In a West Saugerties, New York, house dubbed by its tenants “Big Pink,” Bob Dylan and a band who later named themselves The Band gathered daily for six months in 1967 to mess around with American music, and recorded the results. Dylan was recuperating from a motorcycle crash, and the Big Pink basement was his recovery room. Among the many songs generated down there are some of Dylan’s deepest: “Tears of Rage,” “This Wheel’s on Fire,” “You Ain’t Goin’ Nowhere” and the title song of Todd Haynes’ I’m Not There — a track that, until now, has never been officially released.

Perhaps the most mythical of all Dylan’s unreleased gems, “I’m Not There” is an absolute mystery. A long, extended meditation built around a four-chord acoustic-guitar strum, it was recorded only once by Dylan and never finished or revisited. Lyrics and lines float by, some discernible, others elusive. Among Dylan fanatics, it’s a kind of Rosetta stone because it seems to capture the artist in the midst of his creative process. The magic of “I’m Not There” is its lack of definition. Critic Greil Marcus devotes five pages of The Old, Weird America to the song, writing that “?‘I’m Not There’ is barely written at all. Words are floated together in a dyslexia that is music itself, a dyslexia that seems meant to prove the claims of music over words, to see just how little words can do.”

True, but what’s most engaging about the song is the revelation it provides about Dylan’s creative process. Unlike many outtakes and bootlegged tracks, “I’m Not There” feels like someone channeling, speaking in tongues, handling snakes, conjuring out of the mist the blueprint of a song. In The Old, Weird America, Marcus quotes Band guitarist Robbie Robertson’s wonder at Dylan’s method: “He would pull these songs out of nowhere. We didn’t know if he wrote them or if he remembered them. When he sang them, you couldn’t tell.” No recording better illustrates Robertson’s point than “I’m Not There.” There’s something going on inside the song, but you’re not sure what it is. The narrator might be dead, and contemplating his relationship with an unnamed lover. He might have abandoned her. He seems sorry for something. Or angry.

Bootleg copies of the song have long been available, but until the arrival of the soundtrack to I’m Not There this month, it had remained undergound. For that reason alone, Dylan fans have reason to applaud Haynes and his music supervisors, Jim Dunbar and Randall Poster. With the release, a better picture of the circuitous route the song took from basement to film title is revealing itself. The widely bootlegged version has been tainted by engineers attempting — and failing — to liven the song. The true recording has been buried. “So it’s never been heard — except by a rarefied few folks, obviously — in its pure form, as it was straight to tape,” says Dunbar. “It’s like a field recording, almost.”

Among those rarefied few who heard the original recording was Neil Young, who, it turns out, possessed the most pristine and unadulterated copy of the so-called Basement Tapes, which he received from his longtime engineer Elliot Mazur. Mazur was assigned by Dylan’s manager, Albert Grossman, to transfer the original tapes for storage, and ended up dubbing a copy for himself. A few years later, Mazur duplicated them again with the intention of giving Young a copy, but accidentally gave him the original transfers, which sat in Young’s archives until they were unearthed a few years ago. With the song’s release on the fantastic I’m Not There soundtrack, those not exposed to the bootleg can finally attempt to discern meaning for themselves — if they dare.

Randall Poster would rather not. “I don’t approach it that literally, really,” he says. “To me it’s about a kinetic feeling, a song that brings me into the realm of ‘Positively Fourth Street.’ As a kid, the first time I heard that song, it taught me that there’s something that goes on between men and women that I hadn’t experienced yet, but that I was so hungry to experience. I sort of get that same feeling from ‘I’m Not There.’ In a sense, it speaks to a potential intimacy between people — it clearly exists in a sort of divine realm.”

“The song subtly builds,” adds Dunbar. “For me, it’s very intense. It starts off and you think, ‘Aw, there’s not much going on here.’ But by the end of it, it feels like an epic.” Asked what he thinks the song means, Dunbar pauses. “Uh, I don’t know. It’s, uh, definitely someone with . . . uh . . . uh . . . great regret.” Exactly.