Age-Related Changes in Nociceptive Processing in the Human Brain

Gender Differences in Pain Threshold, Unpleasantness, and Descending Pain Modulatory Activation Across the Adult Life Span: A Cross Sectional Study

The neurobiological underpinnings of gender differences in pain perception, and how these differences may be modified by age, are incompletely understood, placing patients at risk of suboptimal pain management. Using functional magnetic resonance imaging, we examined brain responses in the descending pain modulatory system (DPMS, specifically, dorsolateral prefrontal cortex, anterior cingulate cortex, insula, hypothalamus, amygdala, and periaqueductal gray, during an evoked pain task. We investigated the interaction of age and gender in our sample of healthy adults (27 females, 32 males, 30-86 years) on DPMS response. In a perceptually matched thermal pain paradigm, we investigated pain unpleasantness and neural responses for 3 heat pain percepts: just noticeable pain, weak pain, and moderate pain (MP). Females reported just noticeable pain at a lower temperature, but reported less unpleasantness at weak pain and MP percepts, compared to males. There was a significant age-by-gender interaction during moderate pain in the right anterior cingulate cortex and bilateral insula, such that, males had a stronger positive relationship between DPMS response and age compared to females in these regions. Our results indicate that differences in DPMS responses may explain some gender differences in pain perception and that this effect may change across the adult lifespan. PERSPECTIVE: Gender differences in pain have been well-documented but the brain mechanisms for these differences are still unclear. This article describes potential differences in brain functioning during different levels of pain that could explain differences in pain responses between men and women across the adult lifespan.

Predictive factors of postoperative acute pain in laparoscopic inguinal hernia repair in men: A single-centre retrospective study in Japan

INTRODUCTION

Laparoscopic inguinal hernia repair has significantly reduced the incidence of postoperative acute and chronic pain compared to open repair, but it remains problematic. This study's purpose was to retrospectively identify predictive factors of acute pain after laparoscopic inguinal hernia repair.

METHODS

We reviewed the medical records of 193 patients. After excluding atypical cases and female patients, 156 patients were analysed. Factors affecting rescue analgesic requirements were investigated via multivariable logistic regression analysis. Independent variables included age, body mass index, analgesics used during surgery and surgical factors (unilateral/bilateral, primary/recurrent). The degree of postoperative pain and the hospital stay duration after surgery were also investigated.

RESULTS

Of the 156 patients, 40 (25.6%) required rescue analgesics. Patients under 60 years of age were about seven times more likely to need rescue analgesics than patients over 80 years of age. Primary surgery patients were about 5.5 times more likely to need rescue analgesics than recurrent surgery patients. The maximum verbal rating scale score was less than 3 in 89% of patients. All patients were discharged by two days postoperatively.

CONCLUSION

Laparoscopic inguinal hernia repair results in less postoperative acute pain. However, analgesia management should be considered prudently for younger patients and primary surgery patients.

Effects of spatial attention and limb position on the cortical interaction of bilateral noxious inputs

Bilateral noxious inputs interact in the brain to provide a better representation of physical threat. In the present study, we investigated the effects of spatial attention and limb position on this interaction. Painful laser stimuli were applied randomly on the right hand or on both hands, while varying spatial attention (focal or overall) and limb position (hands near or far from each other). Pain perception and laser-evoked potentials (N1, N2, P2) were compared between conditions in 27 healthy volunteers. Compared with unilateral stimulation, bilateral stimulation increased pain (p = .004), the N2 (p = .0015) and P2 (p < .001) amplitude. The effects on pain and the P2 were greater when hands were in the near compared with the far position (p < .05). The effect on pain was also greater for overall compared with focal pain rating (p = .003). In addition, the N1 amplitude was greater for bilateral stimulation when hands were in the far compared with the near position (p = .01). These results show that increased brain responses and pain for bilateral compared with unilateral noxious stimulation are modulated differentially by spatial attention and limb position. This suggests that the integration of noxious inputs occurs through partially independent pain-related processes, that it is modulated by limb position, and that it is partially independent of pain perception. We propose that this is necessary to produce coordinated, flexible and adapted defensive responses.

