Biomedical subjects

Rupert Hölzl

Publications and source records attributed to Rupert Hölzl.

6 recordsLinked to original sources

PubMed2006

Psychophysical 'perceptual maps' of heat and pain sensations by direct localization of CO2 laser stimuli on the skin.

Brain activation patterns derived from neurofunctional methods are often implicitly regarded as being directly related to subjective perceptual experience in an iso- or at least homomorph manner, neglecting the operational differences between these two dimensions. This paper (a) introduces a method for assessing 'perceptual maps' of stimulation patterns presented to the body surface, providing a means to parametrically relate neural representation and subjective percept, and (b) applies this method to demonstrate the existence of 'somatotopic maps' of hot and painful stimulus patterns independent from mechanoceptive co-activation. Brief (90 ms) CO2 laser pulses were presented in an array of multiple stimulation sites on the dorsal forearms (N. radialis area, C7 dermatome) of healthy subjects. Perceived locations were indicated with a 3D tracker without touching the skin, and (mis-)localizations in distal-proximal direction were analyzed. Stimuli were localized with overall mean errors of 22 mm (SD: 16 mm) toward the wrist and 24 mm (SD: 18 mm) toward the elbow. Somatotopic representation of thermal-nociceptive stimuli could be demonstrated in all subjects, independent from mechanoceptive co-activation. The perceptual maps revealed striking individual (mis-)localization patterns, many subjects exhibiting 'stretched', some 'condensed' somatotopic representations. In estimating the mapping parameters from physical to perceptual space linear regressions generally provided a good fit (adj. R2>0.80 in 10 out of 12 subjects). Nonlinear models were advantageous in some subjects only. Our method can be useful in assessing inter-individual differences or experimentally induced shifts in somatotopic processing.

Adult↗

PubMed2006

Amantadine sulfate reduces experimental sensitization and pain in chronic back pain patients.

We investigated if established psychophysical measures of enhanced experimental sensitization in chronic musculoskeletal pain can be reduced by adjuvant treatment with a N-methyl-d-aspartate receptor antagonist, amantadine sulfate, and whether a reduction in sensitization might be accompanied by a concurrent improvement in clinical pain. Sensitization was evaluated by an experimental tonic heat model of short-term sensitization with concurrent subjective and behavioral psychophysical scaling. Twenty-six patients with chronic back pain were included in the randomized, double-blind, placebo-controlled study and received daily dosages of either placebo or 100 mg of amantadine sulfate during a 1-wk treatment. Participants completed quantitative sensory testing of pain thresholds and experimental sensitization before and after treatment and clinical pain ratings before, during, and after treatment. Experimental sensitization and clinical pain were reduced in patients receiving verum. Initially, experimental sensitization was enhanced in patients, with early sensitization at nonpainful intensities of contact heat and enhanced sensitization at painful intensities, as shown previously. After 1 wk of treatment, experimental sensitization was reduced with amantadine sulfate but not with placebo. We conclude that adjuvant chronic pain treatment with N-methyl-d-aspartate receptor antagonists might be beneficial for chronic pain if enhanced sensitization is involved and that the quantitative sensory test of temporal summation may be used to verify this.

Adult↗

PubMed2005

The saltation illusion demonstrates integrative processing of spatiotemporal information in thermoceptive and nociceptive networks.

In sensory saltation, first reported by Geldard and Sherrick (Science 178:178-179, 1972), a stimulus is displaced towards a second one following closely in time and space as a function of the delay between the stimuli. The distance between stimulus locations is restricted by the extension of sensory fields in the primary somatosensory cortex. Saltation is assumed to reflect dynamic changes in these cortical representations. The present study demonstrates for the first time saltation in thermoceptive and nociceptive pathways with CO(2) laser stimulation. Stimuli were presented to the dorsal forearms of 18 healthy subjects at two intensities. Saltation patterns consisted of a reference stimulus S0 near the wrist, the first test stimulus S1 at the reference location after a fixed onset delay of 1,000 ms, and a second test stimulus S2 at a location 105 mm distant from reference after a variable onset delay of 60-516 ms. Perceived positions were indicated by the subjects without skin contact with a 3D tracker. As expected, subjects mislocalized S1 towards S2. Mean S1 displacement was 51+/-36 mm. Decreasing delays between S1 and S2 resulted in increasing displacements, independent of intensity. However, since no clear-cut discrimination of thermal versus nociceptive activation could be achieved definite conclusions about differences between the two modalities cannot be drawn. In addition, effects of body site on the saltation characteristics were observed. The saltation paradigm constitutes a promising approach to the functional analysis of spatiotemporal dynamics in thermoceptive and nociceptive networks to supplement brain-mapping approaches to cortical sensory fields.

