Percept-related activity in the human somatosensory system: functional magnetic resonance imaging studies

Pneumatical-Mechanical Tactile Stimulation Device for Somatotopic Mapping of Body Surface During fMRI

BACKGROUND

There is a need for devices that allow reproducible stimulation of skin areas of humans for investigating somatosensory mapping of the whole-body surface. However, their design is not simple, due to the magnetic field of MRI scanners.

PURPOSE

To accurately characterize the mapping of somatosensory presentation of the whole-body surface of subjects during functional (f)MRI scans.

STUDY TYPE

Prospective.

POPULATION

A water phantom and six healthy participants (age 23-27 years; two males) were recruited for the fMRI experiment.

FIELD STRENGTH/SEQUENCE

T₁ -weighted magnetization-prepared rapid acquisition gradient-echo, T₂ *-weighted gradient echo sequence at 3T.

ASSESSMENT

The stimulation device for somatotopic mapping was composed of three units: an air-generating unit, a control unit, and an execution unit. The fMRI in response to tactile stimulation was measured to characterize somatotopic mapping of the right-side body consisting of hand, arm, and leg in six healthy subjects.

STATISTICAL TESTS

Pared-samples t-test for the conditions in SII.

RESULTS

The pneumatical-mechanical tactile stimulation offered a wide range of stimulation intensities (0-400 g) in each channel. The predetermined physical pressure was successfully reached within ~5 msec and returned to baseline within 5 msec after the end of stimulation. With this tactile device, the digressive rate of the signal-to-noise ratio (SNR) (271.44 without the device, 269.68 with the device) was 0.65% in the magnetic field environment. For the fMRI experiment, the primary somatosensory activation contralateral to the stimulation site was detected in response to spatial task and attentive task.

DATA CONCLUSION

This stimulation device characterized the mapping of somatosensory representation of the whole-body surface in individual participants during fMRI scans.

LEVEL OF EVIDENCE

2.

TECHNICAL EFFICACY STAGE

1. J. Magn. Reson. Imaging 2020;52:1093-1101.

Pain Neuroimaging in Humans: A Primer for Beginners and Non-Imagers

Human pain neuroimaging has exploded in the past 2 decades. During this time, the broader neuroimaging community has continued to investigate and refine methods. Another key to progress is exchange with clinicians and pain scientists working with other model systems and approaches. These collaborative efforts require that non-imagers be able to evaluate and assess the evidence provided in these reports. Likewise, new trainees must design rigorous and reliable pain imaging experiments. In this article we provide a guideline for designing, reading, evaluating, analyzing, and reporting results of a pain neuroimaging experiment, with a focus on functional and structural magnetic resonance imaging. We focus in particular on considerations that are unique to neuroimaging studies of pain in humans, including study design and analysis, inferences that can be drawn from these studies, and the strengths and limitations of the approach.

Brain imaging tests for chronic pain: medical, legal and ethical issues and recommendations

Chronic pain is the greatest source of disability globally and claims related to chronic pain feature in many insurance and medico-legal cases. Brain imaging (for example, functional MRI, PET, EEG and magnetoencephalography) is widely considered to have potential for diagnosis, prognostication, and prediction of treatment outcome in patients with chronic pain. In this Consensus Statement, a presidential task force of the International Association for the Study of Pain examines the capabilities of brain imaging in the diagnosis of chronic pain, and the ethical and legal implications of its use in this way. The task force emphasizes that the use of brain imaging in this context is in a discovery phase, but has the potential to increase our understanding of the neural underpinnings of chronic pain, inform the development of therapeutic agents, and predict treatment outcomes for use in personalized pain management. The task force proposes standards of evidence that must be satisfied before any brain imaging measure can be considered suitable for clinical or legal purposes. The admissibility of such evidence in legal cases also strongly depends on laws that vary between jurisdictions. For these reasons, the task force concludes that the use of brain imaging findings to support or dispute a claim of chronic pain - effectively as a pain lie detector - is not warranted, but that imaging should be used to further our understanding of the mechanisms underlying pain.

Brain responses to vestibular pain and its anticipation in women with Genito-Pelvic Pain/Penetration Disorder

Objective

In DSM-5, pain-related fear during anticipation of vaginal penetration is a diagnostic criterion of Genito-Pelvic Pain/Penetration Disorder (GPPPD). We aimed to investigate subjective and brain responses during anticipatory fear and subsequent induction of vestibular pain in women with GPPPD.

Methods

Women with GPPPD (n = 18) and age-matched healthy controls (HC) (n = 15) underwent fMRI scanning during vestibular pain induction at individually titrated pain threshold after a cued anticipation period. (Pain-related) fear and anxiety traits were measured with questionnaires prior to scanning, and anticipatory fear and pain intensity were rated during scanning using visual analog scales.

Results

Women with GPPPD reported significantly higher levels of anticipatory fear and pain intensity. During anticipation and pain induction they had stronger and more extensive brain responses in regions involved in cognitive and affective aspects of pain perception, but the group difference did not reach significance for the anticipation condition. Pain-related fear and anxiety traits as well as anticipatory fear ratings were positively associated with pain ratings in GPPPD, but not in HC. Further, in HC, a negative association was found between anticipatory fear ratings and brain responses in regions involved in cognitive and affective aspects of pain perception, but not in women with GPPPD.

Conclusions

Women with GPPPD are characterized by increased subjective and brain responses to vestibular pain and, to a lesser extent, its anticipation, with fear and anxiety associated with responses to pain, supporting the introduction of anticipatory fear as a criterion of GPPPD in DSM-5.

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Both subjective and brain responses during anticipation and induction of vestibular pain are increased in women with GPPPD.

