Parietal pseudothalamic pain syndrome. Clinical features and anatomic correlates

Epidural Posterior Insular Stimulation Alleviates Neuropathic Pain Manifestations in Rats With Spared Nerve Injury Through Endogenous Opioid System

OBJECTIVES

Neuropathic pain (NP) is defined as constant disabling pain secondary to a lesion or disease of the somatosensory nervous system. This condition is particularly difficult to treat because it often remains resistant to most treatment strategies. Despite the recent diversification of neurostimulation methods, some patients still suffer from refractory pain syndromes. The central role of the posterior insular cortex (PI) in the modulation of pain signaling and perception has been repeatedly suggested. The objective of this study is to assess whether epidural insular stimulation (IS) could reverse NP behavior.

MATERIALS AND METHODS

A total of 53 adult Sprague-Dawley rats received left-sided spared nerve injury (SNI) or Sham-SNI to induce NP symptoms. Afterward, epidural electrodes were implanted over the right PI. After two weeks of postoperative recovery, three groups of SNI-operated rats each received a different stimulation modality: Sham-IS, low-frequency-IS (LF-IS), or high-frequency-IS (HF-IS). Behavioral and functional tests were conducted before and after IS. They comprised the acetone test, pinprick test, von Frey test, and sciatic functional index. An additional LF-IS group received a dose of opioid antagonist naloxone before IS. Intergroup means were compared through independent-samples t-tests, and pre- and post-IS means in the same group were compared through paired t-tests.

RESULTS

We found a significant reduction of cold allodynia (p = 0.019), mechanical hyperalgesia (p = 0.040), and functional disability (p = 0.005) after LF-IS but not HF-IS. Mechanical allodynia only showed a tendency to decrease after LF-IS. The observed analgesic effects were reversed by opioid antagonist administration.

CONCLUSION

These results suggest a significant reversal of NP symptoms after LF-IS and offer additional evidence that IS might be beneficial in the treatment of resistant NP syndromes through endogenous opioid secretion. Relying on our novel epidural IS model, further fine tuning of stimulation parameters might be necessary to achieve optimal therapeutic effects.

The Role of the Insular Cortex in Pain

The transition from normal to chronic pain is believed to involve alterations in several brain areas that participate in the perception of pain. These plastic changes are then responsible for aberrant pain perception and comorbidities. The insular cortex is consistently found activated in pain studies of normal and chronic pain patients. Functional changes in the insula contribute to chronic pain; however, the complex mechanisms by which the insula is involved in pain perception under normal and pathological conditions are still not clear. In this review, an overview of the insular function is provided and findings on its role in pain from human studies are summarized. Recent progress on the role of the insula in pain from preclinical experimental models is reviewed, and the connectivity of the insula with other brain regions is examined to shed new light on the neuronal mechanisms of the insular cortex’s contribution to normal and pathological pain sensation. This review underlines the need for further studies on the mechanisms underlying the involvement of the insula in the chronicity of pain and the expression of comorbid disorders.

Network Effects of Brain Lesions Causing Central Poststroke Pain

OBJECTIVE

This study was undertaken to test whether lesions causing central poststroke pain (CPSP) are associated with a specific connectivity profile, whether these connections are associated with metabolic changes, and whether this network aligns with neuromodulation targets for pain.

METHODS

Two independent lesion datasets were utilized: (1) subcortical lesions from published case reports and (2) thalamic lesions with metabolic imaging using 18F- fluorodeoxyglucose positron emission tomography-computed tomography. Functional connectivity between each lesion location and the rest of the brain was assessed using a normative connectome (n = 1,000), and connections specific to CPSP were identified. Metabolic changes specific to CPSP were also identified and related to differences in lesion connectivity. Therapeutic relevance of the network was explored by testing for alignment with existing brain stimulation data and by prospectively targeting the network with repetitive transcranial magnetic stimulation (rTMS) in 7 patients with CPSP.

RESULTS

Lesion locations causing CPSP showed a specific pattern of brain connectivity that was consistent across two independent lesion datasets (spatial r = 0.82, p < 0.0001). Connectivity differences were correlated with postlesion metabolism (r = -0.48, p < 0.001). The topography of this lesion-based pain network aligned with variability in pain improvement across 12 prior neuromodulation targets and across 32 patients who received rTMS to primary motor cortex (p < 0.05). Prospectively targeting this network with rTMS improved CPSP in 6 of 7 patients.

INTERPRETATION

Lesions causing pain are connected to a specific brain network that shows metabolic abnormalities and promise as a neuromodulation target. ANN NEUROL 2022;92:834-845.

Dissecting neuropathic from poststroke pain: the white matter within

ABSTRACT

Poststroke pain (PSP) is a heterogeneous term encompassing both central neuropathic (ie, central poststroke pain [CPSP]) and nonneuropathic poststroke pain (CNNP) syndromes. Central poststroke pain is classically related to damage in the lateral brainstem, posterior thalamus, and parietoinsular areas, whereas the role of white matter connecting these structures is frequently ignored. In addition, the relationship between stroke topography and CNNP is not completely understood. In this study, we address these issues comparing stroke location in a CPSP group of 35 patients with 2 control groups: 27 patients with CNNP and 27 patients with stroke without pain. Brain MRI images were analyzed by 2 complementary approaches: an exploratory analysis using voxel-wise lesion symptom mapping, to detect significant voxels damaged in CPSP across the whole brain, and a hypothesis-driven, region of interest-based analysis, to replicate previously reported sites involved in CPSP. Odds ratio maps were also calculated to demonstrate the risk for CPSP in each damaged voxel. Our exploratory analysis showed that, besides known thalamic and parietoinsular areas, significant voxels carrying a high risk for CPSP were located in the white matter encompassing thalamoinsular connections (one-tailed threshold Z > 3.96, corrected P value <0.05, odds ratio = 39.7). These results show that the interruption of thalamocortical white matter connections is an important component of CPSP, which is in contrast with findings from nonneuropathic PSP and from strokes without pain. These data can aid in the selection of patients at risk to develop CPSP who could be candidates to pre-emptive or therapeutic interventions.

