Few experiences figure as prominently in summer memories as naps in hammocks. Nearly everyone has a story of a summer snooze in a hammock that was a singularly refreshing rest. Recent research shows that those good sleeps have a physiological basis.
Scientists have found that people in a gently swaying bed, one that mimics the motion of a hammock, fall asleep faster. When we're gently rocking we also sleep more deeply -examining the brain waves of sleeping people showed this - which explains why nothing seems as refreshing as a nap in a hammock on a fine summery day.
Bayer and his colleagues (reference below) suggest that "sensor stimulation associated with a swinging motion exerts a synchronizing action in the brain that reinforces endogenous sleep rhythms. These results thus provide scientific support to the traditional belief that rocking can soothe our sleep." The researchers continue, "The use of rocking to soothe sleep thus belongs in our repertoire of adaptive behaviours in which a natural mechanism of sleep (thalamo-cortical synchronization) has been harnessed in the simplest manner since immemorial times." Whew. Until after my nap, that's a lot to absorb.
It seems that once again, we were doing the right thing before we knew why it was best. All the baby rocking and hammock lounging our species have done over the millennia have been a great and natural way to restful sleep.
Laurence Bayer, Irina Constantinescu, Stephen Perrig, Julie Vienne, Pierre-Paul Vidal, Michel Muhlethaler, and Sophie Schwartz. 2011. "Rocking Synchronizes Brain Waves During a Short Nap." Current Biology, vol. 21, no 12, pp. R461-R462.