Short answers, pulled from the story.
Research shows a 44% reduction in the cerebral metabolic rate of glucose and a 25% reduction in oxygen consumption during this state. This drop allows the brain to restore its supply of adenosine triphosphate, which is used for short-term storage and transport of energy.
The suprachiasmatic nucleus serves as the most important nexus for Process C and releases signals that cause the pineal gland to release melatonin at night under direct neural connection. This area shows conspicuous oscillation activity that intensifies during subjective day and drops to almost nothing during subjective night.
Declarative memory improves more during early sleep dominated by slow-wave sleep while procedural memory benefits during late sleep dominated by rapid eye movement sleep. Hippocampal replays of previously encoded neural patterns facilitate long-term consolidation through dialogue between the hippocampus and neocortex.
Sleep duration less than seven hours correlates with coronary heart disease and increased risk of death from that cause. Short sleep duration is also associated with an increased risk of obesity ranging from 45% to 55%.
Historian A. Roger Ekirch notes that segmented sleep began disappearing among urban upper classes in late 17th century Europe. By the 1920s, the idea of first and second sleep had receded entirely from social consciousness due to changes attributed to street lighting and coffee houses.