Clonidine effects on pain evoked SII activity in humans.

We investigated pain evoked activity in the human secondary sensory cortex (SII) following clonidine administration in six healthy volunteers using multi-channel magnetoencephalography (MEG). Pain was elicited by electrical shocks applied intracutaneously to the fingertip. Subjects rated pain intensity and perceptions of tiredness and passiveness by numerical ranking scales.

Cortical correlates of false expectations during pain intensity judgments--a possible manifestation of placebo/nocebo cognitions.

We investigated the effects of expectation on intensity ratings and somatosensory evoked magnetic fields and electrical potentials following painful infrared laser stimuli in six healthy subjects. The stimulus series contained trials preceded by different auditory cues which either contained valid, invalid or no information about the upcoming laser intensity. High and low intensities occurred equally probable across cue types.

How best to fight that nasty itch - from new insights into the neuroimmunological, neuroendocrine, and neurophysiological bases of pruritus to novel therapeutic approaches.

While the enormous clinical and psychosocial importance of pruritus in many areas of medicine and the detrimental effects of chronic 'itch' on the quality of life of an affected individual are widely appreciated, the complexity of this sensation is still often grossly underestimated. The current Controversies feature highlights this complexity by portraying pruritus as a truly interdisciplinary problem at the crossroads of neurophysiology, neuroimmunology, neuropharmacology, protease research, internal medicine, and dermatology, which is combated most successfully if one keeps the multilayered nature of 'itch' in mind and adopts a holistic treatment approach - beyond the customary, frequently frustrane monotherapy with histamine receptor antagonists. In view of the often unsatisfactory, unidimensional, and altogether rather crude standard instruments for pruritus management that we still tend to use in clinical practice today, an interdisciplinary team of pruritus experts here critically examines recent progress in pruritus research that future itch management must take into consideration.

The involvement of the posterior cingulate gyrus in phasic pain processing of humans.

Cingulate cortex (CC) processing of phasic pain starts in caudal parts. This is evidenced by electrical brain source analysis (BESA(R)) and current reconstruction imaging (CURRY(R)) which identify the activated neuronal assemblies in the individual brain morphology, including the boundary element method for volume current calculation. Data were obtained from 30 subjects who experienced, in repeated sessions, infrared laser stimuli applied on temple, hand, and foot, or electrical shocks applied intracutaneously on finger tip.

Dissociation of morphine analgesia and sedation evaluated by EEG measures in healthy volunteers.

Aim: The analgesic effects of morphine (CAS 57-27-2) in clinical use are well described. Sedation is discussed as a relevant side-effect, mostly based on data recorded in normal subjects without pain. The aim of this study was to quantify and to evaluate electrophysiologically the analgesic and sedative effects of morphine for the first time using an experimental pain model.

[Laser-evoked potentials: diagnostic approach to the dorsal root].

Functional diagnostics of the dorsal root are especially effective via nociceptive fibers on account of less intersegmental overlap compared to large-diameter fibers of the mechanoreceptive afferents. Laser-evoked potentials (LEP) are induced by short, painful heat stimuli. The aim of this work was to describe changes of the LEP in cases of dorsal root damage.

Single trial fMRI reveals significant contralateral bias in responses to laser pain within thalamus and somatosensory cortices.

Pain is processed in multiple brain areas, indicating the complexity of pain perception. The ability to locate pain plays a pivotal role in immediate defense and withdrawal behavior. However, how the brain localizes nociceptive information without additional information from somatotopically organized mechano-receptive pathways is not well understood.

Sensory reinnervation of myocutaneous flaps revealed by infrared laser evoked sensations and brain potentials.

The aim of this study was to examine the recovery of sensory function in myocutaneous flaps comparing 2 test methods. Eight flaps in 7 patients were examined by using clinical neurological test procedures (CNT) in comparison with psychophysics and evoked brain potentials (LEP) following infrared laser stimuli. The authors found that only 3 out of 8 flaps in 7 patients exhibited signs of reinnervation when tested with CNT.

Differential effects of isoflurane on excitatory and inhibitory synaptic inputs to thalamic neurones in vivo.

Background: Mechanosensory thalamocortical relay neurones (TCNs) receive glutamatergic excitatory input and are subjected to gamma-aminobutyric acid (GABA)Aergic inhibitory input. This study assessed the effects of an increase in concentration of isoflurane on thalamic excitatory and inhibitory mechanisms.

Methods: TCNs (n = 15) of the thalamic ventral posteromedial nucleus responding to mechanical stimulation of whiskers were investigated in rats anaesthetized with end-tidal concentrations of isoflurane of approximately 0.

Subcortical structures involved in pain processing: evidence from single-trial fMRI.

Pain is processed in multiple cortical and subcortical brain areas. Subcortical structures are substantially involved in different processes that are closely linked to pain processing, e.g.

Attentional modulation of human pain processing in the secondary somatosensory cortex: a magnetoencephalographic study.

The influence of attention on the processing of pain in the secondary somatosensory cortex (SII) was analyzed using magnetoencephalography in response to painful infra-red heat stimuli applied to the left hand in six male healthy subjects, aged 22-28 years. Three experimental paradigms were chosen to deliver attention dependent results under comparable levels of vigilance. Single moving dipole sources for the pain-evoked responses were calculated in the individual cortex anatomy determined by magnetic resonance imaging.

Painful stimuli evoke different stimulus-response functions in the amygdala, prefrontal, insula and somatosensory cortex: a single-trial fMRI study.

