Adenosine is a chemical in the brain that causes sleep pressure. From the time an individual wakes up, adenosine begins increasing in concentration and continues to do so throughout waking hours. When concentrations of adenosine peak, individuals face “an irresistible urge for slumber” (27). It takes eight hours of natural sleep to purge adenosine from an adult body. Thus, individuals that sleep less than this recommended amount will carry adenosine concentrations throughout the day, making them feel sleepy. This sleepiness balance rolls over if individuals continue to not get enough sleep and eventually leads to chronic sleep deprivation.

The amygdala is the structure of the brain that controls strong emotions, including the flight-or-fight response. Sleep-deprived individuals often act irrational because of the decoupling between the amygdala and the prefrontal cortex. Walker notes that, “we cannot rein in our atavistic impulses—too much emotional gas pedal (amygdala) and not enough regulatory brake (prefrontal cortex)” (147).

Sleeping during two periods over the course of 24 hours characterizes the biphasic sleep pattern. Anthropological, biological, and genetic evidence support that this is our “natural pattern of slumber” (70). Modern society disrupts our ability to follow this sleep pattern. Divorcing humans from this innate practice might be a contributing factor in why our lifespans are shortening.