Pixies’ “Dregs of the Wine” is one of the band’s most dynamic songs. Which, considering the band’s wild catalog, is saying a lot. The 2022 tune begins with a gentle-but-ominous picked out guitar, rises to a jaunty indie pop bop, charges into an anthemic rant, cycles through the moods again, crash lands into noise rock, and closes with that same picked out guitar.

“Dregs of the Wine” is pure Pixies even though it came from a surprising source.

“I had the song during COVID on an acoustic guitar,” guitarist Joey Santiago told the Boston Herald. “My girlfriend at the time, who is my wife now, secretly recorded me. I had put down my guitar and said, ‘Well, that sucked.’ Then she said, ‘No, it didn’t. Listen to it.’ ”

Santiago took a second listen and said, “You know, you’re right, it’s not that bad. It’s good. It’s really good.”

A band co-founder whose signature surf-meets-punk style defines much of the Pixies’ sound, Santiago had never co-written a Pixies tune until “Dregs of the Wine.” But band leader Black Francis must have liked what he heard because he’s now co-written a handful of songs with Santiago — a pair on both 2022’s “Doggerel” and 2024’s “The Night the Zombies Came.”

Despite Francis’ work filling the Boston band’s albums, Santiago is as indispensable as he was when the Pixies burst out of Fort Apache Studios with the 1987 EP “Come On Pilgrim” — the band comes home with MGM Music Hall shows July 18 and 19. In an ’87 landscape of Eddie Van Halen and Jimmy Page clones, Santiago had no desire to be another poser.

“It was for two reasons, one, I probably wouldn’t be as (good as those players) and the other reason, I just wasn’t interested,” he said with a laugh. “I never had the outfit for it, never had the hair.”

Both when he plays and when he writes, he has no impulse to shred.

“Something comes up (as I play), and many guitar players might go, ‘OK, could develop this from here,’ where I am like, ‘This is good… it’s simple, to the point, melodic,’” he said. “I don’t really do leads. I do lines.”

To this day, even as the Pixies experience a late career boom — 20 years into a reunion after a decade-long break, the band is playing its biggest shows to date — Santiago doesn’t buy into the rock star vibe.

“When we’re taking on anyone that’s opening up for us, they look more rock ‘n’ roll than we do,” he said. “For me, it’s just me being honest with myself. And they’re being honest with themselves, and they want to do that rock ‘n’ roll lifestyle. I’m just not comfortable with the rock ‘n’ roll image.”

This makes sense if the rock ‘n’ roll image is Van Halen or Led Zeppelin, or even U2. But seeing the Pixies live is seeing rock ‘n’ roll’s highest high. The Pixies just click live, and it’s a vibe that carries back from today to when Santiago and Francis met at UMass Amherst.

“We had an enthusiasm,” Santiago said. “We pretty much knew we had something. I wouldn’t have dropped out of college if I didn’t believe in it.”

For tickets and details, visit pixiesmusic.com