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Between-group differences were found in brain regions involved in cognitive and affective aspects of the pain experience.

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These results support the addition of pain-related fear and anxiety in the diagnostic criteria of GPPPD in DSM-5.

Functional dissociation of stimulus intensity encoding and predictive coding of pain in the insula

The computational principles by which the brain creates a painful experience from nociception are still unknown. Classic theories suggest that cortical regions either reflect stimulus intensity or additive effects of intensity and expectations, respectively. By contrast, predictive coding theories provide a unified framework explaining how perception is shaped by the integration of beliefs about the world with mismatches resulting from the comparison of these beliefs against sensory input. Using functional magnetic resonance imaging during a probabilistic heat pain paradigm, we investigated which computations underlie pain perception. Skin conductance, pupil dilation, and anterior insula responses to cued pain stimuli strictly followed the response patterns hypothesized by the predictive coding model, whereas posterior insula encoded stimulus intensity. This novel functional dissociation of pain processing within the insula together with previously observed alterations in chronic pain offer a novel interpretation of aberrant pain processing as disturbed weighting of predictions and prediction errors.

Interhemispheric Inhibition Induced by Transcranial Magnetic Stimulation Over Primary Sensory Cortex

The present study investigated whether the long-interval interhemispheric inhibition (LIHI) is induced by the transcranial magnetic stimulation over the primary sensory area (S1-TMS) without activation of the conditioning side of the primary motor area (M1) contributing to the contralateral motor evoked potential (MEP), whether the S1-TMS-induced LIHI is dependent on the status of the S1 modulated by the tactile input, and whether the pathways mediating the LIHI are different from those mediating the M1-TMS-induced LIHI. In order to give the TMS over the S1 without eliciting the MEP, the intensity of the S1-TMS was adjusted to be the sub-motor-threshold level and the trials with the MEP response elicited by the S1-TMS were discarded online. The LIHI was induced by the S1-TMS given 40 ms before the test TMS in the participants with the attenuation of the tactile perception of the digit stimulation (TPDS) induced by the S1-TMS, indicating that the LIHI is induced by the S1-TMS without activation of the conditioning side of the M1 contributing to the contralateral MEP in the participants in which the pathways mediating the TPDS is sensitive to the S1-TMS. The S1-TMS-induced LIHI was positively correlated with the attenuation of the TPDS induced by the S1-TMS, indicating that the S1-TMS-induced LIHI is dependent on the effect of the S1-TMS on the pathways mediating the TPDS at the S1. In another experiment, the effect of the digit stimulation given before the conditioning TMS on the S1- or M1-TMS-induced LIHI was examined. The digit stimulation produces tactile input to the S1 causing change in the status of the S1. The S1-TMS-induced LIHI was enhanced when the S1-TMS was given in the period in which the tactile afferent volley produced by the digit stimulation just arrived at the S1, while the LIHI induced by above-motor-threshold TMS over the contralateral M1 was not enhanced by the tactile input. Thus, the S1-TMS-induced LIHI is dependent on the status of the S1 modulated by the tactile input, and the pathways mediating the sub-motor-threshold S1-TMS-induced LIHI are not the same as the pathways mediating the above-motor-threshold M1-TMS-induced LIHI.

Beyond the N1: A review of late somatosensory evoked responses in human infants

Somatosensory evoked potentials (SEPs) have been used for decades to study the development of somatosensory processing in human infants. Research on infant SEPs has focused on the initial cortical component (N1) and its clinical utility for predicting neurological outcome in at-risk infants. However, recent studies suggest that examining the later components in the infant somatosensory evoked response will greatly advance our understanding of somatosensory processing in infancy. The purpose of this review is to synthesize the existing electroencephalography (EEG) and magnetoencephalography (MEG) studies on late somatosensory evoked responses in infants. We describe the late responses that have been reported and discuss the utility of such responses for illuminating key aspects of somatosensory processing in typical and atypical development.

Look but don't touch: Visual cues to surface structure drive somatosensory cortex

When planning interactions with nearby objects, our brain uses visual information to estimate shape, material composition, and surface structure before we come into contact with them. Here we analyse brain activations elicited by different types of visual appearance, measuring fMRI responses to objects that are glossy, matte, rough, or textured. In addition to activation in visual areas, we found that fMRI responses are evoked in the secondary somatosensory area (S2) when looking at glossy and rough surfaces. This activity could be reliably discriminated on the basis of tactile-related visual properties (gloss, rough, and matte), but importantly, other visual properties (i.e., coloured texture) did not substantially change fMRI activity. The activity could not be solely due to tactile imagination, as asking explicitly to imagine such surface properties did not lead to the same results. These findings suggest that visual cues to an object's surface properties evoke activity in neural circuits associated with tactile stimulation. This activation may reflect the a-priori probability of the physics of the interaction (i.e., the expectation of upcoming friction) that can be used to plan finger placement and grasp force.

Nociception, Pain, Negative Moods, and Behavior Selection

Recent neuroimaging studies suggest that the brain adapts with pain, as well as imparts risk for developing chronic pain. Within this context, we revisit the concepts for nociception, acute and chronic pain, and negative moods relative to behavior selection. We redefine nociception as the mechanism protecting the organism from injury, while acute pain as failure of avoidant behavior, and a mesolimbic threshold process that gates the transformation of nociceptive activity to conscious pain. Adaptations in this threshold process are envisioned to be critical for development of chronic pain. We deconstruct chronic pain into four distinct phases, each with specific mechanisms, and outline current state of knowledge regarding these mechanisms: the limbic brain imparting risk, and the mesolimbic learning processes reorganizing the neocortex into a chronic pain state. Moreover, pain and negative moods are envisioned as a continuum of aversive behavioral learning, which enhance survival by protecting against threats.

