@PatJ
For me, white noise-type sounds cause massive problems for my brain (or at least used, I am a bit better now).
The sound of the vacuum cleaner, the sound of a crowd of people cheering at a football match, the sound of a radio tuned in-between stations — these are all examples of white noise-type sounds, and they are all very problematic for my brain.
By definition, white noise contains a random melange of all frequencies, so perhaps trying to process that overloads the brain, leading to noise sensitivity problems.
My hunch is that the sound sensitivity problems (and probably visual sensitivity problems too) of ME/CFS may come from poor or dysfunctional
sensory gating in the brain.
Sensory gating is the
brain's "firewall", which when working normally, actively controls which stimuli from the senses and the environment are allowed into conscious awareness, and which stimuli are suppressed and blotted out of conscious awareness, because they are not relevant to you.
For example, if a healthy person hears a car alarm going off in the street, at first their sensory gating system will allow this sound into consciousness, because it is a new and possibly significant event. However, very soon the sensory gating system will suppress and blot out this sound, because the brain soon realizes this sound is of no importance (except of course if it were your own car alarm).
A normal healthy person will not
consciously hear the ongoing car alarm after a minute or so; their sensory gating system blots it out, and the car alarm sound is relegated to the background of consciousness. A healthy person will thus become completely unaware of the sound after a while (at the conscious level).
But often for ME/CFS patients, an ongoing car alarm sound can become very unpleasant, because the sensory gating system is not working properly, and I think this fails to prevent extraneous irrelevant sounds from reaching and overloading consciousness. So then in ME/CFS, consciousness is overloaded, and you get this horrible feeling of the outside world intruding into your consciousness, intruding into the inner sanctum of your mind.
Sensory gating problems have been found in autism and schizophrenia, and
one small study found sensory gating deficits in ME/CFS.
Why does
very low dose amisulpride (12.5 mg daily) help the sound sensitivity problems / sensory gating deficits in ME/CFS?
I am not really sure. But possibly one explanation is that very low dose amisulpride (but
not normal dose amisulpride) acts to activate the dopamine D2 (and D3) receptors.
Now the dopamine D2 receptor appears to be involved in processes related to focus and attention, and suppression of task-irrelevant behavior, and may act as a filter for unnecessary information. Ref:
1
So by activating D2, as very low dose amisulpride may help reduce brain overload by filtering out extraneous environmental stimuli.