Does how you spend your time during adolescene determines how your brain develops?
In adolescence, the brain starts creating synapses at a rapid rate. Synapses are wires, so to speak, that are located in the prefrontal cortex of the brain. The synapses then communicate thoughts and ideas to the other parts of the brain.
As each skill is used, the brain develops increased synapses to send messages to the prefrontal cortex. Therefore, if an adolescent plays sports more, the prefrontal cortex may get more information about sports. If the adolescent watches more television, the prefrontal cortex may get more information about pop culture. Moreover, as time goes on, the brain starts covering underutilized synapses with a protective coat called myelin. Myelin serves as an insulator and protects those synapses are not being used. So, yes, the activity engaged in while an adolescent shapes further brain development.