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Query: UMLS:C0030193 (pain)
 261,466 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We aimed to compare the effects of distraction on pain-related somatosensory evoked magnetic fields (pain SEF) following painful electrical stimulation with simultaneous recordings of evoked potentials (pain SEP). Painful electrical stimuli were applied to the right index finger of eleven healthy subjects. A table with 25 random two-digit numbers was shown to the subjects, who were asked to add 5 numbers of each line in their mind (calculation task) or to memorize the numbers (memorization task) during the recording. In the SEF recording, 3 short-latency components within 50 ms of the stimulation were generated in the primary sensory cortex (SI) of the hemisphere contralateral to the stimulated finger. Middle-latency components between 100 and 250 ms after the stimuli were recorded from the secondary somatosensory cortex (SII) in the bilateral hemispheres or the cingulate cortex. No SEF components were significantly affected by either task. In the SEP recording, the middle-latency components (N140 and P230) were identified as being maximal around the vertex. Amplitudes of the N140 and P230 were not affected by each task, but the peak-to-peak amplitude (N140-P230) was significantly decreased by both the calculation and memorization tasks, particularly by the former. Subjective pain rating was decreased in both the calculation and memorization tasks, particularly in the former. We concluded that distraction tasks reduced activities in the limbic system, in which the middle-latency EEG component probably generated, while neither the short-latency SEF components generated in SI nor the primary pain-related SEF components generated in SII-insula are affected.
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PMID:Effects of distraction on pain-related somatosensory evoked magnetic fields and potentials following painful electrical stimulation. 1072

Averaged magnetoencephalography (MEG) following somatosensory stimulation, somatosensory evoked magnetic field(s) (SEF), in humans are reviewed. The equivalent current dipole(s) (ECD) of the primary and the following middle-latency components of SEF following electrical stimulation within 80-100 ms are estimated in area 3b of the primary somatosensory cortex (SI), the posterior bank of the central sulcus, in the hemisphere contralateral to the stimulated site. Their sites are generally compatible with the homunculus which was reported by Penfield using direct cortical stimulation during surgery. SEF to passive finger movement is generated in area 3a or 2 of SI, unlike with electrical stimulation. Long-latency components with peaks of approximately 80-120 ms are recorded in the bilateral hemispheres and their ECD are estimated in the secondary somatosensory cortex (SII) in the bilateral hemispheres. We also summarized (1) the gating effects on SEF by interference tactile stimulation or movement applied to the stimulus site, (2) clinical applications of SEF in the fields of neurosurgery and neurology and (3) cortical plasticity (reorganization) of the SI. SEF specific to painful stimulation is also recorded following painful stimulation by CO(2) laser beam. Pain-specific components are recorded over 150 ms after the stimulus and their ECD are estimated in the bilateral SII and the limbic system. We introduced a newly-developed multi (12)-channel gradiometer system with the smallest and highest quality superconducting quantum interference device (micro-SQUID) available to non-invasively detect the magnetic fields of a human peripheral nerve. Clear nerve action fields (NAFs) were consistently recorded from all subjects.
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PMID:The somatosensory evoked magnetic fields. 1074 21

The study of pain integration, in vivo, within the human brain has been largely improved by the functional neuro-imaging techniques available for about 10 years. Positron Emission Tomography (PET), complemented by laser evoked potentials (LEP) and functional Magnetic Resonance Imaging (fMRI) can nowadays generate maps of physiological or neuropathic pain-related brain activity. LEP and fMRI complement PET by their better temporal resolution and the possibility of individual subject analyze. Recent advances in our knowledge of pain mechanisms concern physiological acute pain, neuropathic pain and investigation of analgesic mechanisms. The sixteen studies using PET have demonstrated pain-related activations in thalamus, insula/SII, anterior cingulate and posterior parietal cortices Activity in right pre-frontal and posterior parietal cortices, anterior cingulate and thalami can be modulated by attention (hypnosis, chronic pain, diversion, selective attention to pain) and probably subserve attentional processes rather than pain analysis. Responses in insula/SII cortex presumably subserve discriminative aspects of pain perception while SI cortex is particularly involved in particular aspects of pain discrimination (movement, contact.) In patients, neuropathic pain, angina and atypical facial pain result in PET abnormalities whose significance remain obscure but which are localized in thalamus and anterior cingulate cortices suggesting their distribution is not random while discriminative responses remain detectable in insula/SII. Drug or stimulation induced analgesia are associated with normalization of basal thalamic abnormalities associated with many chronic pains. The need to investigate the significance of these responses, their neuro-chemical correlates (PET), their time course, the individual strategies by which they have been generated by correlating PET data with LEP and fMRI results, are the challenges that remain to be addressed in the next few years by physicians and researchers. To advance our knowledge of the mechanisms generating both abnormal pain and analgesia (drugs and surgical techniques) in patients is the main motivation of such anexciting challenge.
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PMID:[Positron emission tomography to study central pain integration]. 1079 10

