The thing that makes Bro. Davis’ playing so complex is that he's constantly moving his left hand to different chords, chord fragments and notes so you get this terrific feeling of constant movement. He's playing runs—phrases, really—that are several measures long. To play those passages while singing, as Davis does, they have to become part of the cell structure of your fingers, so to speak. You (I) can't be thinking of how to play those passages and also be thinking about singing. Davis also does a lot of alternate (thumb and finger) picking on a single string or pair of strings to get some of the runs he plays. You'll hear the bass drop out during these passages but the whole thing is so powerful and dynamic there is no loss of rhythm.

The Mississippi blues style tends to keep what is often just a drone bass thump constantly going without a break. Fast bass runs are accomplished with a fast series of down strokes with the thumb while fast treble runs are played using a fast series of up strokes with the index finger. There is very little dependence on pattern in Mississippi (Delta) blues and very little of the alternate thumb-index picking to make runs easier.

The thing to remember about all these styles is that they are all thumb or rhythm driven. It isn't a melody with some rhythm added for fill, it's rhythm with some melody suggested around it in a syncopated fashion. Lead with your thumb. Some players keep their thumbs fairly stiff and use their whole forearm to define the rhythm while playing melody with the index finger. This can make it easier to keep the rhythm solid while doing all the other stuff.

      - Mark