Zur Korrespondenz von Schmerzreiz und Schmerzerleben

Neural Correlates of Empathy with Pain Show Habituation Effects. An fMRI Study

Background

Neuroimaging studies have demonstrated that the actual experience of pain and the perception of another person in pain share common neural substrates, including the bilateral anterior insular cortex and the anterior midcingulate cortex. As many fMRI studies include the exposure of participants to repeated, similar stimuli, we examined whether empathic neural responses were affected by habituation and whether the participants' prior pain experience influenced these habituation effects.

Method

In 128 trials (four runs), 62 participants (31 women, 23.0 ± 4.2 years) were shown pictures of hands exposed to painful pressure (pain pictures) and unexposed (neutral pictures). After each trial, the participants rated the pain of the model. Prior to the experiment, participants were either exposed to the same pain stimulus (pain exposure group) or not (touch exposure group). In order to assess possible habituation effects, linear changes in the strength of the BOLD response to the pain pictures (relative to the neutral pictures) and in the ratings of the model’s pain were evaluated across the four runs.

Results

Although the ratings of the model’s pain remained constant over time, we found neural habituation in the bilateral anterior/midinsular cortex, the posterior midcingulate extending to dorsal posterior cingulate cortex, the supplementary motor area, the cerebellum, the right inferior parietal lobule, and the left superior frontal gyrus, stretching to the pregenual anterior cingulate cortex. The participant’s prior pain experience did neither affect their ratings of the model’s pain nor their maintenance of BOLD activity in areas associated with empathy. Interestingly, participants with high trait personal distress and fantasy tended to show less habituation in the anterior insula.

Conclusion

Neural structures showed a decrease of the BOLD signal, indicating habituation over the course of 45 minutes. This can be interpreted as a neuronal mechanism responding to the repeated exposure to pain depictions, which may be regarded as functional in a range of contexts.

The potential for actigraphy to be used as an indicator of sitting discomfort

OBJECTIVE

A novel technique that uses actigraphy, the study of activity involving the use of body-mounted accelerometers, to detect the discomfort-related movements of a sitting individual has been proposed as a potential indicator of sitting discomfort, and the purpose of this study was to test its validity.

BACKGROUND

Objective measurement of sitting discomfort has always been challenging for researchers. Electromyographic measurements, pressure mapping, and a wide range of other techniques have all been investigated with limited success.

METHOD

The activity monitor's ability to detect and measure seated movement was assessed, and 12 participants were tested on four different chairs (100-min sessions for each).

RESULTS

The activity monitor was able to detect participants' sitting movements (Pearson coefficients > 0.9). The chairs were shown to have significantly different subjective discomfort ratings, all of which increased over time. The movements detected by the activity monitor also increased significantly with time, and the amount measured was greater in the chairs rated as most uncomfortable. Regression analysis indicated that the actigraphy data were able to account for 29.6% of the variation in perceived discomfort ratings.

CONCLUSION

Actigraphy can reliably detect sitting movements and may be of use in measuring sitting discomfort.

APPLICATION

Potential applications of this technique exist for seating research in the automotive industry, health care, and office and leisure chairs.

Einfluss negativer Stressverarbeitung auf postoperatives Schmerzerleben und -verhalten

OBJECTIVE

The aim of the study is to show whether negative coping style has an impact on post-operative pain reporting and pain-related behaviour.

METHODS

After informed consent 48 gynaecological patients were enrolled in the study. Negative coping style was assessed by using the stress coping questionnaire SVF-78 (Janke and Erdmann). Patients were dichotomised by scores of the negative coping style. Pain reporting concerned pain intensity and pain quality. Pain-related behaviour was assessed by patient-controlled analgesia (PCA). Pain intensity and pain quality were assessed prior to surgery and 24 h after surgery. Patient-controlled analgesia was recorded up to 24 h after surgery. Trait anxiety (STAI-X2) was used as a control variable.

RESULTS

Patients with high scores in negative coping style report increased levels of pain in both affective and sensory pain perception. At the same time patient-controlled analgesia is used less frequently by this group. This result remains significant considering trait anxiety as a covariate.

CONCLUSIONS

High negative coping style may cause a discrepancy between pain reporting and pain-related behaviour. This should be taken into account in the perioperative care of patients.

Remifentanil-clonidine-propofol versus sufentanil-propofol anesthesia for coronary artery bypass surgery

OBJECTIVE

To compare a remifentanil-clonidine-propofol regimen with conventional sufentanil-propofol anesthesia.

DESIGN

Randomized, nonblinded trial.

SETTING

A single university hospital.

PARTICIPANTS

Male patients scheduled for coronary artery bypass graft (CABG) surgery.