Only recently have neuroimaging studies moved away from describing regions activated by noxious stimuli and started to disentangle subprocesses within the nociceptive system. One approach to characterizing the role of individual regions is to record brain responses evoked by different stimulus intensities. We used such a parametric single-trial functional MRI design in combination with a thulium:yttrium-aluminium-granate infrared laser and investigated pain, stimulus intensity and stimulus awareness (i.

Dissociable neural responses related to pain intensity, stimulus intensity, and stimulus awareness within the anterior cingulate cortex: a parametric single-trial laser functional magnetic resonance imaging study.

Neuroimaging studies have demonstrated activations in the anterior cingulate cortex (ACC) related to the affective component of pain, but not to stimulus intensity. However, it is possible that the low spatial resolution of positron emission tomography, as used in the majority of these studies, obscured areas coding stimulus intensity. We revisited this issue, using a parametric single-trial functional magnetic resonance imaging design, and investigated pain, stimulus intensity, and stimulus awareness (i.

Increased responsiveness of cortical neurons in contrast to thalamic neurons during isoflurane-induced EEG bursts in rats.

The neuronal mechanisms underlying the electroencephalographic (EEG) burst-suppression pattern are not yet understood, however, they are generally attributed to interactions within thalamocortical networks. In contrast, we report that the sensory cortex and the thalamus are disconnected, with thalamic sensory processing being unaffected by cortical EEG bursts. We studied the activity of single neurons of the somatosensory thalamocortical system in rats during burst-suppression EEG induced by the volatile anesthetic, isoflurane.

Brain images of pain.

Combined magneto- and encephalography proves the sequential involvement of multiple cortical structures in pain processing. Bilateral activity in secondary somatosensory cortices reflects the sensory-discriminative component and is reduced in states of unconsciousness. Later activity in the posterior cingulum reflects the emotional-aversive component, which is blocked by narcoanalgesics.

Local GABA(A) receptor blockade reverses isoflurane's suppressive effects on thalamic neurons in vivo.

Many in vitro effects of volatile anesthetics are known, but the mechanisms of action are still under debate. Because suppression of sensory perception is one of the major goals of general anesthesia, we studied the effects of isoflurane on the processing of somatosensory information in anesthetized rats. Local iontophoretic administration of the gamma-aminobutyric acid-A (GABA(A)) receptor antagonist bicuculline in the thalamic ventral posteromedial nucleus reversed suppressive effects of isoflurane on thalamocortical relay neurons (TCNs).

New aspects of itch pathophysiology: component analysis of atopic itch using the 'Eppendorf Itch Questionnaire'.

Itch represents a leading symptom in dermatological practice with many psychophysiological aspects. Instruments for qualitative registration of these central nervous factors and evaluation of therapeutic measures are still missing. We analyzed in detail the subjective itch sensation in 108 patients with acute atopic eczema with a new questionnaire developed in analogy to the McGill pain questionnaire.

Cortical representation of pain: functional characterization of nociceptive areas near the lateral sulcus.

Many lines of evidence implicate the somatosensory areas near the lateral sulcus (Sylvian fissure) in the cortical representation of pain. Anatomical tracing studies in the monkey show nociceptive projection pathways to the vicinity of the secondary somatosensory cortex in the parietal operculum, and to anterior parts of insular cortex deep inside the Sylvian fissure. Clinical observations demonstrate alterations in pain sensation following lesions in these two areas in human parasylvian cortex.

Topography of clonidine-induced electroencephalographic changes evaluated by principal component analysis.

Background: Principal component analysis is a multivariate statistical technique to facilitate the evaluation of complex data dimensions. In this study, principle component analysis was used to reduce the large number of variables from multichannel electroencephalographic recordings to a few components describing changes of spatial brain electric activity after intravenous clonidine.

Methods: Seven healthy volunteers (age, 26 +/- 3 [SD] yr) were included in a double-blind crossover study with intravenous clonidine (1.

The pain inhibiting pain effect: an electrophysiological study in humans.

This study examines the counterirritation phenomenon of experimental pain in human subjects. Phasic pain induced by intracutaneous electrical stimuli was simultaneously applied with tonic pain induced by ischemic muscle work. Pain ratings, spontaneous EEG and evoked potentials were measured.

Isoflurane induces dose-dependent changes of thalamic somatosensory information transfer.

In spite of several reports about suppressive effects of volatile anesthetics on somatosensation, their neuronal mechanisms are largely unknown. The present study investigates somatosensory impulse transmission at the thalamic level in rats under varied concentrations of isoflurane by recordings of neuronal responses to mechanical stimulation of the body surface. Single-unit recordings of thalamo-cortical relay neurons (TCNs, third order neurons; n=28) and presumed trigemino-thalamic fibers (TTFs, second order neurons; n=7) were performed in the ventral posteromedial nucleus.

Neurophysiological evaluation of pain.

Neurophysiological techniques for the evaluation of pain in humans have made important advances in the last decade. A number of features of neuroanatomy and physiology of nociception qualifies pain as a multidimensional phenomenon which is rather unique among the sensory systems and which poses a number of technical and procedural requirements for its appropriate diagnostic assessment. Various stimulation techniques to induce defined pain in humans and used in combination with the methodology of evoked electrical brain potentials and magnetic fields are presented.

Abeta-fiber mediated activation of cingulate cortex as correlate of central post-stroke pain.

A patient is presented who suffered a lateral brainstem infarction which selectively abolished pain and temperature sensitivity in the lower right limb. One year later central post-stroke pain had developed in the affected limb with touch and cold allodynia. P40m dipoles calculated from magnetoencephalographic fields after electrical stimulation of both tibial nerves were localized in SI as is seen in normal subjects.