Regional homogeneity alterations in multi-frequency bands in tension-type headache: a resting-state fMRI study

OBJECTIVES

In this study, we aimed to investigate the spontaneous neural activity in the conventional frequency band (0.01-0.08 Hz) and two sub-frequency bands (slow-4: 0.027-0.073 Hz, and slow-5: 0.01-0.027 Hz) in tension-type headache (TTH) patients with regional homogeneity (ReHo) analyses.

METHODS

Thirty-eight TTH patients and thirty-eight healthy controls (HCs) underwent resting-state functional magnetic resonance imaging (RS-fMRI) scanning to investigate abnormal spontaneous neural activity using ReHo analysis in conventional frequency band (0.01-0.08 Hz) and two sub-frequency bands (slow-4: 0.027-0.073 Hz and slow-5: 0.01-0.027 Hz).

RESULTS

In comparison with the HC group, patients with TTH exhibited ReHo increases in the right medial superior frontal gyrus in the conventional frequency band (0.01-0.08 Hz). The between group differences in the slow-5 band (0.01-0.027 Hz) highly resembled the differences in the conventional frequency band (0.01-0.08 Hz); even the voxels with increased ReHo were spatially more extensive, including the right medial superior frontal gyrus and the middle frontal gyrus. In contrast, no region showed significant between-group differences in the slow-4 band (0.027-0.073 Hz). The correlation analyses showed no correlation between the ReHo values in TTH patients and VAS scores, course of disease and number of seizures per month in conventional band (0.01-0.08 Hz), slow-4 band (0.027-0.073 Hz), as well as in slow-5 band (0.01-0.027 Hz).

CONCLUSIONS

The results showed that the superior frontal gyrus and middle frontal gyrus were involved in the integration and processing of pain signals. In addition, the abnormal spontaneous neural activity in TTH patients was frequency-specific. Namely, slow-5 band (0.01-0.027 Hz) might contain additional useful information in comparison to slow-4 band (0.027-0.073 Hz). This preliminary exploration might provide an objective imaging basis for the understanding of the pathophysiological mechanism of TTH.

Determining the impact of age and sex on the psychophysical and neurophysiological response to thermal pain across the adult lifespan

AIMS

Determine sex- and age-associated psychophysical and neurophysiological differences in the processing of pain across the adult lifespan.

DESIGN

Preliminary, exploratory, cross-sectional study.

METHODS

Using psychophysics (to measure intensity and unpleasantness) and functional magnetic resonance imaging blood oxygenation level dependent methods (to measure stimulus-evoked brain activation), we will examine sex- and age-associated differences in thermal pain processing and their underlying neurophysiology in a broad range of healthy adults (ages 30-89). We will acquire resting state functional connectivity data for secondary analyses exploring whether resting state connectivity predicts psychophysical and neurophysiological responses to thermal pain. To examine the effects of altered blood flow, we will acquire resting-state arterial spin labeling magnetic resonance imaging data to quantify resting cerebral blood flow. We will interpret findings in the context of a proposed neural model of pain, ageing, and sex. Study funding was received in June of 2014. Ethical approval was obtained from the Vanderbilt University IRB prior to study initiation.

CONCLUSION

Exploring the biological reasons for age- and sex-associated differences in pain processing will increase our understanding of pain in older adults. The paucity of neurobiological evidence to support best practice pain management in older adults places these individuals at risk for poor pain management.

IMPACT

Poorly treated pain in older adults is a critical public health problem associated with a poor quality of life and increased healthcare costs. Understanding how age and sex have an impact on central processing of pain across the lifespan is a critical step toward improving personalized pain medicine.

