Complex sentence: The production of melatonin by the pineal gland is stimulated by darkness and inhibited by light, but scientists do not even understand its bio-chemical role in promoting the sleep process, much less what effect (if any) it has on NPT.
Split into simpler sentences: The production of melatonin by the pineal gland is stimulated by darkness and inhibited by light. However, scientists do not even understand its bio-chemical role in promoting the sleep process, much less what effect (if any) it has on NPT.