 per cent in oxygen, iv injection of 0.1 mg fentanyl, oral administration of 975 mg aspirin, and electrical acupunctural stimulation all reduced ERP amplitudes obtained at vertex during painful tooth pulp stimulation. The authors report here the demonstration of a dose-response relationship between increasing concentrations of nitrous oxide in oxygen and measures of ERP amplitude and pain report. Subjects inhaled room air, nitrous oxide 25 per cent, 37 per cent, and 50 per cent in oxygen while ERPs were recorded and pain reports were given. The procedure was repeated on three separate days with each subject experiencing all levels of treatment of each day. Analyses of variance revealed that both ERP amplitude and pain report significantly decreased as dosage increased, and a significant linear trend was observed for the positive-going ERP wave-form deflection between 160 and 240 ms. Pain report scores decreased significantly (P < 0.001) and proportionally as dosage increased, but there was not a significant linear trend. Inhalation of nitrous oxide in oxygen increased peak latency for the negative component at 50 ms and the positive component at 90 ms but not for later components. These outcomes demonstrate that amplitude measures of the vertex ERP obtained with dental dolorimetry correlate consistently with pain and analgesia. Simultaneous assessment of brain electrical activity and subjective report appears to be a useful approach for the assessment of analgesia in humans.

Cognitive reversal of expected nitrous oxide analgesia for acute pain.

In a laboratory experiment, the expected analgesic action of 33% nitrous oxide was reversed by creating the expectancy of heightened awareness of bodily sensations. Pain threshold and tolerance of electrical tooth-pulp stimulation were significantly reduced. Results from a control study gave us a basis for comparison of changes in the verbal expression of pain when nitrous oxide was administered without introducing expectancies beyond those already held by the subjects. Contrasting results from the experimental and control studies confirm the powerful role of mental processes in mediating pain experience.

Tonic pain inhibits phasic pain: evoked cerebral potential correlates in man.

In a sample of 10 healthy volunteers phasic pain ratings and evoked cerebral potentials (EPs) elicited by brief electrical skin stimuli were investigated in periods before, during, and after contralateral tonic ischemia pain. In all subjects the phasic pain ratings and the late EP components P80-N150 and N150-P260 were depressed under concurrent tonic pain. The magnitude of the mean reduction (31%, 40%, and 26%) is comparable to morphine analgesia. The early EP components with latencies below 80 ms, which are considered to be correlates of mechanosensitivity, were not influenced. The findings of tonic pain inhibiting phasic pain are discussed on the basis of changes in attention as well as of pain-specific physiological mechanisms like diffuse noxious inhibitory control.

Cortical power spectrum analysis of hypnotic pain control in surgery

Cortical power spectrum (CPS) of brain potentials was recorded from the scalp between prefrontal and parietal regions in both right hemisphere (RH) and left hemisphere (LH). A pattern of laterality shift in CPS occurred at different stages during an extensive oral surgery, performed under hypnosis, in a young female patient. Video and audio recordings as well as psychophysiological recordings were obtained through the following 6 stages: Baseline, Hypnosis, Surgery (1 hr, no cortical recording), Immediate Postsurgery Procedure, Hypnotic Re-experience, Hypnotic Rest, and Posthypnotic Baseline. Indications of anxiety and pain scores were reported in writing by the patient through verbal command by the hypnotist. In each stage, 10 min of CPS (10 spectrum/stage, 8 epochs/spectrum, 6 seconds/epoch) were analyzed by a PDP-11 computer. The results of CPS analysis demonstrated significant large total power reduction at different stages. There was significant correlation between both hemispheres at baseline, but dissociation of hemispheric power output occurred during hypnosis stages. LH was more dominant than RH during baseline and presurgery hypnosis, but both were leveled-off immediately following the surgery procedure. However, RH became more dominant during all postsurgery hypnosis stages. Interestingly, this pattern shifted back to the original relationship during the posthypnotic baseline stage. Specific changes of spectral power in theta and alpha of EEG activities in both hemispheres also occurred in conjunction with hypnosis.

Behavioral management of childhood headache: a pilot study and case history report

Many chronically recurrent disorders of children and adolescents are often unresponsive to standard medical therapy. The Stress and Headache Management Clinic was established as a prototype behavioral medicine clinic to provide integrated therapeutic modalities. Using biofeedback and relaxation/mental-imagery techniques, 119 patients with the chief complaint of recurrent headache were evaluated. This paper describes the use, application, and efficacy of behavioral techniques for the management of headache in children and adolescents. Relevant treatment factors in behavioral treatment of pediatric headache are also discussed.