Neuropsychiatry was the branch of medicine that dealt with mental disorders attributable to diseases of the nervous system. Among the diseases studied in this branch were tri-lobe regression complex, polar-affective disorder, and Dysphoria Syndrome.
In 2377, when Ravoc tried to diagnose Tuvok's illness, giving the first two suggestions, Kadan chided the younger doctor for his speculations, saying, "Neuropsychiatry isn't a guessing game". (VOY: "Workforce, Part II")