Implicit associations between pain and self-schema in patients with chronic pain

People with painful knee osteoarthritis hold negative implicit attitudes towards activity

ABSTRACT

Negative attitudes/beliefs surrounding osteoarthritis, pain, and activity contribute to reduced physical activity in people with knee osteoarthritis (KOA). These attitudes/beliefs are assessed using self-report questionnaires, relying on information one is consciously aware of and willing to disclose. Automatic (ie, implicit) assessment of attitudes does not rely on conscious reflection and may identify features unique from self-report. We developed an implicit association test that explored associations between images of a person moving/twisting their knee (activity) or sitting/standing (rest), and perceived threat (safe vs dangerous). We hypothesised that people with KOA would have greater implicit threat-activity associations (vs pain-free and non-knee pain controls), with implicit attitudes only weakly correlating with self-reported measures (pain knowledge, osteoarthritis/pain/activity beliefs, fear of movement). Participants (n = 558) completed an online survey: 223 had painful KOA (n = 157 female, 64.5 ± 8.9 years); 207 were pain free (n = 157 female, 49.3 ± 15.3 years); and 99 had non-KOA lower limb pain (n = 74 female, 47.5 ± 15.04 years). An implicit association between "danger" and "activity" was present in those with and without limb pain (KOA: 0.36, 95% CI 0.28-0.44; pain free: 0.13, 95% CI 0.04-0.22; non-KOA lower limb pain 0.11, 95% CI -0.03 to 0.24) but was significantly greater in the KOA group than in the pain free ( P < 0.001) and non-KOA lower limb pain ( P = 0.004) groups. Correlations between implicit and self-reported measures were nonsignificant or weak (rho = -0.29 to 0.19, P < 0.001 to P = 0.767). People with painful KOA hold heightened implicit threat-activity associations, capturing information unique to that from self-report questionnaires. Evaluating links between implicit threat-activity associations and real-world behaviour, including physical activity levels, is warranted.

Assessing how individuals conceptualize numeric pain ratings: validity and reliability of the Pain Schema Inventory (PSI-6) Short Form

Background

While numeric scales to represent pain intensity have been well validated, individuals use various conceptualizations when assigning a number to pain intensity, referred to as pain rating schema. The 18-item Pain Schema Inventory (PSI-18) quantifies pain rating schema by asking for numeric values for multiple mild, moderate or severe pain conditions. This study aimed to assess the validity and reliability of a shortened form of the PSI, using only 6 items (PSI-6).

Methods

A secondary analysis was performed on two existing datasets. The first (n = 641) involved a community-based population that completed the PSI-18. The second (n = 182) included participants with chronic pain who completed the PSI-6 twice, one week apart. We assessed face validity, convergent validity, offset biases, test-retest reliability, and internal consistency of the PSI-6 compared to the PSI-18.

Results

Both the PSI-18 and PSI-6 demonstrated excellent face validity. The PSI-6 demonstrated excellent convergent validity relative to the PSI-18, with correlations from r = 0.88 to 0.92. Bland-Altman plots revealed offset biases near zero (< 0.22 on 0-10 scale) across all categories of mild, moderate, severe and average pain. Internal consistency was excellent, with Cronbach's Alpha = 0.91 and 0.80, for PSI-18 and PSI-6 respectively. Test-retest reliability of the PSI-6 was high with correlations from r = 0.70-0.76.

Conclusion

The PSI-6 is a valid and reliable tool to assess pain rating schema with reduced subject burden, to better interpret individuals' pain ratings and adjust for inter-individual variability.

