Persistent Pain as a Sensory Processing impairment

Apollo, confronting the embodiment of his internal model

Apollo, confronting the embodiment of his internal model

This blog is going to delve into some of the science behind what people feel and how it should inform practice. Sensory processing (also referred to as perception) is the reconciliation of information coming in from the periphery (our senses) on the brain’s internal model of the world and self. Perception is the ascribed meaning about the sensation, the environment, the person, and context. Hot, cold, sharp, dull, these are sensations. “That is so hot it can burn me” and “that is so sharp it can cut me” are perceptions of danger.

How something feels, is how it is perceived. A patient reports that they “feel tight.” They are relaying how the experience is being perceived. It is not a reflection of how the world is, but our brains assessment of the situation. When a patient experiences a symptom, for which a patho-physical source cannot be identified, it should lead you to consider the possibility of the presence of sensory processing impairments. Every symptom is real. The lack of awareness of neuroplasticity and sensory processing in regards to the experience of pain, is extremely problematic for patients in their interactions with healthcare providers and navigation of health systems.

The interpretation of sensory information is not universal and it is not always accurate. What feels good to one person can feel miserable to the next. Some who are tactile defensive can’t stand tags and seams in clothing while others are unbothered by it. There are individuals who can lay on a bed of nails without alarm. You can find headlines recounting stories of athletes sustaining injuries on the field or court and having no idea until someone points it out to them. Their brains did not make a determination that what had occurred, was threatening or perhaps that it had even led to any kind of outcome at all. The internal model informs the conscious experience.

When a patient tells me that something that may seem random and benign to me, is painful to them, it is. Because their sensory processing has determined it to be so. I had a patient awhile back who reported that air conditioning was painful for them. When this was explored deeper, we correlated it to her hospital stay after the major injury which was the catalyst for her pain, The hospital room she stayed in was freezing. The context and prior experience shaped her internal model.

The process, in brief, goes like this: sensory/afferent information is picked up by receptor cells in the periphery, moves to the spinal cord, brain stem, and thalamus, before arriving at the cortex. Once there, the input relays to the primary and secondary somatosensory cortices, and then to association areas. Our internal model is used as the comparator to the incoming information. It is constantly updated for the most current predictions. This is informed by context, prior experience, learning, and adaptation.

Predictive processing is the postulated framework with which this occurs. Prediction errors serve to confirm or update the internal model. An event occurs, and the brain formulates an expectation of meaning and outcome (top down.) There is then a comparison of arriving sensory input, that either confirms or disconfirms the prediction (bottoms up.)

There are a few variants to predictive processing models. These include predictive coding, bayesian interference, and hierarchical temporal memory. But the gist is the same. There exists an internal model for which there is an anticipated expectation of what something is or will be, what will occur, and what it means, that incoming sensory information is compared to.

“A key assumption of the predictive processing framework is that internal models are learned and that experience shapes the circuits required for generating predictions and computing prediction errors…It is the interaction with the world that refines these connections to generate internal models. Sensory experience sculpts the connectivity between neurons in an activity-dependent manner…”pg 430 Keller and Mrsic-Fogel 2018

This is how and why prior pain experience shapes pain perception. Prior experience and repetition shape plasticity by updating the internal model. This is learning. And if we operate from the premise of sensory perception/predictive processing, then we have the opportunity to help the system (aka human) adapt, via neuroplasticity, and sensory processing, away from a persistent pain state and towards a balance of relative safety. Where can we impact the process? At the reconciliation of what was predicted by the internal model, and the experiences and context that lead to prediction errors to update that model.

Viewing persistent pain as a sensory processing impairment can help us to understand that in these states, adaptive neuroplastic updates either didn’t occur or did so in a way that was maladaptive. Our bodies do this all the time in a variety of sensory occurrences. When sensory input comes in, we can reconcile it accurately, inaccurately, or ignore it (neglect.)

How do I capitalize on this clinically? I use context, novelty, imagery, repetition, and priming to update the internal model, prediction, and perception. Repetition, context, and sensory input drive neuroplasticity as it gives the system the opportunity to learn. I’ve said in previous blogs (here.) our goal is to shift from a dominant pattern of danger/pain to a dominant pattern of safety/feeling good. Changing the context can change the meaning. I have a patient who doesn’t like being interrupted when doing a task. She is the caregiver for her mother. When she is mopping the floor and her mother calls for her, she stops what she is doing to go see what she needs. This leads to a flare up. We are working on, among other things, the thought “It’s good that I can help my mother when she needs it.” Or perhaps performing a movement in a different way or for a different purpose may change how it is felt.

Novelty allows for updating of the internal model by augmenting prediction error. I’ll try a modified or new movement through a limited excursion. How does it feel now? Is it tolerable or does it lead to a flare up? Does it need adjusting to grade it down? Can we go further?

Mental practice, imagery, visualization, whichever term you’d like to use, is priming. It’s prepping the system to move. It is a planning committee meeting with the brain. “Hey human, I’m about to do this thing, and it’s going to be okay.” It can be an effective strategy for some to visualize a movement as pain free before performing it, to update the prediction and internal model.

In the opening example, the feeling of tightness isn’t wrong, it just “is”. If I find no movement restriction then I adjust my practice to facilitate the patient’s experience in order to update their internal model. I can contextualize an exercise by stating to them “We are doing this stretch to help you feel more open” or “We’re using the arm bike so you feel less tight.”

Leading with the patient narrative will guide this process clinically.

“…to be truly patient focused, medicine must attend to the predictive process that lies at the basis of symptom perception…” (pg 3 Ongaro &Kaptchuk 2019)

Fardo, F., Auksztulewicz, R., Allen, M., Dietz, M. J., Roepstorff, A., & Friston, K. J. (2017). Expectation violation and attention to pain jointly modulate neural gain in somatosensory cortex. NeuroImage,153, 109-121. doi:10.1016/j.neuroimage.2017.03.041

Flor, H. (2002). Painful memories: Can we train chronic pain patients to forget their pain? EMBO Reports,3(4), 288-291. doi:10.1093/embo-reports/kvf080

Keller, G. B., & Mrsic-Flogel, T. D. (2018). Predictive Processing: A Canonical Cortical Computation. Neuron,100(2), 424-435. doi:10.1016/j.neuron.2018.10.003

Ongaro, G., & Kaptchuk, T. J. (2019). Symptom perception, placebo effects, and the Bayesian brain. Pain,160(1), 1-4. doi:10.1097/00006396-900000000-98882

Zhou, Q., & Verne, G. N. (2013). Microstructural brain reorganization in chronic gastrointestinal disorders. Pain,154(9), 1489-1490. doi:10.1016/j.pain.2013.05.046