Marijuana users are likely to report opioid misuse among adults over 50 years in representative sample of the United States (2002-2014)

Background: In the wake of the rising rate of prescription opioid misuse, there has been increased public health interest in the possibility that cannabis might help to curb or prevent opioid use disorder. Previous studies were limited to young adult marijuana use population. Little is known about whether in older adult population, marijuana use is associated with a different type of nonmedical use opioids. We examined the association between marijuana use and nonmedical prescription opioids dependence and use among older adults.Methods: The National Survey on Drug Use and Health is a nationally U.S. representative cross-sectional survey. We analyzed data for 75,949 adults aged ≥ 50 who participated in the year 2002-2014.Results: Within the overall population, 3.8% of the older adults reported past-year marijuana use (estimate 3.5 million older adults Americans). Past-year marijuana use was very common (25%-37%) among nonmedical opioid dependence respondents compared to those who did not report nonmedical opioid dependence and use (3.5%-3.7%). Past-year marijuana user was significantly associated with an increase in odds of reporting opioid dependence (AOR 9.6 95% CI = 5.8-15.7), and past-year nonmedical use opioids (AOR 6.4 95% CI = 5.2-7.8). Illicit drug heroin was the most prevalent nonmedical used opioid (AOR 6.3 95% CI = 5.0-7.9), compared to codeine (AOR 4.5 95% CI = 3.5-5.7), hydrocodone (AOR 4.9 95% CI = 3.8-6.4), methadone or tramadol (AOR 4.9 95% CI = 2.0-12.3).Conclusion: Policymakers and healthcare providers should remain mindful that older adult marijuana users regardless of initial legitimate medical needs are likely to report nonmedical opioid use including illicit drug heroin.

Thermal Psychophysics and Associated Brain Activation Patterns Along a Continuum of Healthy Aging

OBJECTIVE

To examine psychophysical and brain activation patterns to innocuous and painful thermal stimulation along a continuum of healthy older adults.

DESIGN

Single center, cross-sectional, within-subjects design.

METHODS

Thermal perceptual psychophysics (warmth, mild, and moderate pain) were tested in 37 healthy older adults (65-97 years, median = 73 years). Percept thresholds (oC) and unpleasantness ratings (0-20 scale) were obtained and then applied during functional magnetic resonance imaging scanning. General linear modeling assessed effects of age on psychophysical results. Multiple linear regressions were used to test the main and interaction effects of brain activation against age and psychophysical reports. Specifically, differential age effects were examined by comparing percent-signal change slopes between those above/below age 73 (a median split).

RESULTS

Advancing age was associated with greater thresholds for thermal perception (z = 2.09, P = 0.037), which was driven by age and warmth detection correlation (r = 0.33, P = 0.048). Greater warmth detection thresholds were associated with reduced hippocampal activation in "older" vs "younger" individuals (>/<73 years; beta < 0.40, P < 0.01). Advancing age, in general, was correlated with greater activation of the middle cingulate gyrus (beta > 0.44, P < 0.01) during mild pain. Differential age effects were found for prefrontal activation during moderate pain. In "older" individuals, higher moderate pain thresholds and greater degrees of moderate pain unpleasantness correlated with lesser prefrontal activation (anterolateral prefrontal cortex and middle-frontal operculum; beta < -0.39, P < 0.009); the opposite pattern was found in "younger" individuals.

CONCLUSIONS

Advancing age may lead to altered thermal sensation and (in some circumstances) altered pain perception secondary to age-related changes in attention/novelty detection and cognitive functions.

Pain Processing in Older Adults and Its Association with Prefrontal Characteristics

Aging is known to affect nociceptive processing, e.g., the ability to inhibit pain. This study aims to investigate whether pain responses in older individuals are associated with prefrontal characteristics, namely (i) executive functioning performance and (ii) structural brain variations in the prefrontal cortex. Heat and pressure stimuli were applied to assess pressure pain sensitivity and endogenous pain inhibition in 46 healthy older individuals. Executive functioning performance was assessed in three domains (i.e., cognitive inhibition, shifting, and updating) and structural brain variations were assessed in both gray and white matter. Overall pain responses were significantly associated with the executive functioning domains cognitive inhibition and shifting. However, no specific type of pain response showed an especially strong association. Endogenous pain inhibition specifically showed a significant association with gray matter volume in the prefrontal cortex and with variations in white matter structure of tracts connecting the prefrontal cortex with the periaqueductal gray. Hierarchical regression analyses showed that these variations in the prefrontal cortex can explain variance in pain inhibition beyond what can be explained by executive functioning. This might indicate that known deficits in pain inhibition in older individuals are associated with structural variations in prefrontal areas.