[Hemiplegia cruciata and severe facial pain due to infarction of the cervicomedullary junction: a case report]

We report the case of a 66-year-old female with hemiplegia cruciata and severe facial pain due to infarction of the cervicomedullary junction. She presented to the hospital with complaints of acute-onset left facial pain and gait disturbance. Neurological examination revealed narrow left palpebral fissure, severe left facial pain and hypothermoesthesia, weakness predominantly in the left upper and right lower extremities, decreased pain and temperature sensation in the right lower extremity, decreased vibration sensation in the left lower extremity, hyperreflexia in the left upper extremity, and mild ataxia in the left upper and lower extremities. Brain MRI revealed a high-intensity lesion in the left cervicomedullary junction on diffusion-weighted and fluid-attenuated inversion recovery images. Hemiplegia cruciata due to the pyramidal tract injury at the cervicomedullary junction is an uncommon clinical manifestation. However, in patients with hemiplegia cruciata, identifying the lesion location may be difficult. Clinicians should consider the possibility of pyramidal decussation lesions. Anatomical differences, in the course of pyramidal tract fibers between the upper and lower limbs have been considered in the pyramidal decussation. Hemiplegia cruciata in this case was primarily caused by the impairment of the left upper limb pyramidal fibers after the pyramidal decussation and the right lower limb pyramidal fibers before the pyramidal decussation.

A voxel-based lesion symptom mapping analysis of chronic pain in multiple sclerosis

BACKGROUND

Pain is one of the most disabling symptoms in multiple sclerosis. Chronic pain in multiple sclerosis is often neuropathic in nature, although a clear-cut distinction with nociceptive pain is not easy.

OBJECTIVE

The aim of our study was to analyze the MRIs of multiple sclerosis patients with chronic pain in order to explore possible associations with lesion sites, on a voxel-by-voxel basis.

MATERIALS AND METHODS

We enrolled patients aged > 18 years with multiple sclerosis in accordance with the 2010 McDonald criteria. Patients meeting criteria for persistent pain (frequent or constant pain lasting > 3 months) were included in the "pain group". The other patients were included in the "no pain group". We outlined lesions on FLAIR MRI scans using a semi-automated edge finding tool. To detect the association between lesion localization and persistent pain, images were analysed with the voxel-based lesion symptom mapping methods implemented in the (nonparametric mapping software included into the MRIcron.

RESULTS

We enrolled 208 MS patients (140 F, mean age 55.2 ± 9.4 years; 176 RR, 28 progressive MS; mean EDSS 2.0 + 2.0). Pain group included 96 patients and no pain group 112 patients. Lesions of the right dorsolateral prefrontal area were significantly more prevalent in patients without pain, whereas periventricular posterior lesions were significantly more prevalent in patients with persistent pain.

CONCLUSION

Our data suggest a role of the right dorsolateral prefrontal cortex in the modulation of pain perception and in the occurrence of chronic pain in MS patients. Our data also support a hemispheric asymmetry in pain perception and modulation.

Noninvasive vagus nerve stimulation alters neural response and physiological autonomic tone to noxious thermal challenge

The mechanisms by which noninvasive vagal nerve stimulation (nVNS) affect central and peripheral neural circuits that subserve pain and autonomic physiology are not clear, and thus remain an area of intense investigation. Effects of nVNS vs sham stimulation on subject responses to five noxious thermal stimuli (applied to left lower extremity), were measured in 30 healthy subjects (n = 15 sham and n = 15 nVNS), with fMRI and physiological galvanic skin response (GSR). With repeated noxious thermal stimuli a group × time analysis showed a significantly (p < .001) decreased response with nVNS in bilateral primary and secondary somatosensory cortices (SI and SII), left dorsoposterior insular cortex, bilateral paracentral lobule, bilateral medial dorsal thalamus, right anterior cingulate cortex, and right orbitofrontal cortex. A group × time × GSR analysis showed a significantly decreased response in the nVNS group (p < .0005) bilaterally in SI, lower and mid medullary brainstem, and inferior occipital cortex. Finally, nVNS treatment showed decreased activity in pronociceptive brainstem nuclei (e.g. the reticular nucleus and rostral ventromedial medulla) and key autonomic integration nuclei (e.g. the rostroventrolateral medulla, nucleus ambiguous, and dorsal motor nucleus of the vagus nerve). In aggregate, noninvasive vagal nerve stimulation reduced the physiological response to noxious thermal stimuli and impacted neural circuits important for pain processing and autonomic output.

Pain syndromes and the parietal lobe

Pain was considered to be integrated subcortically during most of the 20^th century, and it was not until 1956 that focal injury to the parietal opercular-insular cortex was shown to produce selective loss of pain senses. The parietal operculum and adjacent posterior insula are the main recipients of spinothalamic afferents in primates. The innermost operculum appears functionally associated with the posterior insula and can be segregated histologically, somatotopically and neurochemically from the more lateral S2 areas. The Posterior Insula and Medial Operculum (PIMO) encompass functional networks essential to initiate cortical nociceptive processing. Destruction of this region selectively abates pain sensations; direct stimulation generates acute pain, and epileptic foci trigger painful seizures. Lesions of the PIMO have also high potential to develop central pain with dissociated loss of pain and temperature. The PIMO region behaves as a somatosensory area on its own, which handles phylogenetically old somesthetic capabilities based on thinly myelinated or unmyelinated inputs. It integrates spinothalamic-driven information - not only nociceptive but also innocuous heat and cold, crude touch, itch, and possibly viscero-somatic interoception. Conversely, proprioception, graphesthesia or stereognosis are not processed in this area but in S1 cortices. Given its anatomo-functional properties, thalamic connections, and tight relations with limbic and multisensory cortices, the region comprising the inner parietal operculum and posterior insula appears to contain a third somatosensory cortex contributing to the spinothalamic attributes of the final perceptual experience.

