Doctor Mizan was a notorious Ktarian exobiologist who was an expert in interspecies reproduction. He considered himself a very sensitive man. His methods of researching his field of expertise were somewhat unconventional.
Mizan attended a psychological conference discussing deep space assignments in 2369. Calling Deanna Troi, "Diane", he talked to her after the reception, explaining that he had heard that she was an empath, then told her that he was doing a thesis on interspecies mating rituals and wished for her to join him in some empirical research.
While on their way back to the USS Enterprise-D, Deanna Troi told Captain Picard, Geordi La Forge, and Data about her encounter with Doctor Mizan, mimicking his voice but not mentioning his name. Geordi recognized Mizan's speech patterns, to Troi's surprise. He explained that the doctor was well known and wasn't merely giving her a line; interspecies mating rituals really was his area of expertise. Data then asked if Troi helped Mizan, to which she answered emphatically in the negative. Data, not understanding the implications of Mizan's request, replied, "I thought it was a topic you were interested in." (TNG: "Timescape")