These synonyms come from NCBI, not NIF and choosing various species from the Preferences pop-up box can control your output. Mammals are the default, but any other combination of species can be chosen. Note, you can save your species preferences by logging into NIF using either your Google or Yahoo mail accounts.
Choosing all of the possible species, then searching again, increased the synonyms brought back for the search.
With the release of NIF 3.6, we have implemented a strict search option. Strict search will focus the search query to columns specifically weighted as more informative. In this way, you are able to remove results that do not necessarily contain the exact term you are searching for. Once you perform a search, to enable to strict search option click the check box shown below. In this example we have searched for schizophrenia. Notice that without the strict search enabled, we receive results that contain closely related, stems of schizophrenia such as "Schizo" in the top results.
NIF Version: 6.2
Ontology Version: 2.9
Level 2.5/3.0 Resources: 239
Registry Entries: 12,598
Total Records: 829,679,866