Somatotopy in human primary somatosensory cortex in pain system

BACKGROUND: Compared with somatotopical organization (somatotopy) in the postcentral gyrus in the tactile system, somatotopy in the pain system is not well understood. The aim of this study is to elucidate whether there is somatotopy in the human pain system. METHODS: To elucidate the somatotopy of nociceptive neurons in the postcentral gyrus, the authors recorded pain-evoked cortical responses to noxious intraepidermal electrical stimulation applied to the left hand and left foot in 11 male subjects, using magnetoencephalography. RESULTS: Brief painful stimuli evoked sustained cortical activity in the primary somatosensory cortex (SI) in the hemisphere contralateral to the stimulated side and in the secondary somatosensory cortex in both hemispheres. In SI, representations of the hand and foot were distinctly separated, with a more medial and posterior location for the foot, whereas no significant difference was found in the locations for the secondary somatosensory cortex dipole. The SI arrangement along the central sulcus was compatible with the homunculus revealed by Penfield using direct cortical stimulation during surgery. CONCLUSIONS: The human pain system contains a somatotopical representation in SI but with less somatotopical organization in the secondary somatosensory cortex. The current results provide supporting evidence of SI involvement in human pain perception and suggest that human SI subserves the localization of the stimulated site in nociceptive processing.     

Somatotopy in Human Primary Somatosensory Cortex in Pain System

Background: Compared with somatotopical organization (somatotopy) in the postcentral gyrus in the tactile system, somatotopy in the pain system is not well understood. The aim of this study is to elucidate whether there is somatotopy in the human pain system.

Methods: To elucidate the somatotopy of nociceptive neurons in the postcentral gyrus, the authors recorded pain-evoked cortical responses to noxious intraepidermal electrical stimulation applied to the left hand and left foot in 11 male subjects, using magnetoencephalography.

Results: Brief painful stimuli evoked sustained cortical activity in the primary somatosensory cortex (SI) in the hemisphere contralateral to the stimulated side and in the secondary somatosensory cortex in both hemispheres. In SI, representations of the hand and foot were distinctly separated, with a more medial and posterior location for the foot, whereas no significant difference was found in the locations for the secondary somatosensory cortex dipole. The SI arrangement along the central sulcus was compatible with the homunculus revealed by Penfield using direct cortical stimulation during surgery.     

The compassionate brain: humans detect intensity of pain from another's face

Understanding another person's experience draws on "mirroring systems," brain circuitries shared by the subject's own actions/feelings and by similar states observed in others. Lately, also the experience of pain has been shown to activate partly the same brain areas in the subjects' own and in the observer's brain. Recent studies show remarkable overlap between brain areas activated when a subject undergoes painful sensory stimulation and when he/she observes others suffering from pain. Using functional magnetic resonance imaging, we show that not only the presence of pain but also the intensity of the observed pain is encoded in the observer's brain-as occurs during the observer's own pain experience. When subjects observed pain from the faces of chronic pain patients, activations in bilateral anterior insula (AI), left anterior cingulate cortex, and left inferior parietal lobe in the observer's brain correlated with their estimates of the intensity of observed pain. Furthermore, the strengths of activation in the left AI and left inferior frontal gyrus during observation of intensified pain correlated with subjects' self-rated empathy. These findings imply that the intersubjective representation of pain in the human brain is more detailed than has been previously thought.     

Preoperative Functional Magnetic Resonance Imaging (fMRI) of the Motor System in Patients with Tumours in the Parietal Lobe

Summary  Intracranial lesions may compromise structures critical for motor performance, and mapping of the cortex, especially of the motor hand area, is important to reduce postoperative morbidity. We investigated nine patients with parietal lobe tumours and used functional MRI sensitized to changes in blood oxygenation to define the different motor areas, especially the primary sensorimotor cortex, in relation to the localization of the tumour. Activation was determined by pixel-by-pixel correlation of the signal intensity time course with a reference waveform equivalent to the stimulus protocol. All subjects showed significant activation of the primary sensorimotor cortex while performing a finger opposition task with the affected and unaffected side. In five patients the finger opposition task additionally activated the ipsilateral sensorimotor cortex and the supplementary motor area (SMA). Extension and flexion of the foot, additionally performed in two patients, also activated the sensorimotor cortex, in one case within the perifocal oedema of the tumour. Tumour localization near the central sulcus induced displacement of the sensorimotor cortex as compared to the unaffected side in all patients with a relevant mass effect. The results of our study demonstrate that functional MRI at 1.5 T with a clinically used tomograph can reproducibly localize critical brain regions in patients with intracranial lesions.     

