Ok, you need to understand-- as you design your test-- that the power of suggestion and the placebo effect are one and the same. They are related to the same aspect of the mind that deals with such "programming". As to how, and how the alpha-theta state relates to this, the answer is that nobody knows for sure. In other posts I made explicit the fact that just alpha-theta or just alpha, or just theta, doesn't really mean much. The same person showing dominant theta patterns could be in REM sleep, hypnogogia, hypnotic trance, or deep meditation. All these states are qualitatively different. The fact remains that the patterns of electrical activation in the brain are very complex. Gross EEG measurements are only a rough indication of general brainwave activity. As for specific research done on the hypnotic state, I believe that in the book Cross-Currents, by somebody Beck or Becker (I cannot remember), I read that in true trance states the electrical potentials across the skin surface of the entire body is weaker, and that there was some change in the back-front vector of brainwave activity... I could be wrong about this info. so I suggest you check it out for yourself.
I have two ways of verifying suggestion effectiveness. First, in self-hypnosis I can create states by suggestion and perceive the change instantaneously-- for instance, if I say "I now float on a wave of euphoria", I immediately feel a strong euphoric sensation rising through my body. The other method I use to verify suggestion effectiveness is just plain-old experience. I keep track of my mind-states throughout the day and notice if any of them have been affected by suggestion.
One interesting phenomenological speculation about the mind, relating to self-hypnosis, is the power of intent. It seems that intent plays a large role in the formation of consciousness-fields (getting into metaphysics here), and that these fields may literally pervade our bodies, including our brain, by nature of their non-spatiality. Obviously, various levels of interconnectedness abound within our consciousness, and these "relationships", have certain elements which are beyond our individual intent unless we specifically address them...these we call subconscious or unconscious "relationships" or bakchak--literally imprints-- in the Tibetan Buddhist tradition. I think that hypnosis is a state in which we have accessed a kind-of channel whereby intent can be directed at the subconscious imprints-- the sum of which we classify as "subconscious". Meditation and other forms of concentration do this as well but in self-hypnosis we use a very directed, verbally oriented route of access. Whereas in meditation one quite frequently is taking a purely "concentrative" approach, the goal of which is to be able to orchestrate "mind-states" which integrate subconscious resources in a different way.
Anyways, sorry about the lecture but I felt it to be neccessary in understanding some about the metaphysical implications of suggestion and intent. I recommend that one check out Rupert Sheldrake's ideas about morphogenesis, and his research on pet psychic powers to understand more about intent. URL:
www.sheldrake.org.