LSD and music often go hand-in-hand: Think of the 1966 Beatles trippy classic Revolver or the psychedelic Lana Del Rey music video for “Freak.”

But scientists have now discovered how LSD makes music seem so meaningful: It hacks the brain’s process for creating relevance.

In a paper published in the journal Current Biology Wednesday, Universität Zürich psychologist and neuroscientist Katrin Preller, Ph.D., discusses how LSD can be used to make one song evoke a meaningful reaction in another.

“In the scanner we saw that LSD in particular increased the attribution of personal relevance to these previously not meaningful stimuli,” she tells Inverse of her acid-tripping participants.

Preller set out to investigate what happens in the brain when we experience something meaningful and how LSD can modulate that. Music, she figured, was the most obvious factor to study because “it is one of the most important relevant stimuli.” In other words, it either means something to us, or it doesn’t.

In her study, Preller dosed her participants with LSD and asked them to rank the level of meaning they attach to three types of music: Songs that they had described as meaningful, which they selected themselves; songs that were similar to the “relevant” music but were new to each participant, and free jazz — “music that was really hard for people to relate to,” she says, laughing. Then, she put her participants in an fMRI scanner and measured their brain activity when they listened to those songs.

“When we looked at their brains in the scanner we saw that the regions of the brains that were usually lit up when they listened to relevant pieces now also lit up when they listened to non-relevant pieces,” she said.

Preller also found a drug called ketanserin to have an interesting effect on the subjects she dosed. Ketanserin blocked all of the psychedelic effects of LSD — and, crucially, its meaning-creating ability. “This shows that the increased attribution of music to meaning is completely dependent on the serotonin receptor,” she says, adding that it was “surprising” it could be blocked by a single drug, because LSD is known to work on many of the brain’s receptors.

Preller concluded that LSD works through the brain’s serotonin receptors to hijack the the process by which we decide whether or not a song is relevant. (This isn’t to say that the person enjoyed the song; Preller is careful to distinguish enjoyment from self relevance.) As far as she can tell, Preller is the first scientist to ever uncover the neuropsychopharmacology of this phenomenon.

Preller’s next plans are to reconfigure her experiment to test for LSD’s role in attributing relevance to tactile and visual stimuli. She’s hoping her discoveries can be applied to research on psychological disorders in which personal relevance attribution is impaired.