Melatonin treatments have been useful in the treatment of

A) adolescents showing extreme delays in the onset of puberty.
B) survivors of trauma that experience persistent flashbacks of the terror.
C) depressed individuals who are in need of increased blood-sugar levels.
D) disturbed sleep-wake cycles in blind people who lack light perception.

Answer: D
Rationale: People with blindness due to retinal damage cannot send light signals from the retina to the SCN and pineal gland. Thus, their circadian rhythms cannot synchronize to day-night cycles. This can be adjusted using doses of melatonin.