Easiest way of doing it is making the brain actor itself do the shield stuff. But here's the code for B22:
Code:
for actor in MovableMan.Actors do
  if actor.PresetName == "Brain Case" then
    for particle in MovableMan.Particles do
      dist = math.sqrt( (actor.Pos.X-particle-Pos.X) ^ 2 + (actor.Pos.Y - particle.Pos.Y) ^ 2)
      totalvel = math.sqrt(particle.Vel.X ^ 2 + particle.Vel.Y ^ 2)
      if dist < 100 and totalvel > 50 then
        particle.Vel = Vector(0,0)
      end
     end
  end
end
Oops, sorry it's 11 lines  

Edit: Copypaste to the beginning of any luaed scene to make the standard brain case have the shield. Change the actor.PresetName == "Brain Case" to actor.PresetName == "Brain Robot" to make it work with the brain bot.