Psychological processing in chronic pain: a neural systems approach

Abstract

Our understanding of chronic pain involves complex brain circuits that include sensory, emotional, cognitive and interoceptive processing. The feed-forward interactions between physical (e.g., trauma) and emotional pain and the consequences of altered psychological status on the expression of pain have made the evaluation and treatment of chronic pain a challenge in the clinic. By understanding the neural circuits involved in psychological processes, a mechanistic approach to the implementation of psychology-based treatments may be better understood. In this review we evaluate some of the principle processes that may be altered as a consequence of chronic pain in the context of localized and integrated neural networks. These changes are ongoing, vary in their magnitude, and their hierarchical manifestations, and may be temporally and sequentially altered by treatments, and all contribute to an overall pain phenotype. Furthermore, we link altered psychological processes to specific evidence-based treatments to put forth a model of pain neuroscience psychology.

Keywords: Allostatic load; Amygdala; Anhedonia; Anterior cingulate cortex; Anxiety; Attention; Behavior; Brain; Catastrophizing; Chronic pain; Cognition; Depression; Fear; Hippocampus; Imaging; Insula; Interoception; Motivation; Neurocircuit; Nociception; Parietal cortex; Perception; Prefrontal cortex; Psychology; Reward.

Figure 1. Neural Pathways involved in Pain

The figure conceptualizes brain regions involved in sensory and emotional processing of chronic pain. DRG = dorsal root ganglion, SpV = spinal nucleus of trigeminal ganglion (dorsal horn), AT = anterior thalamus; VPM = ventroposteromedial thalamus

Figure 2. Physiological and Psychological Systems that integrate Pain Behaviors

Physiological systems including stress-related hormones and brain systems that control these, sleep-wake processes as well as those sensory systems that respond to tissue damage clearly contribute to alterations in neural networks. Some physiological changes can be either objectively measured or reasonably easily interpreted (e.g., pain intensity). Psychological systems to so in a less obvious manner until a forme fruste behavioral aberration is present. These changes alter our normal network profile that is dependent on genetic, epigenetic and live experience to modify behaviors. Clearly the two processes in pain are integrated and result in aberrant behaviors.

Figure 3. Pain, Psychological Processes and Behavioral Consequences

Following a pain (a sensory or emotional experience to an actual trauma or perceived bodily threat), a number of psychological processes including those listed here are involved in response. These change processes may be resilient or resistant to the inciting events or become altered as noted in examples of behavioral consequences. Additionally, alterations in one system may have consequences in another. The understanding of how these systems interact and can be targeted will have significant implications on treatment approaches.

Figure 4. Pain Progression – Complex interactions leading to maladaptive changes and system failure (allostatic load)

The upper part of the figure shows the loss of energy in a bouncing ball – after a while all potential/kinetic energy (height, h) diminishes over time. The comparison is similar for chronic pain (middle figure) where normal function evolves to diminished normal or increased aberrant or abnormal function. Multiple changes in brain function (altered networks, see Figure 6) occur over time following injury as shown in the lower part of the figure where there is a sequential alteration in function (physiological and psychological) that eventually leads to maladaptive changes and system failure.

Figure 5. From Brain Systems to Psychotherapeutic Targets

A network of brain systems underlies alterations in psychological function in the chronic pain state. This figure shows specific psychological treatments that target alterations in psychological function across brain systems.

Figure 6. Altered Networks

The figure shows a model of brain network changes as a consequence of a stimulus in a healthy subject (top) and the same networks in response to pain (bottom). Using tissue damage as an example of a pain stimulus (viz., surgery), there are alterations in sensory inputs (Primary Integrators) that produce changes in Secondary Integrators (these may initially be adaptive e.g., enhanced modulation of pain by higher cortical centers such as the anterior cingulate cortex (See Figure 1), but eventually become maladaptive through individual networks or across networks resulting in altered behavioral responses.

Figure 7. Treatment Paradigm – Neural Network-Directed Decreases in Allostatic Psychological Load with Readout Measures (from (Borsook and Kalso, 2013) with permission)

The figure shows containment and normal adaptive processing to various stressors (noted below in the key); these normal responses are balanced and adaptive (adapt to `homeostatic set-point') over time. In chronic pain responses may be exaggerated (out of `homeostatic set-point') or inhibited. In a multidimensional biological process such as chronic pain each of these stressors may affect an individual differently as represented in the `bar-code' noted on the right.