With melatonin activity blocked, the ability of the fish to form new memories was drastically improved, even at night.

We suspect that suppression of melatonin may be involved in the effects of light at night on depressed affect.

Supposedly warm milk contains melatonin and trytophan and so helps induce sleep, but in fact, a glass of milk doesn't contain enough to have any effect. But it's still a soothing drink.