Here’s an interesting study out of the University of Washington: Shots of growth hormone releasing hormone (GHRH) resulted in significant improvements in cognitive performance compared with placebo. This occurred in people with mild cognitive impairment as well as in healthy individuals.
Growth hormone is normally secreted mostly during deep (Stage 3) sleep. It’s known that Stage 3 sleep diminishes gradually as one gets older. If you also accept that fact that the incidence of obstructive sleep apnea increases significantly as you get older (62% in people over 65 in one study), then it makes sense that giving something that stimulate growth hormone will improve memory and cognitive abilities. Deep sleep is when your muscles become more relaxed, and more prone to obstructed breathing. Whether these obstructions lead to true apneas or micro-arousals, the end result is disrupted sleep taking you out of Stage 3 sleep.
You’ll see more studies linking sleep-breathing disorders and dementia in the coming months and years.