Somatosensory and pain responses to stimulation of the second somatosensory area (SII) in humans. A comparison with SI and insular responses

Somatosensory and pain responses to direct intracerebral stimulations of the SII area were obtained in 14 patients referred for epilepsy surgery. Stimulations were delivered using transopercular electrodes exploring the parietal opercular cortex (SII area), the suprasylvian parietal cortex (SI area) and the insular cortex. SII responses were compared to those from adjacent SI and insular cortex. In the three areas we elicited mostly somatosensory responses, including paresthesiae, temperature and pain sensations. The rate of painful sensations (10%) was similar in SII and in the insula, while no painful sensation was evoked in SI. A few non-somatosensory responses were evoked by SII stimulation. Conversely various types of non-somatosensory responses (auditory, vegetative, vestibular, olfacto-gustatory, etc.) were evoked only by insular stimulation, confirming that SII, like SI, are mostly devoted to the processing of somatosensory inputs whereas the insular cortex is a polymodal area. We also found differences in size and lateralization of skin projection fields of evoked sensations between the three studied areas, showing a spatial resolution of the somatotopic map in SII intermediate between those found in SI and insula. This study shows the existence of three distinct somatosensory maps in the suprasylvian, opercular and insular regions, and separate pain representations in SII and insular cortex.     

Rapid cortical oscillations and early motor activity in premature human neonate

Delta-brush is the dominant pattern of rapid oscillatory activity (8-25 Hz) in the human cortex during the third trimester of gestation. Here, we studied the relationship between delta-brushes in the somatosensory cortex and spontaneous movements of premature human neonates of 29-31 weeks postconceptional age using a combination of scalp electroencephalography and monitoring of motor activity. We found that sporadic hand and foot movements heralded the appearance of delta-brushes in the corresponding areas of the cortex (lateral and medial regions of the contralateral central cortex, respectively). Direct hand and foot stimulation also reliably evoked delta-brushes in the same areas. These results suggest that sensory feedback from spontaneous fetal movements triggers delta-brush oscillations in the central cortex in a somatotopic manner. We propose that in the human fetus in utero, before the brain starts to receive elaborated sensory input from the external world, spontaneous fetal movements provide sensory stimulation and drive delta-brush oscillations in the developing somatosensory cortex contributing to the formation of cortical body maps.     

Muscular activity and torque of the foot dorsiflexor muscles during decremental isometric test: A cross-sectional study

PurposeTo analyse the torque variation level that could be explained by the muscle activation (EMG) amplitude of the three major foot dorsiflexor muscles (tibialis anterior (TA), extensor digitorum longus (EDL), extensor hallucis longus (EHL)) during isometric foot dorsiflexion at different intensities.MethodsIn a cross-sectional study, forty-one subjects performed foot dorsiflexion at 100%, 75%, 50% and 25% of maximal voluntary contractions (MVC) with the hip and knee flexed 90° and the ankle in neutral position (90° between leg and foot). Three foot dorsiflexions were performed for each intensity. Outcome variables were: maximum (100% MVC) and relative torque (75%, 50%, 25% MVC), maximum and relative EMG amplitude. A linear regression analysis was calculated for each intensity of the isometric foot dorsiflexion.ResultsThe degree of torque variation (dependent variable) from the independent variables explain (EMG amplitude of the three major foot dorsiflexor muscles) the increases when the foot dorsiflexion intensity is increased, with values of R² that range from 0.194 (during 25% MVC) to 0.753 (during 100% MVC). The reliability of the outcome variables was excellent.ConclusionThe EMG amplitude of the three main foot dorsiflexors exhibited more variance in the dependent variable (torque) when foot dorsiflexion intensity increases.     