Central neural substrates involved in temperature discrimination, thermal pain, thermal comfort, and thermoregulatory behavior

A phylogenetically novel pathway that emerged with primate encephalization is described, which conveys high-fidelity cutaneous thermosensory activity in "labeled lines" to a somatotopic map in the dorsal posterior insular cortex. It originates in lamina I of the superficial dorsal horn and ascends by way of the lateral spinothalamic tract and a distinct region in posterolateral thalamus. It evolved from the homeostatic sensory activity that represents the physiologic (interoceptive) condition of the body and drives the central autonomic network, which underlies all affective feelings from the body. Accordingly, human discriminative thermal sensations are accompanied by thermally motivated behaviors and thermal feelings of comfort or discomfort (unless neutral), which evidence suggests are associated with activity in the insular, cingulate, and orbitofrontal cortices, respectively. Yet, the substrates for thermoregulatory behavior have not been established, and several strong candidates (including the hypothalamus and the bed nucleus of the stria terminalis) are discussed. Finally, the neural underpinnings for relationships between thermal affect and social feelings (warm-positive/cold-negative) are addressed, including the association of hyperthermia with clinical depression.

Rostral Agranular Insular Cortex Lesion with Motor Cortex Stimulation Enhances Pain Modulation Effect on Neuropathic Pain Model

It is well known that the insular cortex is involved in the processing of painful input. The aim of this study was to evaluate the pain modulation role of the insular cortex during motor cortex stimulation (MCS). After inducing neuropathic pain (NP) rat models by the spared nerve injury method, we made a lesion on the rostral agranular insular cortex (RAIC) unilaterally and compared behaviorally determined pain threshold and latency in 2 groups: Group A (NP + MCS; n = 7) and Group B (NP + RAIC lesion + MCS; n = 7). Also, we simultaneously recorded neuronal activity (NP; n = 9) in the thalamus of the ventral posterolateral nucleus and RAIC to evaluate electrophysiological changes from MCS. The pain threshold and tolerance latency increased in Group A with “MCS on” and in Group B with or without “MCS on.” Moreover, its increase in Group B with “MCS on” was more than that of Group B without MCS or of Group A, suggesting that MCS and RAIC lesioning are involved in pain modulation. Compared with the “MCS off” condition, the “MCS on” induced significant threshold changes in an electrophysiological study. Our data suggest that the RAIC has its own pain modulation effect, which is influenced by MCS.

Pain and temperature processing in dementia: a clinical and neuroanatomical analysis

Symptoms suggesting altered pain and temperature processing have been described in dementia diseases. Using a semi-structured caregiver questionnaire and MRI voxel-based morphometry in patients with frontotemporal degeneration or Alzheimer’s disease, Fletcher et al. show that these symptoms are underpinned by atrophy in a distributed thalamo-temporo-insular network implicated in somatosensory processing.

Symptoms suggesting altered processing of pain and temperature have been described in dementia diseases and may contribute importantly to clinical phenotypes, particularly in the frontotemporal lobar degeneration spectrum, but the basis for these symptoms has not been characterized in detail. Here we analysed pain and temperature symptoms using a semi-structured caregiver questionnaire recording altered behavioural responsiveness to pain or temperature for a cohort of patients with frontotemporal lobar degeneration (n = 58, 25 female, aged 52–84 years, representing the major clinical syndromes and representative pathogenic mutations in the C9orf72 and MAPT genes) and a comparison cohort of patients with amnestic Alzheimer’s disease (n = 20, eight female, aged 53–74 years). Neuroanatomical associations were assessed using blinded visual rating and voxel-based morphometry of patients’ brain magnetic resonance images. Certain syndromic signatures were identified: pain and temperature symptoms were particularly prevalent in behavioural variant frontotemporal dementia (71% of cases) and semantic dementia (65% of cases) and in association with C9orf72 mutations (6/6 cases), but also developed in Alzheimer’s disease (45% of cases) and progressive non-fluent aphasia (25% of cases). While altered temperature responsiveness was more common than altered pain responsiveness across syndromes, blunted responsiveness to pain and temperature was particularly associated with behavioural variant frontotemporal dementia (40% of symptomatic cases) and heightened responsiveness with semantic dementia (73% of symptomatic cases) and Alzheimer’s disease (78% of symptomatic cases). In the voxel-based morphometry analysis of the frontotemporal lobar degeneration cohort, pain and temperature symptoms were associated with grey matter loss in a right-lateralized network including insula (P < 0.05 corrected for multiple voxel-wise comparisons within the prespecified anatomical region of interest) and anterior temporal cortex (P < 0.001 uncorrected over whole brain) previously implicated in processing homeostatic signals. Pain and temperature symptoms accompanying C9orf72 mutations were specifically associated with posterior thalamic atrophy (P < 0.05 corrected for multiple voxel-wise comparisons within the prespecified anatomical region of interest). Together the findings suggest candidate cognitive and neuroanatomical bases for these salient but under-appreciated phenotypic features of the dementias, with wider implications for the homeostatic pathophysiology and clinical management of neurodegenerative diseases.

