At the Vogue Theatre on Saturday, January 27

Someone I know has a poster on her living-room wall that reads "Sad songs make me happy." It's a cute slogan, but there's some science behind it. One study found that, when compared with major-key compositions, music in a minor key caused increased activity in limbic structures of the brain. (If you care about specifics, which you probably don't, those structures include the left parahippocampal gyrus, the bilateral ventral anterior cingulate, and the left medial prefrontal cortex.)

Whatever the reason, people are drawn to sad songs, which explains the appeal of First Aid Kit. Well, part of the appeal, at any rate. There is also something to be said for the fact that the band's core members, Swedish sisters Klara and Johanna Söderberg, each possess a luminously gorgeous singing voice, and that when they combine those voices in angelic harmony, something pretty special happens.

At a sold-out Vogue Theatre show, the Söderbergs employed those voices in the service of songs that, even when they weren't overtly weepy, were at the very least tinged with melancholy. This suits First Aid Kit's style, which has evolved from spare indie folk to a more fleshed-out sound that often veers unapologetically into country. The twangier numbers suit the Stockholm siblings' harmonies well, and they also allow their backing musicians—keyboardist-trombonist Steve Moore, drummer Scott Simpson, and especially pedal-steel player Melvin Duffy—to elevate numbers like "Emmylou" and "Rebel Heart" into widescreen cinematic Americana.

First Aid Kit isn't all about the sweet ache of heartbreak songs, though. "You Are the Problem Here" is a righteously pissed-off protest against rape culture, released months before #metoo became a trending hash tag. When Klara, bashing away at a white Stratocaster, directed the line "I hope you fucking suffer" at the "sweaty, desperate" object of her scorn, it rang true and evidently resonated with the audience, much of which let out a midsong cheer at the line.

The band also proved it could rock out on a suitably blazing cover of "Crazy on You", a song that, as Johanna correctly noted, Heart recorded here in Vancouver. Klara nailed Nancy Wilson's indelible acoustic-guitar intro, and the Söderbergs more than did justice to the original's harmonies.

For encores, First Aid Kit invited Van William—whose opening set with his band was an entertainingly high-energy affair that included a blistering take on Neil Young's "Cinnamon Girl"—back to the stage to sing his own "Revolution". They closed, though, with a sublime version of "My Silver Lining", which includes the lines "Something good comes with the bad/A song's never just sad." That may be true, but, as First Aid Kit proved on Saturday night, sometimes the sad parts really can make you happy.