Interactions of pain intensity and cognitive load: the brain stays on task

Pain naturally draws one's attention. However, humans are capable of engaging in cognitive tasks while in pain, although it is not known how the brain represents these processes concurrently. There is some evidence for a cortical interaction between pain- and cognitive-related brain activity, but the outcome of this interaction may depend on the relative load imposed by the pain versus the task. Therefore, we used 3 levels of cognitive load (multisource interference task) and 2 levels of pain intensity (median nerve stimulation) to examine how functional magnetic resonance imaging activity in regions identified as pain-related or cognitive-related responds to different combinations of pain intensity and cognitive load. Overall, most pain-related or cognitive-related brain areas showed robust responses with little modulation. However, during the more intense pain, activity in primary sensorimotor cortex, secondary somatosensory cortex/posterior insula, anterior insula, paracentral lobule, caudal anterior cingulate cortex, cerebellum, and supplementary motor area was modestly attenuated by the easy task and in some cases the difficult task. Conversely, cognitive-related activity was not modulated by pain, except when cognitive load was minimal during the control task. These findings support the notion that brain networks supporting pain perception and cognition can be simultaneously active.     

Ongoing brain activity fluctuations directly account for intertrial and indirectly for intersubject variability in Stroop task performance

Recent studies have established a relation between ongoing brain activity fluctuations and intertrial variability in evoked neural responses, perception, and motor performance. Here, we extended these investigations into the domain of cognitive control. Using functional neuroimaging and a sparse event-related design (with long and unpredictable intervals), we measured ongoing activity fluctuations and evoked responses in volunteers performing a Stroop task with color-word interference. Across trials, prestimulus activity of several regions predicted subsequent response speed and across subjects this effect scaled with the Stroop effect size, being significant only in subjects manifesting behavioral interference. These effects occurred only in task relevant as the dorsal anterior cingulate and dorsolateral prefrontal cortex as well as ventral visual areas sensitive to color and visual words. Crucially, in subjects showing a Stroop effect, reaction times were faster when prestimulus activity was higher in task-relevant (color) regions and slower when activity was higher in irrelevant (word form) regions. These findings suggest that intrinsic brain activity fluctuations modulate neural mechanisms underpinning selective voluntary attention and cognitive control. Rephrased in terms of predictive coding models, ongoing activity can hence be considered a proxy of the precision (gain) with which prediction error signals are transmitted upon sensory stimulation.     

Functional Magnetic Resonance Mapping of Sensory Motor Cortex for Image-Guided Neurosurgical Intervention

Summary Purpose: This paper describes the potentials of functional magnetic resonance imaging (fMRI) to map sensory motor cortex in patients with mass lesions near primary motor cortex and to guide neurosurgical procedures located close to eloquent brain regions. Material and Methods: 7 patients with mass lesions near the central sulcus and 10 healthy volunteers were studied using a blood oxygenation level dependent 2D multislice multishot T2* weighted gradient echo EPI sequence on a 1.5T Phillips Gyroscan during alternating epochs of rest and motor activation of hand, foot and tongue. Sites of neuronal activation were identified by statistical analysis of the signal time course using Kolmogorov Smirnov statistics. Results: Neuronal activation following motor tasks consistently localised to the contralateral precentral gyrus and the supplementary motor area, even in the presence of local brain pathology. Additionally we could observe activation in primary sensory areas (postcentral gyrus) and supplementary motor area (SMA) in some cases. Conclusion: fMRI is capable of mapping sensory motor cortex even in the presence of distorting brain lesions. Since this information will provide valuable information to the neurosurgeon during pre-operative planning, we consider this method for neurosurgical navigation a valuable tool in the routine diagnostic of intracerebral interventions.     

Anterior tarsal tunnel syndrome

Compression of the deep peroneal nerve is commonly referred to as anterior tarsal tunnel syndrome. Although rare, this syndrome remains poorly diagnosed. The syndrome is characterized by pain, weakness, and sensory changes of the foot and ankle. Non-operative measures should be attempted to reduce or remove the external compression along the anterior aspect of the foot and ankle. Other options include shoe modifications, cortisone injections,and physical therapy. If conservative management fails to relieve the symptoms, surgical decompression of the entrapped nerve can be performed. The deep peroneal nerve is released from compressive forces in the entrapment site. This can be performed at the more proximal level at the extensor retinaculum or more distally at the level of the tarsal metatarsal site.     

