 In this section, some popular approaches for applying quantum theory to brain states will be surveyed and compared, most of them speculative, with varying degrees of elaboration and viability.  Section 3.1  addresses three different neurophysiological levels of description, to which particular quantum approaches refer. Subsequently, the individual approaches themselves will be discussed —  Section 3.2:  Stapp,  Section 3.3:  Vitiello and Freeman,  Section 3.4:  Beck and Eccles,  Section 3.5:  Penrose and Hameroff. 