Quantitative changes in regional cerebral blood flow induced by cold, heat and ischemic pain: a continuous arterial spin labeling study

Cerebral processing of sharp mechanical pain measured with arterial spin labeling

INTRODUCTION

Arterial spin labeling (ASL) is a functional neuroimaging technique that has been frequently used to investigate acute pain states. A major advantage of ASL as opposed to blood-oxygen-level-dependent functional neuroimaging is its applicability for low-frequency designs. As such, ASL represents an interesting option for studies in which repeating an experimental event would reduce its ecological validity. Whereas most ASL pain studies so far have used thermal stimuli, to our knowledge, no ASL study so far has investigated pain responses to sharp mechanical pain.

METHODS

As a proof of concept, we investigated whether ASL has the sensitivity to detect brain activation within core areas of the nociceptive network in healthy controls following a single stimulation block based on 96 s of mechanical painful stimulation using a blunt blade.

RESULTS

We found significant increases in perfusion across many regions of the nociceptive network such as primary and secondary somatosensory cortices, premotor cortex, posterior insula, inferior parietal cortex, parietal operculum, temporal gyrus, temporo-occipital lobe, putamen, and the cerebellum. Contrary to our hypothesis, we did not find any significant increase within ACC, thalamus, or PFC. Moreover, we were able to detect a significant positive correlation between pain intensity ratings and pain-induced perfusion increase in the posterior insula.

CONCLUSION

We demonstrate that ASL is suited to investigate acute pain in a single event paradigm, although to detect activation within some regions of the nociceptive network, the sensitivity of our paradigm seemed to be limited. Regarding the posterior insula, our paradigm was sensitive enough to detect a correlation between pain intensity ratings and pain-induced perfusion increase. Previous experimental pain studies have proposed that intensity coding in this region may be restricted to thermal stimulation. Our result demonstrates that the posterior insula encodes intensity information for mechanical stimuli as well.

Differences in resting cerebellar and prefrontal cortical blood flow in spinal cord injury-related neuropathic pain: A brief report

Context: Little is understood about differences in resting neural activity among those with spinal cord injury (SCI)-related neuropathic pain. The purpose of this pilot study was to determine resting cerebral blood flow differences in persons with SCI-related neuropathic pain compared to healthy, pain-free able-bodied controls.Methods: Five persons with paraplegia and ten able-bodied participants were included in this study. Resting blood flow, as measured by a continuous arterial spin labeling (ASL) method of fMRI, was analyzed via statistical parametric mapping.Results: Persons with SCI-related neuropathic pain had significantly lower resting blood flow in the cerebellum (Crus I/II), rostral ventromedial medulla and left insular cortex. In contrast, greater resting blood flow occurred in the medial orbitofrontal cortex among those with SCI-related neuropathic pain compared to controls.Conclusion: Differences in resting blood flow were observed among those with SCI-related pain, particularly in regions that may be involved in affective-motivational and cognitive-evaluative aspects of pain. Larger ASL studies in addition to functional connectivity studies using fMRI are needed to clarify unique neural patterns in this complex and often intractable form of pain.

Immediate Analgesic Effect of Acupuncture in Patients With Primary Dysmenorrhea: A fMRI Study

Primary dysmenorrhea (PDM) is a common gynecological disease characterized by lower abdominal pain. Acupuncture is considered a good alternative therapy for PDM. However, the central mechanism of the analgesic effect of acupuncture is largely unknown. In this study, eligible patients were randomized into the real and sham acupuncture groups using a computer-generated, permuted block randomization method. The study cohort comprised 34 patients: 19 in the real acupuncture group and 15 in the sham acupuncture group. The clinical characteristics of the patients during their menstrual period were collected, and imaging scans were performed during the first 3 days of the patients' menstrual period. We analyzed task and resting functional magnetic resonance imaging (fMRI) data to investigate the potential central mechanism of the immediate effect of acupuncture intervention on the intensity of PDM pain. The task fMRI study found that the rostral anterior cingulate cortex (rACC) and right supplemental motor area were activated during real acupuncture. Using the resting-state functional connectivity (FC) method, we found a post- versus pre-treatment change in the FC of the rACC and left precentral gyrus in the comparison of real acupuncture versus sham acupuncture. In addition, the FC of the rACC-left precentral gyrus at baseline was negatively correlated with short-term analgesia, while the change in the FC of the rACC-left precentral gyrus was positively correlated with short-term analgesia after acupuncture treatment. These findings support the importance of rACC-left precentral gyrus resting-state FC in the modulation of the intensity of PDM pain through acupuncture, which may shed light on the central mechanism of acupuncture in the treatment of PDM.

