It is more than the chemical assist that comes from adrenaline. It directs the nervous system to forget all else, and concentrate on the fight. Poltergeist activity sometimes is related to Theta activity, and not by accident, as the mind is mentally as well as physically throwing things in order to survive. Alpha is the brain wave belonging to that part of your brain that deals with scope, spiritual as well as physical. It pieces it all together, makes sense of it, or tries to, and listens to the subconscious, where the real story is always recorded.
Meditation is done in Alpha, and hypnosis, and sleep, where dreams emerge.
All this deep understanding of the nature of the world is resisted by yet another part of the brain, that supported by Beta waves, considered the brain waves of the wakeful and alert, intelligent human. Beta supports the physical existence of humans, by processing what the senses perceive and sharing this with the rest of the brain. Beta is grounded. It wants not to know of the deeper meaning, of connections, or what the spirit knows, it wants only to be here and now and can't be bothered with all that other nonsense. The Beta brain helps a creature get through the day, find enough to eat, and escape the flood or fire.