I was having some trouble at the end, so will finish here... when the incorrect pathways to unwanted muscles are not used, they become dormant in a way. I suspect what happened to you was that they started being used again after 6 months. Not sure why. I tell my patients at discharge that they should continue to do the exercises 3x/week for another few months, then can stop altogether. And I also say, if something (smile?) gets worse later, you can restart the pertinent exercises again until control regained. The feedback that I've received from old patients is that they kept what they had gained and did not have to keep doing the exercises on an ongoing basis.
There was a research study done at Sunnybrook Health Science Centre in Toronto (Ross, Nedzelski, et al), published in 1991, that showed good results from facial NMR over a 1 year period (one group=control, one group=mirror feedback, one group=mirror + surface EMG). Both feedback groups made significant progress compared to control. All subjects were 18 months or longer post-onset (so that spontaneous recovery as reason for progress could be ruled out). The interesting thing about this is that they published a follow-up study that looked at the subjects 3 years later (they had not continued facial NMR or home exercises) and this showed that they did not significantly backtrack. This is the only study of it's kind, but it is encouraging in that it indicates you do NOT have to keep exercising daily to keep your facial palsy condition from regressing. The gray area is how long do you actually have to do this retraining? 6 months?, a year? 2 years? That is question I don't yet have an answer to. I just discharged a patient who got her facial palsy from TBI (traumatic brain injury from ATV accident) 2 1/2 years before referred to me. Her palsy had characteristics of a peripheral nerve injury, not a central one, which is important in prognosis . Her smile was about 75% of normal at start, after 5 months of therapy, was 100%. She did her exercises diligently, and in this case it took 5 months.
Hope this sheds some light. Take care,
Todd