Lateral specialization and psychiatric issues: speculations on development and the evolution of consciousness.

At the start of this lecture, I invited you to indulge with me in a "dessert" of speculations. I hope it has been a sufficiency, not a surfeit. In summary, we have examined a hypothetical model of some dissociations of consciousness and the expression of unconscious symptoms in adults; we then explored some possible conditions that would account for the development of separate mental streams. In the course of this exploration we were led to question some basic assumptions about the unity of the self, and we proposed some possible mechanisms by which lateral specialization develops in children. This model of the development of lateral specialization has some implications for the study of evolution of the human brain and consciousness. It would seem useful to examine the relationship between the evolution of the commissural systems and the evolution of different capacities for consciousness. According to this model, the full development of lateral specialization depends upon the later myelination of the commissures, which makes possible the autonomy and competition between hemispheres. By this means, only minimal differences between hemispheres need to be specified genetically, since the rest of lateralization can be produced by progressive differentiation, through interactions with the environment. Thus man's eternal, internal struggle may be the price paid for the evolution of lateral specialization.