Dr. Richard A. Friedman, psychiatrist and a contributing opinion writer on NYT writes about the neuroscience behind rocking the baby to sleep. He also points out the research that proves rocking to sleep works for adults too.
Is it the physical movement of rocking or the repetitive sound waves of the lullaby that induces sleep? It could be a combination of both activities.
Many years ago, I recall a friend in my dorm saying that her mother used to gently make zeroes on her head which made her fall asleep almost instantaneously. It was the boring repetitions that had my friend fall asleep. I have tried this with both my kids and they only get mildly irritated.
I have personally experienced deep sleep on a hammock by the beach in bright daylight. It tells me that there may be some truth behind this research.
Friedman writes on NYT : The researchers found that rocking caused the subjects to fall asleep more quickly and increased their amount of slow-wave deep sleep, a phase of sleep that is associated with feeling refreshed and rested upon waking. They also experienced fewer periods of spontaneous arousal. This was true despite the fact that they were already good sleepers. Rocking did not affect the duration of rapid eye movement or dream sleep.
A reader comments that he recalls seeing adult size rocking beds in Shaker village of New England. Adults took to the rocking bed in this village, when they were towards their end of life.
Now, if you do believe that rocking may induce deep sleep or you are not getting much sleep and are in the market for that ideal bed or mattress there is a company that makes the rocking bed. The rocking bed is at $3450 for all sizes, steep maybe- but in my opinion cost of lack of sleep is too much- dementia, irritability, anxiety among many others.