INTERVENTIONS

In the control group, anesthesia was induced with 0.5 microg/kg of sufentanil and 0.2 to 0.3 mg/kg of etomidate after preoxygenation. Propofol (50 to 100 microg/kg/min) and sufentanil (0.5 to 1.0 microg/kg/h) were started after endotracheal intubation. Sufentanil was stopped after aortic decannulation. In the remifentanil-clonidine group, anesthesia was started with remifentanil (0.15 to 0.3 microg/kg/min), followed by etomidate (0.2 to 0.3 mg/kg). Propofol was started at 50 to 100 microg/kg/min, and after endotracheal intubation, clonidine infusion was started (6 to 20 microg/h). Patients received piritramide (0.15 mg/kg) and metamizole (20 mg/kg) for transitional analgesia. In both groups, propofol infusion was reduced to 30 to 60 microg/kg/min at skin closure and stopped when assisted spontaneous breathing led to adequate gas exchange.

MEASUREMENTS AND MAIN RESULTS

The main outcomes were recovery times; somatic variables; plasma catecholamine levels; and self-recorded pain, nausea, and vomiting. Patients in the remifentanil-clonidine group were extubated earlier and had lower plasma epinephrine and norepinephrine levels. After transitional analgesia, the remifentanil-clonidine patients had similar postoperative analgesic use and self-reported pain and side-effect scores.

CONCLUSION

Compared with a sufentanil-propofol regimen, an anesthetic regimen for CABG surgery that combines remifentanil, clonidine, and propofol provides similar hemodynamics. The remifentanil-clonidine regimen reduces catecholamine levels and hastens recovery from anesthesia.

Pain sensation during cold stimulation of the teeth: differential reflection of A delta and C fibre activity?

Cold stimuli of varying intensities were randomly applied to upper middle incisors of 12 healthy young subjects for a mean duration of 2 min by individually adapted thermodes the temperatures of which ranged from +30 degrees C to -30 degrees C. The subjects were asked to rate the magnitude of their pain sensations during application of the stimuli by means of a linear potentiometer according to a category scale. After each stimulus, they were asked to describe the quality of their pain sensations. Cold stimulation of the teeth evoked pain sensations were reproducible that in subsequent trials and could be graded according to stimulation intensity. Below certain individually different threshold thermode temperatures the onset of a stimulus was followed, after a short latency (1.6 +/- 1 sec), by a sharp and shooting pain sensation which immediately decreased after reaching its maximum value while the stimulus was still present. The mean maxima of the pain intensities were correlated to the thermode temperature. In general, this first pain component was followed by a second one (latency: 29.9 +/- 6.3 sec) with a lower threshold temperature, less of an increase in rate and lower magnitude. This was described as a dull, burning pain which was difficult to localize. The human pain ratings are compared to recordings of intradental nerve fibres in the cat and, under the assumption that the response behaviour of human pulpal nerve fibres is comparable to that of the cat, we hypothesize that the first pain component is evoked by intradental A delta fibres exhibiting their typical phasic response behaviour and firing during the initial steep temperature decrease. After some seconds, intradental temperature reached values sufficient to evoke C-fibre activity associated with the second pain component.

Persistent pain inhibits contralateral somatosensory cortical activity in humans

To assess cortical activity during pain perception, regional cerebral blood flow (rCBF) studies were done in humans using single photon emission computed tomography (SPECT) with the radiotracer Tc99m-HMPAO and magnetic resonance imaging localization. Normalized SPECT data were analyzed by region of interest and change distribution. Contralateral somatosensory rCBF was decreased when the digits of the hand were immersed in a hot water bath for 3 min which was rated as moderately painful (persistent pain). No decrease was observed when the hand was immersed in tepid water (control). In contrast, cortical rCBF was increased during vibratory and sensorimotor tasks, in the contralateral somatosensory and sensorimotor areas, respectively. These results indicate that pain perception in man is associated with somatosensory cortical inhibition.

Pain sensitivity and pain reactivity of pericranial muscles in migraine and tension-type headache

We investigated whether experimentally determined, suprathreshold pain sensitivity of pericranial musculature in patients with tension-type headache differs from that of migraine patients or from that of healthy subjects. Furthermore, we looked to see whether differences could be found in the effects of experimental pain induction on EMG activity of pericranial musculature and whether subgroups could be discovered with higher and lower pericranial pain sensitivity within the three diagnostic groups in terms of neurophysiological, psychological and clinical variables. In 20 patients with tension-type headache, 23 patients with migraine without aura, and 29 healthy individuals experimental pain was induced in the temporal muscle by mechanical pressure; pain sensitivity in the entire metrically subdivided suprathreshold pain sensitivity range was measured. Surface EMG activity of pericranial muscles was determined before, during and after experimental pain induction. In addition, headache characteristics as well as personality and mood states were determined and recorded in a standardized fashion. There were no significant differences in pain sensitivity of pericranial musculature between the three groups. Patients with tension-type headache showed significantly higher EMG scores during suprathreshold pain stimulation than did migraine patients. EMG scores of healthy subjects fell between these two groups. With respect to pericranial tenderness significant differences in clinical, neurophysiological and psychological variables were found only between subgroups within the group of patients with tension-type headache. The results indicate that significant differences in the examined groups are found not in pain perception but in the processing or reaction to experimental headache stimuli. In patients with tension-type headache subgroups evolve based on pericranial pain sensitivity with quantitatively and/or qualitatively impaired reactions; for this reason diagnostic grouping according to the IHS classification seems to be pathophysiologically relevant. The intraindividual phasic comparison of pain reactions appears to be more important than the absolute interindividual tonic comparison.

