Synaptic Epigenesis and the Evolution of Higher Brain Functions

The epigenesis theory of development can be traced back to William Harvey (1651), who stated, in contrast to contemporary preformation views, that the embryo arises by “the addition of parts budding out from one another.” The word epigenesis was subsequently used by Conrad Waddington (Nature 150:563–565, 1942) to specify how genes might interact with their surroundings to produce a phenotype. This is also the meaning we adopted in our paper, Theory of the Epigenesis of Neuronal Networks by Selective Stabilization of Synapses (Changeux et al. Proc Nat Acad Sci U S A 70:2974–2978, 1973), according to which the environment affects the organization of connections in an evolving neuronal network through the stabilization or degeneration (pruning) of labile synapses associated with the state of activity of the network. This definition contrasts with the recent and more restricted sense of the status of DNAmethylation and histone modification in a particular genomic region. The synapse selection theory was introduced to deal with two major features regarding the genetic evolution of the human brain : 1) the non-linear increase in the organizational complexity of the brain despite a nearly constant number of genes ; and 2) the long postnatal period of brain maturation (ca. 15 years in humans), during which critical and reciprocal interactions take place between the brain and its physical, social and cultural environment. This theory will be evaluated and updated in the framework of the recent human/primate genome data, analysis of gene expression patterns during postnatal development, brain imaging of cultural pathways, such as those for language learning, and current views about the neural bases of higher brain function, in particular the global neuronal workspace architectures for access to consciousness (see Dehaene and Changeux Neuron 70:200–227, 2011). J.-P. Changeux (*) Département de Neurosciences, Institut Pasteur, Collège de France, Place Marcellin Berthelot, Paris, 25 Rue de Docteur Roux, Paris, France e-mail: [email protected] P. Sassone-Corsi and Y. Christen (eds.), Epigenetics, Brain and Behavior, Research and Perspectives in Neurosciences, DOI 10.1007/978-3-642-27913-3_2, # Springer-Verlag Berlin Heidelberg 2012 11