There must be a word, and it’s not deja vu, for when you smell new mown grass and suddenly are projected back into the past at your grandmother’s cottage and you briefly experience the green grass and the rain barrel, etc. jThis is what Proust said happen to him when he ate a certain teacake and it started him writing A la recherche du temps perdu, or ABOUT THE SEARCH OF THE TIME LOST. What is this word in psychology? They must have one because they have one for everything else, such as hypnopompic and hypnogogic for just waking up and just before going to sleep, respectively.
The only term I have heard for this is “involuntary memory.”
The Le Monde newspaper talks of ‘olfactive memory (also known as Proustian syndrome)’
http://www.lemonde.fr/article/0,2320,dos-3592-83803-QUO-1-2720-,00.html
I’ve also seen Proustian Effect and Proustian Phenomenon.
let’s try this again:
http://www.lemonde.fr/article/0,2320,dos-3592-83803-QUO-1-2720-,00.html
The teacake was, specifically, a madeleine; and Merriam-Webster gives to that word a secondary meaning: “one that evokes a memory”, of course derived from Proust.
How about a “Marcel Moment”?
I LIKE it!
I’ve always used Frank Herbert’s word from Dune–adab, the demanding memory that comes of itself. This is obviously not standard English (though I still maintain the hope that it will be adopted), but it works well enough for me. 
In analogy with déjà vu (“already seen”) and déjà entendu (“already heard”), I nominate déjà flairé (“already smelled”). Of course the first two normally refer to a false feeling that you have already experienced something, whereas I think what you’re describing is something that triggers a real memory.
How about perdu mais ici, meaning lost but here (nevertheless) when this experience happens. Or a
madelainesque experience. I was sure there was a word derived from Greek or Latin or both in the psychology encyclopedia.
‘perdu mais ici’ is not very idiomatic in French. However, ‘madelainesque experience’ has a certain cachet. I agree with you that there must be a term, derived from Latin or Greek, describing this psychological state. I’ve studied both languages a long time ago; tried to search the recesses of my memory, but to no avail.
From my psych book (Sdorow):
Episodic memory: the subsystem of declarative memory that contains memories of personal experiences tied to particular times and places.
Context-dependent memory: The tendency for recall to be best when the environmental context present during the encoding of a memory is also present during attempts at retrieving it.
Actually, the first would be more where this type of memory is stored, while the latter would be how it is best retrieved. Therefore, your mind stores in its memory banks an episode, such as being back at grandma’s cottage, and the memory is triggered by an environmental aspect present at the time - the cut grass.
The term I was looking for:
MNEMOSYNE