Unravelling nocebo effect: the mediating effect of anxiety between anticipation and pain at wound dressing change

AIMS AND OBJECTIVES

The purpose of this study was to examine the mediating effect of anxiety in the relationship between anticipation and pain in people with chronic wounds.

BACKGROUND

Pain is common in people with chronic wounds. Anticipation or negative expectation of discomfort has been shown to have an augmenting effect on pain; also known as nocebo hyperalgesia.

DESIGN

This was a cross-sectional study with repeated measures.

METHODS

Prior to dressing change, anticipatory pain level was evaluated by a 11-point numerical rating scale and anxiety by the Six-items State-Trait Anxiety Inventory (STAI-6). During wound dressing changes, pain was measured before dressing removal, at dressing removal, at cleansing and dressing application using the numerical scale.

RESULTS

Analysis was completed based on the data from a convenience sample of 96 patients. Participants reported more pain at cleansing and dressing removal than baseline. High levels of anticipation, anxiety and pain at dressing change for wounds were related to heavy exudate and wound that were covered with necrotic tissue. Finally, the relationship between anticipation and pain perception was mediated by anxiety.

CONCLUSION

Anticipation of pain triggers anxiety that can lead to increased pain.

RELEVANCE TO CLINICAL PRACTICE

There is a need to incorporate evaluation of anxiety and personal expectations as part of comprehensive pain assessment. Clinicians should be aware of the impact of emotions and anticipation on overall pain experience.

Circadian fluctuations in three types of sensory modules in healthy subjects

This study was designed to observe and compare the circadian fluctuations in tactile sense, joint reposition sense and two-point discrimination in healthy subjects. Twenty-one healthy adult subjects received perceptual ability tests through these three different sensory modules at approximately 9:00, 13:00 and 18:00 in a day. The distribution of ranking for perceptual ability was significantly different among the three different time points in each individual, with highest perceptual ability in the evening compared with noon and morning, in terms of tactile sense and two-point discrimination. These findings suggest that the perceptual ability of healthy subjects fluctuates according to the time points in a day.

Distinct fine-scale fMRI activation patterns of contra- and ipsilateral somatosensory areas 3b and 1 in humans

Inter-areal and ipsilateral cortical responses to tactile stimulation have not been well described in human S1 cortex. By taking advantage of the high signal-to-noise ratio at 7 T, we quantified blood oxygenation level dependent (BOLD) response patterns and time courses to tactile stimuli on individual distal finger pads at a fine spatial scale, and examined whether there are inter-areal (area 3b versus area 1) and interhemispheric response differences to unilateral tactile stimulation in healthy human subjects. We found that 2-Hz tactile stimulation of individual fingertips evoked detectable BOLD signal changes in both contralateral and ipsilateral area 3b and area 1. Contralateral digit activations were organized in an orderly somatotopic manner, and BOLD responses in area 3b were more digit selective than those in area 1. However, the area of cortex that was responsive to stimulation of a single digit (stimulus-response field) was similar across areas. In the ipsilateral hemisphere, response magnitudes in both areas 3b and 1 were significantly weaker than those of the contralateral hemisphere. Digit activations exhibited no clear somatotopic organizational pattern in either area 3b or area 1, yet digit selectivity was retained in area 1 but not in area 3b. The observation of distinct digit-selective responses of contralateral area 3b versus area 1 supports a higher order function of contralateral area 1 in spatial integration. In contrast, ipsilateral cortices may play a less discriminative role in the perception of unilateral tactile sensation in humans.

New insights into the brain involvement in patients with Crohn's disease: a voxel-based morphometry study

BACKGROUND

Crohn's disease (CD) is a chronic intestinal disorder characterized by overproduction of inflammatory cytokines and recurrent abdominal pain. Recently, brain morphological abnormalities in the pain matrix were found in patients with chronic pain disorders including irritable bowel syndrome. To investigate potential structural brain changes associated with CD, we used magnetic resonance imaging (MRI). Furthermore, we tested whether in patients gray matter (GM) volumes correlated with disease duration.

METHODS

Eighteen CD patients in remission and 18 healthy controls underwent structural MRI. Voxel-based morphometry (VBM) is a fully automated technique allowing identification of regional differences in the amount of GM enabling an objective analysis of the whole brain between groups of subjects. VBM was used for comparisons and correlation analysis.

KEY RESULTS

With respect to controls, CD patients exhibited decreased GM volumes in portion of the frontal cortex and in the anterior midcingulate cortex. Disease duration was negatively correlated with GM volumes of several brain regions including neocortical and limbic areas.

CONCLUSIONS & INFERENCES

Crohn's disease is associated with brain morphological changes in cortical and subcortical structures involved in nociception, emotional, and cognitive processes. Our findings provide new insight into the brain involvement in chronic inflammatory bowel disorders.

BOLD responses to tactile stimuli in visual and auditory cortex depend on the frequency content of stimulation

Although some brain areas preferentially process information from a particular sensory modality, these areas can also respond to other modalities. Here we used fMRI to show that such responsiveness to tactile stimuli depends on the temporal frequency of stimulation. Participants performed a tactile threshold-tracking task where the tip of either their left or right middle finger was stimulated at 3, 20, or 100 Hz. Whole-brain analysis revealed an effect of stimulus frequency in two regions: the auditory cortex and the visual cortex. The BOLD response in the auditory cortex was stronger during stimulation at hearable frequencies (20 and 100 Hz) whereas the response in the visual cortex was suppressed at infrasonic frequencies (3 Hz). Regardless of which hand was stimulated, the frequency-dependent effects were lateralized to the left auditory cortex and the right visual cortex. Furthermore, the frequency-dependent effects in both areas were abolished when the participants performed a visual task while receiving identical tactile stimulation as in the tactile threshold-tracking task. We interpret these findings in the context of the metamodal theory of brain function, which posits that brain areas contribute to sensory processing by performing specific computations regardless of input modality.

