Pain and Learning
What does chronic pain have to do with learning? Here's a quick post with links and quotes from three new papers that help explain the role of associative learning in chronic pain. Because many of the quotes contain a bunch of fancy language, here's a quick bit of background on the key concept - learning through pavlovian association.
Dogs can learn to associate a bell with dinner, so that hearing the bell will cause them to start drooling even before dinner is served. Similarly, humans can learn to associate pain with movement, so that the movement can cause pain, even after it stops causing nociception.
This is great to know because it suggests a simple remedy. Dogs will eventually stop drooling if you ring the bell enough times without bringing dinner. And people can hopefully extinguish their association between pain and a movement by finding a way to move without pain (perhaps by moving slower, or in novel contexts, or with novel intentions or attentions).
This is a great theory to inform a graded exposure approach to treating chronic pain, and to explain the logic of the approach to patients.
Here are links to the papers and quotes. If you want to just skim, just read the bold parts.
Beyond nociception: the imprecision hypothesis of chronic pain
encoding non-nociceptive information predictably coincident with nociceptive input underpins the response to subsequent similar events. Briefly, our hypothesis posits that the precision with which multisensory information (temporal, proprioceptive, spatial) about the painful event is encoded and represented in the brain will determine the degree to which the painful response will subsequently generalize to similar events. Once the nociceptive and non-nociceptive inputs are associated, a process termed “acquisition,” not just the initial multisensory event will elicit the painful response but also events that share some features with that multisensory event.
Put simply (and why wasn't it put simply in the paper?) people can learn to associate nociception with other stimuli so that the other stimuli can cause pain. Broader associations implies more stimuli that can cause pain.
The more “blurred” the encoding, the more generalization occurs . . . imprecise encoding of the original painful event, which may be, for example, bending forward, results in generalization of back pain to similar movements and activities . . . at some point of generalization, the protective function moves from being adaptive or helpful to being maladaptive or unhelpful.
. . .
How different is the Imprecision Hypothesis from the concept of central sensitization? The key difference is that central sensitization has been attributed to entirely nonassociative mechanisms.
. . .
A great deal of clinical and experimental data is consistent with the Imprecision Hypothesis . . . widespread pain is characterized . . . by a wide array of pain triggers that gradually develop over time. A growing body of literature documents imprecision in bodily cortical representations in people with chronic pain . . . spatial and proprioceptive aspects of multisensory events are encoded less precisely in people with chronic pain than they are in people with acute pain or in healthy controls . . . people with chronic pain have lower proprioceptive acuity, disruptions in the perceived size and alignment of body parts, and show poor ability to mentally maneuver the painful body part. . . .
if we are correct, it will open up new possibilities for the treatment of people with acute pain, focusing not on distraction and analgesia but on precisely encoding the painful event. The extant literature on motor learning, spatial attention, sensory training, and neuroplasticity should provide a valuable base on which to embark on such a task.
For more on Moseley’s ideas about imprecision and “blurring “ of cortical maps, click here.
Chronic pain: The role of learning and brain plasticity
This is a recent paper from Apkaria and colleagues, building on their earlier work where they identified, through MRI, changes in the brain occurring shortly after an injury that could predict whether the owner of the brain would eventually experience chronic pain.
Here are some quotes:
Since the work of Pavlov, it has been known that pain is a potent aversive stimulus for creating salient memories. It induces single event learning, with associated memories potentially lasting a lifetime. These concepts have been utilized in the neuroscience of learning and memory for over a century. Surprisingly, they have had little impact on pain research.
. . .
In contrast to the agnostic definition of “pain that persists past the healing process”, we redefine chronic pain as pain that does not extinguish its memory trace. . . .
continued suffering of chronic pain is critically dependent on the state of motivational and emotional mesolimbic-prefrontal circuitry of the brain. The plastic changes that occur within this circuitry in relation to nociceptive inputs dictate the transition to chronic pain, rendering the pain less somatic and more affective in nature. . . .
This [approach] does not deny the respective contribution of peripheral and spinal cord processes in chronic pain but expands the idea by placing the brain emotional learning and memory circuitry as central to an adequate understanding of chronic pain.
Exercise therapy for chronic musculoskeletal pain: Innovation by altering pain memories
This paper takes similar concepts and uses them as very common sense framework for applying principles of graded exposure to treat pain:
Even though nociceptive pathology has often long subsided, the brain of patients with chronic musculoskeletal pain has typically acquired a protective (movement-related) pain memory. Exercise therapy for patients with chronic musculoskeletal pain is often hampered by such pain memories.
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Before initiating exercise therapy, a preparatory phase of intensive pain neuroscience education is required. Next, exercise therapy can address movement-related pain memories by applying the ‘exposure without danger’ principle. By addressing patients' perceptions about exercises, therapists should try to decrease the anticipated danger (threat level) of the exercises by challenging the nature of, and reasoning behind their fears, assuring the safety of the exercises, and increasing confidence in a successful accomplishment of the exercise.
Not a bad approach! I love this because it implies that a problem with very complex causes can nevertheless have a very simple solution. Not easy in practice of course. But simple in principle.