If you know a teen-ager who is staying up later than they used to, don't be alarmed. Later bedtimes may be a good sign that adolescents are eating right and that their brains have reached a significant stage in development, according to a UC Davis researcher. Mari Golub, behavioral neurobiologist and associate adjunct professor at UC Davis recently presented her findings from studies of zinc deficiencies in adolescent monkeys at the Society for Neuroscience annual meeting in San Diego. The shift in sleep patterns usually begins in the early teens and is one of the most dramatic behavioral changes in adolescents. Golub revealed a link between zinc deficiency and slower skeletal and brain maturation during adolescence. A diet that relies heavily on processed foods and little meat or fish can be lacking the sufficient quantities of zinc required for a healthy teen. Malnourished teen-agers may have additional behavioral problems. Monkeys are the only animals known to go through an adolescent stage like humans and because of this, they offer a valuable opportunity to look into the problems of adolescent neurobiology.