"Feeling" others' painful actions: the sensorimotor integration of pain and action information

Sensorimotor regions of the brain have been implicated in simulation processes such as action understanding and empathy, but their functional role in these processes remains unspecified. We used functional magnetic resonance imaging (fMRI) to demonstrate that postcentral sensorimotor cortex integrates action and object information to derive the sensory outcomes of observed hand–object interactions. When subjects viewed others' hands grasping or withdrawing from objects that were either painful or nonpainful, distinct sensorimotor subregions emerged as showing preferential responses to different aspects of the stimuli: object information (noxious vs. innocuous), action information (grasps vs. withdrawals), and painful action outcomes (painful grasps vs. all other conditions). Activation in the latter region correlated with subjects' ratings of how painful each object would be to touch and their previous experience with the object. Viewing others' painful grasps also biased behavioral responses to actual tactile stimulation, a novel effect not seen for auditory control stimuli. Somatosensory cortices, including primary somatosensory areas 1/3b and 2 and parietal area PF, may therefore subserve somatomotor simulation processes by integrating action and object information to anticipate the sensory consequences of observed hand–object interactions. Hum Brain Mapp, 2013. © 2012 Wiley Periodicals, Inc.

FMRI reveals abnormal central processing of sensory and pain stimuli in ill Gulf War veterans

Many veterans chronically ill from the 1991 Gulf War exhibit symptoms of altered sensation, including chronic pain. In this study of 55 veterans of a Construction Battalion previously examined in 1995-1996 and 1997-1998, brain activation to innocuous and noxious heat stimuli was assessed in 2008-2009 with a quantitative sensory testing fMRI protocol in control veterans and groups representing three syndrome variants. Testing outside the scanner revealed no significant differences in warm detection or heat pain threshold among the four groups. In the fMRI study, Syndrome 1 and Syndrome 2, but not Syndrome 3, exhibited hypo-activation to innocuous heat and hyper-activation to noxious heat stimuli compared to controls. The results indicate abnormal central processing of sensory and painful stimuli in 2 of 3 variants of Gulf War illness and call for a more comprehensive study with a larger, representative sample of veterans.

Imaging the functional connectivity of the Periaqueductal Gray during genuine and sham electroacupuncture treatment

Background

Electroacupuncture (EA) is currently one of the most popular acupuncture modalities. However, the continuous stimulation characteristic of EA treatment presents challenges to the use of conventional functional Magnetic Resonance Imaging (fMRI) approaches for the investigation of neural mechanisms mediating treatment response because of the requirement for brief and intermittent stimuli in event related or block designed task paradigms. A relatively new analysis method, functional connectivity fMRI (fcMRI), has great potential for studying continuous treatment modalities such as EA. In a previous study, we found that, compared with sham acupuncture, EA can significantly reduce Periaqueductal Gray (PAG) activity when subsequently evoked by experimental pain. Given the PAG's important role in mediating acupuncture analgesia, in this study we investigated functional connectivity with the area of the PAG we previously identified and how that connectivity was affected by genuine and sham EA.

Results

Forty-eight subjects, who were randomly assigned to receive either genuine or sham EA paired with either a high or low expectancy manipulation, completed the study. Direct comparison of each treatment mode's functional connectivity revealed: significantly greater connectivity between the PAG, left posterior cingulate cortex (PCC), and precuneus for the contrast of genuine minus sham; significantly greater connectivity between the PAG and right anterior insula for the contrast of sham minus genuine; no significant differences in connectivity between different contrasts of the two expectancy levels.

Conclusions

Our findings indicate the intrinsic functional connectivity changes among key brain regions in the pain matrix and default mode network during genuine EA compared with sham EA. We speculate that continuous genuine EA stimulation can modify the coupling of spontaneous activity in brain regions that play a role in modulating pain perception.

Striatal functional connectivity networks are modulated by fMRI resting state conditions

Resting state fluctuations in blood oxygenation level dependent functional connectivity magnetic resonance imaging (BOLD fcMRI) time-series have been increasingly employed to study functional connectivity networks in healthy and diseased brain. FcMRI studies have been conducted under a number of different conditions, including resting eyes open, visual fixation and finger tapping. BOLD fcMRI networks are believed to reflect both anatomically constrained spontaneous fluctuations and state-dependent activity. In this study, state-dependence of functional connectivity to dorsal and ventral striatum was assessed with fcMRI during an eyes open resting state condition (REST) and during continuous 3 Hz transcutaneous electrical nerve stimulation (TENS), with the a priori hypotheses: (1) dorsal striatum connectivity with sensorimotor/attention networks will be stronger during TENS compared to REST, (2) ventral striatum connectivity with limbic system emotion-processing network will be weaker during TENS compared to REST and (3) ventral striatum connectivity with sensorimotor/attention networks will be stronger during TENS compared to REST. These hypotheses were confirmed by the results obtained, indicating that resting state BOLD fMRI networks reflect, in substantial measure, state-dependent activity.

Age- and time-dependent effects on functional outcome and cortical activation pattern in patients with median nerve injury: a functional magnetic resonance imaging study

Object

The authors conducted a study to determine age- and time-dependent effects on the functional outcome after median nerve injury and repair and how such effects are related to changes in the pattern of cortical activation in response to tactile stimulation of the injured hand.