Pharmacological management of central post-stroke pain: a practical guide

Pain is one of the most troublesome sequelae of stroke. Some of this post-stroke pain is caused by the brain lesion itself; this is called central post-stroke pain (CPSP). Although the prevalence of CPSP is low (1-8 %), persistent, often treatment-resistant, painful sensations are a major problem for stroke patients. The pathogenesis of CPSP remains unknown, but suggested underlying causes include hyperexcitation in the damaged sensory pathways, damage to the central inhibitory pathways, or a combination of the two. For pharmacological treatment, amitriptyline, an adrenergic antidepressant, is currently the first-line drug for CPSP. However, its effect is frequently incomplete and a high dose is commonly not tolerated in stroke patients. Lamotrigine, an antiepileptic, was also found to be effective in a controlled trial and can be used as an alternative or additive therapy. GABAergic drugs with potential calcium channel-blocking effects, such as gabapentin or pregabalin, have recently emerged as a potentially useful therapy. These drugs are effective in various neuropathic pain syndromes, but their effect on CPSP remains to be proven. Pregabalin may improve pain-related anxiety and sleep disturbances. Fluvoxamine and mexiletine may be used adjunctively in some patients. Non-pharmacological treatments such as motor cortex stimulation or deep brain stimulation are used in some centers, but are not proven to be effective. Further well designed clinical trials as well as basic research should be performed to improve our understanding of the pathophysiology of CPSP and to develop better treatment strategies.

Insula and sensory insular cortex and somatosensory control in patients with insular stroke

BACKGROUND

In functional imaging studies, the insular cortex (IC) has been identified as an essential part of the processing of a whole spectrum of multimodal sensory input. However, there are no lesion studies including a sufficient number of patients, which would reinforce the functional imaging data obtained from healthy subjects. Such lesion studies should examine how damage to the IC affects sensory perception. We chose acute stroke patients with lesions affecting the IC in order to fill this gap.

METHODS

A comprehensive sensory profiling by applying a quantitative sensory testing protocol was performed and a voxel-lesion behaviour mapping analysis in 24 patients with acute unilateral cortical damage was applied.

RESULTS

Our data demonstrate that patients with lesions of the posterior IC have deficits in temperature perception, but did not show other sensory deficits such as hot or cold pain perception associated with specific lesion locations.

CONCLUSION

Our data allow the conclusion that the posterior IC may represent the major region responsible for encoding warm and cold perception in the brain. To what extent focal IC lesions may also impair pain processing or induce post-stroke pain has to be addressed in future studies including more patients.

Topographically organized projection to posterior insular cortex from the posterior portion of the ventral medial nucleus in the long-tailed macaque monkey

Prior anterograde tracing work identified somatotopically organized lamina I trigemino- and spinothalamic terminations in a cytoarchitectonically distinct portion of posterolateral thalamus of the macaque monkey, named the posterior part of the ventral medial nucleus (VMpo; Craig [2004] J. Comp. Neurol. 477:119-148). Microelectrode recordings from clusters of selectively thermoreceptive or nociceptive neurons were used to guide precise microinjections of various tracers in VMpo. A prior report (Craig and Zhang [2006] J. Comp. Neurol. 499:953-964) described retrograde tracing results, which confirmed the selective lamina I input to VMpo and the anteroposterior (head to foot) topography. The present report describes the results of microinjections of anterograde tracers placed at different levels in VMpo, based on the anteroposterior topographic organization of selectively nociceptive units and clusters over nearly the entire extent of VMpo. Each injection produced dense, patchy terminal labeling in a single coherent field within a distinct granular cortical area centered in the fundus of the superior limiting sulcus. The terminations were distributed with a consistent anteroposterior topography over the posterior half of the superior limiting sulcus. These observations demonstrate a specific VMpo projection area in dorsal posterior insular cortex that provides the basis for a somatotopic representation of selectively nociceptive lamina I spinothalamic activity. These results also identify the VMpo terminal area as the posterior half of interoceptive cortex; the anterior half receives input from the vagal-responsive and gustatory neurons in the basal part of the ventral medial nucleus.

Estrogenic influences in pain processing

Gonadal hormones not only play a pivotal role in reproductive behavior and sexual differentiation, they also contribute to thermoregulation, feeding, memory, neuronal survival, and the perception of somatosensory stimuli. Numerous studies on both animals and human subjects have also demonstrated the potential effects of gonadal hormones, such as estrogens, on pain transmission. These effects most likely involve multiple neuroanatomical circuits as well as diverse neurochemical systems and they therefore need to be evaluated specifically to determine the localization and intrinsic characteristics of the neurons engaged. The aim of this review is to summarize the morphological as well as biochemical evidence in support for gonadal hormone modulation of nociceptive processing, with particular focus on estrogens and spinal cord mechanisms.

The nature of feelings: evolutionary and neurobiological origins

Feelings are mental experiences of body states. They signify physiological need (for example, hunger), tissue injury (for example, pain), optimal function (for example, well-being), threats to the organism (for example, fear or anger) or specific social interactions (for example, compassion, gratitude or love). Feelings constitute a crucial component of the mechanisms of life regulation, from simple to complex. Their neural substrates can be found at all levels of the nervous system, from individual neurons to subcortical nuclei and cortical regions.

Psychogenic nonepileptic seizures and chronic pain: a retrospective case-controlled study

PURPOSE

Psychogenic nonepileptic seizures (PNES) can be challenging to diagnose, but certain clinical features can help to distinguish PNES from epileptic seizures. The purpose of this study is to assess chronic pain and prescribed pain medication use in PNES patients.

METHODS

A case-controlled, retrospective analysis was performed examining pain medication use in 85 PNES patients versus an active control group of 85 patients with idiopathic generalized epilepsy (IGE).