Heterogeneous Acupuncture Effects of Taixi (KI3) on Functional Connectivity in Healthy Youth and Elder: A Functional MRI Study Using Regional Homogeneity and Large-Scale Functional Connectivity Analysis

Heterogeneous neurological responses of acupuncture between different groups have been proposed by previous studies but rarely studied. The study described here was designed to explore the divergence of acupuncture at Taixi (KI3) on spontaneous activity of brain regions and functional connectivity (FC) between healthy youth and elder with functional magnetic resonance imaging (fMRI). 20 healthy young volunteers and 20 healthy elders underwent 10-minute-resting-state fMRI before acupuncture, and then acupuncture at Taixi (KI3) for 3 minutes; after withdrawing the needles, volunteers underwent a second fMRI scan for 10 minutes. Regional homogeneity (ReHo) and large-scale FC analysis using Power 264 atlas were utilized to analyze the changes of brain spontaneous activity. Compared with the resting state, the decreased ReHo after acupuncture at KI3 in both groups were concentrated in the left postcentral, right paracentral lobule, and right SMA. Moreover, the subjects in the HY group showed declined ReHo in brain regions involving the right lingual and precentral. However, those subjects in the HE group presented decreased ReHo in the right postcentral and precentral, left supramarginal gyrus and SMA, and both cingulum middle after needling in KI3. Compared with the resting state, the HY group in the postneedling state showed lower mean intranetwork FC in sensory/somatomotor and subcortical network. And the internetwork FC between sensory/somatomotor and dorsal attention had significantly decreased after acupuncture. Furthermore, the internetwork FC between subcortical and dorsal attention and between subcortical and cerebellar showed the most obvious elevations after needling in the HY group. In the elder group, both FCs of internetwork and intranetwork primarily involving sensory/somatomotor, cingulo-opercular, and dorsal attention were declined after acupuncture. These results indicated that acupuncture at KI3 had heterogeneous acupuncture effects in different age groups. Our study led to converging evidence supporting the acupuncture effect segregation of different condition subjects and supporting evidence for prevention and treatment with acupuncture in the future.

Association of iron levels in hair with brain structures and functions in young adults

BACKGROUND

Iron plays a critical role in normal brain functions and development, but it has also been known to have adverse neurological effects.

METHODS

Here, we investigated the associations of iron levels in hair with regional gray matter volume (rGMV), regional cerebral blood flow (rCBF), fractional anisotropy (FA), mean diffusivity (MD), and cognitive differences in a study cohort of 590 healthy young adults.

RESULTS

Our findings showed that high iron levels were associated with lower rGMV in areas including the hippocampus, lower rCBF in the anterior and posterior parts of the brain, greater FA in areas including the part of the splenium of the corpus callosum, lower MD in the overlapping area including the splenium of the corpus callosum, as well as greater MD in the left hippocampus and areas including the frontal lobe.

CONCLUSION

These results are compatible with the notion that iron plays diverse roles in neural mechanisms in healthy young adults.

