  The physicist Roger Penrose (1989, 1994) and the anesthesiologist Stuart Hameroff (1998) have championed a model according to which consciousness arises through quantum effects occurring within subcellular structures internal to neurons known as microtubules. The model posits so called “objective collapses” which involve the quantum system moving from a superposition of multiple possible states to a single definite state, but without the intervention of an observer or measurement as in most quantum mechanical models. According to the Penrose and Hameroff, the environment internal to the microtubules is especially suitable for such objective collapses, and the resulting self-collapses produce a coherent flow regulating neuronal activity and making non-algorithmic mental processes possible.