Refractory period (sex) after orgasm in which further sexual stimulation does not produce excitement. While the refractory period varies widely among individuals, ranging from minutes to days, most men cannot achieve or maintain an erection during this time, and many perceive a psychological feeling of satisfaction and are temporarily uninterested in further sexual activity; the penis may be hypersensitive and further sexual stimulation may feel painful during this time frame. An increased infusion of the hormone oxytocin during ejaculation is believed to be chiefly responsible for the male refractory period, and the amount by which oxytocin is increased may affect the length of
Period (gene) nucleus as well as areas outside the SCN. Additionally, while Drosophila PER moves between the cytoplasm and the nucleus, mammalian PER is more compartmentalized: mPer1 primarily localizes to the nucleus and mPer2 to the cytoplasm. Familial advanced sleep-phase syndrome known to be associated with mutations in the mammalian Per2 gene. People suffering from the disorder have a shorter period and advanced phase where they go to sleep in the early evening (around 7pm) and wake up before sunrise (around 4am). In 2006, a lab in Germany identified particular phosphorylated residues of PER2 that are mutated in people suffering of FASPS.