Soreness Reminds Me of Grief: Patients With Chronic Pain Show Less Differentiated Representations of Emotional Feelings and Bodily States

People experience similarities between emotional feelings and bodily states on a daily basis, but both the magnitude and pervasiveness of this experiential similarity vary across individuals. Inspired by previous findings that chronic pain (CP) is characterized by strengthened pain-affect coupling and reduced interoceptive accuracy, we conducted 2 cross-sectional studies to examine whether patients with CP would exhibit less differentiated perception and mental representation of emotional feelings and bodily states. In study 1 (N = 500), patients with CP and healthy controls (HCs) completed a self-report questionnaire that asked explicitly about the perceived similarity between 5 basic emotion categories and a series of bodily states. In study 2 (N = 73), a specially designed false memory test was administered to examine whether patients with CP would have reduced differentiation of concepts of negative emotion and somatic distress. We found that patients with CP perceived greater and more pervasive similarities between emotional feelings and bodily states, as indicated by higher questionnaire scores and denser, less specialized bipartite emotion-body networks, both associated with lower subjective interoceptive accuracy. Furthermore, patients with CP formed false memories of negative emotion words (eg, grief) more readily than HCs after memorizing somatic distress words (eg, soreness), as if they represented negative emotion and somatic distress as a single, enmeshed semantic category. Our findings extend previous literature by demonstrating reduced discrimination between emotional and bodily experiences in CP that is not restricted to pain-related emotional and sensory experiences and may be related to a fundamentally less differentiated interoception. PERSPECTIVES: This study shows that patients with chronic pain have a profoundly less differentiated perception and implicit conceptualization of emotional feelings and bodily states, which appears to be associated with altered interoception. These findings may provide new perspectives on why they often experience a stronger pain-affect coupling.

The Management of Chronic Pain: Re-Centring Person-Centred Care

The drive for a more person-centred approach in the broader field of clinical medicine is also gaining traction in chronic pain treatment. Despite current advances, a further departure from 'business as usual' is required to ensure that the care offered or received is not only effective but also considers personal values, goals, abilities, and day-to-day realities. Existing work typically focuses on explaining pain symptoms and the development of standardised interventions, at the risk of overlooking the broader consequences of pain in individuals' lives and individual differences in pain responses. This review underscores the importance of considering additional factors, such as the influence of chronic pain on an individual's sense of self. It explores innovative approaches to chronic pain management that have the potential to optimise effectiveness and offer person-centred care. Furthermore, it delves into research applying hybrid and individual formulations, along with self-monitoring technologies, to enhance pain assessment and the tailoring of management strategies. In conclusion, this review advocates for chronic pain management approaches that align with an individual's priorities and realities while fostering their active involvement in self-monitoring and self-management.

Individual Variation in Pain Sensitivity and Implicit Negative Bias Toward Pain

OBJECTIVE

Although previous studies have shown the linkage between pain sensitivity and pain-related cognitions, this study investigated whether individual variation in pain sensitivity is related to implicit negative bias toward pain.

METHODS

Two groups of participants with low (LPS) or high (HPS) pain sensitivity (LPS group: n = 33; HPS group: n = 31) were recruited based on their scores on pain sensitivity questionnaires. This categorization was later confirmed via pain ratings to electrical stimulations. Implicit negative bias toward pain was assessed using the Implicit Association Test (IAT) involving target (pain and nonpain) and attribute (negative and neutral-affect) concept words. Behavioral and event-related potential responses for congruent and incongruent pairings during the IAT were compared between the LPS and HPS groups.

RESULTS

Relative to the LPS group, participants in the HPS group exhibited greater D-score (Cohen's d = 0.364, p = .004). Event-related potential results showed that, although P3 amplitudes to congruent and incongruent pairings differed significantly for the HPS group (Cohen's d = 0.757, p < .001), this difference was not observed for the LPS group (Cohen's d = 0.089, p = .29). Mediation analysis further revealed that the IAT effect on P3 responses accounted for 17.58% of the association between pain sensitivity and D-score (confidence interval = [0.009-0.051]).

CONCLUSIONS

Individual variation in pain sensitivity relates to implicit negative bias. This linkage is partially accounted for by the electrophysiological response that has been related to cognitive process of stimulus evaluation and categorization. Pain treatment might benefit from techniques designed to alter implicit bias.