Functional Magnetic Resonance Imaging Studies of Pain: An Investigation of Signal Decay during and across Sessions

Background: Several investigations into brain activation caused by pain have suggested that the multiple painful stimulations used in typical block designs may cause attenuation over time of the signal within activated areas. The effect this may have on pain investigations using multiple tasks has not been investigated. The signal decay across a task of four repeating pain stimulations and between two serial pain tasks separated by a 4-min interval was examined to determine whether signal attenuation may significantly confound pain investigations.

Methods: The characteristics of the brain activation of six subjects were determined using whole brain blood oxygenation level-dependent functional magnetic resonance imaging on a 1.5-T scanner. Tasks included both tingling and pain induced by transcutaneous electrical stimulation of the median nerve. The average group maps were analyzed by general linear modeling with corrected cluster P values of less than 0.05. The time courses of individual voxels were further investigated by analysis of variance with P values of less than 0.05.

Results: Significant differences between pain and tingling were found in the ipsilateral cerebellum, contralateral thalamus, secondary somatosensory cortex, primary somatosensory cortex, and anterior cingulate cortex. Highly significant signal decay was found to exist across each single pain task, but the signal was found to be restored after a 4-min rest period.     

Brain networks involved in viewing angry hands or faces

Most neuropsychological research on the perception of emotion concerns the perception of faces. Yet in everyday life, hand actions are also modulated by our affective state, revealing it, in turn, to the observer. We used functional magnetic resonance imaging (fMRI) to identify brain regions engaged during the observation of hand actions performed either in a neutral or an angry way. We also asked whether these are the same regions as those involved in perceiving expressive faces. During the passive observation of emotionally neutral hand movements, the fMRI signal increased significantly in dorsal and ventral premotor cortices, with the exact location of the 'peaks' distinct from those induced by face observation. Various areas in the extrastriate visual cortex were also engaged, overlapping with the face-related activity. When the observed hand action was performed with emotion, additional regions were recruited including the right dorsal premotor, the right medial prefrontal cortex, the left anterior insula and a region in the rostral part of the supramarginal gyrus bilaterally. These regions, except for the supramarginal gyrus, were also activated during the perception of angry faces. These results complement the wealth of studies on the perception of affect from faces and provide further insights into the processes involved in the perception of others underlying, perhaps, social constructs such as empathy.     

Brain processing of the signals ascending through unmyelinated C fibers in humans: an event-related functional magnetic resonance imaging study

Event-related functional magnetic resonance imaging was usedto investigate brain processing of the signals ascending fromperipheral C and A fibers evoked by phasic laser stimuli onthe right hand in humans. The stimulation of both C and A nociceptorsactivated the bilateral thalamus, bilateral secondary somatosensorycortex, right (ipsilateral) middle insula, and bilateral Brodmann'sarea (BA) 24/32, with the majority of activity found in theposterior portion of the anterior cingulate cortex (ACC). However,magnitude of activity in the right (ipsilateral) BA32/8/6, includingdorsal parts in the anterior portion of the ACC (aACC) and pre-supplementarymotor area (pre-SMA), and the bilateral anterior insula wassignificantly stronger following the stimulation of C nociceptorsthan A nociceptors. It was concluded that the activation ofC nociceptors, related to second pain, evokes different brainprocessing from that of A nociceptors, related to first pain,probably due to the differences in the emotional and motivationalaspects of either pain, which are mainly related to the aACC,pre-SMA, and anterior insula.     

Motor evoked potential study suggesting L5 radiculopathy caused by l1-2 disc herniation: case report

A 38-year-old male was referred because of pain in the left 5th lumbar (L5) root territory. Physical examination found moderate motor weakness in the left extensor hallucis longus (EHL) and the left tibialis anterior muscles. Magnetic resonance imaging found no stenotic lesion between L4-L5, but disc herniation was observed on the left between L1-L2. An L5 nerve root block provided temporary relief of the pain but the left foot weakness was exacerbated. Therefore, surgery was performed. Partial laminectomy and left herniotomy were performed at L1-L2, L2-L3, and L3-L4 with motor evoked potential (MEP) monitoring. The MEP amplitude of the left EHL muscle increased immediately after L1-L2 herniotomy. The MEP amplitude of the right EHL muscle also increased after both laminectomy and herniotomy. The postoperative course was uneventful. The left leg pain and motor weakness disappeared. The patient has been doing fine without recurrence for 12 months. Since the MEP of both left and right EHL muscles improved after the L1-2 herniotomy, circulatory insufficiency might have caused the L5 symptoms. Monitoring of the MEP during the surgery was useful for confirming the responsible lesion and also for predicting the postoperative course.     