Methods

The authors studied 11 patients with complete unilateral median nerve injury at the wrist repaired with epineural suture. In addition, 8 patients who were reported on in a previous study were included in the statistical analysis. In the entire study cohort, the mean age at injury was 23.3 ± 13.4 years (range 7–57 years) and the time after injury ranged from 1 to 11 years. Sensory perception was measured with the static 2-point discrimination test and monofilaments. Functional MR imaging was conducted during tactile stimulation (brush strokes) of Digits II–III and IV–V of both hands, respectively.

Results

Tactile sensation was diminished in the median territory in all patients. The strongest predictor of 2-point discrimination was age at injury (p < 0.0048), and when this was accounted for in the regression analysis, the other age- and time-dependent predictors had no effect. The activation ratios (injured/healthy hand) for Digit II–III and Digit IV–V stimulation were positively correlated (rho 0.59, p < 0.011). The activation ratio for Digit II–III stimulation correlated weakly with time after injury (p < 0.041). The activation ratio of Digits IV–V correlated weakly with both age at injury (p < 0.048) and time after injury (p < 0.033), but no predictor reached significance in the regression model. The mean ratio of ipsi- and contralateral hemisphere activation after stimulation of the injured hand was 0.55, which was not significantly different from the corresponding ratio of the healthy hand (0.66).

Conclusions

Following a median nerve injury (1–11 years after injury) there may be an initial increase in the volume of the cortical representation, which subsequently declines during the restoration phase. These dynamic changes may involve both median and ulnar nerve cortical representation, because both showed negative correlation with time after injury. These findings are in agreement with animal studies showing that cortical plasticity is an important mechanism for functional recovery after peripheral nerve injury and repair.

Robust S1, S2, and thalamic activations in individual subjects with vibrotactile stimulation at 1.5 and 3.0 T

Functional magnetic resonance imaging (fMRI) is often used to enhance visualization and provide target localization during the planning phase of neurosurgical procedures. Although parametric maps have been used to identify areas of eloquent cortex such as the primary (S1) and secondary (S2) somatosensory areas for tumor surgery, to date, few fMRI methods exist to localize subcortical targets for surgical interventions used to treat movement disorders. The scanning time required to obtain statistically significant functional signals must be balanced against the possibility of movement artifacts and patient discomfort. We propose a vibrotactile stimulation technique to activate the somatosensory pathway for neurosurgical planning and perform a sensitivity analysis to determine the amount of time required to achieve significant activations of S1, S2, and sensory thalamus in individual subjects. Bilateral stimulation experiments were carried out on two MRI scanners (n = 13 at 1.5 T; n = 5 at 3.0 T). The analysis demonstrates that statistically significant functional activations can be achieved in clinically acceptable times: 16 min at 1.5 T (26/26 experiments) and 6 min at 3.0 T (10/10) for S1 activations; 24 min at 1.5 T (22/26) and 18 min at 3.0 T for S2 activations (9/10); and 32 min at 1.5 T (15/26) and 18 min at 3.0 T (10/10) for activation of thalamic nuclei. These results demonstrate that S1 and S2 activations are robust at 1.5 and 3.0 T, and that robust thalamic activations in individual subjects are possible at 3.0 T. These techniques demonstrate that this technique can be used for preoperative planning for surgical candidates.

Neurocognitive processing of esophageal central sensitization in the insula and cingulate gyrus

The cingulate and insular cortices are parts of the limbic system that process and modulate gastrointestinal sensory signals. We hypothesized that sensitization of these two limbic area may operate in esophageal sensitization. Thus the objective of the study was to elucidate the neurocognitive processing in the cingulate and insular cortices to mechanical stimulation of the proximal esophagus following infusion of acid or phosphate buffer solution (PBS) into the esophagus. Twenty-six studies (14 to acid and 12 to PBS infusion) were performed in 20 healthy subjects (18-35 yr) using high-resolution (2.5 x 2.5 x 2.5 mm(3) voxel size) functional MRI (fMRI). Paradigm-driven, 2-min fMRI scans were performed during randomly timed 15-s intervals of proximal esophageal barostatically controlled distentions and rest, before and after 30-min of distal esophageal acid or PBS perfusion (0.1 N HCl or 0.1 M PBS at 1 ml/min). Following distal esophageal acid infusion, at subliminal and liminal levels of proximal esophageal distentions, the number of activated voxels in both cingulate and insular cortices showed a significant increase compared with before acid infusion (P < 0.05). No statistically significant change in cortical activity was noted following PBS infusion. We conclude that 1) acid stimulation of the esophagus results in sensitization of the cingulate and insular cortices to subliminal and liminal nonpainful mechanical stimulations, and 2) these findings can have ramifications with regard to the mechanisms of some esophageal symptoms attributed to reflux disease.

Reduced brainstem inhibition during anticipated pelvic visceral pain correlates with enhanced brain response to the visceral stimulus in women with irritable bowel syndrome

Cognitive factors such as fear of pain and symptom-related anxiety play an important role in chronic pain states. The current study sought to characterize abnormalities in preparatory brain response before aversive pelvic visceral distention in irritable bowel syndrome (IBS) patients and their possible relationship to the consequences of distention. The brain functional magnetic resonance imaging (fMRI) blood oxygen level-dependent (BOLD) response to anticipated and delivered mild and moderate rectal distention was recorded from 14 female IBS patients and 12 healthy controls. During cued anticipation of distention, activity decreased in the insula, supragenual anterior cingulate cortex (sACC), amygdala, and dorsal brainstem (DBS) of controls. IBS patients showed less anticipatory inactivation. Group differences were significant in the right posterior insula and bilateral DBS. Self-rated measures of negative affect during scanning were higher in patients than controls (p < 0.001), and the anticipatory BOLD decreases in DBS were inversely correlated with these ratings. During subsequent distention, both groups showed activity increases in insula, dorsal ACC, and DBS and decreases in the infragenual ACC. The increases were more extensive in patients, producing significant group differences in dorsal ACC and DBS. The amplitude of the anticipatory decrease in the pontine portion of DBS was associated with greater activation during distention in right orbitofrontal cortex and bilateral sACC. Both regions have been associated previously with corticolimbic inhibition and cognitive coping. Deficits in preparatory inhibition of DBS, including the locus ceruleus complex and parabrachial nuclei, may interfere with descending corticolimbic inhibition and contribute to enhanced brain responsiveness and perceptual sensitivity to visceral stimuli in IBS.