Coupling Robot-Aided Assessment and Surface Electromyography (sEMG) to Evaluate the Effect of Muscle Fatigue on Wrist Position Sense in the Flexion-Extension Plane

Proprioception is a crucial sensory modality involved in the control and regulation of coordinated movements and in motor learning. However, the extent to which proprioceptive acuity is influenced by local muscle fatigue is obscured by methodological differences in proprioceptive and fatiguing protocols. In this study, we used high resolution kinematic measurements provided by a robotic device, as well as both frequency and time domain analysis of signals captured via surface electromyography (sEMG) to examine the effects of local muscle fatigue on wrist proprioceptive acuity in 16 physically and neurologically healthy young adults. To this end, participants performed a flexion/extension ipsilateral joint position matching test (JPM), after which a high-resistive robotic task was used to induce muscle fatigue of the flexor carpi radialis (FCR) muscle. The JPM test was then repeated in order to analyze potential changes in proprioceptive acuity. Results indicated that the fatigue protocol had a significant effect on movements performed in flexion direction, with participants exhibiting a tendency to undershoot the target before the fatigue protocol (−1.218°), but overshooting after the fatigue protocol (0.587°). In contrast, in the extension direction error bias values were similar before and after the fatigue protocol as expected (pre = −1.852°, post = −1.237°) and reflected a tendency to undershoot the target. Moreover, statistical analysis indicated that movement variability was not influenced by the fatigue protocol or movement direction. In sum, results of the present study demonstrate that an individual’s estimation of wrist joint displacement (i.e., error bias), but not precision (i.e., variability), is affected by muscular fatigue in a sample of neurologically and physically healthy adults.

The effect of proprioceptive acuity variability on motor adaptation in older adults

Motor adaptation requires efficient integration of sensory information with predicted sensory consequences of one's own action. However, the effect of reduced sensory acuity on motor adaptation in humans remains to be further investigated. Here, we examined the variability of proprioceptive acuity during an arm-position matching task and the pattern of visuomotor adaptation in older and young adults, and determined the relationship between the two variables. The older adults, a known example of impaired proprioceptive acuity, exhibited greater trial-to-trial variability during the arm-position matching task as compared with the young adults. Furthermore, the older adults showed a slower rate of adaptation to a 30° visuomotor rotation during targeted reaching movements, as well as larger movement errors in the later phase of adaptation, than the young adults. Our correlation analyses indicated a negative association between the variability in proprioceptive acuity and the rate of visuomotor adaptation in the older adults; and no association was observed in the young adults. These findings point to a possibility that an increase in the variability of proprioceptive acuity due to aging may weaken the integration of predicted and actual sensory feedback, which in turn may result in poor visuomotor adaptation in older adults.

Applying a Lifespan Developmental Perspective to Chronic Pain: Pediatrics to Geriatrics

An ideal taxonomy of chronic pain would be applicable to people of all ages. Developmental sciences focus on lifespan developmental approaches, and view the trajectory of processes in the life course from birth to death. In this article we provide a review of lifespan developmental models, describe normal developmental processes that affect pain processing, and identify deviations from those processes that lead to stable individual differences of clinical interest, specifically the development of chronic pain syndromes. The goals of this review were 1) to unify what are currently separate purviews of "pediatric pain," "adult pain," and "geriatric pain," and 2) to generate models so that specific elements of the chronic pain taxonomy might include important developmental considerations.

