The auditory event related potentials in episodic and chronic pain sufferers

Does the presence of chronic pain affect scores on cognitive screening tests/brief cognitive measures for dementia? A systematic review and meta-analysis

OBJECTIVE

Cognitive screening tests can identify potential dementia by indicating a concerning level of cognitive impairment. The older populations for whom this is most relevant are more likely to experience chronic pain, which also impairs cognitive function, but pain's impact on cognitive screening tests specifically remains unknown.

METHOD

We conducted a systematic review and meta-analysis (SR/MA) following PRISMA guidelines evaluating cognitive screening scores in studies involving participants with chronic pain compared with a pain-free control group. Our question was whether the presence of chronic pain (self-reported or based on diagnosis) was associated with poorer performance on these screens, and to identify the heterogeneity across groups and screens.

RESULTS

The 51 studies identified yielded 62 effect size estimates. The pooled g was 0.76 (95% confidence interval 0.57 to 0.95). Heterogeneity was high for the full model (= 93.16%) with some reductions in sub-analyses. Around half of the studies were identified as being at a low risk of bias. There was no evidence of publication bias.

CONCLUSIONS

As a whole, this analysis suggests medium to large effect sizes on cognitive screen performance when people are living with chronic pain. We suggest that clinicians should consider the effect of chronic pain when cognitive screens are employed to investigate dementia. Further research could clarify the effect pain has on different screen sub-domains to aid their effective use with these populations.

Evidence for Cognitive Decline in Chronic Pain: A Systematic Review and Meta-Analysis

Background: People with chronic pain (CP) sometimes report impaired cognitive function, including a deficit of attention, memory, executive planning, and information processing. However, the association between CP and cognitive decline was still not clear. Our study aimed to assess the association of CP as a risk factor with cognitive decline among adults. Methods: We included data from clinical studies. Publications were identified using a systematic search strategy from PubMed, Embase, and Cochrane Library databases from inception to October 10, 2020. We used the mean cognitive outcome data and the standard deviations from each group. The standardized mean difference (SMD) or odds ratio (OR), and 95% confidence intervals (CI) were performed for each cognitive decline outcome. I ²-values were assessed to quantify the heterogeneities. Results: We included 37 studies with a total of 52,373 patients with CP and 80,434 healthy control participants. Because these studies used different evaluative methods, we analyzed these studies. The results showed CP was associated with cognitive decline when the short-form 36 health survey questionnaire (SF-36) mental component summary (SMD = -1.50, 95% CI = -2.19 to -0.81), the Montreal cognitive assessment (SMD = -1.11, 95% CI = -1.60 to -0.61), performance validity testing (SMD = 3.05, 95% CI = 1.74 to 4.37), or operation span (SMD = -1.83, 95% CI = -2.98 to -0.68) were used. However, we got opposite results when the studies using International Classification of Diseases and Related Health Problems classification (OR = 1.58, 95% CI = 0.97 to 2.56), the Mini-Mental State Examination (SMD = -0.42, 95% CI = -0.94 to 0.10; OR = 1.14, 95% CI = 0.91 to 1.42), and Repeatable Battery for the Assessment of Neuropsychological Status memory component (SMD = -0.06, 95% CI = -0.37 to 0.25). Conclusion: There may be an association between CP and the incidence of cognitive decline when some cognitive, evaluative methods were used, such as short-form 36 health survey questionnaire, Montreal cognitive assessment, performance validity testing, and operation span.

Cognition and chronic pain: an analysis on community-dwelling elderly caregivers and non-caregivers

BACKGROUND

In recent years there has been an increasing number of elderly people who care for another elderly person in the same household. These elderly people are more susceptible to overload and the presence of chronic pain, while pain can negatively influence cognitive variables.

OBJECTIVE

To compare the performance and cognitive processing of elderly caregivers and non-caregivers with and without chronic pain.

METHODS

This was a cross-sectional study carried out among 149 elderly people divided into four groups that were matched according to sex, age and schooling. The tests used were a numerical pain assessment scale, the Brief Cognitive Screening Battery (BCSB), Addenbrooke's Cognitive Examination (ACER-R) and cognitive processing through event-related potentials (P300).

RESULTS

Statistically significant differences between participants with and without chronic pain were found with regard to attention/orientation (p=0.045) and visual-spatial skills (p=0.017), and in the total score (p=0.033). In the pain-free group, the caregivers showed better results than the non-caregivers. There were no effects between subjects or interactions (caregiving and pain factors) either on P300 amplitude or on P300 latency.

