I'm working on a book called 'Academic Vocabulary in Use' published by Cambridge University Press. There's a lesson suggesting some nouns commonly associated with particular prepositions. Research is one of them and shown to be followed by either 'into' or 'on'. However, in the piece of exercise below, there is only one correct answer:
I went to an interesting presentation on research into aspects of the human brain. The speaker began by saying that the rationale for/behind his investigation was the need to better understand the ageing process.
For those having two correct answers, both would be shown (as in 'rationale for/behind'). It means on can't follow 'research' in this case. After looking up the word 'research' in different dictionaries, I got no explanation for the difference between 'research on and research into. They are even used interchangeably in an example offered by Cambridge Dictionary:
They are carrying out/conducting/doing some fascinating research into/on the language of dolphins.
Then, is there any difference between 'research on' and 'research into'?