i believe we use it here because most people have come across it in literature on autism. the term, "neurotypical," (NT) is used in a lot of studies and books on autism spectrum disorders. it's much shorter than "persons who do not fall on the autism spectrum."
autistic people present with atypical neurobiology, according to those same studies and books. scientists have been to map the brains of people who have already been diagnosed in order to see what differences (from NT brains) exist in all or most people on the spectrum. testing for these differences is one of the emerging steps in diagnosis.
this atypical neurobiology is one of those things that tells scientists that we're not all faking (i don't think they thought we were, lol). while persons with low functioning autism (LFA) present with more obvious symptoms, high functioning autism (HFA) and Aspergers have historically (and still are) often misdiagnosed.
those with milder "symptoms" are often not diagnosed early or at all. as women often present with milder forms of autism, they are often left undiagnosed. as that atypical neurobiology is present in individuals on all "ends" of the spectrum, if scientists could perform medical tests as part of diagnosing people on the spectrum it'd be an important step forward.
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"Life can be very confusing...filled with good things and filled with bad things. But it's my life...and I have choices." -Amber Brown