Celebrity response to disasters was nothing new. From George Harrison's Concert for Bangladesh in 1971 to Live Aid and USA for Africa in the early '80s, musicians and others have acted in times of need.

But something about Katrina -- something about New Orleans spurred an unprecedented response from the entertainment world that continues four years later, experts and activists say.

"Anybody, whether they're a performer or not, who has studied or been touched by American music has been touched by New Orleans," said Jordan Hirsch, director of the nonprofit aid group Sweet Home New Orleans.

"It's jazz. It's R&B. It's funk. ... For everybody of every generation who's making music in America, there's a touchstone in New Orleans that has affected their work."

In the days after the floods, many of the rich and famous stepped up with perhaps the most obvious response, writing a check.

George Clooney donated $1 million to United Way and Oprah Winfrey added another million through her Angel Network and urged her famous friends to follow suit. Director Steven Spielberg gave $750,000 to the Red Cross and another $750,000 to the Bush-Clinton Fund.

Hip-hop stars P. Diddy and Jay Z pitched in with big checks, as did actor Nicholas Cage and singers Celine Dion and Hillary Duff.

Michael Jackson donated the proceeds of a song, "From the Bottom of My Heart," to relief efforts and actor Jamie Foxx raised $600,000 -- including $200,000 paid for a date with Paris Hilton -- through a celebrity auction.

Others took more direct action.

John Travolta flew relief supplies into the region on his private plane, Sean Penn took a private boat (albeit a leaky one) into New Orleans to rescue people. Brad Pitt founded the Make It Right Foundation, an organization dedicated to rebuilding the Lower 9th Ward in New Orleans.

Almost to a person, the performers who stepped up cited a special love for the city's artistic tradition -- from the Creole brass bands that invented jazz in the city's streets to the colorful Mardi Gras krewes whose elaborate floats and costumes are an emblem of the city's annual pre-Lent bacchanal.

U2 guitarist The Edge helped form Music Rising, a group initially dedicated to providing instruments for New Orleans musicians who had lost their own during the floods. The group gave instruments to 2,700 musicians from the Gulf region before shifting its focus to helping churches and schools rebuild their music programs.

"The New Orleans tragedy was a twofold tragedy," Edge said in 2006 during the city's JazzFest. "It was a tragedy because of the fact that this great city was devastated, but it was a tragedy because of the incredible music culture that was also destroyed."

As the city continues to struggle, assistance is still arriving in a way that's different from the aftermath of most disasters, experts said.

"There have been some institutions created as a result of it," said James Ferris, director of the University of Southern California's Center on Philanthropy and Public Policy.

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