Final answer:
Methylphenidate's effectiveness in treating ADHD is due to its action on dopamine transmission, supporting the theory that ADHD involves understimulation of dopamine.
Step-by-step explanation:
The observation that methylphenidate is an effective treatment for attention-deficit/hyperactivity (ADHD) suggests that ADHD results from understimulation of dopamine transmission. Methylphenidate acts as a stimulant that blocks the reuptake of dopamine as well as stimulates its release, which aligns with the theory that ADHD may involve dysfunction in neurochemical pathways, particularly those involving dopamine. The inverse relationship between stimulant medication and calming effects in ADHD patients indicates that balanced dopamine transmission is crucial for controlling impulsivity and attention, which are typically problematic in ADHD.