Evidence from Drosophila and also vertebrates predicts that two different sets of instructions may determine the development of the rostral and caudal parts of the body. This implies different cellular and inductive processes during gastrulation, whose genetic requirements remain to be understood. To date, four genes encoding transcription factors expressed in the presumptive vertebrate head during gastrulation have been studied at the functional level: Lim‐1, Otx‐2, HNF‐3β and goosecoid. We discuss here the potential functions of these genes in the formation (...) of rostral head as compared to posterior head and trunk, and in the light of recent fate map and expression analyses in mouse, chick, Xenopus and zebrafish. These data indicate that Lim‐1, Otx‐2 and HNF‐3β may be involved in the same genetic pathway controlling the formation of the prechordal mesendoderm, which is subsequently required for rostral head development. goosecoid may act in a parallel pathway, possibly in conjunction with other, yet unidentified, factors. (shrink)

We propose a view of consciousness as a sort of metaphoric “funnel” transforming a fraction of the parallel processes taking place continually in our central nervous system into something intrinsically serial and sequential. A conscious state is the result of this temporary serialization of a set of parallel mental processes. Before this event, everything is parallel, but also after it, everything returns parallel. As a consequence, the simile we propose is that of a “clepsydra” or sandglass. A conscious state coincides (...) with its bottleneck. Here, we explore possible consequences of the adoption of this model. (shrink)