Sex has always come with a soundtrack. And that soundtrack has become part of our collective erotic imagination. "Almost everyone in the world knows what the 'Wakka Chikka Wakka Chikka' represents," explains the blurb for a 2009 compilation album of porn music. Despite featuring literal-minded tracks such as "Brain Wank," the playlist was not meant to seduce. It's the musical version of Proust's Madeleine–summoning a set of associations linked inextricably to sex.

Neuroscientists have studied the phenomenon of "involuntary memory" triggered by taste and smell, and psychologists have written about the fact that sexual desire can be aroused by, well, just about anything. Yet surprisingly little research has been conducted on auditory cues tied to the arousal feedback loop.

Bypassing the naughty cabinet of curiosities that is "Notches: (re)marks on the History of Sexuality," the sex soundtrack currently inhabits the domain of oral history. Just as the sound of Karen Carpenter's silky voice takes writer Tara McGinley back to the "safe, happy place" of childhood, porn soundtracks lead a large chunk of Americans back to the same happy place: the '70s.

It is generally conceded that the '70s was the Golden Age of porn, and the movie that changed everything was "Deep Throat" in 1972. When asked porn superstar Ron Jeremy about the soundtracks he chose for "Deep Throat," he replied:

I remember that the music in "Deep Throat I" was campy and adorable. Porn films always had that boom-chicka-boom-chicka-boom music, but Gerard Damiano (director of Deep Throat 1) always had the desire to go straight, so he put in music that was unlike typical porn music. Not just bouncy stuff, but more fun-goofy-crazy music.

According to Jeremy, Damiano edited the film so the action onscreen would match the beat of the music ("like up and down strokes on the old shaft…it was pretty clever.") But, Jeremy continued, the film's producer had other ideas, insisting on using "real soundtracks" featuring legitimate musicians. Deep Throat was so popular that it spawned a sequel, "Deep Throat II."

For historians of the genre, "Deep Throat" (I and II) was a watershed moment in porn, in no small part because it ditched the half-assed soundtrack in favor of a more sophisticated score. Come on. How "campy and adorable" can porn soundtracks be? Consider "Sweden: Heaven and Hell" ("Svezia, inferno e paradise"), 1968, an Italian film which isn't technically porn but X-rated because it fake-documents lesbian nightclubs, swinging Swedes, and other sex-related topics. One of the more memorable tracks composed by Piero Umiliani was the cheerful "Mah na Mah na" song, later made famous by the childhood fixture known as The Muppets. Who are campy and adorable.

How did that song end up coming out of those cloth-covered faces? In 1969, "Mah na Mah Na" aired on a then-neophyte show called Sesame Street, the producers perhaps being unaware that it had been used on an X-rated Italian film released the previous year. (When I asked Brian Henson, son of the late Jim Henson, if his father had known of the connection, he was unable to confirm it. "But," he added, "it's pretty funny if it's true.")

Shortly thereafter, the "Mah na Mah na" song popped up in a compilation album produced by United Artists, Themes from New Provocative Films, 1970. "Mah na Mah na" went mainstream on "The Benny Hill Show" (1955-91), a politically-incorrect slapstick comedy that ran for decades in Britain.

In other words, depending on which country you grew up in, "Mah na Mah na" cues up very different memories.

If "Deep Throat" brought legitimate music into porn films, the cult classic "Café Flesh," 1982, flipped the script by bringing the porn groove to pop music. The theme to Café Flesh was a "jazzy vamp with some sly chromatic twists," noted the New York Times in a 2005 review of Froom's performance of his old tunes. Was the sound scandalous? Not very. For in the wake of Café Flesh, Froom had gone on to produce Suzanne Vega, Los Lobos, and a host of other original, innovative bands including the Del Fuegos, whose lead guitarist-turned-music-historian, Warren Zanes, remarked that the band, Air, "claimed to have based their sound on that ['70s porn-groove] aesthetic."

By the '90s, in the wake of '80s excess, that sound had become parody. "When I worked at Cinemax in the late 90′s/early 00′s," Brother Cleve notes, "I saw some of the late night 'Skinemax' films, which were dreadful, and they had scores by people who were undoubtedly using assumed names." The sound was "wah-wah funk in the sort of blaxploitation style," he continued.

That "boom-chicka-wah-wah" sound didn't emerge sui generis. It came from "Black American genres such as funk, soul, smooth jazz, and r'n'b…along with disco for gay male porn," musicologist Luis-Manuel Garza told me.  "I think that [sound] still informs how we (in the Western/Northern world) imagine the sound of sexual situations."

These threads all congealed in Robin Thicke's song of last summer, "Blurred Lines," which might as well claim its musical roots in porn grooves, given that it now conjures up the memory of nearly-naked Miley Cyrus twerking at the MTV 2013 music awards. The inadvertent genius of her performance was that it exposed the recipe for a distinctly American cocktail: one part childhood, two parts X-rated content. Lest we forget, Miley popped out of a furry teddy bear wearing a faux-fur bathing suit — the moppet playing the Muppet before taking her clothes off and simulating masturbation onstage.

That Miley's performance was broadcast on regular television (as opposed to pay-per-view) suggests that the porn actress who blogs under the name, "Ms. Naughty," was correct, and soundtracks for actual porn movies are swiftly becoming a thing of the past. Porn-music composers such as James Lynch are lobbying hard for recognition of their craft, but the pop music industry has already co-opted the sound, and it does a better job of selling sex to the masses.

As I'm writing this, the television is spewing the riff from blues legend Howlin' Wolf's "Smokestack Lightning," first recorded in 1956. Inducted into the Grammy Hall of Fame, "Smokestack Lightning" has been performed by everyone from The Who to Aerosmith. The song has rich and meaningful origins in the history of the railway as well as the black American experience; the title refers to sparks shooting out of a train's smokestack as it passes in the night. And yet for millions of Americans, in a sad stroke of irony, it's now nothing more than the soundtrack of a Viagra commercial.