RESULTS

Chronic pain was more frequent among PNES patients (N=40) than active controls (N=10) (p<0.0001). Reported use of prescription pain medication was higher among PNES patients (N=20) versus active controls (N=6) (p=0.0048). The Positive Predictive Value of prescription pain medications for PNES patients was 76.9%. Opioid use in the PNES population was higher compared with active controls (p=0.0096). When excluding patients with a dual diagnosis of PNES and epilepsy from the latter two analyses and comparing these results to those that included this patient population, no statistically significant difference in results was found.

CONCLUSIONS

Patients with PNES are more likely than those with IGE to report chronic pain disorders. A history of chronic pain and opioid use among patients with seizures raises the possibility of PNES. Among patients with PNES and chronic pain, a psychogenic etiology for pain and non-opiate pain management strategies should be considered.

Central poststroke pain: somatosensory abnormalities and the presence of associated myofascial pain syndrome

Background

Central post-stroke pain (CPSP) is a neuropathic pain syndrome associated with somatosensory abnormalities due to central nervous system lesion following a cerebrovascular insult. Post-stroke pain (PSP) refers to a broader range of clinical conditions leading to pain after stroke, but not restricted to CPSP, including other types of pain such as myofascial pain syndrome (MPS), painful shoulder, lumbar and dorsal pain, complex regional pain syndrome, and spasticity-related pain. Despite its recognition as part of the general PSP diagnostic possibilities, the prevalence of MPS has never been characterized in patients with CPSP patients. We performed a cross-sectional standardized clinical and radiological evaluation of patients with definite CPSP in order to assess the presence of other non-neuropathic pain syndromes, and in particular, the role of myofascial pain syndrome in these patients.

Methods

CPSP patients underwent a standardized sensory and motor neurological evaluation, and were classified according to stroke mechanism, neurological deficits, presence and profile of MPS. The Visual Analogic Scale (VAS), McGill Pain Questionnaire (MPQ), and Beck Depression Scale (BDS) were filled out by all participants.

Results

Forty CPSP patients were included. Thirty-six (90.0%) had one single ischemic stroke. Pain presented during the first three months after stroke in 75.0%. Median pain intensity was 10 (5 to 10). There was no difference in pain intensity among the different lesion site groups. Neuropathic pain was continuous-ongoing in 34 (85.0%) patients and intermittent in the remainder. Burning was the most common descriptor (70%). Main aggravating factors were contact to cold (62.5%). Thermo-sensory abnormalities were universal. MPS was diagnosed in 27 (67.5%) patients and was more common in the supratentorial extra-thalamic group (P <0.001). No significant differences were observed among the different stroke location groups and pain questionnaires and scales scores. Importantly, CPSP patients with and without MPS did not differ in pain intensity (VAS), MPQ or BDS scores.

Conclusions

The presence of MPS is not an exception after stroke and may present in association with CPSP as a common comorbid condition. Further studies are necessary to clarify the role of MPS in CPSP.

Psychophysical and cerebral responses to heat stimulation in patients with central pain, painless central sensory loss, and in healthy persons

Patients with central pain (CP) typically have chronic pain within an area of reduced pain and temperature sensation, suggesting an impairment of endogenous pain modulation mechanisms. We tested the hypothesis that some brain structures normally activated by cutaneous heat stimulation would be hyperresponsive among patients with CP but not among patients with a central nervous system lesion causing a loss of heat or nociceptive sensation with no pain (NP). We used H(2)(15)O positron emission tomography to measure, in 15 healthy control participants, 10 NP patients, and 10 CP patients, increases in regional cerebral blood flow among volumes of interest (VOI) from the resting (no stimulus) condition during bilateral contact heat stimulation at heat detection, heat pain threshold, and heat pain tolerance levels. Both patient groups had a reduced perception of heat intensity and unpleasantness on the clinically affected side and a bilateral impairment of heat detection. Compared with the HC group, both NP and CP patients had more hyperactive and hypoactive VOI in the resting state and more hyperresponsive and hyporesponsive VOI during heat stimulation. Compared with NP patients, CP patients had more hyperresponsive VOI in the intralaminar thalamus and sensory-motor cortex during heat stimulation. Our results show that focal CNS lesions produce bilateral sensory deficits and widespread changes in the nociceptive excitability of the brain. The increased nociceptive excitability within the intralaminar thalamus and sensory-motor cortex of our sample of CP patients suggests an underlying pathophysiology for the pain in some central pain syndromes.

Breakthrough pain in malignant and non-malignant diseases: a review of prevalence, characteristics and mechanisms

Breakthrough pain or transient worsening of pain in patients with an ongoing steady pain is a well known feature in cancer pain patients, but it is also seen in non-malignant pain conditions with involvement of nerves, muscles, bones or viscera. Continuous and intermittent pain seems to be a general feature of these different pain conditions, and this raises the possibility of one or several common mechanisms underlying breakthrough pain in malignant and non-malignant disorders. Although the mechanisms of spontaneous ongoing pain and intermittent flares of pain (BTP) may be difficult to separate, we suggest that peripheral and/or central sensitization (hyperexcitability) may play a major role in many causes of BTP. Mechanical stimuli (e.g. micro-fractures) changes in chemical environments and release of tumour growth factors may initiate sensitization both peripherally and centrally. It is suggested that sensitization could be the common denominator of BTP in malignant and non-malignant pain.

Chronic pain following spinal cord injury

Most patients with insults to the spinal cord or central nervous system suffer from excruciating, unrelenting, chronic pain that is largely resistant to treatment. This condition affects a large percentage of spinal cord injury patients, and numerous patients with multiple sclerosis, stroke and other conditions. Despite the recent advances in basic science and clinical research the pathophysiological mechanisms of pain following spinal cord injury remain unknown. Here we describe a novel mechanism of loss of inhibition within the thalamus that may predispose for the development of this chronic pain and discuss a potential treatment that may restore inhibition and ameliorate pain.

