1) Neuroscience of Sleep - https://en.wikipedia.org/wiki/Neuroscience_of_sleep
2) Sleep Epigenetics - https://en.wikipedia.org/wiki/Sleep_epigenetics
3) Sleep deprivation - https://en.wikipedia.org/wiki/Sleep_deprivation
4) Familial natural short sleep - https://en.wikipedia.org/wiki/Familial_natural_short_sleep