The nature of pain perception

Recent advances in neuro-imaging are leading to the identification of pain pathways and parts of the brain associated with the shaping of pain perception. For example, functional magnetic resonance imaging (fMRI) has led to new understandings about how a painful stimulus is translated into pain perception in the brain. These new understandings have begun to clarify the cascade of events that follows the arrival of a ‘pain signal’, after which different parts of the brain become activated. It seems that beliefs, memories and emotions translate a pain signal into ‘unique cerebral signatures’ , which characterise our pain perceptions in terms of possible actions. This opens up the potential for a whole variety of psychological interventions, which might influence cortical activity.

Cognitive processes translate the pain signal into pain perceptions and offer mechanisms whereby the signal is interpreted in terms of its meaning, potential ‘threat value’ and potential significance for action. Legrain et al. offer a neurocognitive model of pain perceptions which makes a distinction between a ‘top-down selection process’ whereby incoming information is prioritised in terms of its significance, and a ‘bottom-up selection’, or involuntary capture of information relevant for escaping from bodily threat in which salient events are given a stronger neuronal representation . They suggest that top-down attentional processes prioritise the information that enters our subsequent awareness in terms of its value for goal-directed activity.

Influence of cognitive processes on the experience of pain

Reflecting on the role of hypnosis in chronic pain management, Jenson noted that there was clear evidence that the experience of chronic pain is closely related to supraspinal nervous system activity, that hypnosis has direct effects on the supraspinal sites that are linked to the experience of pain and that self-hypnosis training is effective for reducing the severity of pain . Three important findings emerge from these experimental studies: (1) beliefs influence the perception of pain; (2) pain beliefs can be modified; and (3) modification of beliefs is associated with activation of key anatomical sites and pathways. It would seem that in terms of pain perception, we might not be as ‘hard-wired’ as had been supposed.

Within this complex set of inter-relating mechanisms, there appears to be a number of key elements that individually, and in combination, influence the experience of pain. The role of attention is central in pain perception, but the important role of anticipation of pain based on prior (or imagined) experience has not always been recognised. In the context of specific beliefs about illness and in conjunction with emotional responses, anticipation of pain can establish unhelpful patterns of escape and avoidance, resulting in some control of pain, but at a cost of unnecessary pain-associated limitations.

Weich et al. have highlighted three factors that influence the experience of pain that might be valuable in the context of treating chronic pain: the role of memory; cognitive appraisal and hypervigilance; and catastrophising . These are discussed in more detail in Box 1 .

More recently, studies have focussed on the possible function of catastrophisation in the context of communication goals . It has been suggested that pain catastrophisers might engage in exaggerated pain expression in order to solicit assistance or empathic responses from others in their social environment, rather than just to manage their pain. Therefore, catastrophisation appears to be important not only as a component of chronic pain but also in the development of chronicity. It would seem therefore that the cognitions associated with catastrophising are best understood as but one facet of a complex style of response to pain and the threat of pain.

Beliefs, emotions and behaviour

Emotional processes not only colour pain perception but also can inhibit or facilitate pain by engaging physiological mechanisms involved with pain modulation . The appraisal of pain is thus influenced not only by our specific beliefs and the degree of conviction with which we hold those beliefs, but also by attribution of its emotional significance. Both are important as possible therapeutic targets and/or as potential obstacles to recovery.

The emotional impact of pain can range from the mildly distressing to the overwhelming. The typical patient lies somewhere between these two extremes and it should be appreciated that a certain degree of distress is appropriate when confronted with persisting pain or pain-associated limitations. A greater level of emotional impact is a predictor of chronicity and should be viewed as a ‘yellow flag’ , although if of sufficient intensity it should be viewed as an ‘orange flag’ indicating a significant mental health problem for which help from a mental health specialist should be sought .

The level of distress is not simply explained by pain intensity, but appears to be mediated by a number of cognitive factors as discussed above, as well as influenced by the nature and extent of the impact of the pain on function and quality of life. Arguably the almost exclusive focus on sickness and disability, as opposed to factors which may protect us from, or minimise the emotional impact, has led us to underestimate the importance of self-reliance in the battle against pain.

