amygdala: part of the limbic system in the brain, which is involved with emotions and emotional responses and is particularly active during puberty
dopamine: a neurotransmitter in the brain that plays a role in pleasure and the reward system; increases in the limbic system and later in the prefrontal cortex during adolescence
frontal lobes: the parts of the brain involved in impulse control, planning, and higher-order thinking; still developing in adolescence
limbic system: structures in the brain (including the amygdala) that involve processing emotional experience and social information and determining rewards and punishments; develops years before the prefrontal cortex
melatonin: sleep hormone whose levels rise later at night and decrease later in the morning for teens, compared to children and adults
myelination: insulation of neurons’ axons with a fatty substance (myelin sheath) that helps speed up the processing of information; myelination starts to increase in the prefrontal cortex during adolescence
prefrontal cortex: part of the frontal lobes, involved with decision making, cognitive control, and other higher-order functions; prefrontal cortex develops further during adolescence
serotonin: “calming chemical,” a neurotransmitter in the brain involved with the regulation of mood and behavior; serotonin levels increase in the limbic system during adolescence
synaptic pruning: connections in the brain that are not used much are lost so that other connections can be strengthened; this pruning happens with prefrontal cortex connections in adolescence
major depression: feelings of hopelessness, lethargy, and worthlessness that last two weeks or more
suicide: the act of intentionally causing one’s own death
suicidal ideation: thinking about suicide, usually with some serious emotional and intellectual or cognitive overtones