The adolescent brain is in a critical period of development, with the prefrontal cortex not fully mature until around age 25. Nicotine exploits this window — it binds to acetylcholine receptors, flooding the nucleus accumbens with dopamine and creating a powerful reward signal that the developing brain is ill-equipped to resist.
Longitudinal imaging studies show that even brief nicotine exposure during adolescence produces measurable changes in white-matter connectivity and reduces the density of dopaminergic receptor sites, making the brain permanently more susceptible to addiction.