Neurological diseases and pain

Chronic pain is a frequent component of many neurological disorders, affecting 20-40% of patients for many primary neurological diseases. These diseases result from a wide range of pathophysiologies including traumatic injury to the central nervous system, neurodegeneration and neuroinflammation, and exploring the aetiology of pain in these disorders is an opportunity to achieve new insight into pain processing. Whether pain originates in the central or peripheral nervous system, it frequently becomes centralized through maladaptive responses within the central nervous system that can profoundly alter brain systems and thereby behaviour (e.g. depression). Chronic pain should thus be considered a brain disease in which alterations in neural networks affect multiple aspects of brain function, structure and chemistry. The study and treatment of this disease is greatly complicated by the lack of objective measures for either the symptoms or the underlying mechanisms of chronic pain. In pain associated with neurological disease, it is sometimes difficult to obtain even a subjective evaluation of pain, as is the case for patients in a vegetative state or end-stage Alzheimer's disease. It is critical that neurologists become more involved in chronic pain treatment and research (already significant in the fields of migraine and peripheral neuropathies). To achieve this goal, greater efforts are needed to enhance training for neurologists in pain treatment and promote greater interest in the field. This review describes examples of pain in different neurological diseases including primary neurological pain conditions, discusses the therapeutic potential of brain-targeted therapies and highlights the need for objective measures of pain.

Stimulation of the human cortex and the experience of pain: Wilder Penfield's observations revisited

Thanks to the seminal work of Wilder Graves Penfield (1891-1976) at the Montreal Neurological Institute, electrical stimulation is used worldwide to localize the epileptogenic cortex and to map the functionally eloquent areas in the context of epilepsy surgery or lesion resections. In the functional map of elementary and experiential responses he described through >20 years of careful exploration of the human cortex via stimulation of the cortical surface, Penfield did not identify any 'pain cortical area'. We reinvestigated this issue by analysing subjective and videotaped behavioural responses to 4160 cortical stimulations using intracerebral electrodes implanted in all cortical lobes that were carried out over 12 years during the presurgical evaluation of epilepsy in 164 consecutive patients. Pain responses were scarce (1.4%) and concentrated in the medial part of the parietal operculum and neighbouring posterior insula where pain thresholds showed a rostrocaudal decrement. This deep cortical region remained largely inaccessible to the intraoperative stimulation of the cortical surface carried out by Penfield after resection of the parietal operculum. It differs also from primary sensory areas described by Penfield et al. in the sense that, with our stimulation paradigm, pain represented only 10% of responses. Like Penfield et al., we obtained no pain response anywhere else in the cortex, including in regions consistently activated by pain in most functional imaging studies, i.e. the first somatosensory area, the lateral part of the secondary somatosensory area, anterior and mid-cingulate gyri (mid-cingulate cortex), anterior frontal, posterior parietal and supplementary motor areas. The medial parietal operculum and posterior insula are thus the only areas where electrical stimulation is able to trigger activation of the pain cortical network and thus the experience of somatic pain.

Interhemispheric balance sets nostril differences in color-induced nasal thermal judgments

Sniffing out of sight always the same colorless and odorless solution containing no thermal agents while viewing a bottle with colored water increases sensitivity of the left nostril/right hemisphere (RH) for warming sensations and sensitivity of the right nostril/left hemisphere (LH) for cooling sensations. It is likely that engagement in a temperature judgment task and the development of specific expectancies due to the presence of color cues alter and enhance processing in brain areas involved in thermosensory processing. The lateralized patterns thus intimate hemispheric specialization for thermosensory processing probably originating in reciprocal inhibition that confers balance between the hemispheres. If the inhibition-balance hypothesis were correct then the more the left nostril proves sensitive to warming the more the right nostril would prove sensitive to cooling. One hundred and ninety one healthy volunteers were tested here. The left nostril dominance for warming and the right dominance for cooling were replicated once more. The dominance of the left nostril for warming (left minus right nostril) correlated highly with the dominance of the left nostril to cooling (right minus left nostril) and the individual patterns of results were distributed along an axis starting from the expected left nostril/warming - right nostril/cooling pattern and ending at the opposite left nostril/cooling - right nostril/warming pattern. Furthermore, the point where the left nostril dominance for warming responses dropped and inverted perfectly coincided with the point where the right nostril dominance for cooling responses inverted too. Such a good continuum between the expected and the opposite patterns supports the inhibition-balance hypothesis. Finally, 66% of subjects exhibited the expected left-warming/right-cooling pattern suggesting, therefore, that, despite this continuum, there is a dominant lateral specialization for temperature processing.

MRI of the central nervous system in MS patients with and without pain

BACKGROUND

Central pain (CP) is a common symptom in MS. Multiple theories are present about the mechanism of CP. Previous studies suggested that lesion of the spinothalamic tract is a necessary condition for development of CP. No previous study has in detail evaluated the association between the specific site of demyelinations and the presence of CP in MS.

OBJECTIVE

The study aimed to evaluate the location of plaques in MS patients with CP including a group of MS patients without pain as a reference group.

METHODS

All patients underwent a bedside sensory examination and MRI of the brain and spinal cord. MR imaging was acquired on an 1.5 Tesla MR equipment. A trained neuroradiologist, blinded to pain status, evaluated the MRI.

RESULTS

Thirteen MS patients with CP and 10 MS patients without pain were included. Allodynia and/or dysesthesia were more frequent in pain patients (11/13 vs. 1/10, P<0.01). No difference was found in the number of patients with plaques in spinothalamic tract, dorsal column-medial lemniscus, dorsolateral funiculus, grey substance, thalamus or capsula interna. A non-significantly lower number of pain patients had lesions in thalamo-cortical pathways (8/13 vs. 10/10, P=0.027).

