Researchers have used heat, electricity, chemicals, and pressure to evoke pain in FM patients and controls, and in every study people with FM have felt pain at lower levels of stimulation than healthy controls.
People with Fibromyalgia report they have problems with sensitivity to stimuli in general. This suggests FM is not just a pain condition, but that the FM patient’s entire sensory apparatus is a bit out of kilter
One study finding reduced electrical responses in the sensory cortices of the brain to sounds in FM suggested that this part of the brain was, oddly enough, under-responding to stimuli, not over-responding.
This is a different pattern than has normally been seen with pain
Other studies show that the insula – the part of the brain that integrates sensory inputs from around the body and determines how much attention should be paid to them – is activated in Fibromyalgia patients more than expected. One of the sensations the insula evokes is the sensation of “unpleasantness”.
The findings suggest that a slow initial processing of stimuli in the lower brain regions is followed by a greatly accelerated one in the higher brain regions.
Altered fMRI responses to non-painful sensory stimulation in fibromyalgia patients: Brain response to non-painful multi-sensory stimulation in fibromyalgia (no link)
These researchers used functional MRI to assess the brain functioning of FM patients when they were presented with non-painful sensory stimuli such as sound, light, and touch. Pain levels and levels of sensory unpleasantness were assessed.
They found significantly reduced responses to the sensory signals when they first hit the brain (sensory/auditory cortices, hippocampi, basal ganglia) and increased activity in the higher parts of the brain – the insula – that integrate both pain and sensory signals together.
Distressingly Slowed Processing
The study also found that the levels of unpleasantness associated with non-painful stimuli – the sensory overload effect – was associated with and appeared to be coming from slowed initial brain response at the auditory and visual cortices. Somehow the brain’s inability to process normal sensory signals at a normal rate was causing distress.
The fact that the more pain the FM patients were experiencing the more bothered they were with the stimuli suggested that the pain and sensory problems are connected in FM.
The insula is believed to be a center of “interoception” and an important regulator of homeostasis in the body
In humans, the insula participates in higher brain functions such as the conscious awareness and assessment of how one’s body is functioning.
The study suggests that the problems with over-stimulation in FM are, ironically, caused by reduced, not heightened sensory processing. Why the brains of people with Fibromyalgia are slower at processing sensory signals is unclear, but three ideas stick out:
- Reduced cerebral blood flow in some parts of the brain could play a role.
- The areas of the brain in question could be so depleted of resources (perhaps because of reduced blood flows) that they’re simply not functioning well.
- The higher regions of the brain could also be having so much trouble integrating the various sensory inputs that they’re shutting down the pipelines to them in order to save themselves.
Migraine, Fibromyalgia, and Chronic Fatigue Syndrome
Both sensory dysregulation and problems with blood flows may be occurring in all three disorders.
A similar under/over-activation pattern (in a different part of the brain) occurs in migraine. Decreased pre-activation of the cerebral cortex in migraine is associated with increased hyper-responsiveness of the visual cortex.
Using transcranial direct current stimulation (tDS) to increase the pre-activation of the visual cortex reduced the hyperesponsiveness in the visual cortex itself, and, more importantly, migraine frequency, and the length of migraine attacks in one study. It also reduced the need for medication. This suggests that “simply” stimulating one part of the brain can cause other parts of the brain to calm down.
Could sensory relay and blood flow problems characterize many so-called functional disorders?
One Fibromyalgia study found that simply adding warmth to a painful area reduced pain by about 20%for an hour or so in about 30% of patients. Massage therapy actually gets the highest effectiveness rating of any treatment on PatientsLikeMe for Fibromyalgia.
This isn’t the first FM study to find problems with processing sensory information. Check out Sensory Overload: Study Suggests Brains in Fibromyalgia Are Being Pummeled With Too Much Information
Slowed processing of sensory signals and increased activity of the insular cortex in the brain contributes both to the pain and stimuli issues found in Fibromyalgia.
The cause of the slowed sensory stimuli processing is not clear, but could result from reduced blood flows, exhaustion of the areas processing the signals, or a deliberate down-regulation of these areas by higher brain regions that are having trouble integrating sensory inputs from across the body.