Understanding suicidal ideation and behaviour in individuals with chronic pain: a review of the role of novel transdiagnostic psychological factors

Individuals with chronic pain are at an elevated risk of suicide, yet psychosocial factors that might be involved in increasing or decreasing vulnerability for suicidal ideation and behaviour have received little attention. Extant literature on the topic of suicide in individuals with chronic pain incorporates only a few of the wide array of known vulnerability and protective factors. This Review focuses on transdiagnostic psychological processes, (ie, those of relevance for both chronic pain and suicide). We reviewed a selection of published literature on chronic pain and suicide, concentrating on previously unexplored and underexplored lines of research, including future orientation, mental imagery, and psychological flexibility. A greater degree of crosspollination between the fields of chronic pain and suicide research is required to progress our understanding of why some people with chronic pain become suicidal and others do not.

Evaluation of implicit associations between back posture and safety of bending and lifting in people without pain

Background and aims Despite lack of support from recent in vivo studies, bending and lifting (especially with a round-back posture) are perceived as dangerous to the back. In light of this view, it has been proposed that pain-free people may hold a common implicit belief that is congruent with the idea that bending and lifting with a round-back represents danger to a person's back, however this has not been evaluated. The aims of this study were: (1) to evaluate implicit associations between back posture and safety related to bending and lifting in pain-free people; (2) to explore correlations between the implicit measure and explicit measures of back beliefs, fear of movement and safety of bending; (3) to investigate self-reported qualitative appraisal of safe lifting. Methods Exploratory cross-sectional study including 67 pain-free participants (no pain, or average pain ≤3/10 for less than one week over the previous 12 months) (52% male), who completed an online survey containing demographic data and self-reported measures of: fear of movement (Tampa Scale for Kinesiophobia for General population - TSK-G), back beliefs (Back Pain Attitudes Questionnaire BackPAQ), and bending beliefs (Bending Safety Belief - BSB - a pictorial scale with images of a person bending/lifting with round and straight back postures). Implicit associations between back posture and safety related to bending and lifting were evaluated with the Implicit Association Test (IAT). A qualitative assessment of descriptions of safe lifting was performed. Results An implicit association between "danger" and "round-back" bending/lifting was evident in all participants (IATD-score=0.65 (SD=0.45; 95% CI [0.54, 0.76]). Participants' profile indicated high fear of movement, unhelpful back beliefs, and perceived danger to round-back bending and lifting (BSBThermometer: 5.2 (SD=3.8; 95% CI [4.26, 6.13] range -10 to 10; t(67)=11.09, p<0.001). There was a moderate correlation between IAT and BSBThermometer (r=0.38, 95% CI [0.16, 0.62]). There were weaker and non-statistically significant correlations between IAT and TSK-G (r=0.28, 95% CI [-0.02, 0.47]), and between IAT and BackPAQDanger (r=0.21, 95% CI [-0.03, 0.45]). Qualitative assessment of safe lifting descriptions indicated that keeping a "straight back" and "squatting" when lifting were the most common themes. Conclusions Pain-free people displayed an implicit bias towards bending and lifting with a "round-back" as dangerous. Our findings support the idea that pain-free people may have a pre-existing belief about lifting, that the back is in danger when rounded. Research to evaluate the relationship between this implicit bias and lifting behaviour is indicated. Implications The findings of this study may have implications for ergonomic guidelines and public health information related to bending and lifting back postures. Additionally, clinicians may need to be aware of this common belief, as this may be reflected in how a person responds when they experience pain.

Effect of Cognitive-Behavioral Training on Pain Self-Efficacy, Self-Discovery, and Perception in Patients with Chronic Low-Back Pain: A Quasi-Experimental Study

Background

Correcting false cognitions and establishing preventive behaviors in patients with chronic low-back pain can improve self-efficacy and self-discovery of these patients against the physical and psychological consequences of chronic back pain through reinforcing thoughts and constructive behaviors.

