Pain sensitization affected by focus and expectancy

Below are 2 PubMed articles about pain sensitization and how affected that is by focus and expectancy.

Characteristics of sensitization associated with chronic pain conditions – Clin J Pain.  Apr 2015

Objectives: To describe and understand varieties and characteristics of sensitization contributing to hyperalgesia for patients with chronic pain conditions.

Methods: Thermal stimulation was delivered to the face, forearm and calf of pain-free subjects and individuals with irritable bowel syndrome (IBS), temporomandibular pain disorder (TMD) and fibromyalgia syndrome (FMS).   

Results:

Thermal pain ratings during ascending series were greater at each site for individuals diagnosed with chronic pain.

Strong pain at the time of testing further enhanced the ratings at all sites, but mild or moderate clinical pain did not have this effect.

Thermal pain for all subjects was greater during descending series than during ascending series of arm and leg stimulation.

The hypersensitivity during descending series was comparable for pain-free, FMS and TMD subjects but was increased in duration for arm or leg stimulation of FMS subjects.

Discussion:

The widespread sensitization for IBS and TMD subjects does not rely on mechanisms of spatial and temporal summation often invoked to explain widespread hyperalgesia associated with chronic pain.

Increased sensitivity during descending series during stimulation of an arm or leg but not the face indicates a propensity for sensitization of nociceptive input to the spinal cord.

Abnormally prolonged sensitization for FMS patients reveals a unique influence of widespread chronic pain referred to deep somatic tissues.

 

Opposing Effects of Expectancy and Somatic Focus on PainPLoS One. Jun 2012

Abstract

High-pain expectancy increases pain and pain-related brain activity, creating a cycle of psychologically maintained pain. Though these effects are robust, little is known about how expectancy works and what psychological processes either support or mitigate its effects.

To address this, we independently manipulated pain expectancy and “top-down” attention to the body, and examined their effects on both a performance-based measure of body-focus and heat-induced pain.

Multi-level mediation analyses showed that high-pain expectancy substantially increased pain, replicating previous work.

However, attention to the body reduced pain, partially suppressing the effects of expectancy.

Furthermore, increased body-focus had larger pain-reducing effects when pain expectancy was high, suggesting that attempts to focus on external distractors are counterproductive in this situation.

Overall, the results show that attention to the body cannot explain pain-enhancing expectancy effects, and that focusing on sensory/discriminative aspects of pain might be a useful pain-regulation strategy when severe pain is expected.

Introduction

Recent studies have found that expectations about pain intensity and pain-mitigating treatments modulate pain reports and brain responses to noxious stimuli

While expectancies are increasingly recognized as meaningful influences on nociception, the psychological processes that constitute expectations and mediate their effects on pain (and other affective events) have not been well described

Expectancies may work by influencing attention, affective appraisals, or other processes.

Expectations about the environment drive visual attention; likewise, high-pain expectancy may redirect endogenous “top-down” attention toward pain and/or enhance “bottom-up” vigilance, both of which could intensify pain experience.

Conversely, low-pain expectations could act as a safety signal, allowing attention to be directed elsewhere.

As distraction–the diversion of attention–can have large and reliable effects on experimental pain, and can also influence the processing of pain-related signals in the cortex, attention to or away from the body might mediate the cue-based expectancy effects on pain

The current study was designed to directly address this question by independently manipulating pain expectancies and top-down attention toward the body, or somatic focus. These manipulations allowed us to test whether the effects of expectancy cues on pain are mediated by changes in somatic focus.

Discussion

Somatic focus was enhanced by two ‘top-down’ manipulations: Task instructions that incentivized discrimination of heat intensity, and cues that signaled increased pain intensity

It may be natural to think of pain expectancy as increasing attention toward the body, which thus enhances pain processing. However, our results suggest that this is not the case. Mediation analyses showed that pain expectancy exerts strong enhancing effects on pain experience that are not mediated by increased somatic focus.

Rather, strikingly, somatic focus was associated with reduced rather than enhanced pain, partially suppressing the direct pain-enhancing effects of aversive expectancy. Thus, attention to the body promoted pain relief, and this was particularly true when pain expectancies were high.

These results both confirm prior work showing that pain perception assimilates towards expectations, and show, for the first time, that expectations have effects that are strongly dissociable from the effects of attention to the body.

Several reviews on these effects have pointed out that the benefits of attention to vs. away from the body are strikingly inconsistent, with multiple studies finding either significant enhancement or significant reductions in pain, and others failing to find effects in either direction

These findings also suggest that the best cognitive strategies for mitigating pain might depend on the intensity of anticipated pain and the level of threat it entails

our results suggest that the benefits of directing attention to the body do vary as function of pain expectancy. In the present study, the benefits of attention to the body were particularly important when pain expectancy was high.

Together, these results indicate that expectancy-based enhancement of pain is not due to increases in attention to the body per se.

It could be caused by attention to the specifically affective aspects of pain, or to affective valuation processes independent of the focus of attention.

Whatever the case may be, focus on the site of pain (and particularly the heat intensity) may actually have beneficial effects on pain, particularly when high pain expectancies make focusing elsewhere more difficult.

Finally, high pain cues had multiple, opposing effects on pain, both increasing pain directly and reducing pain through increased somatic focus.

This finding suggests a greater variety of anticipatory processes than have previously been appreciated, whose underlying brain mechanisms and behavioral sequelae remain to be elucidated.

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