Reproducible activation in BA2, 1 and 3b associated with texture discrimination in healthy volunteers over time

We aimed to quantify specific location and reproducibility of brain activation associated with discrimination of a moving textured surface in adult healthy volunteers over a 6-month interval. A sensory stimulation device was developed to provide a texture stimulus to the fingertips at a controlled speed and pressure. Repeat measurements of regional cerebral blood flow, using positron emission tomography (PET), were obtained in 10 healthy individuals, aged 33 to 80 years (mean=55.8 years), at scanning sessions separated by 6 months. Stimulation and rest conditions were presented to either the right, dominant (n=5) or left non-dominant (n=5) hand. Activation location was objectively quantified with reference to probabilistic cytoarchitectonic maps. Differences in activation over time and regions of common activation were also quantified. Participants consistently activated Brodmann areas (BA) 2, 3b and 1, somatosensory areas of postcentral gyrus, at initial and 6-month studies: 93.1% of common activation for the right-hand (RH) and 60.6% for left-hand (LH) stimulation group were in these areas. Reproducible activation in BA6, 4a and 4p was also observed for the RH group (6.8% of common activation) and LH group (39.4%). There were no sites of significant difference over time for either hand. Highly consistent location of activation over time suggests that changes in loci of activation may be confidently monitored in adults using this paradigm. Use of probabilistic cytoarchitectonic maps permitted objective quantification of the anatomical location of the core of reproducible activation.

An ARX model-based approach to trial by trial identification of fMRI-BOLD responses

Being able to estimate the fMRI-BOLD response following a single task or stimulus is certainly of value, since it allows to characterize its relationship to different aspects either of the stimulus, or of the subject's performance. In order to detect and characterize BOLD responses in single trials, we developed and validated a procedure based on an AutoRegressive model with eXogenous Input (ARX). The use of an individual exogenous input for each voxel makes the modeling sensitive enough to reveal differences across regions, avoiding any a priori assumption about the reference signal. The detection of variability across trials is ensured by a suitable choice, for each voxel, of the order of the moving average, which in our implementation determines the relative delay between the recorded and the reference signal. This is a quality useful in finding different time profiles of activation from high temporal resolution fMRI data. The results obtained from simulated fMRI data resulting from synthetic activations in actual noise indicate that such approach allows to evaluate important features of the response, such as the time to onset, and time to peak. Moreover, the results obtained from real high temporal resolution fMRI data acquired at l.5 T during a motor task are consistent with previous knowledge about the responses of different cortical areas in motor programming and execution. The proposed procedure should also prove useful as a pre-processing step in different approaches to the analysis of fMRI data.

Effects of autogenic training on nitroglycerin-induced headaches

OBJECTIVES

To investigate the prophylactic and acute effects of autogenic training (AT) during a nitroglycerin-induced migraine attack.

METHODS

Thirty female migraineurs (without aura) and 11 controls participated in the study. Of these, 11 migraineurs and 5 controls practiced AT regularly for at least 6 months prior to and during the sublingual nitroglycerin test. Headache intensity and characteristics were recorded with a standardized method. During the nitroglycerin challenge, blood was collected for plasma cortisol determination and blood pressure and pulse rate were recorded.

RESULTS

As a long-term preventive treatment, AT significantly decreased the mean headache frequency and intensity (P = .001) compared to the pretreatment period in the migraineurs who regularly practiced AT (n = 11). During the nitroglycerin challenge, AT successfully attenuated the nitroglycerin-induced acute decrease in blood pressure and pulse rate (P = .013; n = 16 AT subjects vs n = 25 non-AT subjects). However, it was not effective in preventing immediate headache (P = .71), did not decrease the frequency of acute migraine attacks (P = .79), and could not alleviate acute migraine pain (P = .78; n = 16 AT subjects vs n = 25 non-AT subjects). Plasma cortisol concentration significantly increased (P = .003) during the acute migraine attack (n = 22), and migraine intensity correlated with plasma cortisol elevations (P < .001; n = 41) and showed a tendency of negative correlation with morning plasma cortisol concentration (P = .08; n = 41). However, AT did not alter plasma cortisol responses (P = .99; n = 16 AT subjects vs n = 25 non-AT subjects).

CONCLUSION

(1) The long-term AT therapy proved to be a significantly effective preventive intervention in migraine sufferers. We hypothesized that this long-term effect of AT is based on modulation of the pain anticipation system, which is strongly correlated with function of the anterior cingulate cortex. (2) We demonstrated that AT could not alter the nitroglycerin-induced acute migraine attacks, which are directly related to the dysfunctional brainstem activation according to previous studies. (3) Our results suggested that there are multiple, complex relationships between cortisol responses and migraine pain, which are possibly mediated by the brain serotonergic system. (4) In addition, our results provide further evidence that nitroglycerin-induced vasodilatation is not directly connected to either immediate headache or delayed migraine attack.