Objectives

This study aimed to investigate the effectiveness of cognitive-behavioral training in self-efficacy, self-discovery, and pain perception of patients with chronic low-back pain.

Methods

Based on a quasi-experimental design, 40 patients with chronic low-back were selected through purposive sampling and assigned into two groups of intervention (n = 20) and control (n = 20). After administering the pain self-efficacy (PSE) scale, the self-discovery scale (SDS), and the pain perception questionnaire (MPQ) to both groups, the intervention group received the cognitive-behavioral training while the control group did not receive the intervention. The post-test was performed on both groups and the data were analyzed using SPSS.

Results

The scores of pain self-efficacy and self-discovery (self-awareness and acceptance, commitment and attraction, transcendence and development, and personal growth) were higher in the intervention group than in the control group (P < 0.01). The highest increase with an effect size of 0.514 was related to the self-awareness and acceptance subscale. In addition, the pain assessment perception was the only reduced subscale among the other dimensions of pain perception (P < 0.01).

Conclusions

Psychosocial complementary therapies can provide patients suffering from chronic pain with better physical and mental conditions to have a higher quality of life.

Physiotherapists implicitly evaluate bending and lifting with a round back as dangerous

BACKGROUND

Beliefs can be assessed using explicit measures (e.g. questionnaires) that rely on information of which the person is 'aware' and willing to disclose. Conversely, implicit measures evaluate beliefs using computer-based tasks that allow reduced time for introspection thus reflecting 'automatic' associations. Thus far, physiotherapists' beliefs about back posture and safety have not been evaluated with implicit measures.

OBJECTIVES

(1) Evaluate implicit associations between bending lifting back posture (straight-back vs round-back) and safety (safe vs danger); (2) Explore correlations between implicit and explicit measures of beliefs towards vulnerability of the back.

DESIGN

Exploratory cross-sectional quantitative study.

METHODS

47 musculoskeletal physiotherapists completed explicit measures of fear of movement (TSK-HC), back beliefs (BackPAQ_Danger) and beliefs related to bending and lifting back posture and safety (BSB). An Implicit Association Test (IAT) was used to assess implicit associations between (i) images of people bending/lifting with a 'round-back' or with a 'straight-back' posture, and (ii) words representing 'safety' and 'danger'. A one-sample t-test assessed the degree and direction of the sample's IAT score. Cohen's d provided an effect size of the estimated bias. Correlation between IAT and each explicit measure was assessed using Pearson's coefficient.

RESULTS

The sample displayed an implicit association between 'round-back' and 'danger' (μ = 0.213, 95% CI [0.075-0.350], p = .003), with an effect size magnitude of 0.45. There were fair to moderate correlations between IAT and BSB (r = 0.320, 95% CI [0.036-0.556], p = .029) and, IAT and BackPAQ_Danger (r = 0.413, 95%CI [0.143-0.626], p = .004).

CONCLUSIONS

Physiotherapists displayed an implicit bias towards bending and lifting with a round-back as dangerous.

Implicit Attachment Schemas and Therapy Outcome for Panic Disorder Treated with Manualized Confrontation Therapy

BACKGROUND

Different studies have shown that a patient's attachment correlates with the psychotherapy outcome. However, these findings are based on the traditional interview and paper and pencil attachment methods. Latency-based methods like the Implicit Association Test (IAT) have not yet been investigated in clinical attachment research, specifically in therapy outcome research.

OBJECTIVES

It can be hypothesized that patients with positive schemas of their mother and their partner may show a better psychotherapeutic outcome than those with less positive schemas of their mother/partner.

METHOD

A sample of 103 patients suffering from panic disorder with or without agoraphobia (age 36.73, SD = 10.80), including 56% of patients with affective or other anxiety disorders as comorbidities without a personality disorder, based on the Structured Clinical Interview for DSM-IV (SCID-I/II), were treated with a manualized cognitive-behavioral confrontation therapy. Two IATs (for mother and partner) were implemented before the therapy (t1). The symptom reduction was assessed by the Symptom Checklist-90 (SCL-90) and the Beck Depression Inventory (BDI) with symptoms at t1 and IAT at t1 as predictors of symptoms at t2.