Imaging Clinically Relevant Pain States Using Arterial Spin Labeling

Arterial Spin Labeling (ASL) is a perfusion-based functional magnetic resonance imaging technique that uses water in arterial blood as a freely diffusible tracer to measure regional cerebral blood flow (rCBF) noninvasively. To date its application to the study of pain has been relatively limited. Yet, ASL possesses key features that make it uniquely positioned to study pain in certain paradigms. For instance, ASL is sensitive to very slowly fluctuating brain signals (in the order of minutes or longer). This characteristic makes ASL particularly suitable to the evaluation of brain mechanisms of tonic experimental, post-surgical and ongoing/or continuously varying pain in chronic or acute pain conditions (whereas BOLD fMRI is better suited to detect brain responses to short-lasting or phasic/evoked pain). Unlike positron emission tomography or other perfusion techniques, ASL allows the estimation of rCBF without requiring the administration of radioligands or contrast agents. Thus, ASL is well suited for within-subject longitudinal designs (e.g., to study evolution of pain states over time, or of treatment effects in clinical trials). ASL is also highly versatile, allowing for novel paradigms exploring a flexible array of pain states, plus it can be used to simultaneously estimate not only pain-related alterations in perfusion but also functional connectivity. In conclusion, ASL can be successfully applied in pain paradigms that would be either challenging or impossible to implement using other techniques. Particularly when used in concert with other neuroimaging techniques, ASL can be a powerful tool in the pain imager's toolbox.

The Effect of Sedation on Cortical Activation: A Randomized Study Comparing the Effects of Sedation With Midazolam, Propofol, and Dexmedetomidine on Auditory Processing

BACKGROUND

Every day, millions of people undergo surgical procedures facilitated by anesthesia. Yet, there is no clinically accepted measure to predict the effects of sedation or anesthesia on the central nervous system. Auditory brain activation may provide an objective and quantifiable method to measure of the effects of sedation on neuronal processing.

METHODS

This is a randomized clinical trial. Forty-eight healthy volunteers were randomly assigned to receive 1 of 3 sedative drugs (midazolam [n = 11], propofol [n = 12], or dexmedetomidine [n = 12]) at a concentration adjusted to achieve mild sedation by self-rating, or to a no-drug control group (n = 13). Participants underwent functional magnetic resonance imaging while listening to music in a 5-minute block design experiment. We tested the hypothesis that mild sedation changes the magnitude or extent of cortical activation of an auditory stimulus.

RESULTS

We observed a significant reduction in auditory activation in both the dexmedetomidine (P = .001) and midazolam (P = .029) but not the propofol group (P = .619) when compared with saline control.

CONCLUSIONS

Our findings indicate that, compared with saline control, there is a significant reduction of brain activation in the auditory cortex in response to midazolam and dexmedetomidine but not propofol when given at mildly sedative doses. This method serves as a novel approach to quantify the effects of sedative agents in an objective fashion.

Evidence of a Synergistic Effect of Acupoint Combination: A Resting-State Functional Magnetic Resonance Imaging Study

Objective: This study aimed to find evidence of a synergistic effect of acupoint combinations by analyzing different brain regions activated after acupuncture at different acupoint combinations.

Methods: A total of 57 healthy subjects were randomly distributed into three groups: LR3 plus KI3 acupoints, LR3 plus sham acupoint, or LR3 alone. They underwent a magnetic resonance imaging scan before and after acupuncture. The amplitude of low-frequency fluctuation (ALFF) and regional homogeneity (ReHo) values of different brain regions were analyzed to observe changes in brain function.

Results: ALFF and ReHo produced an activated area in the cerebellum posterior lobe after acupuncture at LR3 plus KI3 acupoints versus LR3 alone. ALFF and ReHo revealed altered activity in Brodmann area 10 (BA10), BA18, and brainstem pons after acupuncture at LR3 plus sham acupoint compared with at LR3 alone. A comparison of acupuncture at LR3 plus KI3 acupoints with LR3 plus sham acupoint demonstrated an increase in BA6 of ALFF and a downregulation of ReHo.

Conclusions: The increased number of brain regions with altered brain activity after acupuncture at acupoint combinations versus a single acupoint are evidence of the synergistic effect of acupoint combinations. BA6 was significantly activated after acupuncture at LR3 plus KI3 acupoints compared with at LR3 plus sham acupoint, suggesting that BA6 is the specific region of synergistic effect of acupoint combinations of LR3 plus KI3 acupoints. Affected brain regions were different between acupuncture at LR3 plus sham acupoint and LR3 alone, which indicates that the sham acupoint may have some psychological effect. However, the specific mechanism of acupoint combinations requires further research.