Different modalities of painful somatosensory stimulations affect anticipatory cortical processes: A high-resolution EEG study

Pain sensation is characterized by multiple features that allow to differentiate pricking, burning, aching, stinging, and electrical shock. These features are sub-served by neural pathways that might give flexibility and selectivity to the cerebral anticipatory processes. In this line, the present high-resolution electroencephalography (EEG) study tested the hypothesis that the anticipatory cortical processes are stronger for painful thermal (biologically relevant) than electrical ("artificial") stimuli with similar intensity. EEG data (128 electrodes) were recorded in normal subjects during the expectancy of painful electrical or laser stimuli (visual omitted stimulus paradigm; interval between two painful stimuli: 16s), delivered over the median nerve region of the right arm (nonpainful stimuli as controls). After each stimulus, the subject reported the perceived stimulus intensity. Surface Laplacian estimation of the EEG data spatially enhanced the anticipatory stimulus-preceding negativity (SPN), which reflects motivational relevance of the stimulus. Subjects perceived no difference in the intensity of the electrical versus laser stimuli in both painful and nonpainful conditions. However, the anticipatory SPN appeared over large scalp regions before painful laser but not electrical stimulation. The same was true for the nonpainful stimulations. The present results suggest that the motivational anticipatory cortical processes are induced by nonpainful and painful biologically/ecologically relevant laser stimuli rather than by "artificial" electrical stimuli with similar intensity.

Somatosensory cortex stimulation for deafferentation pain

Functional neuroimaging has demonstrated that a relationship exists between the intensity of deafferentation pain and the degree of deafferentation-related reorganization of the primary somatosensory cortex. It has also revealed that this cortical reorganization can be reversed after the attenuation of pain. Deafferentation pain is also associated with hyperactivity of the somatosensory thalamus and cortex. Therefore, in order to suppress pain, it seems logical to attempt to modify this deafferentation-related somatosensory cortex hyperactivity and reorganization. This can be achieved using neuronavigation-guided transcranial magnetic stimulation (TMS), a technique that is capable of modulating cortical activity. If TMS is capable of suppressing deafferentation pain, this benefit should be also obtained by the implantation of epidural stimulating electrodes over the area of electrophysiological signal abnormality in the primary somatosensory cortex. The first studies demonstrated a statistically significant pain suppression in all patients and a clinically significant pain suppression in 80% of them. This clinical experience suggests that somatosensory cortex stimulation may become a neurophysiology-based new approach for treating deafferentation pain in selected patients. In this chapter, we review the relevant recent reports and describe our studies in this field.

Test-retest study of fMRI signal change evoked by electroacupuncture stimulation

Recent efforts to use fMRI to investigate the effects of acupuncture needle manipulation on the brain have yielded discrepant results. This study was designed to test the reliability of fMRI signal changes evoked by acupuncture stimulation. Six subjects participated in six identical scanning sessions consisting of four functional scans, one for each of the four conditions: electroacupuncture stimulation (2 Hz) at GB 37, UB 60, non-acupoint (NP), and a control task of the finger tapping. In the group analysis across all subjects and sessions, both the average ratings on a Subjective Acupuncture Sensation Scale and the average fMRI signal changes (increases and decreases) were similar for GB37, UB 60, and NP. Visual inspection of the activation maps from individual sessions and ICC analysis revealed that fMRI signal changes evoked by electroacupuncture stimulation were significantly more variable than those from the control finger-tapping task. The relatively large variability across different sessions within the same subject suggests multiple sessions should be used to accurately capture the activation patterns evoked by acupuncture stimulation at a particular point for a specific subject.

Sex differences in regional brain response to aversive pelvic visceral stimuli

To explore sex differences in the response of seven brain regions to an aversive pelvic visceral stimulus, functional magnetic resonance images were acquired from 13 healthy adults (6 women) during 15 s of cued rectal distension at two pressures: 25 mmHg (uncomfortable), and 45 mmHg (mild pain), as well as during an expectation condition (no distension). Random-effects analyses combining subject data voxelwise found 45-mmHg pressure significantly activated the insular and anterior cingulate cortices in both sexes. In men only, the left thalamus and ventral striatum were also activated. Although all activations appeared more extensive in men, no sex difference attained significance. To explore the presence of deactivations, which are generally cancelled by more numerous activations when subjects are combined for each voxel, the number of activated voxels, number of deactivated voxels, and ratio of deactivated voxels to total voxels affected were assessed via random-effects, mixed-model analyses combining subject data at the region level. Greater insula activation in men compared with women was seen during the expectation condition and during the 25-mmHg distension. Greater deactivations in women were seen in the amygdala (25-mmHg distension) and midcingulate (45-mmHg distension). Women had a significantly higher proportion of deactivated voxels than men in all four subcortical structures during 25-mmHg distension. Greater familiarity of females with physiological pelvic visceral discomfort may have enhanced brain systems that dampen arousal networks during lower levels of discomfort.

Recent advances and future prospects in neuroimaging of acute and chronic pain

The advent of modern functional brain imaging has created new possibilities for exploring the brain mechanisms that underly acute and chronic pain. It is now possible to explore how specific aspects of the pain experience are represented in the brain and the impact of individual attributes on these representations. This review provides an overview of the capabilities of positron emission tomography and functional magnetic resonance imaging and their utility in identifying pain-evoked forebrain responses in both acute and chronic pain conditions. Also presented are sophisticated approaches to the design and implementation of such studies, with the ability to isolate cortical responses related to specific pain constructs, the complexities of interpreting hemodynamic-based responses in consideration of the underlying neurophysiology and the impact of imaging pain for diagnostic considerations. Finally, it is predicted that the ability to identify functional brain abnormalities will challenge classical boundaries between neurology, gastroenterology and psychiatry.

