Adolescence is a critical time period when physical, sexual, cognitive, emotional, and social maturation occur (see [1]). While there has been a tendency to define adolescence by endocrine events such as puberty, it actually involves changes in the brain that may occur in a separate time frame from the endocrine events associated with puberty [2]. During adolescence, there are major changes that occur in brain morphology including the selective removal of 40-50% of the synapses (i.e. synaptic pruning) in cortical and subcortical brain regions [3-6], continued myelination of cortical regions [7-9] and dramatic changes in neurotransmitter levels [10-15] as well as receptor levels and their sensitivity [4, 12].
