New Technique Shows Promise as Adjunct In Chronic Pain Management
Chronic pain is one of the most difficult problems to treat, especially when central sensitization (CS) has occurred. There are a number of articles in the literature that suggest that poorly managed pain leads to CS, which worsens with anxiety and lack of sleep.1,2
Long-term potentiation (LTP) causes a pain circuit to become hyperaroused. It literally becomes “stuck” in a high-volume firing state. LTP maintains pain even after an injury heals, causing pain to become a chronic self-perpetuating illness.
It is important to differentiate CS from central pain syndrome, which was formerly known as thalamic pain syndrome or Dejerine-Roussy syndrome. Although central pain syndrome involves both CS and chronic pain, it is further characterized by actual damage to the central nervous system, through spinal cord ischemia or stroke, for example. The chronic pain cases used in this presentation involve only CS.
New Research Focuses on Brain Plasticity
Fortunately for the millions of patients who suffer from chronic pain, pioneering research is driving the development of new treatments focused on brain plasticity, with the more promising developments based on modulating activity in the limbic system. Since maladaptive brain plasticity creates chronic pain (ie, CS), it makes sense to address this process directly.
Stress and the release of stress hormones play a role in the development of CS because they generate hyperalgesia and chronic pain through both peripheral and central mechanisms. Peripherally, catecholamines secreted by the adrenal medulla cause hyperalgesia. CS causes spinal neuroinflammation, decreasing the mechanical nociceptor threshold, and increasing sensory hypersensitivity and long-lasting anxiety-induced hyperalgesia.3-5
The various components of CS are muscle pain, dyesthesia, hyperpathia, allodynia, shooting pain, circulatory pain that mimics circulatory insufficiency, and peristaltic pain in the visceral organs,6,7 which makes this a challenging disorder to treat. Many people who have CS are sensitive to bright lights, loud noises, medications, temperature, and may have hypersensitivity to touch and mechanical pressure.8
Role of Limbic System
Recent studies are clarifying the role that the brain and limbic system play in the experience of chronic pain.9-11 A clear example of maladaptive plasticity in the brain is phantom limb pain, where the physical pain and emotional trauma of an accident has created a memory circuit in the brain that continues to register pain signals from a limb that is no longer attached to the body.12
It is well established that trauma creates potentiated or sensitized neural circuits in the limbic system, especially the amygdala, that perpetuate problematic emotions.13,14 The amygdala receives sensory input of all types, including nociceptive information in the latero-capsular portion of the central nucleus.15 In the amygdala, emotional feelings of threat or helplessness are integrated with nociceptive pain sensations. Together, this establishes neural memories of fear and pain, which can lead to the development of chronic pain, as described previously.15
This subconscious helplessness can promote maladaptive plasticity and an aberration of memory.16,17 The pain memory circuits fire and the patient feels pain as if the injury is still there, much like the amputee with phantom pain.
Attention Deficit Disorder Treatment Used for Pain
The Bio-Acoustical Utilization Device (BAUD, Insight NeuroSystems, Olathe, KS) is a sound-based treatment that was originally developed for the treatment of attention deficit disorder (ADD)/attention deficit hyperactivity disorder (ADHD) and was subsequently discovered to be useful in the treatment of stress and negative emotional symptoms.18 Initial functional magnetic resonance imaging (fMRI) research suggests it works by disrupting reorganization of long-term processing memory circuits in the limbic system.19
Since BAUD has been successful in reducing negative emotional perceptions, we reasoned that it might have a similar effect on pain due to the close relationship of those circuits in the amygdala. If so, we hypothesized that it could be a safe and effective adjunct treatment for chronic pain.20 To test that theory, we tested the device on 3 patients with chronic pain.
How it Works
BAUD is a FDA-approved class II biofeedback device that emits 2 adjustable frequency tones that intersect to create a third binaural beat, producing an acoustical neuromodulation (Figure 1). This stimulation appears to affect the amygdala and the hippocampus of the limbic system by theta wave stimulation. Theta activity has been established as essential to both the consolidation and reconsolidation of all memories, including pain memories.21,22
The BAUD instrument produces a square wave, perceived by the patient to be unpleasant. The sound resembles that created by a swarm of angry bees. Kumar et al postulated that adverse sound has an arousal effect on the amygdala through the medial geniculate nucleus via the thalamus23 (Figure 2).The result creates both a stimulation and temporary disruption of a sensitized circuit, which stimulates a neural ‘reset’ courtesy of the brain’s ability to self-regulate. Research has shown that once a memory circuit is activated, it can be modified.24
During treatment, the patient is given earphones and asked to set the volume controls to a moderately loud level in each ear. The patient is instructed to focus on the area(s) of pain. The pitch of the sound is adjusted such that the person feels the sound connect to the body’s location of his or her pain. For example, if the person’s pain is in the shoulder, the sound feels like it resonates there.
Therefore, in the first step—tuning the base frequency—the patient will feel some change in the pain sensation. Even though the stimulation is to the brain, it is felt in the connected body area. This has most often been described as a feeling of resonance or vibration likened to a slight stimulation, or intensification of the pain, or other individual sensations. But note that this is a neurological response to the sound input, so the actual sensation varies with individuals. In this step, we are looking for any change in sensation that indicates the chosen frequency is affecting the pain circuit. This type of attentional modulation has been shown to increase neural activity of pain circuits.25