CONCLUSION

In general, it was observed that pain-free individuals presented better performance. No relationship was observed between the factors care and pain regarding cognitive performance.

Brain Excitability in Tension-Type Headache: a Separate Entity from Migraine?

PURPOSE OF REVIEW

Tension-type headache is often regarded as the "normal" headache due to its high prevalence and mild disability in contrast with migraine. Clinically, both headaches are common comorbidities to each other. To date there has been many studies linked migraine to a brain excitability disorder. This review summarized earlier studies on brain excitability of TTH and discuss if TTH is a separate clinical entity from migraine as suggested by the diagnostic criteria.

RECENT FINDINGS

A recent magnetoencephalographic study from our group enrolled patients with "strict-criteria" TTH (i.e., absence of any migraine characteristics and associated symptoms) to compare the somatosensory excitability with patients with migraine and controls. This study provided evidence that TTH and migraine differ in excitability profiles and the measurement of preactivation excitability was able to discriminate TTH from migraine. Earlier studies on brain excitability of TTH yielded negative findings or a common change shared with migraine. Future studies using strict diagnostic criteria to avoid the unwanted interference from migraine comorbidity may help decipher the "true" pathophysiology of TTH, which may pave the way to a TTH-specific brain signature and treatment.

Portable EEG monitoring for older adults with dementia and chronic pain - A feasibility study

Given the reduced ability of people with dementia to self-report pain, this study examined the feasibility of using a portable electroencephalography (EEG) headband (MUSE 2) as a pain measurement tool for long-term care residents with dementia. Ten minutes of resting-state EEG was acquired by MUSE 2 from people with dementia experiencing ongoing pain (n = 3) and without current pain (n = 1) over three days. The MUSE 2 was acceptable and feasible for use in people with dementia while challenges regarding software, data collection and analysis in using this device are reported. Compared to the resident not experiencing pain, EEG signals of residents with ongoing pain showed different EEG patterns, and this could be a potential biomarker to support pain measurement in people with dementia. Further research with larger sample size is warranted to verify study results.

Neuronal Correlates of Cognitive Control Are Altered in Women With Endometriosis and Chronic Pelvic Pain

Endometriosis is a debilitating women's health condition and is the most common cause of chronic pelvic pain. Impaired cognitive control is common in chronic pain conditions, however, it has not yet been investigated in endometriosis. The aim of this study was to explore the neuronal correlates of cognitive control in women with endometriosis. Using a cross-sectional study design with data collected at a single time-point, event-related potentials were elicited during a cued continuous performance test from 20 women with endometriosis (mean age = 28.5 ± 5.2 years) and 20 age- and gender-matched controls (mean age = 28.5 ± 5.2 years). Event-related potential components were extracted and P3 component amplitudes were derived with temporal principal components analysis. Behavioral and ERP outcomes were compared between groups and subjective pain severity was correlated with ERP component amplitudes. No significant behavioral differences were seen in task performance between the groups (all p > 0.094). Target P3b (all p < 0.034) and SW (all p < 0.040), and non-target early P3a (eP3a; all p < 0.023) and late P3a (lP3a; all p < 0.035) amplitudes were smaller for the endometriosis compared to the healthy control group. Lower non-target eP3a (p < 0.001), lP3a (p = 0.013), and SW (p = 0.019) amplitudes were correlated with higher pain severity scores. Findings suggest that endometriosis-associated chronic pelvic pain is linked to alterations in stimulus-response processing and inhibitory control networks, but not impaired behavioral performance, due to compensatory neuroplastic changes in overlapping cognitive control and pain networks.

Are Functional Brain Alterations Present in Low Back Pain? A Systematic Review of EEG Studies

This systematic review analyzed available literature on functional brain alterations in low back pain (LBP) measured with electroencephalography (EEG), as until now evidence thereof was unclear. Four electronic databases were systematically searched the 10th of March 2018, resulting in 12 included studies. Studies showed a risk of bias of 37.5 to 75% using the Newcastle-Ottawa Scale for case-control studies. Limited evidence reported higher amplitudes of balance-related potentials and early components of somatosensory evoked potentials (SEP) to noxious stimuli, and altered feedback-related negativity and P300 potentials during decision-making in chronic LBP (CLBP). These findings suggest postural strategies requiring a higher cortical attention-demand, increased sensory-discriminative processing of noxious input, and altered decision-making in CLBP. However, further research is warranted as these inferences were based on single studies. Moderate evidence for unaltered amplitude of late-phase SEPs to noxious stimuli and auditory evoked potentials in LBP implies that the affective-emotional processing of stimuli might be unaffected in LBP. Furthermore, moderate evidence indicated disturbed habituation of somatosensory stimuli in LBP. Most studies examined nonspecific or mixed CLBP populations, hence EEG-quantified brain activity in (sub)acute or recurrent LBP still needs to be explored. PERSPECTIVE: This review presents an overview of the current understanding of the functional LBP brain measured with EEG. The limited evidence in current research suggests altered cortical function regarding balance control, somatosensory processing, and decision making in LBP, and highlights opportunities for future EEG-research.

