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Objective: Our aim was to investigate CO(2) laser-evoked potential (LEP) habituation to experimental pain in a group of patients affected by medication-overuse headache, with a history of episodic migraine becoming chronic, before and after treatment, consisting in acute medication withdrawal and a preventive treatment cycle., Background: One of the main features of LEPs in migraineurs is a lower habituation to repetitive noxious stimuli during the interictal phase., Methods: LEPs were recorded to stimulation of both the right hand and the right perioral region in 14 patients and in 14 healthy subjects. The habituation of both the N1 and the vertex N2/P2 components was assessed by measuring the LEP amplitude changes across 3 consecutive repetitions of 30 trials each., Results: In the 8 patients who had clinically improved after treatment, the N2/P2 amplitude habituation was significantly higher after treatment than before treatment following both hand (F = 43.2, P < .0001) and face stimulation (F = 6.9, P = .01). In these patients, the N2/P2 amplitude habituation after treatment was not different from that obtained in healthy controls (P = .18 and P = .73 for hand and face stimulation, respectively). On the contrary, in the patients who did not improve, the N2/P2 amplitude still showed reduced habituation after both hand (F = 3.1, P = .08) and face (F = 0.7, P = .4) stimulation., Conclusion: The deficient habituation of the vertex N2/P2 complex was partly restored after successful treatment of medication-overuse headache, reflecting a modification in pain-processing pathways., (© 2012 American Headache Society.)

Charcot-Marie-Tooth (CMT) disease is the most common inherited neuropathy. The CMT1A type can be considered the typical phenotype of this disease. Although pain is not considered a relevant symptom in CMT patients by physicians and no study assessed it comprehensively, this symptom is frequently complained by patients. The objective of the present study was to investigate the nociceptive system in a sample of CMT1A patients suffering from pain by laser-evoked potentials (LEPs). Moreover, we also used a pain specific questionnaire in order to obtain patient-oriented data about their painful symptoms, the Neuropathic Pain Diagnostic Questionnaire (DN4). We evaluated 16 patients affected by CMT1A and 14 controls. All subjects underwent a standard LEP recording session (foot, hand, and face stimulation) and filled in the DN4. While the N2/P2 amplitude to foot stimulation was lower in CMT patients than in controls (p=0.003), no difference in LEP amplitude to both hand and face stimulation was found between patients and healthy subjects (p>0.05). This result is probably due to a length-dependent Adelta-fiber loss which involves mostly the longer fibers coming from the lower limb. In our patients, there was a significant association between a reduced N2/P2 amplitude to foot stimulation and a high DN4 score (p=0.03), meaning that patients with highly probable neuropathic pain had also low N2/P2 amplitude values to painful foot stimulation. This suggests that in our CMT1A patients neuropathic pain is probably related to a reduction of the Adelta afferents., (Copyright 2010 International Association for the Study of Pain. Published by Elsevier B.V. All rights reserved.)

Seeing actions, emotions and feelings of other individuals may activate resonant mechanisms that allow the empathic understanding of others' states. Being crucial for implementing pro-social behaviors, empathy is considered as inherently altruistic. Here we explored whether the personal experience of pain make individuals less inclined to share others' pain. We used laser-evoked potentials (LEPs) to explore whether observation of painful or non-noxious stimuli delivered to a stranger model induced any modulation in the pain system of onlookers who were suffering from pain induced by the laser stimuli. After LEPs recording, participants rated intensity and unpleasantness of the laser pain, and of the pain induced by the movie in themselves and in the model. Mere observation of needles penetrating the model's hand brought about a specific reduction of the N1/P1 LEP component, related to the activation of somatic nodes of the pain matrix. Such reduction is stronger in onlookers who rated the pain intensity induced by the pain movie as higher in themselves and lower in the model. Conversely, the N2a-P2 component, supposedly associated to affective pain qualities, did not show any specific modulation during observation of others' pain. Thus, viewing 'flesh and bone' pain in others specifically modulates neural activity in the pain matrix sensory node. Moreover, this socially-derived inhibitory effect is correlated with the intensity of the pain attributed to self rather than to others suggesting that being in pain may bias the empathic relation with stranger models towards self-centred instead than other-related stances.

Objective: To investigate the possible presence of multiple spino-thalamic pathways with different conduction velocities (CVs) in the human spinal cord., Methods: Laser evoked potentials (LEPs) were recorded in 10 healthy subjects after stimulation of the dorsal midline at four vertebral level: C5, T2, T6, and T10. This method allowed us to minimize the influence of the conduction in the peripheral fibers and to calculate the spinal CV in two different ways: (1) the reciprocal of the slope of the regression line was obtained from the latencies of the different LEP components, and (2) the distance between C5 and T10 was divided by the latency difference of the responses at the two sites. In particular, we considered the middle-latency N1 potential (latencies of around 135, 150, 157, and 171 ms after stimulation at C5, T2, T6, and T10 levels, respectively), which is generated in the second somatosensory (SII) area, and the late P2 response (latencies of around 336, 344, 346, and 362 ms after stimulation at C5, T2, T6, and T10 levels, respectively), which is generated in the anterior cingulate cortex (ACC)., Results: The calculated CV of the spinal fibers generating the N1 potential (around 9 m/s) was significantly different (P<0.05) from the one of the pathway producing the P2 response (around 13 m/s)., Conclusions: Our results suggest that the N1 and the P2 LEP components are generated by two parallel spinal pathways., Significance: Both the N1 and P2 potentials should be recorded in the clinical routine since a dissociated abnormality of either response may be found in lesions of the nociceptive system not only in the brain, but also at spinal cord level.

