Neural correlates of evoked phantom limb sensations.

Previous work showed the existence of changes in the topographic organization within the somatosensory cortex (SI) in amputees with phantom limb pain, however, the link between nonpainful phantom sensations such as cramping or tingling or the percept of the limb and cortical changes is less clear. We used functional magnetic resonance imaging (fMRI) in a highly selective group of limb amputees who experienced inducible and reproducible nonpainful phantom sensations. A standardized procedure was used to locate body sites eliciting phantom sensations in each amputee. Selected body sites that could systematically evoke phantom sensations were stimulated using electrical pulses in order to induce phasic phantom sensations. Homologous body parts were also stimulated in a group of matched controls. Activations related to evoked phantom sensations were found bilaterally in SI and the intraparietal sulci (IPS), which significantly correlated with the intensity of evoked phantom sensations. In addition, we found differences in intra- and interhemispheric interaction between amputees and controls during evoked phantom sensations. We assume that phantom sensations might be associated with a functional decoupling between bilateral SI and IPS, possibly resulting from transcallosal reorganization mechanisms following amputation.

[Event-related functional magnetic resonance imaging of cerebral pain processing]. / Ereigniskorrelierte funktionelle Magnetresonanztomographie zur Erforschung der zerebralen Schmerzverarbeitung.

Neurofunctional magnetic resonance imaging (fMRI) offers the possibility to map cerebral activity non-invasively. The development of event-related techniques during the past years allows to study brain processes with high spatial and temporal resolution. Based on these techniques, EPI- and FLASH sequences were developed in this study, to investigate cerebral processing of experimental thermal pain stimulation. Phasic and tonic stimulation paradigms were developed with an MR-compatible contact thermode. Functional mapping of pain-relevant areas was performed with these paradigms, as well as a specification of the temporal characteristics of the activation. Further, a randomized paradigm with several stimulus intensities could differentiate graded functional responses, dependent on stimulus intensity in specific "regions-of-interest". In this design, randomizing the stimulus order reduced habituation effects, while continuous subjective magnitude estimation of the stimuli kept attention of subjects maximal.

Psychophysical measures of sensitization to tonic heat discriminate chronic pain patients.

Sensitization to continued nociceptive stimulation is supposed to be involved in the development of chronic pain at several levels of the CNS, but experimental studies investigating the perceptual dynamics of sensitization in humans are rare, and the diagnostic validity of experimental pain models is not known. The present study used a tonic heat paradigm to assess early sensitization (15-100 s) to experimental pain in 30 chronic pain patients (15 musculoskeletal/back pain, 15 headache) and 23 healthy controls. Change in pain sensation during prolonged stimulation was measured by a dual sensitization method which combines subjective ratings and behavioural responses in an indirect psychophysical protocol protected against response bias. Phasic and tonic pain thresholds were measured for control purposes. The degree of sensitization was linearly related to stimulus temperature, and groups differed significantly in this 'sensitization gradient': chronic pain patients sensitized earlier and stronger than healthy subjects, musculoskeletal pain patients showed the strongest effect. Pain thresholds were lowered in headache patients only. Discriminant analysis demonstrated good sensitivity and specificity of individual sensitization measures for distinguishing pain syndromes, particularly in combination with pain thresholds. The results are in accordance with current models of spinal plasticity contributing to pathological pain states. They argue for the diagnostic value of psychophysical measures of sensitization.

Subclinical hyperthyroidism: physical and mental state of patients.

We investigated whether subclinical hyperthyroidism [subnormal basal thyroid-stimulating hormone (TSH) level, attenuated TSH response to thyrotropin-releasing hormone (TRH) stimulation, peripheral thyroid hormones within normal range] is accompanied by physical and mental changes. Thirty-five subclinically hyperthyroid patients (27 female, 8 male) were compared with 60 overtly hyperthyroid patients (51 female, 9 male) and with 28 euthyroid control patients (18 female, 10 male) with respect to physical symptoms, affective state, short-term memory, ability to concentrate and psychomotor performance. Patients with subclinical hyperthyroidism ranged between the other two groups. The major difference between controls and subclinically hyperthyroid patients was an increase in frequency of nervous symptoms and symptoms due to an increase of metabolic rate and thermal regulation changes. The major differences between subclinically hyperthyroid and overtly hyperthyroid patients were psychomotor impairment and symptoms of increased metabolic rate. Self-ratings of affective state tended to be similar in patients with subclinical and overt hyperthyroidism. The ability to concentrate and short-term memory were not impaired in any group. Symptoms in patients with subclinical hyperthyroidism probably result from central changes which lead to attenuated TSH responses to TRH, or from elevated but still normal thyroxine levels, which possibly enhance the effect of catecholamines.

[The role of TSH psychological and somatic changes in thyroid dysfunctions]. / Die Rolle des TSH für psychische Veränderungen und Befindlichkeitsveränderungen bei Schilddrüsenfunktionsstörungen.

The characteristic psychic and somatic features found in patients with overt hyper- or hypothyroidism are usually attributed to elevated or diminished levels, respectively, of thyroid hormones. This concept does not sufficiently explain our previous investigations in which the same symptoms, albeit attenuated, were also seen in patients suffering from so-called latent disturbances of thyroid function. This state of disorder, however, exhibits normal concentrations of peripheral thyroid hormones. Only the response of thyroid-stimulating hormone (TSH) to thyrotropin-releasing hormone (TRH) stimulation is in accordance with the behaviour of the overt thyroid dysfunction and enables its differentiation from the euthyroid state. In this context, we investigated the question as to whether pathologic signs in thyroid disorders are correlated to alterations of peripheral thyroid hormones or to changes in the hypothalamus pituitary axis. Therefore, we investigated two groups of ten patients each who suffered from latent hyper- or hypothyroidism, respectively, and ten euthyroid controls. All were matched from sex and age. Endocrine function was estimated by TRH testing, TT3, TT4 and thyroxine binding globulin (TBG). Psychologic testing was performed by questionnaires concerning subjective somatic symptoms, emotional disturbances, psychomotoric performance, cognitive impairment and personality. Patients with latent hyperthyroidism were more subject to somatic symptoms and affective complaints than were those who had latent hypothyroidism. As compared with controls, there were significant differences in exhaustion and pain in the limbs and heart. In terms of affective complaints, patients were more depressive, anxious, touchy and irritable; their personalities showed a higher degree of emotional lability, excitement and irritability.(ABSTRACT TRUNCATED AT 250 WORDS)