Brain Mechanisms of Anticipated Painful Movements and Their Modulation by Manual Therapy in Chronic Low Back Pain

Heightened anticipation and fear of movement-related pain has been linked to detrimental fear-avoidance behavior in chronic low back pain (cLBP). Spinal manipulative therapy (SMT) has been proposed to work partly by exposing patients to nonharmful but forceful mobilization of the painful joint, thereby disrupting the relationship among pain anticipation, fear, and movement. Here, we investigated the brain processes underpinning pain anticipation and fear of movement in cLBP, and their modulation by SMT, using functional magnetic resonance imaging. Fifteen cLBP patients and 16 healthy control (HC) subjects were scanned while observing and rating video clips depicting back-straining or neutral physical exercises, which they knew they would have to perform at the end of the visit. This task was repeated after a single session of spinal manipulation (cLBP and HC group) or mobilization (cLBP group only), in separate visits. Compared with HC subjects, cLBP patients reported higher expected pain and fear of performing the observed exercises. These ratings, along with clinical pain, were reduced by SMT. Moreover, cLBP, relative to HC subjects, demonstrated higher blood oxygen level-dependent signal in brain circuitry that has previously been implicated in salience, social cognition, and mentalizing, while observing back straining compared with neutral exercises. The engagement of this circuitry was reduced after SMT, and especially the spinal manipulation session, proportionally to the magnitude of SMT-induced reduction in anticipated pain and fear. This study sheds light on the brain processing of anticipated pain and fear of back-straining movement in cLBP, and suggests that SMT may reduce cognitive and affective-motivational aspects of fear-avoidance behavior, along with corresponding brain processes. PERSPECTIVE: This study of cLBP patients investigated how SMT affects clinical pain, expected pain, and fear of physical exercises. The results indicate that one of the mechanisms of SMT may be to reduce pain expectancy, fear of movement, and associated brain responses.

Keywords:   Expectation; Fear-avoidance; Pain anticipation; Physical exercise; Spinal Manipulative Therapy; chronic Low Back Pain; functional Magnetic Resonance Imaging.

From the FULL TEXT Article:

Background

There are more articles like this @

LOW BACK PAIN Section

Elevated anticipation of motion-related pain is common in chronic low back pain (cLBP), [69] and is associated with fear of movement and excessive avoidance behavior, which can be detrimental to health and quality of life, and prevent recovery. [50] Higher fear-avoidant behavior is associated with higher disability, [12, 29, 68, 69, 71] and reduction in fear/anxiety can predict successful therapy. [70] The fear-avoidance model of chronic pain posits that chronification of pain is often characterized by a vicious cycle whereby catastrophizing about pain leads to fear of movement and hypervigilance, which in turn can incite hypersensitization and exacerbation of pain, leading to yet more avoidance. [40]

This cycle has been linked to Pavlovian and operant conditioning, [21, 67] in which pain initially represents an unconditioned response to a nociceptive unconditioned stimulus, but may be elicited by a progressively wider range of nonharmful movements (conditioned stimulus). [27, 46] While a large literature implicates psychological mechanisms of fear-avoidance behavior in pain, less is known about the brain mechanisms involved in the anticipation and fear of movement-evoked pain. Understanding these mechanisms is critically important, as they influence behavioral decisions to approach or avoid situations where a perceived harmful physical movement may occur.

Initial neuroimaging studies of cLBP patients observing back-straining maneuvers have found increased sympathetic responses [25] and altered brain processing in circuitry consistent with social cognition, salience, and mentalizing, such as the ventrolateral (vlPFC) and dorsomedial (dmPFC) prefrontal cortex, mid-anterior insula (m/aINS), middle temporal gyrus (MTG), superior temporal sulcus (STS), and amygdala. Notably, in these studies, participants passively viewed static pictures [4, 5, 61] or videos [43, 44] depicting people in back-straining positions, without any actual prospect of executing physical activity by the participants themselves. Thus, the behavioral relevance of the context — and in turn fear — may have been limited.

Conditioned responses — such as fear of potentially harmful maneuvers — can be “unlearned” when the conditioned stimulus or conditioned response consistently occurs without leading to unconditioned response (eg, a perceived harmful motion is not followed by pain or harm). There is evidence that exposing patients to (feared) nonharmful physical activity, to extinguish fear responses, can reduce avoidance behavior in chronic musculoskeletal pain. [20, 67, 70] Interestingly, one proposed effect of spinal manipulative therapy (SMT), which involves salient sensory and proprioceptive feedback through passive mobilization of spine joints, is that it might help disrupt the association between fear, back-motion, and pain. [9, 74] However, it has not yet been investigated whether SMT affects motivational aspects relevant to avoidance — such as anticipated pain and fear of movement. Moreover, very little is known about how SMT affects brain processing. [22]

Here, we investigated the brain-based underpinnings anticipated pain and fear of physical exercises, and the effect of 2 SMT techniques (grade 3 mobilization and grade 5 manipulation) on these outcomes. We hypothesized that, in cLBP, observation of back-straining, relative to neutral, exercises would elicit brain responses in circuitry involved in social cognition, fear, salience, and pain processing (eg, the anterior cingulate cortex, insulae, and amygdalae), in addition to visual and frontoparietal attention regions. Further, we hypothesized that SMT would reduce clinical pain, as well as fear, expected pain of back-straining exercises, and corresponding brain responses to observation of such exercises. Finally, we hypothesized that these effects would be stronger for SMT manipulation relative to mobilization, reflecting a dose response.

Read the rest of this Full Text article now!