Functional magnetic resonance imaging studies of pain: an investigation of signal decay during and across sessions

BACKGROUND: Several investigations into brain activation caused by pain have suggested that the multiple painful stimulations used in typical block designs may cause attenuation over time of the signal within activated areas. The effect this may have on pain investigations using multiple tasks has not been investigated. The signal decay across a task of four repeating pain stimulations and between two serial pain tasks separated by a 4-min interval was examined to determine whether signal attenuation may significantly confound pain investigations. METHODS: The characteristics of the brain activation of six subjects were determined using whole brain blood oxygenation level-dependent functional magnetic resonance imaging on a 1.5-T scanner. Tasks included both tingling and pain induced by transcutaneous electrical stimulation of the median nerve. The average group maps were analyzed by general linear modeling with corrected cluster P values of less than 0.05. The time courses of individual voxels were further investigated by analysis of variance with P values of less than 0.05. RESULTS: Significant differences between pain and tingling were found in the ipsilateral cerebellum, contralateral thalamus, secondary somatosensory cortex, primary somatosensory cortex, and anterior cingulate cortex. Highly significant signal decay was found to exist across each single pain task, but the signal was found to be restored after a 4-min rest period. CONCLUSIONS: This work shows that serial pain tasks can be used for functional magnetic resonance imaging studies using electrical nerve stimulation as a stimulus, as long as sufficient time is allowed between the two tasks.     

Correlation of clinical examination characteristics with three sources of chronic low back pain.

BACKGROUND CONTEXT: Research has demonstrated some progress in using a clinical examination to predict discogenic or sacroiliac (SI) joint sources of pain. No clear predictors of symptomatic lumbar zygapophysial joints have yet been demonstrated. PURPOSE: To identify significant components of a clinical examination that are associated with symptomatic lumbar discs, zygapophysial joints and SI joints. STUDY DESIGN: A prospective, criterion-related concurrent validity study performed at a private radiology practice specializing in spinal diagnostics. PATIENT SAMPLE: The sample consisted of 81 patients with chronic lumbopelvic pain referred for diagnostic injections. OUTCOME MEASURES: Contingency tables were constructed for nine features of the clinical evaluation compared with the results of diagnostic injections. Statistical analysis included chi-squared test for independence, phi and odds ratios with confidence intervals. METHOD: Patients received blinded clinical examinations by physical therapists, and diagnostic injections were used as the criterion standard. RESULTS: Significant relationships were found between discogenic pain and centralization of pain during repeated movement testing, and pain when rising from sitting. Lumbar zygapophysial joint pain was associated with absence of pain when rising from sitting. Sacroiliac joint pain was related to three or more positive pain provocation tests, pain when rising from sitting, unilateral pain and absence of lumbar pain. CONCLUSIONS: Significant correlations exist between clinical examination findings and symptomatic lumbar discs, zygapophysial and SI joints. The strongest relationships were seen between SI joint pain and three or more positive pain provocation tests, centralization of pain for symptomatic discs and absence of pain when rising from sitting for symptomatic lumbar zygapophysial joints.     

Dissociable brain activation responses to 5-Hz electrical pain stimulation: a high-field functional magnetic resonance imaging study

BACKGROUND: To elucidate neural correlates associated with processing of tonic aching pain, the authors used high-field (3-T) functional magnetic resonance imaging with a blocked parametric study design and characterized regional brain responses to electrical stimulation according to stimulus intensity-response functions. METHODS: Pain was induced in six male volunteers using a 5-Hz electrical stimulus applied to the right index finger. Scanning sequences involved different levels of stimulation corresponding to tingling sensation (P1), mild pain (P2), or high pain (P3). Common effects across subjects were sought using a conjunction analyses approach, as implemented in statistical parametric mapping (SPM-99). RESULTS: The contralateral posterior/mid insula and contralateral primary somatosensory cortex were most associated with encoding stimulus intensity because they showed a positive linear relation between blood oxygenation level-dependent signal responses and increasing stimulation intensity (P1 < P2 < P3). The contralateral secondary somatosensory cortex demonstrated a response function most consistent with a role in pain intensity encoding because it had no significant response during the innocuous condition (P1) but proportionally increased activity with increasingly painful stimulus intensities (0 < P2 < P3). Finally, a portion of the anterior cingulate cortex (area 24) and supplementary motor area 6 demonstrated a high pain-specific response (P3). CONCLUSIONS: The use of response function modeling, conjunction analysis, and high-field imaging reveals dissociable regional responses to a tonic aching electrical pain. Most specifically, the primary somatosensory cortex and insula seem to encode stimulus intensity information, whereas the secondary somatosensory cortex encodes pain intensity information. The cingulate findings are consistent with its proposed role in processing affective-motivational aspects of pain.     