RESULTS

The results confirmed a moderate to high therapeutic effect of the confrontation therapy. Furthermore, the mother's IAT at t1 predicted the Global Severity Index (β = 0.20) as well as the Anxiety subscale (β = 0.18) at t2 above and beyond the t1 measurement of the criteria.

CONCLUSIONS

Implicit attitudes of the mother predicted the symptom reduction and a better therapeutic outcome. Relationship aspects with less impact awareness predicted the therapeutic outcome, even though mostly cognitive-behavioral techniques were used.

The Effect of Unihemispheric Concurrent Dual-Site Transcranial Direct Current Stimulation of Primary Motor and Dorsolateral Prefrontal Cortices on Motor Function in Patients With Sub-Acute Stroke

It is believed that unihemispheric concurrent dual-site transcranial direct current stimulation (tDCS_UHCDS) of the primary motor cortex (M1) and the dorsolateral prefrontal cortex (DLPFC) causes an increase in motor cortex excitability. However, the clinical effect of this type of stimulation on patients with neurological conditions is not yet known. The aim of the present study was to assess the effect of anodal-tDCS_UHCDS (a-tDCS_UHCDS) on upper limb motor function in subacute stroke patients. Fifteen patients participated in this sham-controlled crossover study. The main outcome measures were the reaction time (RT) to visual stimuli, completion time of a nine-pin pegboard (9-PPB), and the scores from the Fugl–Meyer assessment (FMA) for the upper limb of the involved side before and after three brain stimulation conditions. For a-tDCS_UHCDS, the anodal electrodes were placed on the M1 and the DLPFC, while for a-tDCS, the anodal electrode was placed on the M1. For the sham stimulation, the tDCS was turned off after 30 s. For brain stimulation, the selected current was 1 mA for 20 min. After a-tDCS_UHCDS, there was a significant reduction in the RT and completion time of the 9-PPB compared with the times after a-tDCS and the sham stimulation: p = 0.013 and p = 0.022, respectively). However, there was no significant difference in the FMA scores after the three types of stimulations (p = 0.085). Compared with a-tDCS, a-tDCS_UHCDS temporarily improved the RT and dexterity of the involved hand in subacute stroke patients.

Clinical Trial Registration: Iranian Registry of Clinical Trials (IRCT), identifier IRCT2015012520787N1.

Transcranial Direct Current Stimulation as a Therapeutic Tool for Chronic Pain

Transcranial direct current stimulation (tDCS) modulates spontaneous neuronal activity that can generate long-term neuroplastic changes. It has been used in numerous therapeutic trials showing significant clinical effects especially when combined with other behavioral therapies. One area of intensive tDCS research is chronic pain. Since the initial tDCS trials for chronic pain treatment using current parameters of stimulation, more than 60 clinical trials have been published testing its effects in different pain syndromes. However, as the field moves in the direction of clinical application, several aspects need to be taken into consideration regarding tDCS effectiveness and parameters of stimulation. In this article, we reviewed the evidence of tDCS effects for the treatment of chronic pain and critically analyzed the literature pertaining its safety and efficacy, and how to optimize tDCS clinical effects in a therapeutic setting. We discuss optimization of tDCS effects in 3 different domains: (i) parameters of stimulation, (ii) combination therapies, and (iii) subject selection. This article aims to provide insights for the development of future tDCS clinical trials.