PERSPECTIVE

A lifespan developmental model is applied to the forthcoming Analgesic, Anesthetic, and Addiction Clinical Trial Translations, Innovations, Opportunities, and Networks-American Pain Society Pain Taxonomy to ascertain the degree to which general "adult" descriptions apply to pediatric and geriatric populations, or if age- or development-related considerations need to be invoked.

Age changes in pain perception: A systematic-review and meta-analysis of age effects on pain and tolerance thresholds

Demographic changes, with substantial increase in life expectancy, ask for solid knowledge about how pain perception might be altered by aging. Although psychophysical studies on age-related changes in pain perception have been conducted over more than 70 years, meta-analyses are still missing. The present meta-analysis aimed to quantify evidence on age-related changes in pain perception, indexed by pain thresholds and pain tolerance thresholds in young and older healthy adults. After searching PubMed, Google Scholar and PsycINFO using state-of-art screening (PRISMA-criteria), 31 studies on pain threshold and 9 studies assessing pain tolerance threshold were identified. Pain threshold increases with age, which is indicated by a large effect size. This age-related change increases the wider the age-gap between groups; and is especially prominent when heat is used and when stimuli are applied to the head. In contrast, pain tolerance thresholds did not show substantial age-related changes. Thus, after many years of investigating age-related changes in pain perception, we only have firm evidence that aging reduces pain sensitivity for lower pain intensities.

Anticipation of thermal pain in diverticular disease

BACKGROUND

The relative importance of peripheral nerve injury or central pain processing in painful diverticular disease (DD) is unclear. Functional magnetic resonance imaging (fMRI) has demonstrated that dysfunctional central pain processing predominates in irritable bowel syndrome (IBS). This study aims to identify anticipatory changes in symptomatic DD (SDD) compared to asymptomatic DD (ADD) and IBS patients.

METHODS

Gastrointestinal symptoms and somatization were evaluated via the Patient Health Question-12 Somatic Symptom and the SDD group divided into low (≤6 [LSDD]) and high (≥7 [HSDD]) somatization. Cued painful cutaneous thermal stimuli were delivered to the left hand and foot during fMRI. Fixed effect group analysis of the 'cued' anticipatory phase was performed.

KEY RESULTS

Within the right posterior insula, greater deactivation was found in the ADD compared to other groups. In emotion processing centers, anterior and middle insula, greater activation was identified in all patient compared to the ADD group, and in LSDD compared to IBS and HSDD groups. In comparison, amygdala deactivation was greater in ADD than the IBS and HSDD groups, and in LSDD vs HSDD groups. Descending nociceptive control centers, such as the superior medial frontal and orbitofrontal cortex, also showed greater deactivation in the ADD and LSDD compared to the HSDD and IBS groups.

CONCLUSIONS & INFERENCES

The HSDD group have altered anticipatory responses to thermal pain, similar to IBS group. The LSDD are similar to ADD group. This suggests underlying differences in pain pathophysiology, and the need for individualized treatment strategies to target the cause of their chronic pain.

Altered pain sensitivity in elderly women with chronic neck pain

Background

Age-related changes occur in both the peripheral and central nervous system, yet little is known about the influence of chronic pain on pain sensitivity in older persons. The aim of this study was to investigate pain sensitivity in elders with chronic neck pain compared to healthy elders.

Methods

Thirty elderly women with chronic neck pain and 30 controls were recruited. Measures of pain sensitivity included pressure pain thresholds, heat/cold pain thresholds and suprathreshold heat pain responses. The pain measures were assessed over the cervical spine and at a remote site, the tibialis anterior muscle.

Results

Elders with chronic neck pain had lower pressure pain threshold over the articular pillar of C5-C6 and decreased cold pain thresholds over the cervical spine and tibialis anterior muscle when compared with controls (p < 0.05). There were no between group differences in heat pain thresholds and suprathreshold heat pain responses (p > 0.05).

Conclusion

The presence of pain hypersensitivity in elderly women with chronic neck pain appears to be dependent on types of painful stimuli. This may reflect changes in the peripheral and central nervous system with age.