Dipolar source modeling might help in clarifying whether somatosensory evoked potentials (SEPs) after electrical stimulation at painful intensity contain any information related to the nociceptive processing. SEPs were recorded after left median nerve stimulation at three different intensities: intense but nonpainful (intensity 2); slightly painful (pain threshold; intensity 4); and moderately painful (intensity 6). Scalp SEPs at intensities 2, 4, and 6 were fitted by a five-dipole model. When the strength modifications of the source activities up to 40 ms were examined across the different stimulus intensities, no significant difference was found. In the later epoch (40-200 ms), a posterior parietal dipole and two bilateral sources probably located in the second somatosensory (SII) areas increased significantly their dipole moments when the stimulus was increased from 2 to 4 and became painful. Since no difference was found when the stimulus intensity was increased from 4 to 6, the observed increase of the dipolar strengths is probably related to a variation of the stimulus quality (nonpainful vs. painful), rather than of the stimulus intensity per se. Our findings lead us to conclude that a large convergence of nociceptive and non-nociceptive afferents probably occurs bilaterally in the SII areas.
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PMID:Dipolar source modeling of somatosensory evoked potentials to painful and nonpainful median nerve stimulation. 1091 55

Reports on phantom limb patients concerning neuronal reorganization using non-invasive methods have focused mainly on the cortical regions and suggest the presence of pain as the cause of this reorganization. The phantom limb, however, includes other somatic and motor sensations other than pain. Here we describe the results of non-painful stimulation in cortical and subcortical lateralization and reorganization and also examine the involvement of subcortical structures in phantom limb telescoping perception. We describe an enlarged contralateral cortical representation of the stump, a cortical and thalamic bilateral representation of the remaining leg, and a neuronal correlate of a telescoping perception of the phantom limb. The missing leg produces an enlarged cortical representation due to abnormal information and the remaining leg has a bilateral SII representation, which could be related to new, compensatory functions. The telescoping perception of a phantom limb by the stimulation of misallocation points was correlated with lenticular nuclei, thalamic and cingulate gyrus activation. We therefore propose that the reorganization concept of a phantom limb, applied mainly to the cortex, must extend to the thalamic and the somatosensory and motor systems (pathways and relay nuclei).
Eur J Pain 2000
PMID:Brain somatic representation of phantom and intact limb: a fMRI study case report. 1098 67

Brain responses to pain, assessed through positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) are reviewed. Functional activation of brain regions are thought to be reflected by increases in the regional cerebral blood flow (rCBF) in PET studies, and in the blood oxygen level dependent (BOLD) signal in fMRI. rCBF increases to noxious stimuli are almost constantly observed in second somatic (SII) and insular regions, and in the anterior cingulate cortex (ACC), and with slightly less consistency in the contralateral thalamus and the primary somatic area (SI). Activation of the lateral thalamus, SI, SII and insula are thought to be related to the sensory-discriminative aspects of pain processing. SI is activated in roughly half of the studies, and the probability of obtaining SI activation appears related to the total amount of body surface stimulated (spatial summation) and probably also by temporal summation and attention to the stimulus. In a number of studies, the thalamic response was bilateral, probably reflecting generalised arousal in reaction to pain. ACC does not seem to be involved in coding stimulus intensity or location but appears to participate in both the affective and attentional concomitants of pain sensation, as well as in response selection. ACC subdivisions activated by painful stimuli partially overlap those activated in orienting and target detection tasks, but are distinct from those activated in tests involving sustained attention (Stroop, etc.). In addition to ACC, increased blood flow in the posterior parietal and prefrontal cortices is thought to reflect attentional and memory networks activated by noxious stimulation. Less noted but frequent activation concerns motor-related areas such as the striatum, cerebellum and supplementary motor area, as well as regions involved in pain control such as the periaqueductal grey. In patients, chronic spontaneous pain is associated with decreased resting rCBF in contralateral thalamus, which may be reverted by analgesic procedures. Abnormal pain evoked by innocuous stimuli (allodynia) has been associated with amplification of the thalamic, insular and SII responses, concomitant to a paradoxical CBF decrease in ACC. It is argued that imaging studies of allodynia should be encouraged in order to understand central reorganisations leading to abnormal cortical pain processing. A number of brain areas activated by acute pain, particularly the thalamus and anterior cingulate, also show increases in rCBF during analgesic procedures. Taken together, these data suggest that hemodynamic responses to pain reflect simultaneously the sensory, cognitive and affective dimensions of pain, and that the same structure may both respond to pain and participate in pain control. The precise biochemical nature of these mechanisms remains to be investigated.
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PMID:Functional imaging of brain responses to pain. A review and meta-analysis (2000). 1112 40

