I am not sure that any of this means that it's physically impossible for an adult to relearn to wet like an infant. I think it just means that it's physically impossible for an infant younger than a certain age to be potty trained.
wohermiston wrote:In the infant, urination/voiding/micturition is purely a local reflex centered in the lower portion of the spinal cord. In infants two years old and under, involuntary voiding occurs whenever the bladder is sufficiently full. This results in stretch receptors in the urinary bladder wall transmitting impulses to a special area in the spinal cord known as the sacral micturition center. The sacral micturition center responds by causing detrusor muscle contraction of the bladder.
OK, all this means is that in infants, the only working pathway is: stretch receptors -> sacral micturition center -> bladder detrusor muscles.
Between the ages of 2 and 3 as the child's nerves, muscle and brain mature, a special area in the brain gradually develops. Simultaneously, the development of special nerve pathways to that center allows the child to detect a sensation of bladder fullness.
The next stage in the child's maturity occurs when the area in the lower part of the brain, known as the pontine micturition center, develops enough to coordinate sphincter relaxation during voiding.
I'm assuming that the "special area in the brain" mentioned here is the pontine micturition center. It sounds like the new paths are stretch receptors -> mind, and pontine micturition center -> sphincter control muscles (controlled by the mind once the ability to do so develops). But according to the next paragraph, the sacral micturition center is still active at this point ...
During the last stage of development, the young child learns conscious bladder control , and during toilet training, develops the ability to inhibit the bladder center in the lower spine (back). Continence during sleep results from the unconscious inhibition of detrusor muscle contraction by an area in the brain known as the basal ganglia).
The sacral micturition center's reflexive control of the detrusor muscle must still be active at this point, or there would be no need to inhibit it. If the child has learned to do that, we have conscious mind -> detrusor muscles (possibly by way of the basal ganglia), and by this time we also probably have conscious mind -> pontine micturition center -> sphincter control muscles. When the child is asleep, this states that the unconscious mind can also inhibit that detrusor contraction reflex from the sacral micturition center: unconscious mind -> basal ganglia -> detrusor muscles.
So the pathways are now:
1. bladder stretch receptors -> sacral micturition center -> bladder detrusor muscles
2. bladder stretch receptors -> mind
3. mind -> pontine micturition center -> sphincter control muscles
4. mind -> basal ganglia -> bladder detrusor muscles (path 1 is still there, but can be overridden by this)
What I'm getting at is the idea that everything here leads back to either the conscious or unconscious mind. The detrusor contraction reflex doesn't seem to go away; it's just inhibited. So all that has to be done is to teach the mind (conscious and unconscious) not to inhibit the reflex. The mind has also learned to control the sphincters, but that behavior can also be changed. I don't think anything is "hardwired" other than the physical ability of the mind to control the sphincters and to override the detrusor reflex. Just because those nerves are in place and functioning, that doesn't mean the mind has to make use of them if it can accept that it doesn't need to, and relearn the original behavior of not doing so.