Dissociable Brain Activation Responses to 5-Hz Electrical Pain Stimulation: A High-field Functional Magnetic Resonance Imaging Study

Background: To elucidate neural correlates associated with processing of tonic aching pain, the authors used high-field (3-T) functional magnetic resonance imaging with a blocked parametric study design and characterized regional brain responses to electrical stimulation according to stimulus intensity-response functions.

Methods: Pain was induced in six male volunteers using a 5-Hz electrical stimulus applied to the right index finger. Scanning sequences involved different levels of stimulation corresponding to tingling sensation (P1), mild pain (P2), or high pain (P3). Common effects across subjects were sought using a conjunction analyses approach, as implemented in statistical parametric mapping (SPM-99).

Results: The contralateral posterior/mid insula and contralateral primary somatosensory cortex were most associated with encoding stimulus intensity because they showed a positive linear relation between blood oxygenation level-dependent signal responses and increasing stimulation intensity (P1 < P2 < P3). The contralateral secondary somatosensory cortex demonstrated a response function most consistent with a role in pain intensity encoding because it had no significant response during the innocuous condition (P1) but proportionally increased activity with increasingly painful stimulus intensities (0 < P2 < P3). Finally, a portion of the anterior cingulate cortex (area 24) and supplementary motor area 6 demonstrated a high pain-specific response (P3).     

Comparison of altered signal intensity, position, and morphology of the TMJ disc in MR images corrected for variations in surface coil sensitivity.

OBJECTIVE: The purpose of this study is to evaluate the corrections of signal intensity of the temporomandibular joint (TMJ) disc caused by variations in sensitivity of the magnetic resonance imaging (MRI) surface coil, to compare the modified signal intensities of the posterior and anterior bands, and then to evaluate the relationship of the signal intensity difference to altered disc position and morphology in a group of TMJ patients. STUDY DESIGN: MRI was performed on 96 joints. All patients underwent imaging in axial, coronal, and sagittal planes using fast-spin echo sequences (FSE). The images were taken in the closed, partially opened, and maximum opened mouth positions in 2 sequences. Classifications were made according to the position and morphology of the disc. TMJs were divided into normal, anterior disc displacement with reduction (ADDwR), anterior disc displacement without reduction (ADDwoR), and partial anterior disc displacement with reduction (PDDwR). Disc morphology was subdivided as biconcave, lengthened, biconvex, thick posterior band, and others (defined as folded and rounded). The correction of the inhomogeneous sensitivity of the surface coil was done with the original software. The signal intensities (SI) of the posterior band and anterior band of TMJ discs were measured. The correlations among the groups of TMJs and disc morphologies and SI were statistically analyzed by using Bonferroni/Dunn multicomparison method test. RESULTS: Of the total number of joints studied with the help of MRI, 37 were normal, 12 exhibited ADDwR, 32 ADDwoR, and 9 PDDwR. The corrected MR images indicated that SI of the posterior bands were higher than the anterior band of the discs. It can also be concluded that the SI of the posterior bands increased significantly in the following order: normal, PDDwR, ADDwR, and ADDwoR, while there is no statistical difference in the SI of the anterior band of the discs. In ADDwR and ADDwoR, thick posterior band is the most common shape. In normal TMJ, the biconcave shape is identified as the most frequently encountered shape. CONCLUSIONS: It was demonstrated that the SI of the posterior bands increase with the progress of internal derangement, and was found to be higher than that of the anterior band of the discs. It appears that disc degeneration starts from the posterior band of the disc.