The traditional view that the cerebral cortex is not involved in pain processing has been abandoned during the past decades based on anatomic and physiologic investigations in animals, and lesion, functional neuroimaging, and neurophysiologic studies in humans. These studies have revealed an extensive central network associated with nociception that consistently includes the thalamus, the primary (SI) and secondary (SII) somatosensory cortices, the insula, and the anterior cingulate cortex (ACC). Anatomic and electrophysiologic data show that these cortical regions receive direct nociceptive thalamic input. From the results of human studies there is growing evidence that these different cortical structures contribute to different dimensions of pain experience. The SI cortex appears to be mainly involved in sensory-discriminative aspects of pain. The SII cortex seems to have an important role in recognition, learning, and memory of painful events. The insula has been proposed to be involved in autonomic reactions to noxious stimuli and in affective aspects of pain-related learning and memory. The ACC is closely related to pain unpleasantness and may subserve the integration of general affect, cognition, and response selection. The authors review the evidence on which the proposed relationship between cortical areas, pain-related neural activations, and components of pain perception is based.
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PMID:Neurophysiology and functional neuroanatomy of pain perception. 1115 77

We evaluated the effectiveness of the Multiple Signal Classification (MUSIC) algorithm by analysing pain-related somatosensory-evoked magnetic fields (SEFs) by 148-channel whole-head-type magnetoencephalography. MUSIC peaks of middle latency components were located around the primary somatosensory cortex (SI), contralateral to the stimulated finger. Long latency components were located around the bilateral secondary somatosensory cortices (SII) and cingulate gyri. Peaks at the SII and cingulate gyri were more prominent on very painful and moderately painful stimulation than on weak stimulation. The results were in very good agreement with results from single dipole estimation. These findings suggest that the MUSIC algorithm could be a useful tool for analysis of pain-related SEFs.
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PMID:Analysis of pain-related somatosensory evoked magnetic fields using the MUSIC (multiple signal classification) algorithm for magnetoencephalography. 1140 35

The primary (SI) and secondary (SII) somatosensory cortices have been shown to participate in human pain processing. However, in humans it is unclear how SI and SII contribute to the encoding of nociceptive stimulus intensity. Using magnetoencephalography (MEG) we recorded responses in SI and SII in eight healthy humans to four different intensities of selectively nociceptive laser stimuli delivered to the dorsum of the right hand. Subjects' pain ratings correlated highly with the applied stimulus intensity. Activation of contralateral SI and bilateral SII showed a significant positive correlation with stimulus intensity. However, the type of dependence on stimulus intensity was different for SI and SII. The relation between SI activity and stimulus intensity resembled an exponential function and matched closely the subjects' pain ratings. In contrast, SII activity showed an S-shaped function with a sharp increase in amplitude only at a stimulus intensity well above pain threshold. The activation pattern of SI suggests participation of SI in the discriminative perception of pain intensity. In contrast, the all-or-none-like activation pattern of SII points against a significant contribution of SII to the sensory-discriminative aspects of pain perception. Instead, SII may subserve recognition of the noxious nature and attention toward painful stimuli.
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PMID:Differential coding of pain intensity in the human primary and secondary somatosensory cortex. 1153 93

In this study we compare the intrinsic characteristics and localization of nociceptive CO(2) laser evoked potential (LEP) and non-nociceptive electrical EP (SEP) sources recorded by deep electrodes (one to two electrodes per patient, 10-15 contacts per electrode) directly implanted in the supra-sylvian cortex of 15 epileptic patients. Early CO(2) laser (N140-P170) and electrical (N60-P90) evoked potentials were recorded by all of the electrodes implanted in the supra-sylvian cortex contralateral to stimulation. SEPs and LEPs had similar waveforms and inter-peak latencies. The LEPs appeared 84+/-15 ms later and were, on average, 14.2+/-22.2 microV smaller than the SEPs. These differences may be accounted for by the characteristics and the sizes of the different peripheral fibers (Adelta vs. Abeta) activated by the two types of stimuli. The stereotactic Talairach coordinates of the SEP and LEP sources covered the pre- and post-rolandic upper bank of the sylvian fissure, and were not significantly different for noxious and non-noxious stimuli. The spatial distribution of these contralateral responses fits with that of the modeled sources of scalp CO(2) LEPs, magneto-encephalographic studies, and PET data from pain and vibrotactile activation studies. These results permit us to define the SII cortex as a cortical integration area of non-nociceptive and nociceptive inputs. This is supported by: (i) anatomical data reporting that the SII area receives inputs from both posterior columns and spino-thalamic pathways conveying the non-noxious and noxious information, respectively, and (ii) single cell recordings in monkeys, demonstrating that the SII area contains both nociceptive-specific neurons and wide-dynamic-range neurons receiving convergent input from nociceptive and non-nociceptive somatosensory afferents.
Pain 2001 Oct
PMID:Responses of the supra-sylvian (SII) cortex in humans to painful and innocuous stimuli. A study using intra-cerebral recordings. 1157 46


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