Cognitive Functional Therapy: An Integrated Behavioral Approach for the Targeted Management of Disabling Low Back Pain

Biomedical approaches for diagnosing and managing disabling low back pain (LBP) have failed to arrest the exponential increase in health care costs, with a concurrent increase in disability and chronicity. Health messages regarding the vulnerability of the spine and a failure to target the interplay among multiple factors that contribute to pain and disability may partly explain this situation. Although many approaches and subgrouping systems for disabling LBP have been proposed in an attempt to deal with this complexity, they have been criticized for being unidimensional and reductionist and for not improving outcomes. Cognitive functional therapy was developed as a flexible integrated behavioral approach for individualizing the management of disabling LBP. This approach has evolved from an integration of foundational behavioral psychology and neuroscience within physical therapist practice. It is underpinned by a multidimensional clinical reasoning framework in order to identify the modifiable and nonmodifiable factors associated with an individual's disabling LBP. This article illustrates the application of cognitive functional therapy to provide care that can be adapted to an individual with disabling LBP.

Implicit evaluations and physiological threat responses in people with persistent low back pain and fear of bending

BACKGROUND AND AIMS

Pain and protective behaviour are dependent on implicit evaluations of danger to the body. However, current assessment of perceived danger relies on self-report, on information of which the person is aware and willing to disclose. To overcome this limitation, attempts have been made to investigate implicit evaluation of movement-related threatening images in people with persistent low back pain (PLBP) and pain-related fear. Lack of specificity of the sample and stimuli limited those explorations. This study investigated implicit evaluations and physiological responses to images of tasks commonly reported as threatening by people with PLBP: bending and lifting. We hypothesized that people who differ in self-reported fear of bending with a flexed lumbar spine (fear of bending) would also differ in implicit evaluations and physiological responses.

METHODS

This study used a convenience sample of 44 people (54% female) with PLBP, who differed in self-reported fear of bending. Participants completed a picture-viewing paradigm with pleasant, neutral and unpleasant images, and images of people bending and lifting with a flexed lumbar spine ('round-back') to assess physiological responses (eye-blink startle modulation, skin conductance). They also completed an implicit association test (IAT) and an affective priming task (APT). Both assessed implicit associations between (i) images of people bending/lifting with a flexed lumbar spine posture ('round-back' posture) or bending/lifting with a straight lumbar spine posture ('straight-back' posture), and (ii) perceived threat (safe vs. dangerous).

RESULTS

An implicit association between 'danger' and 'round-back' bending/lifting was evident in all participants (IAT (0.5, CI [0.3; 0.6]; p<0.001) and APT (24.2, CI [4.2; 44.3]; p=0.019)), and unrelated to self-reported fear of bending (IAT (r=-0.24, 95% CI [-0.5, 0.04], p=0.117) and APT (r=-0.00, 95% CI [-0.3, 0.3], p=0.985)). Levels of self-reported fear of bending were not associated with eye-blink startle (F(3, 114)=0.7, p=0.548) or skin conductance responses (F(3, 126)=0.4, p=0.780) to pictures of bending/lifting.

CONCLUSIONS

Contrary to our expectation, self-reported fear of bending was not related to physiological startle response or implicit measures. People with PLBP as a group (irrespective of fear levels) showed an implicit association between images of a round-back bending/lifting posture and danger, but did not display elevated physiological responses to these images. These results provide insight to the understanding of the relationship between pain and fear of movement.

IMPLICATIONS

The potential clinical implications of our findings are twofold. First, these results indicate that self-report measures do not always reflect implicit associations between particular movements and threat. Implicit association tasks may help overcome this limitation. Second, a lack of the predicted physiological and behavioural responses may reflect that the visualization of a threatening task by people in pain does not elicit the same physiological defensive responses measured in people with fear of specific objects. It may be necessary to expose the person to the actual movement to elicit threat-responses. Together, these results are consistent with current views of the role of 'fear' in the fear-avoidance model, in which a fear response may only be elicited when the threat is unavoidable.

