For starters, this piece is played in E Dorian, which is what happens when D major and E minor decide to share an apartment in Park Slope. In slightly more technical terms, it means the principal scale used in Lightning Fast looks equivalent to D major on the fretboard. Like so: ...but instead of using this scale to solo over chord changes in D major, you use it to solo over changes in E minor. In such a scenario, what you're looking at is no longer D major, but really an altered form of E minor that sounds ever-so-slightly major. This works because E minor and D major are almost identical to begin with. In fact, the only difference between them is that D major has a c# where E minor has a c natural. Thus throwing a c# into the E minor scale introduces chordal possibilities that are normally found in D major and not normally found in E minor. The reason we call it E Dorian, and not D major, is that the song itself still hovers around E and the E minor chord as a tonal center.

That's one way of describing it, anyway. A better way is to just listen. To hear the classic Dorian rock sound, try strumming from E minor, to A major, to E minor. The Amaj chord is not normally available in E minor, because it contains a c#. Hence deliberately juxtaposing an A major chord against a riff in E minor will create Dorian-ness (Dorian-osity?). Like so:
Throw in some groovy rhythm, and it sounds like Stayin' Alive, or maybe The Wall, eh? The Dorian mode was popular in the disco era for extended vamps with a feeling somewhere between major and minor. But there are no backing tracks in Lightning Fast, and the overall effect isn't particularly disco-like (or "cowboy-like", as Vinnie Moore once described the Dorian mode). So why bother?

In this case, believe it or not, Mike's rationale for picking the Dorian mode probably has more to do with fingerings than anything else. If you're familiar with the E minor fingering at the 10th/12th fret, it's a little squirrely: This scale position is not as popular among shredders as it could be, mostly due to the awkwardness created by its motley grouping of fretboard shapes. The scale starts with three identical shapes on the 6th, 5th, and 4th strings. So far so good. But it follows with two different shapes and two position shifts on the 3rd, 2nd, and 1st strings. That's a bunch of movement in a short period of time. Compare this to the Dorian fingering we saw earlier:
Ah, fresh air. Here we've got only three fretboard shapes, and they occur in pairs on the strings, directly across from one another. This means that the left hand can cover two strings at a time without any change in fingering or position. There are still three positions in total, but they're evenly spaced, which gives the left hand some breathing room. Overall, it's much easier for the left hand to play the E Dorian scale than the E minor scale in this position, and that's why Mike uses it. Yes, this gives the solo a "Dorian" sound instead of a "minor" sound, but there are no backing tracks to highlight this. Mike's solo lines don't dwell on it either, so the change in tonality is not really noticeable. In his free-form improvising, Mike frequently combines the Dorian scale with the blues scale because they work well together for the left hand.

In the rock-paper-scissors world that is guitar playing, easy fingerboard shapes beat out musical concerns every time. (Can you say Nirvana?) In fact, notice that if you use the Dorian scale, and stick to just two strings at a time -- the ones with the identical, or parallel fingerings -- the left hand barely moves at all. If you look at the tab for Lightning Fast, you'll see that with the exception of only three measures (15, 16, and 17), Mike uses parallel fingerings for the entire freakin' solo. Armed with this knowledge, and a few astute observations, we can actually sketch a formula for making your own solos sound just like Lightning Fast.