Why Norepinephrine Reuptake Inhibitor Medications Have Some Effect on Dopamine
If you strip off the outer insulator of your Cat5 network cable (used on home networks if not using wireless), you'll see several pairs, two wires each, twisted together. Twisting wires together insulates them from "cross talk" (unwanted signals called noise) from other wires wrapped in the same outer insulation of the cable.
According to a theoretical neural model proposed by neuroscientists, the brain runs parallel dopamine and norepinephrine neuron "wires" to destinations that require multiple neurotransmitters to activate and maintain attention and focus functions in demand. The two paths, one for dopamine and the other for norepinephrine, have limited insulation between them allowing for a degree of "cross talk." Norepinephrine reuptake inhibitor medications cause some dopamine reuptake inhibition as a result.
Attention and focus functions are equally dependent on dopamine and norepinephrine among a slew of other neurotransmitters that evidently play lessor roles.