Mechanisms of central neuropathic pain: a combined psychophysical and fMRI study in syringomyelia

The pathophysiology of central pain syndromes is still poorly understood and their treatment remains a major challenge. It has long been suggested that lesions of the spinothalamic pathways are necessary for developing these pain syndromes. The recently proposed thermosensory disinhibition theory suggests that reduction of the inhibition of thermal sensory afferents that affect nociceptive systems may play a major pathophysiological role. Syringomyelia, which is frequently associated with central neuropathic pain, is characterized by a selective or preferential lesion of the spinothalamic tract resulting in thermosensory deficits of various extents and magnitudes. Thus, syringomyelia represents a unique 'pathological model' particularly suited to investigating the relationship between spinothalamic tract dysfunction, thermosensory deficits and pain. Here, we systematically compared the sensory loss (thermal and mechanical), using quantitative sensory testing, between 46 consecutive syringomyelia patients with or without neuropathic pain. We then further investigated the mechanisms of evoked pains in these patients, using functional MRI (fMRI) in a subgroup of patients with cold or brush-evoked allodynia, compared with patients without pain and healthy volunteers. We found no significant difference in the magnitude or extent of sensory deficits between patients with or without neuropathic pain, suggesting that lesions of the spinothalamic pathways are not sufficient for developing central pain. However, a different pattern of sensory deficits was observed between patients with spontaneous pain only (n = 11) and patients with both spontaneous pain and allodynia (n = 20), suggesting that the mechanisms of central pain are not univocal. In patients with spontaneous pain only, the thermal sensory loss was significantly more asymmetrical and there was a direct relationship between the extent of thermosensory deficits (i.e. deafferentation) and the intensity of burning pain. In contrast, patients with allodynia had reduced thermal deficits, in terms of both magnitude and extent. In addition, the sensory deficits were different between patients with cold or tactile allodynia, suggesting distinct pathophysiological mechanisms related to the sub-modalities of allodynia. Our fMRI study further confirmed this, showing that different sub-types of allodynia were associated with distinct patterns of brain activity, which do not necessarily correspond to the 'pain matrix' involved in acute physiological pain. The prefrontal cortex was the only area consistently activated by pathological evoked pains, suggesting that alteration of high-level pain modulatory mechanisms might play a major role in allodynia due to central lesion.

Novel evidence for hypersensitivity of visceral sensory neural circuitry in irritable bowel syndrome patients

BACKGROUND & AIMS

Visceral hypersensitivity in irritable bowel syndrome (IBS) patients has been documented by evaluation of perceived stimulations that can reflect abnormalities of both sensory neurocircuitry and cognitive processes. The presence of actual neurohypersensitivity in human beings has not been documented separately. Because subliminal stimulations are free from the influence of stimulus-related cognitive processes, functional magnetic resonance imaging (fMRI) cortical response to these stimuli can be considered a measure of activity of the neural circuitry alone. The aim of this study was to compare quantitatively the cerebral cortical fMRI activity response to equal subliminal stimulations between IBS patients and age-matched controls.

METHODS

We studied 10 IBS patients and 10 healthy controls using a computerized barostat-controlled rectal distention device. fMRI activity volume and percent maximum signal intensity change for equal subliminal distention pressures were compared between controls and patients.

RESULTS

Three levels of subliminal distention pressures (eg, 10, 15, and 20 mm Hg), were represented in both controls and patients and were analyzed for fMRI response. In all 3 distention levels the fMRI activity volume in IBS patients was significantly larger than age- and sex-matched controls (P < .05). The percent maximum signal intensity change was similar between IBS patients and controls.

CONCLUSIONS

The volume of cerebral cortical activity response to equal subliminal distention pressures in IBS patients is significantly larger than in controls, documenting the existence of hypersensitivity of the neural circuitry in this patient group irrespective of stimulus-related cognitive processes.

Cingulate cortex: a closer look at its gut-related functional topography

Earlier studies have documented activation of the cingulate cortex during gut related sensory-motor function. However, topography of the cingulate cortex in relationship to various levels of visceromotor sensory stimuli and gender is not completely elucidated. The aim was to characterize and compare the activation topography of the cingulate cortex in response to 1) subliminal, 2) perceived rectal distensions, and 3) external anal sphincter contraction (EASC) in males and females. We studied 18 healthy volunteers (ages 18-35 yr; 10 women, 8 men) using functional MRI blood-oxygenation-level-dependent technique. We obtained 11 axial slices (voxel vol. 2.5-6.0 x 2.5 x 2.5 mm(3)) through the cingulate cortex during barostat-controlled subliminal, liminal, and supraliminal nonpainful rectal distensions as well as EASC. Overall, for viscerosensation, the anterior cingulate cortex exhibited significantly more numbers of activated cortical voxels for all levels of stimulations compared with the posterior cingulate cortex (P < 0.05). In contrast, during EASC, activity in the posterior cingulate was larger than in the anterior cingulate cortex (P < 0.05). Cingulate activation was similar during EASC in males and females (P = 0.58), whereas there was a gender difference in anterior cingulate activation during liminal and supraliminal stimulations (P < 0.05). In females, viscerosensory cortical activity response was stimulus-intensity dependent. Intestinal viscerosensation and EASC induce different patterns of cingulate cortical activation. There may be gender differences in cingulate cortical activation during viscerosensation. In contrast to male subjects, females exhibit increased activity in response to liminal nonpainful stimulation compared with subliminal stimulation suggesting differences in cognition-related recruitment.