The fear-avoidance model explains the development of chronic disability by assigning key roles to the appraisal of threat and fear (manifest as “catastrophizing”) as mediators in the establishment of patterns of avoidance behaviour and increasing invalidism.

In patients who have developed chronic pain and significant pain-associated limitations, there is often a change in self-identity, associated with loss of self-worth, demoralisation and the emergence of a constellation of beliefs indicative of a marked change in self-identity since the development of their chronic pain problem. The process has been described as ‘enmeshment’ , where individuals feel pessimism about the possibility of re-gaining control over pain or its impact.

In clinical management of persisting low back pain therefore, whether adopting a traditional cognitive–behavioural therapy (CBT) approach and tackling beliefs ‘head-on’, or viewing beliefs as obstacles which need to be circumvented, as in the acceptance and commitment therapy (ACT) approach , clarification of the nature and function of the patient’s beliefs is an essential platform from which to construct a clinical intervention.

Types of beliefs

DeGood and Tait identify four principal dimensions of belief (regarding aetiology, diagnostics, treatment expectations and outcome goals) . For purposes of clinical management, the most influential types of belief appear to be beliefs about the nature of pain, specific fears of hurting, harming and further injury and self-efficacy beliefs. Other sorts of beliefs influencing consulting and participation in treatment are reviewed in the next section.

Beliefs about the nature of pain

Pain researchers have identified a number of different types of belief or appraisal about the nature of pain. Beliefs about the extent to which pain can be controlled appear to be among the most powerful determinants of adjustment to pain or the development of incapacity, possibly mediating the influence of pain and depression. These core constructs can also be viewed as specific therapeutic targets. Correction of fundamental misunderstandings about the nature of pain, its effects and probable course are likely not only to facilitate optimal management but also prevent unnecessary iatrogenic misunderstandings and distress. An important stage in optimal adaptation to a chronic condition seems to depend upon patients’ ability to come to terms with what they can and cannot control. This in turn may be affected by specific fears of hurting, harming and further injury.

Specific fears of hurting, harming and further injury

Since the early-mid 1990s, there has been an increasing research focus on the role of fear and avoidance in the development and maintenance of disability . Among people with chronic low back pain, pain-related fear has been found to be associated with reduced lumbar flexion ; pain-related fear and pain catastrophising have been found to be stronger predictors of overall disability than pain intensity. One study found that pain-related fear was also the strongest predictor of performance . However, in acute low back pain, only modest correlations between pain intensity, pain-related fear, avoidance behaviour and disability have been detected .

Self-efficacy beliefs

According to self-efficacy theory, once a situation has been perceived as involving harm, loss, threat or challenge, and individuals have considered a range of coping strategies open to them, what they do will be dependent on what they believe they can achieve . Self-efficacy beliefs were originally considered with reference to specific behaviours required to produce a particular outcome. Thus the action taken by an individual is seen as a consequence firstly of their conviction that they have the skill/ability to execute the behaviour required to produce the desired outcome (self-efficacy expectation), and secondly of their estimation that a chosen behaviour will lead to the desired outcome (outcome expectancy). Asghari and Nicholas have shown that pain self-efficacy beliefs are an important determinant of pain behaviours and disability associated with pain, over and above the effects of pain, distress and personality variables .

Taken together, clinical and experimental investigations suggest that perceived coping inefficacy might lead to preoccupation with distressing thoughts and concomitant physiological arousal, thereby increasing pain, decreasing pain tolerance and leading to increased use of medication, lower levels of functioning, poorer exercise tolerance and increased invalidism. Such beliefs therefore would seem to have considerable potential as targets within clinical management.