Adult↗

PubMed2005

Sensitization and habituation of AMH and C-fiber related percepts of repetitive radiant heat stimulation.

OBJECTIVE: Pain perception involves neuronal plasticity at peripheral and central stages, resulting in sensitization or habituation, depending on intensity and temporal features of stimulation. Concurrent assessment of perceptual change over different time spans is therefore important for understanding the dynamics of pain processing. METHODS: A new psychophysical procedure was established to assess sensitization and habituation during repetitive radiant heat stimulation. Short-term perceptual change (<1 min) during trials with 10 stimuli applied at 3 frequencies (0.2-0.6-1.8 Hz) and 3 intensities was assessed for AMH-II or C-fiber related percepts. Perceptual changes were monitored for medium-term (1-15 min) and for long-term (15-90 min) time spans. RESULTS: Short-term sensitization occurred only at frequencies above 0.3 Hz and was affected by both stimulus frequency and intensity, but the AMH-fiber related sensitization depended on intensity only above 0.6 Hz. Multiple stimulation of the same skin area during medium-term time spans resulted in habituation. No long-term perceptual changes occurred. CONCLUSIONS: The procedure permits concurrent assessment of short-term sensitization and medium-term habituation, assumed to be related to spinal windup and cutaneous nociceptive fiber fatigue, respectively. SIGNIFICANCE: The method is suitable for quantitative sensory testing of dynamic pain processing over different time spans, relevant in clinical testing of pain and in drug assessment.

Adult↗

PubMed2005

Implicit operant learning of pain sensitization.

Operant conditioning mechanisms have been demonstrated to be important in the development of chronic pain behavior, but it is not clear whether and how this extends to pain perception itself. The fear-avoidance theory suggests that hypersensitivity may be induced by anticipatory pain avoidance learned through negative reinforcement by acute reductions of pain and fear. But the precise mechanism of the assumed 'sensory decalibration' has not been specified. The present study with healthy subjects investigated whether operant learning of enhanced short-term sensitization may provide the 'proximal' mechanism and whether gradual learning of hypersensitivity can take place without subjects' awareness. We used an experimental model of implicit learning based on a behavioral adjustment method of sensitization measurement developed and validated previously, combining it with standard methods of operant response shaping of increased sensitization or habituation. Results indicated that operant discrimination training with reinforcement of short-term sensitization in the seconds range can produce gross up or down changes in sensitivity within an hour without subjects' awareness of reinforcement contingencies. Consequently, implicit learning of enhanced pain sensitization may be a suitable model to investigate operant plasticity of pain perception in addition to basic sensory and neuronal mechanisms and to link these with the clinical construct of pain-fear avoidance.

Adaptation, Physiological↗

PubMed2005

Extending and applying the demand-control model: the role of soldier's coping on a peacekeeping deployment.

The purpose of this study was to extend the demand-control model (R. A. Karasek, 1979) by examining coping as an additional factor. It was hypothesized that perceived job control only buffered the demand-strain relationship when individuals used active coping and exacerbated the relationship when individuals used passive coping. Soldiers (N=638) were surveyed before and during a 6-month peacekeeping deployment to Kosovo. Results partially confirmed the hypotheses. Even after controlling for general psychological health at predeployment, job control moderated the relationship between demands and psychological health during deployment when soldiers used active coping. No significant 3-way interactions were found for religious coping and passive coping. Implications for demand-control modeling and potential applications of the findings to soldier and leader training are discussed.

Adaptation, Psychological↗