identify the speaker and context / meaning of the following quote, "i got old jane gallagher on the brain again"

The speaker is Holden Caulfield, the narrator of the cult novel "The Catcher in the Rye", by recluse writer J. D. Salinger. Holden is a teenager who escapes a boarding school in order to spend a few days in New York, where he interacts with strangers and experiences new things.

Meaning and context: When Holden says he has Jane Gallagher on the brain again, he means he cannot stop thinking about her. Jane is a girl whom he deeply admires, but at the same time he never makes the first move. When he learns his roommate has a date with Jane, he is assaulted by jealousy. The complete quote goes like this:

"All of a sudden, on my way out to the lobby, I got old Jane Gallagher on the brain again. I got her on, and I couldn't get her off."