Passive Paradigm Single-Tone Elicited ERPs in Tension-Type Headaches and Migraine

The active 'oddball' event-related potential (ERP) P3 is elongated or reduced in migraine and tension-type headaches, indicating a deficit of active attention in these primary headaches. It is then reasonable to study the passive attention function in these headaches through the technology of passive paradigm singletone elicited ERPs. We invited 32 patients suffering from chronic tension-type headache (CTTH), 17 from frequent episodic tension-type headache (FETH) and 32 from interictal migraine without aura, as well as 28 healthy subjects to undergo passive paradigm single-tone ERPs. There were no statistically significant differences when the mean latencies and amplitudes of N1, P2, N2 or the mean latencies of P3 of the four groups were considered. In contrast, the P3 amplitudes were significantly reduced in the patient groups when compared with healthy controls. However, no further significant difference was found between patient groups when considering P3 amplitude. Our study demonstrated a deficit of passive attention in CTTH, FETH and migraine, but could not separate these headache types in this regard. The reduced P3 in patients might be due to the head pain experienced.

Pearls and pitfalls: electrophysiology for primary headaches

BACKGROUND

Primary headaches are functional neurological diseases characterized by a dynamic cyclic pattern over time (ictal/pre-/interictal). Electrophysiological recordings can non-invasively assess the activity of an underlying nervous structure or measure its response to various stimuli, and are therefore particularly appropriate for the study of primary headaches. Their interest, however, is chiefly pathophysiological, as interindividual, and to some extent intraindividual, variations preclude their use as diagnostic tools.

AIM OF THE WORK

This article will review the most important findings of electrophysiological studies in primary headache pathophysiology, especially migraine on which numerous studies have been published.

RESULTS

In migraine, the most reproducible hallmark is the interictal lack of neuronal habituation to the repetition of various types of sensory stimulations. The mechanism subtending this phenomenon remains uncertain, but it could be the consequence of a thalamocortical dysrythmia that results in a reduced cortical preactivation level. In tension-type headache as well as in cluster headache, there seems to be an impairment of central pain-controlling mechanisms but the studies are scarce and their outcomes are contradictory. The discrepancies between studies might be as a result of methodological differences as well as patients' dissimilarities, which are also discussed.

CONCLUSIONS AND PERSPECTIVES

Electrophysiology is complementary to functional neuroimaging and will undoubtedly remain an important tool in headache research. One of its upcoming applications is to help select neurostimulation techniques and protocols that correct best the functional abnormalities detectable in certain headache disorders.

Habituation and sensitization in primary headaches

The phenomena of habituation and sensitization are considered most useful for studying the neuronal substrates of information processing in the CNS. Both were studied in primary headaches, that are functional disorders of the brain characterized by an abnormal responsivity to any kind of incoming innocuous or painful stimuli and it's cycling pattern over time (interictal, pre-ictal, ictal). The present review summarizes available data on stimulus responsivity in primary headaches obtained with clinical neurophysiology. In migraine, the majority of electrophysiological studies between attacks have shown that, for a number of different sensory modalities, the brain is characterised by a lack of habituation of evoked responses to repeated stimuli. This abnormal processing of the incoming information reaches its maximum a few days before the beginning of an attack, and normalizes during the attack, at a time when sensitization may also manifest itself. An abnormal rhythmic activity between thalamus and cortex, namely thalamocortical dysrhythmia, may be the pathophysiological mechanism subtending abnormal information processing in migraine. In tension-type headache (TTH), only few signs of deficient habituation were observed only in subgroups of patients. By contrast, using grand-average responses indirect evidence for sensitization has been found in chronic TTH with increased nociceptive specific reflexes and evoked potentials. Generalized increased sensitivity to pain (lower thresholds and increased pain rating) and a dysfunction in supraspinal descending pain control systems may contribute to the development and/or maintenance of central sensitization in chronic TTH. Cluster headache patients are characterized during the bout and on the headache side by a pronounced lack of habituation of the brainstem blink reflex and a general sensitization of pain processing. A better insight into the nature of these ictal/interictal electrophysiological dysfunctions in primary headaches paves the way for novel therapeutic targets and may allow a better understanding of the mode of action of available therapies.