Bladder Distension Increases Blood Flow in Pain Related Brain Structures in Subjects with Interstitial Cystitis

PURPOSE

In healthy control subjects certain brain regions of interest demonstrate increased regional cerebral blood flow in response to painful stimuli. We examined the effect of bladder distension on arterial spin label functional magnetic resonance imaging measures of regional cerebral blood flow in regions of interest in subjects with interstitial cystitis.

MATERIALS AND METHODS

A total of 11 female subjects with interstitial cystitis and 11 healthy controls underwent 3 brain perfusion scan studies using arterial spin label functional magnetic resonance imaging, including 1) with a full bladder, 2) with an empty bladder and 3) while experiencing heat pain. Regional cerebral blood flow was calculated using custom software and individual scans were spatially normalized to the MNI (Montreal Neurological Institute) template. Region of interest based, absolute regional cerebral blood flow was determined for each condition and for the within group/within subject regional cerebral blood flow distribution changes induced by each condition.

RESULTS

Bladder distension was associated with robust increases in regional cerebral blood flow in subjects with interstitial cystitis. The increases were greater than those in healthy controls in multiple regions of interest, including the supplemental motor area (mainly Brodmann area 6), the motor and sensory cortex, the insula bilaterally, the hippocampal structures bilaterally, and the middle and posterior cingulate areas bilaterally. During heat pain healthy controls had more robust regional cerebral blood flow increases in the amygdala bilaterally. At baseline with an empty bladder there was lower regional cerebral blood flow in the insula, and the mid and posterior cingulate cortex bilaterally in subjects with interstitial cystitis.

CONCLUSIONS

Compared to healthy controls, subjects with interstitial cystitis have limited differences in regional cerebral blood flow in baseline (empty bladder) conditions as well as during heat pain. However, they had robust regional cerebral blood flow increases in the full bladder state in regions of interest typically associated with pain, emotion and/or motor control, indicating altered processing of bladder related sensations.

Arterial Spin Labeling Techniques 2009-2014

PURPOSE

Arterial spin labeling (ASL) techniques have been implemented across a diverse range of clinical and experimental applications. This review aims to evaluate the current feasibility of ASL in clinical neuroradiology based on recent improvements to ASL sequences and highlight areas for potential clinical applications.

METHODS AND MATERIALS

In December 2014, a literature search was conducted on PubMed Central, EMBASE, and Scopus using the search terms: "arterial spin labeling, neuroradiology," for studies published between 2009 and 2014 (inclusive). Of 483 studies matching the inclusion criteria, the number of studies using continuous, pseudocontinuous, pulsed, and velocity-selective ASL sequences was 42, 209, 226, and 3, respectively. Studies were classified based on several common clinical applications according to the type of ASL sequence used. Studies using pulsed ASL and pseudo-continuous ASL were grouped based on common sequences.

RESULTS

The number of clinical studies was 264. Numerous studies applied ASL to stroke management (43 studies), drug testing (21 studies), neurodegenerative diseases (40 studies), and psychiatric disorders (26 studies).

CONCLUSIONS

This review discusses several factors hindering the implementation of clinical ASL and ASL-related radiofrequency safety issues encountered in clinical practice. However, a limited number of search terms were used. Further development of robust sequences with multislice imaging capabilities and reduced radiofrequency energy deposition will hopefully improve the clinical acceptance of ASL.

Hypnosis and pain perception: An Activation Likelihood Estimation (ALE) meta-analysis of functional neuroimaging studies

BACKGROUND AND OBJECTIVE

Several studies reported that hypnosis can modulate pain perception and tolerance by affecting cortical and subcortical activity in brain regions involved in these processes. We conducted an Activation Likelihood Estimation (ALE) meta-analysis on functional neuroimaging studies of pain perception under hypnosis to identify brain activation-deactivation patterns occurring during hypnotic suggestions aiming at pain reduction, including hypnotic analgesic, pleasant, or depersonalization suggestions (HASs).

DATABASES AND DATA TREATMENT

We searched the PubMed, Embase and PsycInfo databases; we included papers published in peer-reviewed journals dealing with functional neuroimaging and hypnosis-modulated pain perception. The ALE meta-analysis encompassed data from 75 healthy volunteers reported in 8 functional neuroimaging studies.