Systematic changes in position sense accompany normal aging across adulthood

Background

Development of clinical neurological assessments aimed at separating normal from abnormal capabilities requires a comprehensive understanding of how basic neurological functions change (or do not change) with increasing age across adulthood. In the case of proprioception, the research literature has failed to conclusively determine whether or not position sense in the upper limb deteriorates in elderly individuals. The present study was conducted a) to quantify whether upper limb position sense deteriorates with increasing age, and b) to generate a set of normative data that can be used for future comparisons with clinical populations.

Methods

We examined position sense in 209 healthy males and females between the ages of 18 and 90 using a robotic arm position-matching task that is both objective and reliable. In this task, the robot moved an arm to one of nine positions and subjects attempted to mirror-match that position with the opposite limb. Measures of position sense were recorded by the robotic apparatus in hand-and joint-based coordinates, and linear regressions were used to quantify age-related changes and percentile boundaries of normal behaviour. For clinical comparisons, we also examined influences of sex (male versus female) and test-hand (dominant versus non-dominant) on all measures of position sense.

Results

Analyses of hand-based parameters identified several measures of position sense (Variability, Shift, Spatial Contraction, Absolute Error) with significant effects of age, sex, and test-hand. Joint-based parameters at the shoulder (Absolute Error) and elbow (Variability, Shift, Absolute Error) also exhibited significant effects of age and test-hand.

Conclusions

The present study provides strong evidence that several measures of upper extremity position sense exhibit declines with age. Furthermore, this data provides a basis for quantifying when changes in position sense are related to normal aging or alternatively, pathology.

Effect of aging on the cerebral processing of thermal pain in the human brain

The perception of pain changes as people age. However, how aging affects the quality of pain and whether specific pain-processing brain regions mediate this effect is unclear. We hypothesized that specific structures in the cerebral nociceptive system mediate the effect of aging on the variation in different pain psychophysical measures. We examined the relationships between painful heat stimulation to the foot and both functional magnetic resonance imaging signals and gray matter volume in 23 healthy subjects (aged 25∼71 years). Increased age was related to decreased subjective ratings of overall pain intensity and the "sharp" quality of pain. Group activation maps of multiple linear regression analyses revealed that age predicted responses in the middle insular cortex (IC) and primary somatosensory cortex (S1) to pain stimuli after controlling for their gray matter volumes. Blood oxygenation level-dependent signals in the contralateral middle IC and S1 were related to ratings of "sharpness," but not any affective descriptors of pain. Importantly, activity in the contralateral middle IC specifically mediated the effect of age on overall pain perception, whereas activity in the contralateral S1 mediated the relationship between age and sharp sensation to pain. The analyses of gray matter volume revealed that key nociceptive cerebral regions did not undergo significant age-related gray matter loss. However, the volume of the cingulate cortex covaried with pain perception after adjusting for corresponding neural activity to pain. These results suggest that age-related functional alterations in pain-processing regions are responsible for changes in pain perception during normal aging.

Age-related differences in pain sensitivity and regional brain activity evoked by noxious pressure

Compared with young adults, older people report more chronic pain complaints, and show reduced tolerance to experimental pain. Atrophy of brain parenchyma in normal ageing is well documented, with grey matter reduction occurring across many regions known to be involved in pain processing. However, the functional consequences of these changes, in particular their contribution toward age-related differences in pain perception and report, are yet to be elucidated. The present study investigated the effects of ageing on supraspinal pain processing by comparing regional brain responses to noxious pressure stimulation in 15 young (aged 26+/-3 years) and 15 older (aged 79+/-4 years) adults. Both groups showed significant pain-related activity in a common network of areas including the insula, cingulate, posterior parietal and somatosensory cortices. However, compared with older adults, young subjects showed significantly greater activity in the contralateral putamen and caudate, which could not be accounted for by increased age-associated shrinkage in these regions. The age-related difference in pain-evoked activity seen in the present study may reflect reduced functioning of striatal pain modulatory mechanisms with advancing age.