The effects of anodal-tDCS on corticospinal excitability enhancement and its after-effects: conventional vs. unihemispheric concurrent dual-site stimulation

Previous researchers have approved the ability of anodal transcranial direct current stimulation (a-tDCS) of the primary motor cortex (M1) to enhance corticospinal excitability (CSE). The primary aim of the current study was to investigate the effect of concurrent stimulation of M1 and a functionally connected cortical site of M1 on CSE modulation. This new technique is called unihemispheric concurrent dual-site a-tDCS (a-tDCSUHCDS). The secondary aim was to investigate the mechanisms underlying the efficacy of this new approach in healthy individuals. In a randomized crossover study, 12 healthy right-handed volunteers received a-tDCS under five conditions: a-tDCS of M1, a-tDCSUHCDS of M1-dorsolateral prefrontal cortex (DLPFC), a-tDCSUHCDS of M1-primary sensory cortex (S1), a-tDCSUHCDS of M1-primary visual cortex (V1), and sham a-tDCSUHCDS. Peak-to-peak amplitude of transcranial magnetic stimulation (TMS) induced MEPs, short-interval intracortical inhibition (SICI) and intracortical facilitation (ICF) were assessed before and four times after each condition. A-tDCSUHCDS conditions induced larger MEPs than conventional a-tDCS. The level of M1 CSE was significantly higher following a-tDCSUHCDS of M1-DLPFC than other a-tDCSUHCDS conditions (p < 0.001), and lasted for over 24 h. The paired-pulse TMS results after a-tDCS of M1-DLPFC showed significant facilitatory increase and inhibitory change. A-tDCSUHCDS of M1-DLPFC increases M1 CSE twofold that of conventional a-tDCS. A-tDCSUHCDS of M1-DLPFC enhances the activity of glutamergic mechanisms for at least 24 h. Such long-lasting M1 CSE enhancement induced by a-tDCSUHCDS of M1-DLPFC could be a valuable finding in clinical scenarios such as learning, motor performance, or pain management. The present study has been registered on the Australian New Zealand Clinical Trial at http://www.anzctr.org.au/ with registry number of ACTRN12614000817640.

How does anodal transcranial direct current stimulation of the pain neuromatrix affect brain excitability and pain perception? A randomised, double-blind, sham-control study

Background

Integration of information between multiple cortical regions of the pain neuromatrix is thought to underpin pain modulation. Although altered processing in the primary motor (M1) and sensory (S1) cortices is implicated in separate studies, the simultaneous changes in and the relationship between these regions are unknown yet. The primary aim was to assess the effects of anodal transcranial direct current stimulation (a-tDCS) over superficial regions of the pain neuromatrix on M1 and S1 excitability. The secondary aim was to investigate how M1 and S1 excitability changes affect sensory (STh) and pain thresholds (PTh).

Methods

Twelve healthy participants received 20 min a-tDCS under five different conditions including a-tDCS of M1, a-tDCS of S1, a-tDCS of DLPFC, sham a-tDCS, and no-tDCS. Excitability of dominant M1 and S1 were measured before, immediately, and 30 minutes after intervention respectively. Moreover, STh and PTh to peripheral electrical and mechanical stimulation were evaluated. All outcome measures were assessed at three time-points of measurement by a blind rater.

Results

A-tDCS of M1 and dorsolateral prefrontal cortex (DLPFC) significantly increased brain excitability in M1 (p < 0.05) for at least 30 min. Following application of a-tDCS over the S1, the amplitude of the N20-P25 component of SEPs increased immediately after the stimulation (p < 0.05), whilst M1 stimulation decreased it. Compared to baseline values, significant STh and PTh increase was observed after a-tDCS of all three stimulated areas. Except in M1 stimulation, there was significant PTh difference between a-tDCS and sham tDCS.

Conclusion

a-tDCS of M1 is the best spots to enhance brain excitability than a-tDCS of S1 and DLPFC. Surprisingly, a-tDCS of M1 and S1 has diverse effects on S1 and M1 excitability. A-tDCS of M1, S1, and DLPFC increased STh and PTh levels. Given the placebo effects of a-tDCS of M1 in pain perception, our results should be interpreted with caution, particularly with respect to the behavioural aspects of pain modulation.

Trial Registration

Australian New Zealand Clinical Trials, ACTRN12614000817640, http://www.anzctr.org.au/.