RESULTS

HASs during experimentally-induced pain compared to control conditions correlated with significant activations of the right anterior cingulate cortex (Brodmann's Area [BA] 32), left superior frontal gyrus (BA 6), and right insula, and deactivation of right midline nuclei of the thalamus.

CONCLUSIONS

HASs during experimental pain impact both cortical and subcortical brain activity. The anterior cingulate, left superior frontal, and right insular cortices activation increases could induce a thalamic deactivation (top-down inhibition), which may correlate with reductions in pain intensity.

Regional anesthesia for pediatric knee surgery: a review of the indications, procedures, outcomes, safety, and challenges

The indications for surgery on the knee in children and adolescents share some similarity to adult practice in that there are an increasing number of sports-related injuries requiring surgical repair. In addition, there are some unique age-related conditions or congenital abnormalities that may present as indications for orthopedic intervention at the level of the knee. The efficacy and safety of peripheral nerve blocks (PNBs) for postoperative analgesia following orthopedic surgery has been well established in adults. Recent studies have also demonstrated earlier functional recovery after surgery in patients who received PNBs. In children, PNB is gaining popularity, and increasing data are emerging to demonstrate the feasibility, efficacy, and safety in this population. In this paper, we will review some of the most common indications for surgery involving the knee in children and the anatomy of knee, associated dermatomal and osteotomal innervation, and the PNBs most commonly used to produce analgesia at the level of the knee. We will review the evidence in support of regional anesthesia in children in terms of both the quality conferred to the immediate postoperative care and the role of continuous PNBs in maintaining effective analgesia following discharge. Also we will discuss some of the subtle challenges in utilizing regional anesthesia in the pediatric patient including the use of general anesthesia when performing regional anesthesia and the issue of monitoring for compartment syndrome. Finally, we will offer some thoughts about areas of practice that are in need of further investigation.

Evidence against pain specificity in the dorsal posterior insula

The search for a “pain centre” in the brain has long eluded neuroscientists.  Although many regions of the brain have been shown to respond to painful stimuli, all of these regions also respond to other types of salient stimuli. In a recent paper, Segerdahl et al. (Nature Neuroscience, 2015)  claims that the dorsal posterior insula (dpIns) is a pain-specific region based on the observation that the magnitude of regional cerebral blood flow (rCBF) fluctuations in the dpIns correlated with the magnitude of evoked pain.  However, such a conclusion is, simply, not justified by the experimental evidence provided.  Here we discuss three major factors that seriously question this claim.

Assessing pain objectively: the use of physiological markers

Pain diagnosis and management would benefit from the development of objective markers of nociception and pain. Current research addressing this issue has focused on five main strategies, each with its own advantages and disadvantages. These encompass: (i) monitoring changes in the autonomic nervous system; (ii) biopotentials; (iii) neuroimaging; (iv) biological (bio-) markers; and (v) composite algorithms. Although each strategy has shown areas of promise, there are currently no validated objective markers of nociception or pain that can be recommended for clinical use. This article introduces the most important developments in the field and highlights shortcomings, with the aim of allowing the reader to make informed decisions about what trends to watch in the future.

Pain response measured with arterial spin labeling

The majority of functional MRI studies of pain processing in the brain use the blood oxygenation level-dependent (BOLD) imaging approach. However, the BOLD signal is complex as it depends on simultaneous changes in blood flow, vascular volume and oxygen metabolism. Arterial spin labeling (ASL) perfusion imaging is another imaging approach in which the magnetically labeled arterial water is used as an endogenous tracer that allows for direct measurement of cerebral blood flow. In this study, we assessed the pain response in the brain using a pulsed-continuous arterial spin labeling (pCASL) approach and a thermal stimulation paradigm. Using pCASL, response to noxious stimulation was detected in somatosensory cortex, anterior cingulate cortex, anterior insula, hippocampus, amygdala, thalamus and precuneus, consistent with the pain response activation patterns detected using the BOLD imaging approach. We suggest that pCASL is a reliable alternative for functional MRI pain studies in conditions in which blood flow, volume or oxygen extraction are altered or compromised.