The clinical neurophysiology of tension-type headache

Despite being widely investigated, the pathogenesis of tension-type headache (TTH) continues to be debated. Among the different approaches used to explore the mechanisms underlying TTH, clinical neurophysiology plays an important role. Studies to date have focused mainly on two areas: (1) evaluation of peripheral factors (i.e., by electromyography (EMG)); and (2) exploration of the role of the pain control system. In the second of these areas, a large number of studies have explored trigeminal pathways, in particular using reflexes (e.g., the trigeminofacial reflex, trigeminotrigeminal reflexes). More recently, the descending inhibitory system, known to modulate both the trigeminal and the spinal system, has also been investigated. In addition, several studies have sought to establish whether there are neurophysiological parameters that could be markers of this condition, but the results of these were inconclusive, since some abnormalities could frequently be observed in migraine too. This chapter critically reviews the clinical neurophysiology of TTH. It concludes that the majority of neurophysiological studies on TTH present serious methodological flaws that will have to be overcome to allow further understanding of the mechanisms of TTH.

Imaging CNS Modulation of Pain in Humans

Pain is a highly complex and subjective experience that is not linearly related to the nociceptive input. What is clear from anecdotal reports over the centuries and more recently from animal and human experimentation is that nociceptive information processing and consequent pain perception is subject to significant pro- and anti-nociceptive modulations. These modulations can be initiated reflexively or by contextual manipulations of the pain experience including cognitive and emotional factors. This provides a necessary survival function since it allows the pain experience to be altered according to the situation rather than having pain always dominate. The so-called descending pain modulatory network involving predominantly medial and frontal cortical areas, in combination with specific subcortical and brain stem nuclei appears to be one key system for the endogenous modulation of pain. Furthermore, recent findings from functional and anatomical neuroimaging support the notion that an altered interaction of pro- and anti-nociceptive mechanisms may contribute to the development or maintenance of chronic pain states. Research on the involved circuitry and implemented mechanisms is a major focus of contemporary neuroscientific research in the field of pain and should provide new insights to prevent and treat chronic pain states.

Imaging pain modulation in health and disease

PURPOSE OF REVIEW

In this review, we discuss recent advances in pain imaging research. We focus on the involvement of endogenous pain control mechanisms in the healthy central nervous system and the potential contribution of failure within this system for chronic pain states.

RECENT FINDINGS

Nociceptive information processing and related pain perception is subject to substantial pro and antinociceptive modulation. Recent studies demonstrate that this modulation can take place at any stage of ascending information processing. A network of cortical, predominantly mesial and frontal areas, in combination with specific brainstem nuclei, appear to be the key players in the context of endogenous pain modulation. Recent findings from functional and anatomical neuroimaging support the notion that an altered interaction of pro and antinociceptive mechanisms may contribute to the development or maintenance of chronic pain states. The additional use of pharmacological intervention in pain imaging research provides an alternative tool for investigating mechanisms of pain modulation.

SUMMARY

Top-down pain modulation relies on both cortical and subcortical structures. Research on the involved circuitry, including the implemented mechanisms, is a major focus of contemporary neuroscientific research in the field of pain and will provide new insights into the prevention and treatment of chronic pain states.

Habituation to painful stimulation involves the antinociceptive system

The perception of pain results from an interaction between nociceptive and antinociceptive mechanisms. A better understanding of the neural circuitry underlying these physiological interactions provides an important opportunity to develop better treatment strategies for and ultimately even prevent pain. Here, we investigated how repeated painful stimulation over several days is processed, perceived and finally modulated in the healthy human brain. Twenty healthy subjects were stimulated daily with a 20min pain paradigm for 8 consecutive days, and functional MRI performed on days 1, 8 and 22. Repeated painful stimulation over several days resulted in substantially decreased pain ratings to identical painful stimuli. The decreased perception of pain over time is reflected in decreased BOLD responses to nociceptive stimuli in classical pain areas, including thalamus, insula, SII and the putamen. In contrast to this finding, we found that pain-related responses in the rACC, specifically the subgenual anterior cingulate cortex (sgACC), significantly increased over time. Given this area's predominant role in endogenous pain control, this response pattern suggests that habituation to pain is at least in part mediated by increased antinociceptive activity.