CONCLUSIONS

No association between CP and site of demyelinations was found, although a trend toward a higher prevalence of intact thalamo-cortical pathways was seen in pain patients. CP was associated with allodynia, suggesting central hyperexcitability.

Physical temperature effects on trust behavior: the role of insula

Trust lies at the heart of person perception and interpersonal decision making. In two studies, we investigated physical temperature as one factor that can influence human trust behavior, and the insula as a possible neural substrate. Participants briefly touched either a cold or warm pack, and then played an economic trust game. Those primed with cold invested less with an anonymous partner, revealing lesser interpersonal trust, as compared to those who touched a warm pack. In Study 2, we examined neural activity during trust-related processes after a temperature manipulation using functional magnetic resonance imaging. The left-anterior insular region activated more strongly than baseline only when the trust decision was preceded by touching a cold pack, and not a warm pack. In addition, greater activation within bilateral insula was identified during the decision phase followed by a cold manipulation, contrasted to warm. These results suggest that the insula may be a key shared neural substrate that mediates the influence of temperature on trust processes.

Operculo-insular pain (parasylvian pain): a distinct central pain syndrome

Central pain with dissociated thermoalgesic sensory loss is common in spinal and brainstem syndromes but not in cortical lesions. Out of a series of 270 patients investigated because of somatosensory abnormalities, we identified five subjects presenting with central pain and pure thermoalgesic sensory loss contralateral to cortical stroke. All of the patients had involvement of the posterior insula and inner parietal operculum. Lemniscal sensory modalities (position sense, graphaestesia, stereognosis) and somatosensory evoked potentials to non-noxious inputs were always preserved, while thermal and pain sensations were profoundly altered, and laser-evoked potentials to thermo-nocoiceptive stimuli were always abnormal. Central pain resulting from posterior parasylvian lesions appears to be a distinct entity that can be identified unambiguously on the basis of clinical, radiological and electrophysiological data. It presents with predominant or isolated deficits for pain and temperature sensations, and is paradoxically closer to pain syndromes from brainstem lesions affecting selectively the spinothalamic pathways than to those caused by focal lesions of the posterior thalamus. The term 'pseudo-thalamic' is therefore inappropriate to describe it, and we propose parasylvian or operculo-insular pain as appropriate labels. Parasylvian pain may be extremely difficult to treat; the magnitude of pain-temperature sensory disturbances may be prognostic for its development, hence the importance of early sensory assessment with quantitative methods.

Differences in brain structure and function in older adults with self-reported disabling and nondisabling chronic low back pain

OBJECTIVE

The primary aim of this pilot study was to identify structural and functional brain differences in older adults with self-reported disabling chronic low back pain (CLBP) compared with those who reported nondisabling CLBP.

DESIGN

Cross-sectional.

PARTICIPANTS

Sixteen cognitively intact older adults, eight with disabling CLBP and eight with nondisabling CLBP. Exclusions were psychiatric or neurological disorders, substance abuse, opioid use, or diabetes mellitus.

METHODS

Participants underwent: structural and functional brain MRI; neuropsychological assessment using the Repeatable Battery for the Assessment of Neuropsychological Status, Trail Making Tests A and B; and physical performance assessment using the Short Physical Performance Battery.

RESULTS

In the disabled group, there was significantly lower white matter (WM) integrity (P < 0.05) of the splenium of the corpus callosum. This group also demonstrated activation of the right medial prefrontal cortex at rest whereas the nondisabled demonstrated activation of the left lateral prefrontal cortex. Combined groups analysis revealed a strong positive correlation (r(s) = 0.80, P < 0.0002) between WM integrity of the left centrum semiovale with gait-speed. Secondary analysis revealed a strong negative correlation between total months of CLBP and WM integrity of the SCC (r(s) = -0.59, P < 0.02).

CONCLUSIONS

Brain structure and function is different in older adults with disabling CLBP compared with those with nondisabling CLBP. Deficits in brain morphology combining groups are associated with pain duration and poor physical function. Our findings suggest brain structure and function may play a key role in chronic pain related disability and may be important treatment targets.

Altered pain and thermal sensation in subjects with isolated parietal and insular cortical lesions

Studies of sensory function following cortical lesions have often included lesions which multiple cortical, white matter, and thalamic structures. We now test the hypothesis that lesions anatomically constrained to particular insular and parietal structures and their subjacent white matter are associated with different patterns of sensory loss. Sensory loss was measured by quantitative sensory testing (QST), and evaluated statistically within patients relative to normal values. All seven subjects with insular and/or parietal lesions demonstrated thermal hypoesthesia, although the etiology of the lesions was heterogeneous. Cold and heat hypoalgesia were only found in the subject with the most extensive parietal and insular lesion, which occurred in utero. Cold allodynia occurred clinically and by thresholds in two subjects with isolated ischemic lesions of the posterior insular/retroinsular cortex, and by thresholds in two subjects with a lesion of parietal cortex with little or no insular involvement. Central pain occurred in the two subjects with clinical allodynia secondary to isolated lesions of the posterior insular/retroinsular cortex, which spared the anterior and posterior parietal cortex. These results suggest that nonpainful cold and heat sensations are jointly mediated by parietal and insular cortical structures so that lesions anywhere in this system may diminish sensitivity. In contrast, thermal pain is more robust requiring larger cortical lesions of these same structures to produce hypoalgesia. In addition, cold allodynia can result from restricted lesions that also produce thermal hypoesthesia, but not from all such lesions.