The aim of the study was to compare the cerebral generators following painful stimulation of the sigmoid colon and the abdominal skin in 11 healthy subjects. The evoked potentials (EPs) were recorded from 31 surface electrodes following painful electrical stimuli of the sigmoid colon, and of the referred pain area on the abdomen. Current dipole models estimating the EPs amplitude and topography were calculated. For colon stimulation, the earliest cortical activities were described by dipoles in the bilateral insula and in the anterior cingulate cortex, while both secondary somatosensory areas were activated later. When the skin was stimulated, early bilateral dipoles in the primary and secondary somatosensory areas were estimated, followed by a dipole in the frontal region. This suggests that painful cutaneous and visceral stimuli are processed differently in the brain.

Objective: To investigate possible neuroplastic changes induced by pain in cerebral areas devoted to nociceptive input processing., Methods: CO(2) laser-evoked potentials (LEPs) were recorded from 10 healthy subjects after stimulation of the right and left hand dorsum. Acute pain was obtained by topical application of capsaicin on the skin of right hand dorsum. LEPs were recorded after right and left hand stimulation before capsaicin, at the peak pain and 10-20 min after capsaicin removal. Right hand LEPs were evoked by laser stimuli delivered over the zone of secondary hyperalgesia during capsaicin and on both the zones of primary and secondary hyperalgesia after capsaicin removal., Results: After right hand stimulation, the vertex LEPs, which are generated in the cingulate cortex, were significantly decreased in amplitude during capsaicin application and after capsaicin removal. Moreover, the topography of these potentials was modified after capsaicin removal, shifting from the central toward the parietal region. Dipolar modelling showed that the dipolar source in the anterior cingulate cortex moved backward after capsaicin removal. All these changes were not observed after stimulation of the left hand, contralateral to the application of capsaicin, thus suggesting that functional changes are selective for the painful skin and the adjacent territories., Conclusions: Our results suggest that acute cutaneous pain may inhibit the neural activity in regions of central nervous system processing nociceptive inputs and cortical representation of these inputs can be rapidly modified in presence of acute pain.

Contact heat evoked potentials (CHEPs) were collected in 12 healthy subjects by stimulating the forearm skin with a couple of thermodes at a painful intensity. The stimulated area was 628 mm2 and the repetition rate was 0.1 Hz. The electroencephalogram was recorded by 31 electrodes placed on the scalp according to an extended 10–20 System. A dipolar model explaining the scalp CHEP distribution was built by using the brain electrical source analysis. The model includes two dipoles located bilaterally in the perisylvian region, one dipole in the deep midline region and two dipoles located bilaterally in the deep temporal lobe. This dipolar model is very similar to that previously described to explain the topography of evoked potentials to radiant heat stimulation by laser pulses. Since laser stimuli activate the nociceptive fibres, the strong similarity of the cerebral dipoles activated by contact heat stimuli and by laser pulses suggests that only nociceptive inputs are involved in the scalp painful CHEP building. Therefore, CHEP recording can be useful for clinical examination of the nociceptive system. [Copyright &y& Elsevier]

Our study aimed at investigating the scalp topography of ultra-late CO2 laser evoked potentials (LEPs), which are related to C fiber activation, and at exploring the effect of attention deviation on ultra-late LEPs. Brain responses to non-painful CO2 laser stimuli were recorded in ten healthy subjects in three different conditions: (i) neutral condition in which subjects did not have any task; (ii) distraction condition in which subjects were asked to perform a mathematical task; and (iii) attention condition in which subjects had to count the number of stimuli. In all subjects, also Að fiber-related late LEPs were recorded after painful CO2 laser stimulation. The ultra-late LEPs in attention condition included an earlier negative potential (ultra-late N1) in the contralateral temporal region and a simultaneous frontal positive response (ultra-late P1). Later, a vertex biphasic component (ultra-late N2a and ultra-late P2) was identifiable. The vertex ultra-late LEP amplitude was significantly decreased in both neutral and distraction condition. Ultra-late LEPs showed a longer latency than late LEPs, but the scalp distributions of both ultra-late and late LEPs were very similar, thus suggesting that the same cerebral areas may be involved in their generation. Since attention deviations have a strong effect on ultra-late LEP amplitude, the subject''s attention should be addressed to CO2 laser stimuli when ultra-late LEPs are used for clinical purposes. [Copyright &y& Elsevier]