"Jam bands" seem to have managed the musically impossible: to have become popular with both snooty jazz critics and well-cranked college stu dents. Picking up from where the Grateful Dead and fusion jazz left off in the '90s, jam bands recombine complex, extended improvisations and body-shaking rhythms. The better groups know just how to blend jazz soloing with good-time rock and dance-inducing funk.

Medeski, Martin and Wood ponder which riff to play next.

Two of the best from this thriving scene -- Soulive and Medeski, Martin and Wood -- bring their fresh, intelligent performances to Tokyo this month.

With an eye to the college crowd, MMW never sacrifices complexity in the search for a crowd-pleasing groove. Their experiments on "The Dropper," their most recent release, whack your ears with so many intriguing riffs that it's hard to know where to listen.

MMW came together in the early '90s, after playing with such avant-garde luminaries as the Lounge Lizards, John Zorn and Marc Ribot. (Ribot appears on three of "The Dropper's" cuts.) The influence of this downtown NY scene is evident in the way MMW seamlessly integrates an eclectic mix, which can include chill-out keyboard synthing, hip-hop drumming, ambient circling feedback, jazz modals and the occasional Who-like bass line. Yet, since it's all piled onto straightforward riffs, it comes out surprisingly minimalist, and without the cerebral pretensions that plague many progressive bands.

Soulive puts a toe-tapping spin on '60s soul-funk jazz.

The trio's previous acoustic CD, "Tonic," was a serious jazz workout. It showcased their youthful energy, digging into originals with a verve and ingenuity that many straight jazz players would envy. Before that, MMW's keyboard-based sound relied on catchy grooves over which they improvised endlessly. Their groove-based CDs, "Combustication" and "Shack-man," became surprisingly popular, spawning bootlegs and a devout following.

However, "The Dropper," released last year on Blue Note Records, shot off in another direction altogether. The catchy riffs are still there, but they're so combustible that they evaporate as soon as they're poured out. The beat has disappeared into swirling eddies and dense, surging layers of synthesized mixes, delay-loops and other aural hallucinations. The result is, at times, magnificent, and at other times, just good-natured fooling around. In other words, it's genuine experimentation.

MMW requires a certain degree of patience, as directions charted are not always followed: You have to either pay close attention or space out entirely. Since MMW delivers it all up with such sincerity and attention, it somehow works, and it's a real pleasure to hear a band that's unafraid to color outside the lines.

In contrast to the genre-melding edginess of MMW, Soulive has a well-practiced reclamation of different styles. It's easy to think of them as simply the latest incarnation of '60s soul-funk jazz. But they so restlessly search the depths and interfoldings of their influences that they sound altogether new.

All three of Soulive's members -- Alan Evans on drums, Neal Evans on Hammond B-3 organ and Eric Krasno on guitar -- have obviously spent time at the altar of the jazz masters. Their lead lines and jams contain heavy debts to Jimmy Smith, Herbie Hancock, Grant Green and Kenny Burrell.

Along with other recent jazz-funk jam-masters such as Galactic, the Greyboy Allstars or Liquid Soul, the band takes a serious approach to original compositions and intense interaction.

On their only CD to date, "Turn It Out" (on the hip New York label Velour Records), they've created tunes so hummable it sounds as if the soulful, singing vocals were somehow left out of the final mix. Around this core, they weave funky, driving rhythms and soaring, sweaty jams. After the critical acclaim and popular appeal of "Turn It Out," they signed with Blue Note Records, which will release the new Soulive CD next month.

Soulive's playing style is primarily jazz-based, in that each member improvises individually. But they interact and support each other with an almost spiritual intensity. They prod each other for changes in direction that dig a little deeper, and then answer each other with harmonies, pumps and accents.

While other funky organ players, such as Larry Goldings or Joey DeFrancesco, stay more firmly in the jazz idiom, Soulive knows how to just dig into a good groove and enjoy the ride. And they have a lot to say on the way.

Soulive strikes a perfect balance between the mesmerizing power of repetition of riffs and the clever invention of open-ended, creative flow. Thus is reborn the '60s jazz combo staple -- organ, guitar and drums -- for another generation. The Dead would appreciate that.

While Soulive goes for the heart and the toes, MMW gets to the inner nooks and crannies of the gray matter. Both these groups take the endless creative power of jazz in fascinating and unapologetically fun directions.