On the "absoluteness" of category and magnitude scales of pain

The concept of "absolute scaling" (Zwislocki & Goodman, 1980) implies that direct judgments of sensory magnitude not only reflect the relative positions of the stimuli being judged, but also permit us to assess level differences in sensation. In order to explore this notion for different scaling methods, in the present investigation we compared magnitude estimation with category partitioning, a verbally anchored categorization procedure, in scaling painful pressure stimuli covering different intensity ranges. The results indicate that when the same stimulus range was presented after 1 week, both methods appeared to be highly reliable, with category partitioning faring somewhat better than magnitude estimation. When the stimulus range was unobtrusively changed between sessions, both methods reflected the within-subjects shift in absolute level. When two different sets of subjects judged the slightly different stimulus ranges, both methods resulted in scale values consistent with absolute scaling, though only category partitioning was sensitive enough to differentiate the two stimulus ranges. The results are discussed in the context of different possibilities of anchoring direct scaling methods in order to obtain "absolute" level information.

Changes in cerebral haemodynamics in cases of post-lumbar puncture headache: a prospective transcranial Doppler ultrasound study

We used transcranial Doppler ultrasonography in 45 patients to investigate if changes in haemodynamics in the major arteries of the brain base occurred after lumbar puncture and whether or not patients with or without post-lumbar puncture headache differ with respect to their cerebral haemodynamic parameters before and after lumbar puncture. Before lumbar puncture, patients with post-lumbar puncture headache differed from patients without post-lumbar puncture headache in that they showed significantly higher flow velocities and significant asymmetry of flow velocities with lateralization to the right (p less than or equal to 0.05). Patients without post-lumbar puncture headache, on the other hand, showed non-significant flow velocity lateralization to the left. Forty-eight hours after lumbar puncture, both groups demonstrated symmetrical flow velocities. In addition, only patients with post-lumbar puncture headache showed a significant reduction in the flow velocity of the right middle cerebral artery (p less than or equal to 0.05). These findings suggest that it is not only absolute flow velocity that plays a part in the event of headache, the interhemispheric relation of cerebral haemodynamics also plays a fundamental role.

Post-lumbar puncture headache: the relation between experimental suprathreshold pain sensitivity and a quasi-experimental clinical pain syndrome

The relation between general experimental pain sensitivity and the clinical expression of post-lumbar puncture syndrome (PLPS) was examined in a prospective double-blind study of patients who underwent a lumbar puncture with a 20-gauge spinal needle. In 44 neurology patients randomized pain was induced on the middle phalanges of fingers II-IV of both hands using a tension device on the day before lumbar puncture. Pain intensity was measured using the category sub-dividing procedure. The correspondence between experimental pain stimuli and induced pain intensities could best be described by a logarithmic function. PLPS symptoms were documented in a multi-dimensional quantitative fashion using various scales. Pronounced position-dependent headache occurred in 31% of the patients. There proved to be very significant effects of experimental pain sensitivity on intensity and duration of position-dependent headaches, as well as on vegetative symptoms of PLPS (P less than or equal to 0.01). The results provide an explanation for the varying interindividual manifestation of PLPS symptoms, in addition to factors already identified such as the size of needle used in individual patients.

[Algesimetric experiment on pain sensitivity in the pericranial musculature. Circadian rhythms and corresponding psychic variables.]

Many types of headache that occur in the form of attacks show a notably high incidence at certain times of the day. Attacks are often accompanied by emotional instability, irritability, exhaustion and other impairments of well-being. The cause for the frequent daytime occurrence of attacks is not clear. One possible explanation could be the variability in a person's sensitivity to headache over the course of the day. For this reason we set out to investigate whether pain sensitivity to experimentally-induced headache varies in a circadian manner and whether this variation correlates to changes in the current state of well-being over the course of the day. In 24 healthy, voluntary subjects, headache was induced experimentally at 0200, 0600, 1000, 1400, 1800, and 2200 hours. Blood criculation in both superficial temporal and occipital arteries was reduced by applying a cuff to the head and inflating it to 200 mmHg, thereby producing a continuously increasing, bilateral, dull, frontal headache. The subjects scaled the intensity continually, using the category subdividing procedure ranging from pain threshold to pain tolerance level. In addition, 17 dimensions of the current state of well-being and 12 personality traits were recorded at the above-mentioned times in a standardized quantitative manner. At low levels of headache intensity there were no significant differences in pain sensitivity. Sensitivity to very intense headache, however, varied significantly over the course of the day: sensitivity was greatest at 0200 hours; it decreased at a constant rate until 1400 hours, and increased again continuously until 2200 hours (P</=0.05). Sensitivity to low levels of headache intensity did not prove to be significantly correlated to dimensions of current well-being. By comparison, however, the findings showed significant correlations between sensitivity to very high headache intensities and multiple dimensions of the current state of well-being. These findings show that headache sensitivity follows circadian patterns. Daytime variations, however, are only significant for sensitivity to high intensities. Thus these results may explain, in part, why violent attacks of pain occur predominantly at night and in the early morning.