The present observations, therefore, indicate the patients’ inability to recruit inhibitory and self defensive circuits against sensory repetition. The authors
Is thinking harder than it used to be? Do even little mental tasks seem effortful at times? It might not be that you’re thinking too little; it might be that you’re thinking too much.
The three pound supercomputer we call our brain is a powerful instrument; the most complex thinking instrument ever devised but even it has its limits. It has to pick and choose how it uses its resources. Throw all the stimuli in our environment at it and circuits are going to fry. In order to get by in our complex world – to plan, to organize, to decide, even just to move our bodies – requires that our brains disregard some stimuli and pay attention to others.
At its most basic level it goes like this: your brain picks up a background noise, a glint of light or an odor, checks it out; determines if it’s useful or a threat or nothing special – and proceeds accordingly. If it’s innocuous – the category the vast majority of stimuli fit into – it files it into the “don’t pay attention to” category and moves on to more important things.
At least that’s what is supposed to happen.
We know the brain is not doing so well with stimuli in fibromyalgia. It’s misinterpreting minor stimuli as pain. It doesn’t like crowded, high intensity environments. It often feels that the environment is too cold or too hot or it’s too loud. This hyper-reactive response to pain and other stimuli is thought to be the result of hyped up pain producing and slumbering pain inhibiting pathways.
These researchers wanted to know if a similar breakdown in inhibition was occurring at a very, very basic level. Were FM patients brains turning themselves off when faced with innocuous stimuli or were they remaining stubbornly on?
Many types of stimuli (temperature, pressure, light, odor) exist but these researchers used sound to test FM patients brains. They took 19 FM patients and healthy controls, plopped a magnetic helmet on their heads, covered their ears with earphones and had them watch slides of “Where’s Wally” while they stealthily introduced small sounds and then measured the electrical signals it evoked in the brain. If signals moderate over time the brain has given them a pass and begun using its resources to do other things. If the signals stayed strong the brain essentially was stuck.
They found that the FM patients brains stayed stubbornly fixated on the sounds; no evidence of a normal pattern of “habituation” was seen.
What to make of this? This isn’t the only place FM patients brains fail at inhibition. Perhaps in the same way their brains fail to inhibit pain producing pathways, they also fail to inhibit attention to stimuli. Studies indicate that a network in the brain designed specifically to tone things down called “the inhibitory network”) is er….inhibited in FM.
FM patients are not alone in this. The same pattern of reduced habituation has also been found in migraine and irritable bowel syndrome. This suggests, of course, that chronic pain comes with an extra added component – a distracted, inefficient and easily overwhelmed brain.
Why this is happening isn’t clear. Problems with the thalamus in migraine are believed to cause sensory gating issues in that disorder. Sensory gating refers to a process where the thalamus filters out unnecessary information before it gets to the upper regions of the brain. Without gating or filtering stimuli the brain would be overwhelmed. Both thalamic and sensory gating problems have been found in FM and chronic fatigue syndrome. A recent study, though, suggested that sensory gating might not be the issue.
Recent studies suggest that FM patients brains may simply have trouble encoding or figuring out what to do with a stimulus; i.e. they can’t figure out which basket to put it in.
A 2015 study exploring the processing of non-painful stimuli such as sound and light found that sensory processing cortices of the brain were under-performing. That slowed response in the lower (or outer) brain regions was accompanied by increased activation of the higher brain regions. (A similar pattern is seen in migraine.) That low-high pattern suggested that the higher regions of the brain might be struggling to interpret bad information passed onto them by the sensory cortices.
Reduced blood flows, exhaustion of the sensory cortices or a defensive down-regulation of the sensory cortices by the upper brain regions have been proposed to explain the problems with sensory processing.
- Sensory Overload: Study Suggests Brains in Fibromyalgia Are Being Pummeled With Too Much Information
- Japanese Sensory Gating Study Reveals Profound Cognitive Deficits Present in Chronic Fatigue Syndrome
- Sensory Distress: The Other Side of Fibromyalgia
At its core FM appears to be more a pain and sensory inhibiting disease than a pain producing one. Because the pain pathways in the brain need to respond like lightning to an injury, they’re essentially always on-always ready to engage. The problem in fibromyalgia is that they’re not being turned off.
The same appears to be true with sensory inhibition and with the autonomic nervous system. The brain is not turning off its attention to innocuous stimuli and the parasympathetic nervous system is not jumping in to tone down the sympathetic or “fight and flight” system. Deficiencies in the levels of inhibitory neurotransmitters (serotonin, y-aminobutyric acid) and in the feel-good endogenous opioid system have also been seen. Fibromyalgia is looking more and more like a disorder of blunted inhibition than anything else.
The authors suggest that future studies examine both sensory gating and the very early stages of stimuli processing. Whatever the cause, this and other studies suggest that the problems with processing sensory data extend far beyond the pain most associate with fibromyalgia.
On a personal level the consequences of poor sensory processing and the inability to turn off one’s attention to innocuous stimuli might include such things as problems with following conversations particularly in higher stimuli environments, difficulty concentrating, short attention spans, mental fatigue, the need to get to your cave, etc.
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