Nicholas has suggested broadening the construct of self-efficacy to encompass a more general belief system associated with self-reliance or resilience enabling people to cope, to a greater or lesser extent, with what life throws at them . However, it is not known to what extent such general core beliefs are modifiable. Therefore, in terms of individual clinical management, it would appear more useful to focus on beliefs about specific aspects of pain or treatment, whether as specific targets for cognitive intervention, or as potential obstacles to optimal engagement in treatment. Self-efficacy has been found to account for the greatest proportion of variance in physical performance even after anticipated pain and re-injury have been excluded, although pain intensity was also a significant (albeit limited) predictor of performance . This challenged the view of harm expectancies and pain catastrophising as primary causal determinants of function, and suggests that they may be components of one’s confidence of successful task performance . Treatment recommendations derived from this interpretation emphasise the importance of goal and quota setting, and monitoring of pain and task performance as components of pain management and as such fit well within modern pain management.

Types of beliefs

DeGood and Tait identify four principal dimensions of belief (regarding aetiology, diagnostics, treatment expectations and outcome goals) . For purposes of clinical management, the most influential types of belief appear to be beliefs about the nature of pain, specific fears of hurting, harming and further injury and self-efficacy beliefs. Other sorts of beliefs influencing consulting and participation in treatment are reviewed in the next section.

Beliefs about the nature of pain

Pain researchers have identified a number of different types of belief or appraisal about the nature of pain. Beliefs about the extent to which pain can be controlled appear to be among the most powerful determinants of adjustment to pain or the development of incapacity, possibly mediating the influence of pain and depression. These core constructs can also be viewed as specific therapeutic targets. Correction of fundamental misunderstandings about the nature of pain, its effects and probable course are likely not only to facilitate optimal management but also prevent unnecessary iatrogenic misunderstandings and distress. An important stage in optimal adaptation to a chronic condition seems to depend upon patients’ ability to come to terms with what they can and cannot control. This in turn may be affected by specific fears of hurting, harming and further injury.

Specific fears of hurting, harming and further injury

Since the early-mid 1990s, there has been an increasing research focus on the role of fear and avoidance in the development and maintenance of disability . Among people with chronic low back pain, pain-related fear has been found to be associated with reduced lumbar flexion ; pain-related fear and pain catastrophising have been found to be stronger predictors of overall disability than pain intensity. One study found that pain-related fear was also the strongest predictor of performance . However, in acute low back pain, only modest correlations between pain intensity, pain-related fear, avoidance behaviour and disability have been detected .

Self-efficacy beliefs

According to self-efficacy theory, once a situation has been perceived as involving harm, loss, threat or challenge, and individuals have considered a range of coping strategies open to them, what they do will be dependent on what they believe they can achieve . Self-efficacy beliefs were originally considered with reference to specific behaviours required to produce a particular outcome. Thus the action taken by an individual is seen as a consequence firstly of their conviction that they have the skill/ability to execute the behaviour required to produce the desired outcome (self-efficacy expectation), and secondly of their estimation that a chosen behaviour will lead to the desired outcome (outcome expectancy). Asghari and Nicholas have shown that pain self-efficacy beliefs are an important determinant of pain behaviours and disability associated with pain, over and above the effects of pain, distress and personality variables .

Taken together, clinical and experimental investigations suggest that perceived coping inefficacy might lead to preoccupation with distressing thoughts and concomitant physiological arousal, thereby increasing pain, decreasing pain tolerance and leading to increased use of medication, lower levels of functioning, poorer exercise tolerance and increased invalidism. Such beliefs therefore would seem to have considerable potential as targets within clinical management.

Nicholas has suggested broadening the construct of self-efficacy to encompass a more general belief system associated with self-reliance or resilience enabling people to cope, to a greater or lesser extent, with what life throws at them . However, it is not known to what extent such general core beliefs are modifiable. Therefore, in terms of individual clinical management, it would appear more useful to focus on beliefs about specific aspects of pain or treatment, whether as specific targets for cognitive intervention, or as potential obstacles to optimal engagement in treatment. Self-efficacy has been found to account for the greatest proportion of variance in physical performance even after anticipated pain and re-injury have been excluded, although pain intensity was also a significant (albeit limited) predictor of performance . This challenged the view of harm expectancies and pain catastrophising as primary causal determinants of function, and suggests that they may be components of one’s confidence of successful task performance . Treatment recommendations derived from this interpretation emphasise the importance of goal and quota setting, and monitoring of pain and task performance as components of pain management and as such fit well within modern pain management.

