Alternative Thumb Picking
There is no common way to notate alternatively thumb picked strings. Some sheet music with this technique will not notate it at all, while some may choose to show the direction of the pick on every note.
The alternative thumb picking technique is used instead of regular picking to keep a group of notes sounding similar in tone, or to play lower strings repeatedly while giving the other fingers convenient access to the others.
This technique is less useful when the plucked bass notes are slow (such as the video), but excel at pieces that require faster playing.
To pick alternatively with the thumb, pick down with the underside of the thumb nail as you normally would, and pick upwards with the back of the thumbnail. Only pick upwards far enough for your thumb to be be below the string directly above the picked string.
While practicing the technique, as long as no other notes are being played by the other fingers, it helps to move your wrist slightly up and down to assist with the picking.
There is no continuation to this technique.