What symptom is commonly treated with methylphenidate?

Methylphenidate is commonly used to treat attention-deficit hyperactivity disorder (ADHD), which is characterized by symptoms such as inattention, hyperactivity, and impulsivity. This medication is a central nervous system stimulant that works by increasing dopamine levels and norepinephrine in the brain, which helps to improve focus and self-regulation in individuals diagnosed with ADHD. This is why the correct answer is associated with ADHD, as it directly addresses the symptoms and behavioral issues prevalent in this condition. Other options like depression, epilepsy, and schizophrenia are typically treated with different classes of medications, such as antidepressants, antiepileptics, and antipsychotics, respectively.