Quadriceps EMG in Open and Closed Kinetic Chain Tasks in Women With Patellofemoral Pain

The authors investigated whether the discrepancy noted in the literature regarding delayed and decreased activity in vastus medialis obliquus (VMO) in people with patellofemoral pain (PFP) depends on the nature of the open kinetic chain (OKC) and the closed kinetic chain (CKC) in the experimental task. They hypothesized that activity in VMO would be more delayed and decreased in CKC tasks than in OKC tasks. Women with PFP (n = 17) and healthy controls (n = 17) performed isometric quadriceps contractions in CKC and OKC tasks. The authors manipulated only the application of resistance. Electromyographs (EMGs) showed that participants with PFP reacted later and activated the quadriceps more in the CKC task but had intramuscular quadriceps coordination similar to that of controls. The nature of the OKC task or the CKC task does not seem to explain contradictory findings regarding VMO activation.

Habituation of sympathetic skin response in migraine and tension type headache

This study aimed to investigate the changes of habituations in the autonomic function of patients suffering from migraine or tension type headache through sympathetic skin responses. Patients with migraine without aura (n=26), with episodic tension type headache without migraine (n=28) and 30 healthy controls were studied. During continuous stimulation, four blocks of 20 responses were sequentially recorded. Mean amplitude changes in the second, third and fourth blocks are expressed as the percentages of the first block. In both headache groups, there was a lack of habituation compared to the control group.

Central nervous system abnormalities in migraine

Migraine is associated with structural and functional CNS changes, for example, ictal hyperalgesia and allodynia and interictal neural excitation. Structural abnormalities, most notably white matter changes, occur in greater prevalence in migraineurs (16 - 40%). Several studies have examined the neuropsychological correlates of migraine and/or white matter abnormalities. These studies suggest mild, interictal dysfunction in migraineurs. More research is needed to correlate migraine severity, frequency and/or treatment with neuropsychological testing. Additional studies should: identify interictal cognitive changes; clarify the contribution to long-term cognitive changes from migraine genotype, sequelae of repeated pain episodes or their treatment and the consequences of co-morbid vascular disease; and include cognitive measures as secondary end points in clinical trials.

P300-amplitudes in upper limb amputees with and without phantom limb pain in a visual oddball paradigm

The aim of the study was to investigate to what extent cortical hyper-reactivity to visual stimuli is present in upper limb amputees. Five amputees with phantom limb pain (PLP), five amputees without PLP (Non-PLP) and 10 healthy controls (HC) were investigated using a visual oddball paradigm. Two hundred visual stimuli were presented with target stimuli occurring at a probability of 25% and standard stimuli at a probability of 75%. Event-related potentials were recorded from nine scalp positions (F3, F4, Fz, C3, C4, Cz, P3, P4, Pz). The PLP-patients had significantly higher P300-amplitudes to both types of stimuli compared to the non-PLP-patients. The HC were not significantly different from both amputee groups. P300-amplitude to targets at frontal sites in the hemisphere contralateral to the amputation was higher in the PLP patients. P300-latencies to target stimuli differed only at frontal sites with PLP-patients showing significantly longer latencies than non-PLP-patients. To standard stimuli, however, they showed significantly shorter latencies at central and parietal scalp positions. The HC had significantly shorter latencies than both amputee groups. The size of the P300-amplitude was positively correlated with the intensity of PLP. These findings suggest a higher magnitude of non-specific cortical excitability in amputees with PLP and a reduced excitability in amputees without PLP. This extends previous findings of differences in cortical excitability in PLP and non-PLP patients in the sensorimotor domain.

Auditory event-related brain potentials in fibromyalgia syndrome

OBJECTIVE

The aim of this study was to investigate cognitive functions using auditory event-related brain potentials (ERP) in fibromyalgia syndrome (FMS).

METHODS

The P300 component of ERP was studied in 36 female FMS patients and 22 control subjects. The short form 36 (SF-36) medical outcome study was used to determine quality of life. Number of tender points and disease duration were noted. Cognitive functions were evaluated with P300.

RESULTS

The symptoms were discrepant in FMS (P<0.001). The scores of the eight SF-36 subgroups in FMS patients were significantly lower than in the control group (P<0.001). Fibromyalgia syndrome patients had prolonged latency and reduced amplitude of P300 (P<0.001). No correlation was found between the subgroups of SF-36, tender point count, disease duration, and P300.

CONCLUSION

The results of our study reveal that FMS affects quality of life and dysfunction in cognitive abilities can be determined by brain event-related potentials.