Analgesia in conjunction with normalisation of thermal sensation following deep brain stimulation for central post-stroke pain

The aetiology of central post-stroke pain (CPSP) is poorly understood and such pains are often refractory to treatment. We report the case of a 56-year-old man, who, following a temporo-parietal infarct, suffered from debilitating and refractory hemi-body cold dysaesthesia and severe tactile allodynia. This was associated with thermal and tactile hypoaesthesia and hypoalgesia on his affected side. Implantation of a deep brain stimulating electrode in his periventricular gray (PVG) region produced an improvement in his pain that was associated with a striking normalisation of his deficits in somatosensory perception. This improvement in pain and thermal sensibility was reversed as stimulation became less effective, because of increased electrode impedance. Therefore, we postulate that the analgesic benefit may have occurred as a consequence of the normalisation of somatosensory function and we discuss these findings in relation to the theories of central pain generation and the potential to engage useful plasticity in central circuits.

Emotional moments across time: a possible neural basis for time perception in the anterior insula

A model of awareness based on interoceptive salience is described, which has an endogenous time base that might provide a basis for the human capacity to perceive and estimate time intervals in the range of seconds to subseconds. The model posits that the neural substrate for awareness across time is located in the anterior insular cortex, which fits with recent functional imaging evidence relevant to awareness and time perception. The time base in this model is adaptive and emotional, and thus it offers an explanation for some aspects of the subjective nature of time perception. This model does not describe the mechanism of the time base, but it suggests a possible relationship with interoceptive afferent activity, such as heartbeat-related inputs.

Zona incerta: a role in central pain

Central pain syndrome (CPS) is a debilitating condition that affects a large number of patients with a primary lesion or dysfunction in the CNS. Despite its discovery over a century ago, the pathophysiological processes underlying the development and maintenance of CPS are poorly understood. We recently demonstrated that activity in the posterior thalamus (PO) is tightly regulated by inhibitory inputs from zona incerta (ZI). Here we test the hypothesis that CPS is associated with abnormal inhibitory regulation of PO by ZI. We recorded single units from ZI and PO in animals with CPS resulting from spinal cord lesions. Consistent with our hypothesis, the spontaneous firing rate and somatosensory evoked responses of ZI neurons were lower in lesioned animals compared with sham-operated controls. In PO, neurons recorded from lesioned rats exhibited significantly higher spontaneous firing rates and greater responses to noxious and innocuous stimuli applied to the hindpaw and to the face. These changes were not associated with increased afferent drive from the spinal trigeminal nucleus or changes in the ventroposterior thalamus. Thus CPS can result from suppressed inputs from the inhibitory nucleus zona incerta to the posterior thalamus.

Cerebral white matter: neuroanatomy, clinical neurology, and neurobehavioral correlates

Lesions of the cerebral white matter (WM) result in focal neurobehavioral syndromes, neuropsychiatric phenomena, and dementia. The cerebral WM contains fiber pathways that convey axons linking cerebral cortical areas with each other and with subcortical structures, facilitating the distributed neural circuits that subserve sensorimotor function, intellect, and emotion. Recent neuroanatomical investigations reveal that these neural circuits are topographically linked by five groupings of fiber tracts emanating from every neocortical area: (1) cortico-cortical association fibers; (2) corticostriatal fibers; (3) commissural fibers; and cortico-subcortical pathways to (4) thalamus and (5) pontocerebellar system, brain stem, and/or spinal cord. Lesions of association fibers prevent communication between cortical areas engaged in different domains of behavior. Lesions of subcortical structures or projection/striatal fibers disrupt the contribution of subcortical nodes to behavior. Disconnection syndromes thus result from lesions of the cerebral cortex, subcortical structures, and WM tracts that link the nodes that make up the distributed circuits. The nature and the severity of the clinical manifestations of WM lesions are determined, in large part, by the location of the pathology: discrete neurological and neuropsychiatric symptoms result from focal WM lesions, whereas cognitive impairment across multiple domains--WM dementia--occurs in the setting of diffuse WM disease. We present a detailed review of the conditions affecting WM that produce these neurobehavioral syndromes, and consider the pathophysiology, clinical effects, and broad significance of the effects of aging and vascular compromise on cerebral WM, in an attempt to help further the understanding, diagnosis, and treatment of these disorders.

Parsing pain perception between nociceptive representation and magnitude estimation

Assessing the size of objects rapidly and accurately clearly has survival value. A central multisensory module for subjective magnitude assessment is therefore highly likely, suggested by psychophysical studies, and proposed on theoretical grounds. Given that pain perception is fundamentally an assessment of stimulus intensity, it must necessarily engage such a central module. Accordingly, we compared functional magnetic resonance imaging (fMRI) activity of pain magnitude ratings to matched visual magnitude ratings in 14 subjects. We show that brain activations segregate into two groups, one preferentially activated for pain and another equally activated for both visual and pain magnitude ratings. The properties of regions in the first group were consistent with encoding nociception, whereas those in the second group with attention and task control. Insular cortex responses similarly segregated to a pain-specific area and an area (extending to the lateral prefrontal cortex) conjointly representing perceived magnitudes for pain and vision. These two insular areas were differentiated by their relationship to task variance, ability to encode perceived magnitudes for each stimulus epoch, temporal delay differences, and brain intrinsic functional connectivity. In a second group of subjects (n=11) we contrasted diffusion tensor imaging-based white matter connectivity for these two insular areas and observed anatomical connectivity closely corresponding to the functional connectivity identified with fMRI. These results demonstrate that pain perception is due to the transformation of nociceptive representation into subjective magnitude assessment within the insula. Moreover, we argue that we have identified a multisensory cortical area for "how much" complementary and analogous to the "where" and "what" as described for central visual processing.