The pain matrix reloaded: a salience detection system for the body

Neuroimaging and neurophysiological studies have shown that nociceptive stimuli elia salience detection system for the bodycit responses in an extensive cortical network including somatosensory, insular and cingulate areas, as well as frontal and parietal areas. This network, often referred to as the "pain matrix", is viewed as representing the activity by which the intensity and unpleasantness of the perception elicited by a nociceptive stimulus are represented. However, recent experiments have reported (i) that pain intensity can be dissociated from the magnitude of responses in the "pain matrix", (ii) that the responses in the "pain matrix" are strongly influenced by the context within which the nociceptive stimuli appear, and (iii) that non-nociceptive stimuli can elicit cortical responses with a spatial configuration similar to that of the "pain matrix". For these reasons, we propose an alternative view of the functional significance of this cortical network, in which it reflects a system involved in detecting, orienting attention towards, and reacting to the occurrence of salient sensory events. This cortical network might represent a basic mechanism through which significant events for the body's integrity are detected, regardless of the sensory channel through which these events are conveyed. This function would involve the construction of a multimodal cortical representation of the body and nearby space. Under the assumption that this network acts as a defensive system signaling potentially damaging threats for the body, emphasis is no longer on the quality of the sensation elicited by noxious stimuli but on the action prompted by the occurrence of potential threats

The effect of heterotopic noxious conditioning stimulation on A-, C- and A-fibre brain responses in humans

Human studies have shown that heterotopic nociceptive conditioning stimulation (HNCS) applied to a given body location reduces the percept and brain responses elicited by noxious test stimuli delivered at a remote body location. It remains unclear to what extent this effect of HNCS relies on the spinal-bulbar-spinal loop mediating the effect of diffuse noxious inhibitory controls (DNICs) described in animals, and/or on top-down cortical mechanisms modulating nociception. Importantly, some studies have examined the effects of HNCS on the brain responses to nociceptive input conveyed by Aδ-fibres. In contrast, no studies have explored the effects of HNCS on the responses to selective nociceptive C-fibre input and non-nociceptive Aβ-fibre input. In this study, we measured the intensity of perception and event-related potentials (ERPs) to stimuli activating Aδ-, C- and Aβ-fibres, before, during and after HNCS, obtained by immersing one foot in painful cold water. We observed that (i) the perceived intensity of nociceptive Aδ- and C-stimuli was reduced during HNCS, and (ii) the ERPs elicited by Aδ- and Aβ- and C-stimuli were also reduced during HNCS. Importantly, because Aβ-ERPs are related to primary afferents that ascend directly through the dorsal columns without being relayed at spinal level, the modulation of these responses may not be explained by an influence of descending projections modulating the transmission of nociceptive input at spinal level. Therefore, our results indicate that, in humans, HNCS should be used with caution as a direct measure of DNIC-related mechanisms.status: publishe

Assessment of spinal somatosensory systems with diffusion tensor imaging in syringomyelia: spinal diffusion tensor imaging in syringomyelia

International audienceWe tested the use of diffusion tensor imaging with three-dimensional fiber tracking (DTI-FT) for the assessment of spinal sensory tract lesions. We systematically examined the relationships between tract lesions quantified with DTI-FT, and somatosensory dysfunction assessed with quantitative sensory testing (QST) and laser evoked potentials (LEP), in patients with syringomyelia

Long term clinical outcome of peripheral nerve stimulation in patients with chronic peripheral neuropathic pain

BACKGROUND: Chronic neuropathic pain after injury to a peripheral nerve is known to be resistant to treatment. Peripheral nerve stimulation is one of the possible treatment options, which is, however, not performed frequently. In recent years we have witnessed a renewed interest for PNS. The aim of the present study was to evaluate the long-term clinical efficacy of PNS in a group of patients with peripheral neuropathic pain treated with PNS since the 1980s. METHODS: Of an original series of 11 patients, 5 patients could be invited for clinical examination, detailed assessment of clinical pain and QST examination. The assessments were done both during habitual use of PNS and with the stimulator off. RESULTS: Average pain intensity and pain unpleasantness ratings as assessed with visual analog and verbal rating scales showed significant beneficial effects of PNS. Quality of life measures (sleep and daily functioning) also showed positive effects. Quantitative Sensory Testing results did not show significant differences in cold pain and heat pain thresholds between the "ON" and "OFF" conditions. CONCLUSION: In selected patients with peripheral neuropathic pain PNS remains effective even after more than 20 years.status: publishe

Respiratory hypoalgesia? Breath-holding, but not respiratory phase modulates nociceptive flexion reflex and pain intensity

Several observations suggest that respiratory phase (inhalation vs. exhalation) and post-inspiratory breath-holds could modulate pain and the nociceptive reflex. This experiment aimed to investigate the role of both mecha- nisms. Thirty-two healthy participants received supra-threshold electrocutaneous stimulations to elicit both the Nociceptive Flexion Reflex (NFR) and pain, either during spontaneous inhalations or exhalations, or during three types of instructed breath-holds: following exhalation, at mid-inhalation and at full-capacity inhalation. Whether the electrocutaneous stimulus was applied during inhalation or exhalation did not affect the NFR or pain. Self-reported pain was reduced and the NFR was increased during breath-holding compared to spontane- ous breathing. Whereas the type of breath-hold did not impact on self-reported pain, breath-holds at full- capacity inhalation and following exhalation were associated with a lower NFR amplitude compared to breath- holds at mid-inhalation. The present findings confirm that breath-holding can modulate pain (sensitivity) and suggest that both attentional distraction and changes in vagal activity may underlie the observed effects

Recommendations for using opioids in chronic non-cancer pain.

1. The management of chronic pain should be directed by the underlying cause of the pain. Whatever the cause, the primary goal of patient care should be symptom control. 2. Opioid treatment should be considered for both continuous neuropathic and nociceptive pain if other reasonable therapies fail to provide adequate analgesia within a reasonable timeframe. 3. The aim of opioid treatment is to relieve pain and improve the patient's quality of life. Both of these should be assessed during a trial period. 4. The prescribing physician should be familiar with the patient's psychosocial status. 5. The use of sustained-release opioids administered at regular intervals is recommended. 6. Treatment should be monitored. 7. A contract setting out the patient's rights and responsibilities may help to emphasize the importance of patient involvement. 8. Opioid treatment should not be considered a lifelong treatment