How does evolution build a complex brain?

To understand how complex brains evolve one can examine a variety of the products of the evolutionary process and then infer the mechanisms that generate the differences observed. We address this issue using a number of techniques. We combine neurophysiological recording techniques with neuroanatomical tracing techniques and histochemical methods in an effort to accurately determine the functional subdivisions of the neocortex in a variety of mammals. By using these techniques we can determine common features of neocortical organization, or common cortical areas, which are considered homologous. We can observe modifications to patterns of cortical organization, or to cortical fields specifically, that are independently evolved and generally related to morphological and behavioural specializations. Comparative studies have led us to consider the development of the neocortex and the specific changes in developmental mechanisms that might account for the observed changes in extant adults. Both comparative studies and developmental studies allow us to formulate hypotheses regarding how the neocortex is constructed in the life of an individual, and in a lineage over time.