The decision to consult

Patients’ attitudes, perceptions and beliefs about their back pain, its likely course and the usefulness of specific treatments may influence an individual’s decision to seek health care and to embark on complete treatment, although the evidence to support this is limited by the challenges of data collection from those who do not seek health care. There is evidence from community surveys that about half of those who experience low back pain in a 1-year period will consult an HCP, and that while pain severity influences consulting behaviour in the acute phase (<2 weeks), after this, those who consult are more likely to have increased disability, externalised locus of control beliefs for pain management and depressive symptoms .

From consultation cohorts, there is evidence that psychological factors are associated with pain and disability at the first health-care consultation; these factors include dissatisfaction with current symptoms, concern about future pain persistence and difficulty coping with the pain . An individual’s attitudes and beliefs about the relationship between their pain and function appear to be constructs that partially explain disability levels . In general, those who believe more strongly that their pain means they should avoid physical activities and abandon normal roles report higher levels of disability than those with opposite beliefs, and are thus more likely to consult, re-consult and use further health-care resources.

Engagement/participation in treatment

Patients’ beliefs, expectations and preferences about treatments for back pain are likely to influence their engagement in and adherence to treatment plans, yet empirical data are lacking. Patients’ treatment expectations may contribute to treatment response when that treatment is received, because it may serve to enhance motivation and compliance with the treatment or it may predict patient satisfaction with the consultation and their care. Expectations research emphasises the complexity of mind–body interactions, the role of multiple pathways, endogenous opioids and other non-opioid mechanisms , intermediate processes such as improvements in therapeutic alliance between patient and professional and changes in patients’ perceptions of their problem and coping strategies . These factors may thus affect the degree to which patients engage in and adhere to back pain management advice and treatments.

Treatment outcome

Intuitively, it makes sense that if patients with back pain get the treatment they prefer or for which they hold higher expectations of benefit, then their outcomes might be improved. There is growing evidence from systematic reviews across a wide range of health conditions that patients’ expectations influence their health outcomes. Although a review of different health conditions found little evidence for a ‘preference effect’ , data from musculoskeletal pain studies, and in particular, back pain, demonstrate relationships between treatment preferences and expectations and patients’ clinical and return-to-work outcomes .

Positive attitudes towards treatment and confidence in benefit from specific treatments have been shown to lead to a two- to fivefold greater likelihood of improvement , although this finding is not consistent across all studies . In addition, general outcome/recovery expectations, irrespective of treatment, have been shown to influence outcome. The largest prospective population-based study to date of risk factors for work disability after back problems showed that patients’ baseline recovery expectations predicted work disability at 6 and 12 months follow-up . Those with very low baseline recovery expectations were 3 times more likely to be off work at 6 months. A large prospective consultation-based cohort demonstrated that patients’ who expect their back pain to last a long time, who perceive serious consequences and who hold weak beliefs in the controllability of their back problem are more likely to have poor clinical outcomes 6 months after consultation .

There are several common limitations to the evidence base in this field, including the challenge of capturing the beliefs, expectations or preferences of patients who decline to participate in cohort studies or clinical trials; the study of these factors is usually a secondary objective, and thus, the statistical comparisons often lack power. In addition, few studies have measured beliefs, expectations or preferences beyond the baseline measurement point. It is also likely, but as yet, there are few data to support the hypothesis that the effects of patients’ treatment preferences and expectations may differ according to the nature, invasiveness or unpleasantness of the interventions.

In summary, it seems probable that there are a large number of potential ‘pathways to chronicity’. However, as a precursor to the design of further interventions, we still require a clearer understanding of the nature of change and the underlying processes involved. Attempting to address such beliefs within a reactivation framework has become an integral part of new approaches to the prevention of pain-associated incapacity both in health-care settings and in occupational settings .