Thomas Brandt: Hypothetical Mechanism for CSD (PPV)
May 5, 2015 17:40:31 GMT -5
Michael T likes this
Post by eliuri on May 5, 2015 17:40:31 GMT -5
I had been meaning to start a discussion on this by first putting it all into my own words so as to simplify it. I've not yet been able to do so without making it even more confusing and raising some questions of my own.
So I'll simply cut n paste it for now. And open it for discussion..
Keep in mind that Dr Brandt feels that the key to recovery is by elucidating the mechanism to the patient so that they can accept it. How deeply he goes into it with them, I wish I knew..
He thereby puts forth a possible neurological mechanism for confusion of voluntary and involuntary minor adjustments as well as confusion of self-motion and motion of the environment.
I was struck by that little paragraph about healthy people in state of exhaustion (in blue italics above). When sleep deprived, I do get these very brief little "shifts" where I'd sense self-motion when there wasn't any deliberate movement. Possibly many get this as well when really exhausted, but it's so transient and understandable that we don't take much note of it or fret it much. But if these tiny "shifts" or "decouplings" simply go on and on-- becoming more generalized by phobic conditioning so as to become part of the day by day struggle with feeling balanced-- perhaps we'd enter that alarming state of Chronic Subjective Dizziness.
When I read that online observation by a neurologist, Dr Stryzhak about sleep loss being a major etiologic factor in CSD and dramatic improvement when sleep quality improved, I was reminded of Dr Brandt's observation above about this "decoupling" happening very transiently in states of exhaustion. Seems quite logical then that in prolonged states of sleep deprivation as often happens in depression, PTSD, etc..that this can become more generalized and become a condition rather than isolated episodes.
Hope this makes some sense. It does to me.
PS: I posted Dr Stryzhak's remarks to this forum yesterday in the Triggers and Instigators section.
~eli
So I'll simply cut n paste it for now. And open it for discussion..
Keep in mind that Dr Brandt feels that the key to recovery is by elucidating the mechanism to the patient so that they can accept it. How deeply he goes into it with them, I wish I knew..
Hypothetical mechanism: a disturbance of space constancy caused by decoupling of the efference copy signal.
We are not aware of the subtle self-generated bodily fluctuations or involuntary head movements that occur at upright stance. The environment also appears stationary during active movements, although relative movements between head and surroundings cause shifts of the retinal image.
Space constancy seems to be maintained as follows: The voluntary impulse for initiation of a movement is simultaneously accompanied by an appropriate efference copy signal to make identification possible. Von Holst and Mittelstaedt [27] suggested that the efference copy is used to readjust the perceptual systems (based on previous experience) to interpret incoming sensory information such as results from movement of the observer relative to a stationary environment rather than vice versa. A decoupling would cause the sensory effects of normal postural adjustments (of which we are usually unaware) to be interpreted as arising from either external body perturbations or motion of the surroundings. If there is no efference copy for body motion, e.g., if we move our eyeball by placing the finger on the eyelid, we see illusory movements of the environments, oscillopsia.
The description of the sensation of vertigo in phobic patients (involving involuntary bodily fluctuations and the occasional perception of individual head movements as disturbing external acceleration) can be explained by a transient uncoupling of efference and efference copy, leading to a mismatch between anticipated and actual motion. [1,2]
Healthy people can experience mild sensations of vertigo of that kind without simultaneous anxiety if they are in a state of exhaustion, when the difference between voluntary head movements and involuntary fluctuations becomes blurred.
In the phobic patient, this partial uncoupling Figure 2 could be caused by being preoccupied with constant anxious controlling and checking of balance regulation.
This leads to the perception of sensorimotor adjustments that would otherwise occur unconsciously by means of learned and automatically released muscle activation programs to maintain the upright posture.
From:Thomas Brandt, MD Phobic Postural Vertigo: Neurology June 1996 vol. 46 no. 6 1515-1519
We are not aware of the subtle self-generated bodily fluctuations or involuntary head movements that occur at upright stance. The environment also appears stationary during active movements, although relative movements between head and surroundings cause shifts of the retinal image.
Space constancy seems to be maintained as follows: The voluntary impulse for initiation of a movement is simultaneously accompanied by an appropriate efference copy signal to make identification possible. Von Holst and Mittelstaedt [27] suggested that the efference copy is used to readjust the perceptual systems (based on previous experience) to interpret incoming sensory information such as results from movement of the observer relative to a stationary environment rather than vice versa. A decoupling would cause the sensory effects of normal postural adjustments (of which we are usually unaware) to be interpreted as arising from either external body perturbations or motion of the surroundings. If there is no efference copy for body motion, e.g., if we move our eyeball by placing the finger on the eyelid, we see illusory movements of the environments, oscillopsia.
The description of the sensation of vertigo in phobic patients (involving involuntary bodily fluctuations and the occasional perception of individual head movements as disturbing external acceleration) can be explained by a transient uncoupling of efference and efference copy, leading to a mismatch between anticipated and actual motion. [1,2]
Healthy people can experience mild sensations of vertigo of that kind without simultaneous anxiety if they are in a state of exhaustion, when the difference between voluntary head movements and involuntary fluctuations becomes blurred.
In the phobic patient, this partial uncoupling Figure 2 could be caused by being preoccupied with constant anxious controlling and checking of balance regulation.
This leads to the perception of sensorimotor adjustments that would otherwise occur unconsciously by means of learned and automatically released muscle activation programs to maintain the upright posture.
From:Thomas Brandt, MD Phobic Postural Vertigo: Neurology June 1996 vol. 46 no. 6 1515-1519
I was struck by that little paragraph about healthy people in state of exhaustion (in blue italics above). When sleep deprived, I do get these very brief little "shifts" where I'd sense self-motion when there wasn't any deliberate movement. Possibly many get this as well when really exhausted, but it's so transient and understandable that we don't take much note of it or fret it much. But if these tiny "shifts" or "decouplings" simply go on and on-- becoming more generalized by phobic conditioning so as to become part of the day by day struggle with feeling balanced-- perhaps we'd enter that alarming state of Chronic Subjective Dizziness.
When I read that online observation by a neurologist, Dr Stryzhak about sleep loss being a major etiologic factor in CSD and dramatic improvement when sleep quality improved, I was reminded of Dr Brandt's observation above about this "decoupling" happening very transiently in states of exhaustion. Seems quite logical then that in prolonged states of sleep deprivation as often happens in depression, PTSD, etc..that this can become more generalized and become a condition rather than isolated episodes.
Hope this makes some sense. It does to me.
PS: I posted Dr Stryzhak's remarks to this forum yesterday in the Triggers and Instigators section.
~eli