Within my experiences of depression, and hearing voices i.e Schizophrenia they both started within my enviroment with the onset of first rejection,gaslighting,emotional abuse and isolation.
That’s how this starts.
SZ can cause those. I self isolated when my SZ symptoms started, I was hearing voices.
More TI stuff 
No, gaslighting and TI are not the same, that would be like saying Doxxing is Bio Polar!
I had two factors preceding my symptom onset, amphetamine abuse and emotional trauma. Hard for me to determine which or both factors caused the onset of my SZ. I guess technically it could have involved another factor, but you consistently hear about “social defeat” preceding the onset of SZ in so many cases…
What does TI mean?
It’s a conspiracy theory. Basically it says that 100,000’s of people are all involved in making your life miserable in some way.
When in fact you just have paranoid schizophrenia.